HEAVY METAL- AND ODOUR-FREE NANOPARTICULATE COMPOSITIONS
20210002408 ยท 2021-01-07
Inventors
- Atsushi GOTO (Singapore, SG)
- Jit SARKAR (Singapore, SG)
- Longqiang XIAO (Singapore, SG)
- Feifei LI (Singapore, SG)
- Alexander M. Van Herk (Singapore, SG)
- Alexander William JACKSON (Singapore, SG)
Cpc classification
C08F222/102
CHEMISTRY; METALLURGY
C08F222/102
CHEMISTRY; METALLURGY
A61K9/5138
HUMAN NECESSITIES
C08F299/024
CHEMISTRY; METALLURGY
B82Y30/00
PERFORMING OPERATIONS; TRANSPORTING
B82Y40/00
PERFORMING OPERATIONS; TRANSPORTING
C08F220/06
CHEMISTRY; METALLURGY
C08F220/14
CHEMISTRY; METALLURGY
C08F220/14
CHEMISTRY; METALLURGY
C08F220/06
CHEMISTRY; METALLURGY
International classification
C08F293/00
CHEMISTRY; METALLURGY
Abstract
The present invention relates to a nanoparticulate composition comprising nanoparticles formed from an amphipathic block copolymer comprising a hydrophilic block and a hydrophobic block, where the nanoparticles are provided in the form of micelles, cylindrical worm structures or vesicles and the size of the nanoparticles is from 25 to 500 nm, wherein: the composition is substantially free of heavy metals and compounds comprising sulfur. Also disclosed herein is a method of forming said nanoparticulate composition by polymerization induced self-assembly (PISA) via non-transition-metal catalysed controlled radical polymerization (NTMC-CRP).
Claims
1. A nanoparticulate composition comprising: nanoparticles formed from an amphipathic block copolymer comprising a hydrophilic block and a hydrophobic block, where the nanoparticles are provided in the form of micelles, cylindrical worm structures or vesicles and the size of the nanoparticles is from 25 to 500 nm, wherein: the composition is substantially free of compounds comprising sulfur; and the composition is substantially free of a heavy metal.
2. The composition according to claim 1, wherein the amphipathic block copolymers are terminated by a halogen atom.
3. The composition according to claim 1, wherein the composition further comprises an active agent encapsulated in the nanoparticles.
4. The composition according to claim 3, wherein the active agent is selected from one or more of the group consisting of vitamin C, peptides, glycerol, dyes, flavours, perfume oils, citronellal, silicon oils, organosilicons, pesticides, Beta-carotene and a pharmacologically active agent.
5. (canceled)
6. (canceled)
7. The composition according to claim 1, wherein when the nanoparticles are in the form of a vesicle, the amphipathic block copolymer is arranged in the form of a membrane with an outer and inner surface, which inner surface defines a core region.
8. The composition according to claim 7, wherein the core region comprises one or both of an active agent and a liquid.
9. The composition according to claim 7, wherein the amphipathic block copolymer is arranged so that the outer and inner surface of the membrane are formed from the hydrophilic blocks of the copolymer.
10. The composition according to claim 9, wherein one or more of the followinq apply: (AA) the composition further comprises a hydrophilic active agent that is substantially encapsulated in the core region of the vesicle; (BB) the composition further comprises a hydrophobic active agent that is substantially encapsulated in the membrane of the vesicle; or (CC) the composition further comprises a polar liquid that is encapsulated in the core region of the vesicle.
11. (canceled)
12. (canceled)
13. The composition according to claim 7, wherein the amphipathic block copolymer is arranged so that the outer and inner surface of the membrane are formed from the hydrophobic blocks of the copolymer.
14. The composition according to claim 13, wherein ore or more of the followinq apply: (DD) the composition further comprises a hydrophobic active agent that is substantially encapsulated in the core region of the vesicle; (EE) the composition further comprises a hydrophilic active agent that is substantially encapsulated in the membrane of the vesicle; or (FF) the composition further comprises a non-polar liquid that is encapsulated in the core region of the vesicle.
15.-17. (canceled)
18. The composition according to claim 1, wherein one of the following applies: (A) when the nanoparticles are in the form of a micelle, the amphipathic block copolymer has an average ratio of hydrophobic repeating units to hydrophilic repeating units of from 1:100 to 10:1 or vice versa; or (B) when the nanoparticles are in the form of cylindrical worm structures, the amphipathic block copolymer has an average ratio of hydrophobic repeating units to hydrophilic repeating units of from 1:1 to 100:1 or vice versa.
19.-21. (canceled)
22. The composition according to claim 1, wherein the amphipathic block copolymer is a poly(acrylic acid-co-acrylate ester) or a poly((polyethylene glycol ether methacrylate)-co-acrylate ester.
23. The composition according to claim 1, wherein the amphipathic block copolymer is crosslinked.
24. A method of forming a nanoparticulate composition according to claim 1 using polymerisation induced self-assembly, the method comprising the step of forming a block copolymer by reacting a monomeric material with a macroinitiator compound in the presence of an initiator compound, a catalyst and a solvent, wherein: if the monomeric material polymerises to provide a hydrophobic polymer block, then the macroinitiator compound is a hydrophilic polymer or oligomer or if the monomeric material polymerises to provide a hydrophilic polymer block, then the macroinitiator compound is a hydrophobic polymer or oligomer; the macroinitiator compound is terminated with a halogen atom; the monomeric material, the macroinitiator compound, the initiator compound, the catalyst and the solvent are all substantially free of compounds comprising sulfur; and the monomeric material, the macroinitiator compound, the initiator compound, the catalyst and the solvent are all substantially free of a heavy metal.
25.-29. (canceled)
30. The method according to claim 24, wherein: (i) the monomeric material is an acrylate ester, and the macroinitiator compound is a poly(acrylic acid) or an oligo(acrylic acid); or (ii) the monomeric material is an acrylic acid and the macroinitiator compound is a poly(acrylate ester) or an oliqo(acrylate ester).
31.-36. (canceled)
37. The method according to claim 24, wherein the step of forming a block copolymer is conducted in the presence of a crosslinking agent.
38. (canceled)
39. The method according to claim 24, wherein the step of forming a block copolymer is conducted in the presence of an active agent.
40. (canceled)
41. The method according to claim 24, wherein after the nanoparticle has been formed an active agent is encapsulated into the nanoparticle by osmosis.
42. (canceled)
43. The method according to claim 24, wherein one of the followinq applies: (a) the nanoparticles are obtained as vesicles when the molar ratio of monomeric material to macroinitiator compound in the solvent is from 100:1 to 500:1, and the reaction is allowed to occur for a period of time such that an average ratio of monomeric material repeating units to macroinitiator repeating units from 1:9 to at least 9:1 is obtained; (b) the nanoparticles are obtained as micelles when the molar ratio of monomeric material to macroinitiator compound in the solvent is from 40:1 to 100:1 and the reaction is allowed to occur for a period of time such that an average ratio of monomeric material repeating units to macroinitiator repeating units from 1:100 to 10:1 is obtained; or (c) the nanoparticles are obtained as cylindrical worm structures when the molar ratio of monomeric material to macroinitiator compound in the solvent is from 40:1 to 200:1 and the reaction is allowed to occur for a period of time such that an average ratio of monomeric material repeating units to macroinitiator repeating units from 1:1 to 100:1 is obtained.
44.-45. (canceled)
46. The method according to claim 24, wherein the macroinitiator compound is formed by polymerising a monomeric material with a dormant initiator compound in the presence of an initiator compound, a catalyst and a solvent, wherein the dormant initiator compound is a hydrocarbon comprising a halogen atom; the monomeric material, the dormant initiator compound, the initiator compound, the catalyst and the solvent are all substantially free of compounds comprising sulfur; and the monomeric material, the dormant initiator compound, the initiator compound, the catalyst and the solvent are all substantially free of a heavy metal.
47.-52. (canceled)
Description
DRAWINGS
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DESCRIPTION
[0094] Thus, in a first aspect of the invention, there is provided a nanoparticulate composition comprising: [0095] nanoparticles formed from an amphipathic block copolymer comprising a hydrophilic block and a hydrophobic block, where the nanoparticles are provided in the form of micelles, cylindrical worm structures or vesicles and the size of the nanoparticles is from 25 to 500 nm, wherein: [0096] the composition is substantially free of compounds comprising sulfur; and [0097] the composition is substantially free of a heavy metal.
[0098] In embodiments herein, the word comprising may be interpreted as requiring the features mentioned, but not limiting the presence of other features. Alternatively, the word comprising may also relate to the situation where only the components/features listed are intended to be present (e.g. the word comprising may be replaced by the phrases consists of or consists essentially of). It is explicitly contemplated that both the broader and narrower interpretations can be applied to all aspects and embodiments of the present invention. In other words, the word comprising and synonyms thereof may be replaced by the phrase consisting of or the phrase consists essentially of or synonyms thereof and vice versa.
[0099] When used herein, the term micelle refers to a spheroidal nanoparticle that is a two-layer structure formed from a solid core and a solid shell (i.e. sphere is not hollow). In other words, the core and shell are formed from the polymeric material, with the hydrophilic blocks on the exterior surface of the nanoparticle (to form the shell) and the hydrophobic blocks forming the core of the nanoparticle (or vice versa). While the shell is solid, these nanoparticles can still be used as a carrier because other molecules (e.g. active agents) can still be dispersed within the core of the micelle (e.g. by diffusion or other suitable means), thereby allowing the micelle to act as a carrier for an active agent.
[0100] When used herein, the term cylindrical worm structure refers to a solid nanoparticulate material that is similar to a micelle in that it has a solid core and a solid shell (i.e. the interior portion of the cylinder is not hollow). In other words, the core and shell are formed from the polymeric material, with the hydrophilic blocks on the exterior surface of the nanoparticle (to form the shell) and the hydrophobic blocks forming the core of the nanoparticle (or vice versa). While the shell is solid, these nanoparticles can still be used as a carrier because other molecules (e.g. active agents) can still be dispersed within the core of the cylindrical worm structure (e.g. by diffusion or other suitable means), thereby allowing the cylindrical worm structure to act as a carrier for an active agent.
[0101] When used herein, the term vesicle refers to a spheroidal nanoparticle structure that has a hollow core and a solid shell. The solid shell is formed by a bilayer of the amphipathic block copolymer, with outer and inner surfaces of the shell being formed by the hydrophilic blocks and the hydrophobic blocks therebetween (or vice versa).
[0102] As noted above, one of the problems encountered with prior methods of constructing nanoparticles of the kind described herein is that the process used to manufacture them makes use of a heavy metal and so the final products are commonly contaminated with said heavy metals, which are hard (if not impossible) to remove from the final compositions without removing the desired active agents and/or destroying the assembled nanoparticles. When used herein the term heavy metal may refer to a metal having a density greater than 5 g/cm.sup.3. For example, the heavy metal may be any of titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, germanium, arsenic, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, indium, tin, tellurium, lutetium, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, mercury, thallium, lead, bismuth, polonium, astatine, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, actinium, thorium, protactinium, uranium, neptunium, plutonium, americium, curium, berkelium, californium, einsteinium, fermium, nobelium, radium, lawrencium, rutherfordium, dubnium, seaborgium, bohrium, hassium, meitnerium, darmstadtium, roentgenium, copernicium, and elements 113-118. Particular heavy metals that may be important to ensure are not present (or are only present in minute quantities) in the composition include radioactive elements and toxic heavy metals such as cadmium, mercury, lead, chromium and arsenic.
[0103] As noted above, the nanoparticulate composition is substantially free of heavy metals, such as those referred to above. In this context, substantially free may refer to the situation where there is absolutely no heavy metal present, or it may refer to a situation where the level of heavy metal is below the limits of detection of the analytical equipment used to conduct the analysis, or it may refer to a situation where only a very small amount of heavy metal is present. For example, in embodiments of the current invention, the amount of heavy metal in the composition may be from 0 to 0.01 wt %, such as from 0 to 0.0001 wt %.
[0104] As will be appreciated, the reduction or elimination of heavy metals from the nanoparticulate compositions disclosed herein (due to the processes of manufacture detailed below) makes these products more suitable for use in a biological system, such as a human or animal patient and for use in medical, healthcare, cosmetics, and agrochemical release applications. This is because the nanoparticulate compositions disclosed herein will be significantly less toxic to such subject due to the substantial reduction or entire elimination of heavy metals from the composition.
[0105] For similar reasons to the presence of heavy metals, the previous methods used to make such nanoparticulate compositions often used compounds that comprise sulfur. While the presence of such compounds may not be toxic, they tend to have an unpleasant odour, which may be off-putting. As such, the nanoparticles and nanoparticulate compositions disclosed herein may be substantially free of compounds that comprise sulfur. More particularly, the compounds that contain sulfur may be compounds that comprise sulfur in a form that causes an odour, such as a thiol, thiocarboxylic acid, thioesters, thiocarbonates, and thiocarbamates. In this context, substantially free may refer to the situation where there is absolutely no compounds that comprise sulfur present, or it may refer to a situation where the level of the sulfur comprising compound is below the limits of detection of the analytical equipment used to conduct the analysis, or it may refer to a situation where only a very small amount of a compound that comprises sulfur is present. For example, in embodiments of the current invention, the amount of a compound that comprises sulfur in the composition may be from 0 to 0.01 wt %, such as from 0 to 0.0001 wt %. For the avoidance of doubt, when used herein a compound that comprises sulfur refers to compounds produced as a by-product, as an impurity or in some other incidental manner in the manufacture of the nanoparticulate composition. This term is not intended to exclude the inclusion of active agents that comprise sulfur, which agents would be introduced intentionally into the composition and which may contain a sulfur atom (or atoms) in a form that does not produce a disagreeable odour.
[0106] As will be appreciated, the reduction or elimination of unpleasant odours from a composition makes it significantly easier to provide to a human or animal subject, or to use such compositions in other settings such as healthcare, cosmetics, and agrochemical release applications. This is because it reduces the need to include further ingredients in the composition to mask the unpleasant odour/taste associated with compounds that contain sulfur, which may increase patient compliance for pharmaceutical preparations making use of such compositions and increase customer compliance for medical, healthcare, cosmetics, and agrochemical release applications.
[0107] In particular embodiments that may be mentioned herein, the amphipathic block copolymers may be terminated by a halogen atom. The presence of the halogen atom is the result of the method of manufacture of the compositions disclosed herein. However, it is possible to remove the halogen atom and replace it by, for example, hydrogen, lactones, hydroxyl, thiol, carboxylic acid, amines, different halogen and so on, using sodium borohydride, sodium hydroxide, sodium carbonate, tributylamine, amino ethanol, cysteine, amino ethyl carboxylic acid, diaminoethane, sodium chloride, sodium bromide, sodium iodide and so on, for example. When used herein, the term halogen atom refers to an atom of iodine, chlorine and bromine In yet further embodiments of the invention that may be mentioned herein, when present, the halogen atom that terminates the amphipathic block copolymers may be iodine.
[0108] As will be noted from the above disclosure, the nanoparticulate compositions disclosed herein may be used as a vehicle for an active agent. In other words, said nanoparticulate compositions may further comprise an active agent encapsulated in the nanoparticles. When used herein, the term encapsulated refers to the enclosure of an active agent within the core of body of the nanoparticles described herein. For example, in embodiments of the invention where the nanoparticles have a solid core, as defined above for micelles and cylindrical worms, then the active agent will be held within the polymer matrix of the nanoparticles in the core of said particles. Alternatively, in embodiments where the nanoparticles are in the form of vesicles, then the active agents may be held within the hollow core of the vesicle.
[0109] In embodiments of the invention, nanoparticulate compositions that further comprise an active agent may contain from 0.01 to 50 weight % of the active agent relative to the weight of the composition as a whole. For example, the active agent may be present in an amount of from 1 to 30 weight %, such as from 5 to 10 weight % relative to the weight of the composition as a whole.
[0110] For the avoidance of doubt, it is explicitly contemplated herein that the top and bottom values provided in a set of ranges in relation to a specific feature may be combined in any way to generate further ranges that are also explicitly contemplated. For example, with respect to the weight percentages provided above, the following ranges are to be considered as explicitly disclosed:
0.01 to 1 weight %, 0.01 to 5 weight %, 0.01 to 10 weight %, 0.01 to 30 weight %, 0.01 to 50 weight %;
1 to 5 weight %, 1 to 10 weight %, 1 to 30 weight %, 1 to 50 weight %;
5 to 10 weight %, 5 to 30 weight %, 5 to 50 weight %;
10 to 30 weight %, 10 to 50 weight %; and
30 to 50 weight %.
[0111] When used, herein the active agent may be selected from one or more of the group consisting of vitamin C, peptides, glycerol, dyes, flavours, perfume oils, citronellal, silicon oils, organosilicons, pesticides, Beta-carotene and a pharmacologically active agent.
[0112] The term pharmacologically active agent when used herein may refer to a substance useful for the treatment of or the prevention of a condition affecting a human or other animal. Said condition may be a disease, a disorder or a physiological condition. It will be appreciated that the active agent may not directly affect the underlying condition, but may be used as an adjuvant with a further active agent to enhance the effectiveness of the other active agent. Thus, the term pharmacologically active agent herein includes all classes of pharmacologically active agents, whether adjuvant or therapeutic, that may be provided to a subject through oral administration. When used herein, the term pharmacologically active agent and drug may be used interchangeably and so the term drug may be interpreted based on the definition of active agent. Examples of pharmacologically active agents include, but are not limited to ibuprofen, fenofibrate, and isotrentinoin.
[0113] Further active agents that may be mentioned herein may include, but are not limited to, carbon metabolites (e.g. glucose, fructose, fumarate, etc.), electron acceptors (e.g. nitrate, peroxide, etc.), as well as a vitamin, such as vitamin A, B1, B2, B3, B6, B12, D, E, biotin, folate, and panothenate; minerals such as calcium, magnesium, selenium, and zinc; an amino acid such as asparagine, carnitine, glutamine, and serine; an antioxidant selected from coenzyme Q10, glutathione, and cysteine; or a metabolite such as lipoic acid, oleic add, choline, inositol, fructose, glucose, insulin, epigallocatechin gallate, and mixtures thereof.
[0114] As noted above, the nanoparticulate compositions may be a composition where some or all of the nanoparticles are in the form of a vesicle. When the nanoparticles are in the form of a vesicle, the amphipathic block copolymer may be arranged in the form of a membrane with an outer and inner surface, which inner surface defines a core region. This is analogous to a phospholipid cell membrane.
[0115] In embodiments of the invention, where some or all of the nanoparticles are in the form of a vesicle, said vesicle may have a core region that may comprise an active agent and/or aliquid. The nature of the active agent and liquid in the core will be determined by the nature of the nanoparticles that have been formed, as discussed in more detail below. Vesicles that may be mentioned herein may be nanoparticles having an average diameter of from 100 to 500 nm.
[0116] For example, the amphipathic block copolymer may be arranged so that the outer and inner surface of the membrane are formed from the hydrophilic blocks of the copolymer. In such vesicles, the amphipathic block copolymer may have an average ratio of hydrophobic repeating units to hydrophilic repeating units of from 1:9 to at least 9:1, such as from 1:1 to 5000:1, such as from 4:1 to 2000:1, such as from 9:1 to 1000:1. Vesicles of this type may be particularly suited to encapsulating hydrophilic active agents and polar liquids in the core of the vesicle.
[0117] For example, in vesicles where the amphipathic block copolymer may be arranged so that the outer and inner surface of the membrane are formed from the hydrophilic blocks of the copolymer, a hydrophilic active agent may be substantially (e.g. 90 wt %, such as 95 wt %, such as 99.9 wt %) encapsulated in the core region of the vesicle. Examples of hydrophilic active agents include, but are not limited to vitamin C, peptides, glycerol, dyes and flavours.
[0118] In addition or in place of the hydrophilic active agent, the composition may further comprise a polar liquid that is encapsulated in the core region of the vesicle. For example, the polar liquid may consist of one or more of the group consisting of water, a C.sub.1-6 monoalcohol, a C.sub.3-6 ketone, a glycol, acetonitrile, an amide, and a sulfoxide.
[0119] Examples of C.sub.1-6 monoalcohols include, but are not limited to, ethanol, methanol, propanol, isopropanol, and butanol. Examples of C.sub.3-6 ketones include, but are not limited to, acetone. Examples of glycols include, but are not limited to, ethylene glycols and polyethylene glycols. Examples of amides include, but are not limited to, dimethylformamide. Examples of sulfoxides include, but are not limited to, dimethylsulfoxide.
[0120] In alternative or additional embodiments of such vesicles (where the surfaces are formed from hydrophilic copolymer blocks), the composition may further comprise a hydrophobic active agent that is substantially (e.g. 90 wt %, such as 95 wt %, such as 99.9 wt %) encapsulated in the membrane of the vesicle. Examples of hydrophobic active agents include, but are not limited to, perfume oils, citronellal, silicon oils, organosilicons, pesticides, ibuprofen, fenofibrate, isotrentinoin and beta-carotene.
[0121] As will be appreciated, the polarity of the copolymeric blocks can be reversed, such that the amphipathic block copolymer may be arranged so that the outer and inner surface of the membrane are formed from the hydrophobic blocks of the copolymer. In such vesicles, the amphipathic block copolymer may have an average ratio of hydrophilic repeating units to hydrophobic repeating units of from 1:9 to at least 9:1, such as from 1:1 to 5000:1, such as from 4:1 to 2000:1, such as from 9:1 to 1000:1. Vesicles of this type may be particularly suited to encapsulating hydrophobic active agents and non-polar liquids in the core of the vesicle.
[0122] For example, in vesicles where the amphipathic block copolymer may be arranged so that the outer and inner surface of the membrane are formed from the hydrophobic blocks of the copolymer, a hydrophobic active agent may be substantially (e.g. 90 wt %, such as 95 wt %, such as 99.9 wt %) encapsulated in the core region of the vesicle. Examples of hydrophobic active agents include, but are not limited to perfume oils, citronellal, silicon oils, organosilicons, pesticides, ibuprofen, fenofibrate, isotrentinoin and beta-carotene. In addition or in place of the hydrophobic active agent, the composition may further comprise a non-polar liquid that is encapsulated in the core region of the vesicle. For example, the non-polar liquid consists of one or more of the group consisting of a C.sub.5-10 alkane, a C.sub.5-10 alkene, a C.sub.5-10 alkyne, and a C.sub.6-10 arene, where said non-polar liquids are unsubstituted or substituted by one or more halogen atoms.
[0123] Examples of C.sub.5-10 alkanes include, but are not limited to, hexane. Examples of C.sub.5-10 alkenes include, but are not limited to, hexene. Examples of C.sub.5-10 alkynes include, but are not limited to, hexyne. Examples of C.sub.6-10 arenes include, but are not limited to, benzene and toluene. In addition, the above-mentioned examples may be substituted by one or more halogen atoms (e.g. Br, Cl, I or, more particularly, F). Examples of such substituted compounds include, but are not limited to, hexafluorobenzene, and tetrahydrofuran.
[0124] In alternative or additional embodiments of such vesicles (where the surfaces are formed from hydrophilic copolymer blocks), the composition may further comprise a hydrophilic active agent that is substantially (e.g. 90 wt %, such as 95 wt %, such as 99.9 wt %) encapsulated in the membrane of the vesicle. Examples of hydrophilic active agents are provided hereinbefore.
[0125] In embodiments of the invention, where some or all of the nanoparticles are in the form of a micelle, said micelle may have a core region that may comprise an active agent. The nature of the active agent in the core will be determined by the nature of the nanoparticles that have been formed. For example, micelles formed such that the hydrophilic blocks of the amphipathic block copolymer are arranged on the surface of the nanoparticle may be suitable for the encapsulation of hydrophobic active agents (as described hereinbefore). Alternatively, micelles formed such that the hydrophobic blocks of the amphipathic block copolymer are arranged on the surface of the nanoparticle may be suitable for the encapsulation of hydrophilic active agents (as described hereinbefore). Micelles that may be mentioned herein may be nanoparticles having an average diameter of from 25 to 100 nm, such as from 28 to 80 nm.
[0126] For example, when the nanoparticles are in the form of a micelle, the amphipathic block copolymer may have an average ratio of hydrophobic repeating units to hydrophilic repeating units of from 1:100 to 10:1, such as from 1:10 to 10:1, such as from 1:1 to 5:1, such as from 1.8:1 to 4:1. In such materials, the hydrophobic repeating units will form the surface of the nanoparticles, with the hydrophilic repeating units forming the core. In embodiments that have the opposite arrangement, the amphipathic block copolymer may have an average ratio of hydrophilic repeating units to hydrophobic repeating units of from 1:100 to 10:1, such as from 1:10 to 10:1, such as from 1:1 to 5:1, such as from 1.8:1 to 4:1. In such materials, the hydrophilic repeating units will form the surface of the nanoparticles, with the hydrophobic repeating units forming the core.
[0127] In embodiments of the invention, where some or all of the nanoparticles are in the form of cylindrical worm structures, said cylindrical worm structures may have a core region that may comprise an active agent. The nature of the active agent in the core will be determined by the nature of the nanoparticles that have been formed. For example, cylindrical worm structures formed such that the hydrophilic blocks of the amphipathic block copolymer are arranged on the surface of the nanoparticle may be suitable for the encapsulation of hydrophobic active agents (as described hereinbefore). Alternatively, cylindrical worm structures formed such that the hydrophobic blocks of the amphipathic block copolymer are arranged on the surface of the nanoparticle may be suitable for the encapsulation of hydrophilic active agents (as described hereinbefore). Cylindrical worm structures that may be mentioned herein may be nanoparticles having an average diameter of from 50 to 200 nm, such as from 70 to 150 nm.
[0128] For example, when the nanoparticles are in the form of cylindrical worm structures, the amphipathic block copolymer may have an average ratio of hydrophobic repeating units to hydrophilic repeating units of from 1:1 to 100:1, such as from 4:1 to 9:1. In such materials, the hydrophobic repeating units will form the surface of the nanoparticles, with the hydrophilic repeating units forming the core. In embodiments that have the opposite arrangement, the amphipathic block copolymer may have an average ratio of hydrophilic repeating units to hydrophobic repeating units of from 1:1 to 100:1, such as from 4:1 to 9:1. In such materials, the hydrophilic repeating units will form the surface of the nanoparticles, with the hydrophobic repeating units forming the core.
[0129] The amphipathic block copolymer may be a poly(acrylic acid-co-acrylate ester) or a poly(polyethylene glycol ether methacrylate)-co-acrylate ester, optionally where the amphipathic block copolymer may be poly(methacrylic acid-co-methyl methacrylate) and/or poly((polyethylene glycol monomethyl ether methacrylate)-co-methyl methacrylate). In certain embodiments, the amphipathic block copolymer may be a poly(acrylic acid-co-acrylate ester), such as poly(methacrylic acid-co-methyl methacrylate).
[0130] In certain embodiments, the amphipathic block copolymer may be crosslinked to permanently stabilise the obtained assembly structures (micelles, worms, and vesicles) and hence to give them long term stability.
[0131] While it is possible to make compositions that only comprise one of micelles, cylindrical worm structures or vesicles, it is also possible to form compositions where any two or all three of these structures are formed. In preferred embodiments that may be mentioned herein, the compositions are formed from only one of micelles, cylindrical worm structures or vesicles or from mixtures of micelles and cylindrical worm structures or cylindrical worm structures and vesicles. When present in a mixture comprising any two of micelles, cylindrical worm structures or vesicles, the mixture may contain from 0.1 to 99.9 wt % of each type of nanoparticle (with the sum adding to 100 wt %). When present in a mixture comprising all three of micelles, cylindrical worm structures or vesicles, the mixture may contain from 0.05 to 99.9 wt % of each type of nanoparticle (with the sum adding to 100 wt %).
[0132] As will be appreciated, the current invention also relates to methods of making the above-mentioned nanoparticulate compositions. Thus, there is also disclosed a method of forming a nanoparticulate composition as described above using polymerisation induced self-assembly, the method comprising the step of forming a block copolymer by reacting a monomeric material with a macroinitiator compound in the presence of an initiator compound, a catalyst and a solvent, wherein: [0133] if the monomeric material polymerises to provide a hydrophobic polymer block, then the macroinitiator compound is a hydrophilic polymer or oligomer or if the monomeric material polymerises to provide a hydrophilic block, then the macroinitiator compound is a hydrophobic polymer or oligomer; [0134] the macroinitiator compound is terminated with a halogen atom; [0135] the monomeric material, the macroinitiator compound, the initiator compound, the catalyst and the solvent are all substantially free of compounds comprising sulfur; and [0136] the monomeric material, the macroinitiator compound, the initiator compound, the catalyst and the solvent are all substantially free of a heavy metal.
[0137] The method disclosed above does not make use of heavy metals and/or sulfur as either part of a catalyst or as a reactant/reagent. As such, the compositions produced are either completely free of sulfur and heavy metals or contain a substantially reduced amount of said materials relative to compostions made using other methods.
[0138] Any suitable catalyst may be used in the method disclosed herein. For example, the catalyst may be a metal halide, where the halogen atom of the macroinitiator compound and the halide atom have the same atomic number and the metal may be selected from sodium, potassium, magnesium, and calcium. For example, the metal in the metal halide may be selected from sodium or potassium. In particular embodiments, the metal halide used as a catalyst may be sodium iodide and/or the halogen atom in the macroinitiator compound may be iodine.
[0139] Any suitable initiator compound may be used in the method disclosed herein. For example, the initiator compound may be an azo initiator, such as 2,2-azobis(2,4-dimethylvaleronitrile).
[0140] The macroinitiator compound used herein may contain a suitable number of repeating units. For example, the macroinitiator compound may contain an average of from 1 to 1000 repeating units, such as from 5 to 100 repeating units, such as from 10 to 20 repeating units.
[0141] In certain embodiments of the invention, the monomeric material may be an acrylate ester (e.g. methyl methacrylate), and the macroinitiator may be a poly(acrylic acid) or an oligo(acrylic acid) (e.g. poly(methylacrylic acid) or an oligo(methacrylic acid)). In such embodiments, the solvent used for conducting the method may be a polar solvent. Examples of suitable polar solvents include, but are not limited to, water, a C.sub.1-6 monoalcohol, a C.sub.3-6 ketone, a glycol, acetonitrile, an amide, and a sulfoxide.
[0142] Examples of C.sub.1-6 monoalcohols include, but are not limited to, ethanol, methanol, propanol, isopropanol, and butanol. Examples of C.sub.3-6 ketones include, but are not limited to, acetone. Examples of glycols include, but are not limited to, ethylene glycols and polyethylene glycols. Examples of amides include, but are not limited to, dimethylformamide. Examples of sulfoxides include, but are not limited to, dimethylsulfoxide.
[0143] In embodiments of the invention where the macroinitiator may be a poly(acrylic acid) or an oligo(acrylic acid), the macroinitiator compound may have the formula I:
##STR00003##
where x is from 1 to 1000, such as from 5 to 100, such as from 10 to 20; and R is a branched or unbranched C.sub.1-10 alkyl group that is unsubstituted or substituted by one or more of CN, aryl and CO.sub.2R, wherein R is H or C.sub.1-6 a alkyl group, optionally wherein R is CH(CH.sub.3).sub.2CN.
[0144] The term aryl when used herein includes C.sub.6-14 (such as C.sub.6-13 (e.g. C.sub.6-10)) aryl groups. Such groups may be monocyclic, bicyclic or tricyclic and have between 6 and 14 ring carbon atoms, in which at least one ring is aromatic. The point of attachment of aryl groups may be via any atom of the ring system. However, when aryl groups are bicyclic or tricyclic, they are linked to the rest of the molecule via an aromatic ring. C.sub.6-10 aryl groups include phenyl, naphthyl and the like, such as 1,2,3,4-tetrahydronaphthyl, indanyl, indenyl and fluorenyl. Embodiments of the invention that may be mentioned include those in which aryl is phenyl.
[0145] In alternative embodiments of the invention, the monomeric material may be an acrylic acid (e.g. methacrylic acid) and the macroinitiator compound may be a poly(acrylate ester) or an oligo(acrylate ester), such as poly(methacrylate) or oligo(methacrylate). In such embodiments, the solvent may be a non-polar solvent. Examples of suitable non-polar solvents include, but are not limited to, C.sub.5-10 alkane, a C.sub.5-10 alkene, a C.sub.5-10 alkyne, and a C.sub.6-10 arene, where said non-polar liquids are unsubstituted or substituted by one or more halogen atoms.
[0146] Examples of C.sub.5-10 alkanes include, but are not limited to, hexane. Examples of C.sub.5-10 alkenes include, but are not limited to, hexene. Examples of C.sub.5-10 alkynes include, but are not limited to, hexyne. Examples of C.sub.6-10 arenes include, but are not limited to, benzene and toluene. In addition, the above-mentioned examples may be substituted by one or more halogen atoms (e.g. Br, Cl, I or, more particularly, F). Examples of such substituted compounds include, but are not limited to, hexafluorobenzene, and tetrahydrofuran.
[0147] In embodiments of the invention where the macroinitiator may be a poly(acrylate ester) or an oligo(acrylate ester), the macroinitiator compound may have the formula II:
##STR00004##
where y is from 1 to 1000, such as from 5 to 100, such as from 10 to 20; and R is a branched or unbranched C.sub.1-10 alkyl group that is unsubstituted or substituted by one or more of CN, aryl and CO.sub.2R, wherein R is H or a C.sub.1-6 alkyl group, optionally wherein R is CH(CH.sub.3).sub.2CN.
[0148] In the methods described above:
[0149] (a) the molar ratio of monomeric material to macroinitiator compound in the solvent is from 30:1 to 500:1, such as from 50:1 to 300:1; and/or
[0150] (b) the molar ratio of monomeric material to catalyst in the solvent is from 150:1 to 300:1, such as from 190:1 to 200:1; and/or
[0151] (c) the molar ratio of monomeric material to initiator in the solvent is from 150:1 to 300:1, such as from 190:1 to 200:1. For the avoidance of doubt, these are generic features that may be shared between any of the embodiments described hereinbefore.
[0152] In certain embodiments, the step of forming a block copolymer may be conducted in the presence of a crosslinking agent. Any suitable crosslinking agent may be used. Examples of suitable crosslinking agents include, but are not limited to, an ethylene glycol diacrylate ester (e.g. ethylene glycol dimethyacrylate) when the monomeric material is an acrylate ester or an ethylene glycol diacrylic acid (e.g. ethylene glycol dimethacrylic acid) when the monomeric material is an acrylic acid. In embodiments where a crosslinking agent is present, the molar ratio of monomeric material to crosslinking agent in the solvent may be from 10:1 to 50:1, such as from 20:1 to 40:1.
[0153] In certain embodiments of the invention, the step of forming a block copolymer may be conducted in the presence of an active agent. This allows for the convenient formation of the composition. In such embodiments, the molar ratio of monomeric material to active agent in the solvent may be from 1:1 to 300:1, such as from 100:1 to 250:1, such as from 150:1 to 225:1, such as from 190:1 to 200:1. However, this method may not be suitable for all potential active agents (e.g. peptides). For such active agents (peptides) the active agent may be conveniently encapsulated after the nanoparticle has been formed by osmosis, using standard techniques.
[0154] The active agents described hereinbefore may be incorporated using the methods described above. It will be appreciated that the methods described above may provide particles having shells/surfaces that are hydrophilic or hydrophobic in nature and the active agents that may be deposited in the relevant compartments are discussed hereinbefore in relation to the final products and so will not be repeated here.
[0155] The method described above may be used to obtain nanoparticles in the form of vesicles under suitable conditions (whether only vesicles or in a mixture with micelles and cylindrical worm structures or vesicles and cylindrical worm structures). Suitable conditions include those in which the molar ratio of monomeric material to macroinitiator compound in the solvent is from 100:1 to 500:1, such as from 110:1 to 300:1 and the reaction is allowed to occur for a period of time such that an average ratio of monomeric material repeating units to macroinitiator repeating units from 1:9 to at least 9:1, such as from 1:1 to 5000:1, such as from 4:1 to 2000:1, such as from 9:1 to 1000:1 is obtained.
[0156] The method described above may be used to obtain nanoparticles in the form of micelles under suitable conditions (whether only micelles or in a mixture with vesicles and cylindrical worm structures or micelles and cylindrical worm structures). Suitable conditions include those in which the molar ratio of monomeric material to macroinitiator compound in the solvent is from 40:1 to 100:1, such as from 60:1 to 90:1 and the reaction is allowed to occur for a period of time such that an average ratio of monomeric material repeating units to macroinitiator repeating units is from 1:100 to 10:1, such as from 1:10 to 10:1, such as from 1:1 to 5:1, such as from 1.8:1 to 4:1 is obtained.
[0157] The method described above may be used to obtain nanoparticles in the form of cylindrical worm structures under suitable conditions (whether only cylindrical worm structures or in a mixture with vesicles and micelles, micelles and cylindrical worm structures or vesicles and cylindrical worm structures). Suitable conditions include those in which the molar ratio of monomeric material to macroinitiator compound in the solvent is from 40:1 to 200:1, such as from 60:1 to 150:1 and the reaction is allowed to occur for a period of time such that an average ratio of monomeric material repeating units to macroinitiator repeating units is from 1:1 to 100:1, such as from 4:1 to 9:1 is obtained.
[0158] The macroinitiator compound used in the methods described herein may be formed by polymerising a monomeric material with a dormant initiator compound in the presence of an initiator compound, a catalyst and a solvent, wherein [0159] the dormant initiator compound is a hydrocarbon comprising a halogen atom; [0160] the monomeric material, the dormant initiator compound, the initiator compound, the catalyst and the solvent are all substantially free of compounds comprising sulfur; and [0161] the monomeric material, the dormant initiator compound, the initiator compound, the catalyst and the solvent are all substantially free of a heavy metal.
[0162] Any suitable catalyst may be used in this macroinitiator formation method. For example, the metal halides described above to form the nanoparticulate composition may be used. For example, the metal halide may be sodium iodide and the halogen atom in the dormant initiator compound may be iodine. The initiator used in this macroinitiator formation method may be the same as used to form the nanoparticulate composition, as described above. That is, the initiator compound may be an azo initiator, such as is 2,2-azobis(2,4-dimethylvaleronitrile).
[0163] In certain embodiments that may be described herein, the macroinitiator may contain an average of from 1 to 1000 repeating units, such as from 5 to 100 repeating units, such as from to 20 repeating units.
[0164] Any suitable substance may be used as the dormant initiator compound. Examples of a suitable dormant initiator compound include, but are not limited to, 2-iodo-2-methylpropionitrile.
[0165] The invention will now be described with reference to the following non-limiting examples.
EXAMPLES
Materials
[0166] Methyl methacrylate (MMA) (>99.8%, Tokyo Chemical Industry (TCI), Japan), methacrylic acid (MAA) (>99%, TCI), ethylene glycol dimethacrylate (EGDMA) (98%, Sigma Aldrich), iodo-2-methylpropionitrile (CP-I) (>95%, TCI), NaI (>99.5%, Kanto), 2,2-azobis(2,4-dimethyl valeronitrile) (V65) (95%, Wako Pure Chemical, Japan), and trimethylsilyldiazomethane (10% in hexane) (TCI) were used as received.
Analytical Methods
[0167] For the gel permeation chromatography (GPC) analysis, PMAA-1 and PMAA-PMMA-1 were methylated prior to the analysis (L. Couvreur, et al., Macromolecules, 2003, 36, 8260-8267). PMAA-1 (purified by reprecipitation) (15 mg) or PMAA-PMMA-1 (not purified but dried after the polymerization) (15 mg) was first dissolved in tetrahydrofuran (THF) (1 mL). Trimethylsilyl)diazomethane (1.5 equivalents to the COOH group) was added into the solution. The solution was stirred overnight at room temperature and analysed with GPC. The GPC analysis was performed on a Shodex GPC-101 liquid chromatograph (Tokyo, Japan) equipped with two Shodex KF-804L mixed gel columns (3008.0 mm; bead size=7 m; pore size=20-200 ). The eluent was THF at a flow rate of 1.0 mL/min. Sample detection was conducted using a Shodex differential refractometer RI-101. The column system was calibrated with standard poly(methyl methacrylate)s (PMMAs).
[0168] The NMR spectra were recorded on a Bruker (Germany) AV500 spectrometer (500 MHz) and Bruker BBFO400 spectrometer (400 MHz) at ambient temperature. DMSO-d.sub.6 (Cambridge Isotope Laboratories (CIL), USA) and D.sub.2O (CIL) were used as the solvents for the NMR analysis.
[0169] Transmission electron microscopy (TEM) images were obtained on a JEM-1400 transmission electron microscope (JEOL, Japan) operated at 100 kV. The TEM grid was carbon-coated on 200 mesh (copper) (Ted Pella, USA). The cryogenic TEM (cryo-TEM) image was obtained in a FEI Titan Krios transmission electron microscope equipped with an auto sampler and a field emission gun (FEG) and performed under 300 kV. The image was captured with a Falcon II camera (4*4) with magnification of 29,000 and a pixel size of 2.873 . The vitrification of the sample was performed using a vitrification robot (FEI Vitrobot Mark IV, Hillsboro, Oreg., USA). A 5 L stock solution was added on a grid (Quantifoil, R2/2, Holey Carbon film) which was freshly glow-discharged before use at 20 mA for 60 s. An excess sample was blotted away with a filter paper at room temperature, in 100% humidity, in a blotting time of 2 s, and with a blotting force of 1. Then it was vitrified in liquid ethane and immediately transferred to a cryo-holder.
[0170] The dynamic light scattering (DLS) measurement was carried out on a Malvern Zetasizer Nano ZSP (Worcestershire, UK). The test angle for the DLS analysis was 173 (backscattering detection). Water was used as the solvent.
Example 1. Synthesis and Characterisation of PMAA.SUB.20.-PMMA.SUB.180 .Block Copolymer by NTMC-CRP and PISA (Via NTMC-CRP)
[0171] The PMAA.sub.x-PMMA.sub.y block copolymer of the current invention was synthesised by a combination of two processes sequentially (where x represents the DP of PMAA and y represents the DP of PMMA). The PMAA-I macroinitiators were first synthesised by non-transition-metal catalysed controlled radical polymerisation (NTMC-CRP), which were then subsequently reacted with MMA monomers in polymerisation-induced self-assembly (PISA) to form the PMAA-PMMA block copolymer. In this specific example, PMAA.sub.20-PMMA.sub.180 was synthesised.
Synthesis of PMAA-I Macroinitiators by NTMC-CRP
Experimental Procedures
[0172] PMAA-I hydrophilic macroinitiators were prepared using NaI-catalysed NTMC-CRP (
[0173] In one specific example, a mixture (2 g) of MAA (8 M), CP-I (160 mM), V65 (266 mM), NaI (160 mM), and water (50 wt % of the mixture) was heated in a Schlenk flask at 45 C. under argon atmosphere with magnetic stirring. The reaction mixture was diluted with 1 mL ethanol. The polymer was reprecipitated in diethyl ether and dried under vacuum.
Characterisation
[0174] The as-synthesised PMAA-I polymer was first methylated with trimethylsilyldiazomethane to form PMMA-I, prior to characterisation by GPC using THF as an eluent. A PMAA-I with M.sub.n=1700 (DP=20) and PDI=1.15 (after the purification) was obtained, where M.sub.n is the number-average molecular weight, DP is the degree of polymerisation and PDI is the polydispersity index. Similarly, PMAA-I polymers with DP=11 and 5 were also obtained using a reaction time of 0.7 h and 0.5 h respectively (Table 1, entries 2 and 3). These PMAA-I polymers were used as hydrophilic macroinitiators in the following PISA experiments.
TABLE-US-00001 TABLE 1 Synthesis of PMAA-I macroinitiators with various DP. [MAA].sub.0/[CP-I].sub.0/[V65].sub.0/[NaI].sub.0 T t Conv. Entry (mM).sup.a ( C.) (h) (%) M.sub.n.sup.b DP.sup.b PDI.sup.b 1 8000/160/266/160 45 1.2 26 1700 20 1.15 2 8000/160/266/160 45 0.7 15 900 11 1.12 3 8000/160/266/160 45 0.5 11 400 5 1.12 .sup.aSolution polymerisation in 50 wt % water (solvent). .sup.bThe M.sub.n, DP, and PDI values of PMAA-I determined after purification (reprecipitation). PMAA-I was methylated to form PMMA-I, which was analysed with GPC using THF as the eluent. The M.sub.n values (e.g. 1700 in entry 1) for PMAA-I were calculated from those (e.g. 2000 in entry 1) determined for PMMA-I, considering the molecular weights of MAA (86) and MMA (100) monomer units.
Synthesis of PMAA.sub.20-PMMA.sub.180 block copolymer by PISA (via NTMC-CRP)
Experimental Procedures
[0175] For the PISA reaction, methyl methacrylate (MMA) was chosen as the hydrophobic monomer and ethanol was chosen as the solvent. Typically, to synthesise PMAA.sub.20-PMMA.sub.180, a mixture of MMA (300 eq.), PMAA-I (DP=20) (1 eq., macroinitiator), V65 (1.5 eq., azo initiator), NaI (1.5 eq., catalyst) and ethanol was heated at 60 C. for 14 h (
[0176] In an optimised reaction, a mixture (1.5 g) of MMA (8 M), PMAA-I (DP=20, 27 mM), NaI (40 mM), V65 (40 mM), and ethanol (90 wt % of the mixture) was heated in a Schlenk flask at 60 C. under argon atmosphere with magnetic stirring. After the prescribed time t, an aqueous solution (50 L) of NaHCO.sub.3 (0.9 equivalents to the COOH group) was added to the reaction mixture. An aliquot (0.1 mL) of the solution was dried under vacuum, methylated, and analysed with GPC. Another aliquot (0.1 mL) was diluted with DMSO-de (0.9 mL) and analysed with .sup.1H NMR for obtaining the monomer conversion. Another aliquot (0.1 mL) was diluted with an aqueous solution (0.5 mL) of KCl (1 mM), which then formed the stock solution. The stock solution (50 L) was further diluted with water (0.6 mL) and analysed by DLS. The stock solution (10 L) was also dropped on a TEM grid, dried under vacuum, and analysed by TEM.
[0177] The addition of NaHCO.sub.3 and KCl stabilised the self-assemblies and prevented their aggregation upon storage at room temperature. Without this treatment, after cooling from the reaction temperature of 60 C., the self-assemblies gradually aggregated and precipitated. This treatment was required due to the nature of the PMAA-PMMA polymer, but may not be required for other types of polymers synthesised by this method.
Characterisation
[0178] It was observed from the GPC curves that a large fraction of the macroinitiator chains smoothly extended to block copolymers, indicating high block-efficiency (
[0179] At 14 h, PMAA.sub.20-PMMA.sub.180 (with 180 DP of PMMA) was generated and self-assembled to vesicles, as shown by the TEM image (
[0180] The treated polymer sample was also frozen in liquid ethane and a cryogenic TEM (cryo-TEM) analysis was conducted. The cryo-TEM (in situfrozen sample) (
[0181] Although the expected morphologies were observed in both the TEM and cryo-TEM images, they do not represent the only morphologies in the system (as this could be partially due to sample preparation and/or morphological changes that may occur immediately after the reaction. A direct evidence was obtained as shown by the crosslinking experiments (as discussed in Example 3), in which the morphologies were fixed by crosslinking in situ during the polymerisation process. The crosslinking results supported that the morphologies (sphere, worm, and vesicle) observed with TEM below were the actual morphologies generated during the polymerisation process, and not generated during the aqueous treatment or the TEM sample preparation.
[0182] The dynamic light scattering (DLS) analysis shows that the hydrodynamic size (DLS peak top) of the assembly was 465 nm (Table 2, entry 11). The contour length of this block copolymer (200 units) was determined to be 50 nm. The assembly size of 465 nm was much larger than twice of the contour length (which is 100 nm), indicating that the assembly was not a micelle but a vesicle. Notably, the solid content was as high as 7.6 wt % (0.5 wt % from the original macroinitiator and 7.1 wt % from the PMMA segment generated in the polymerisation). Therefore, this indicated that the NTMC-CRP-PISA system successfully yielded nano-capsules at a high solid content.
Example 2. Synthesis and Characterisation of PMAA.SUB.x.-PMMA.SUB.y .Block Copolymer (of Various x and y Values) and their Respective Morphologies
[0183] The synthesis of PMAA.sub.x-PMMA.sub.y block copolymer with various x and y values was carried out following the method described in Example 1. PMAA.sub.x-PMMA.sub.y block copolymer of various lengths were achieved by varying the DP of the PMAA-I macroinitiators, the concentrations of MMA monomers to PMAA-I macroinitiators, and the reaction time (t), as listed in Table 2.
[0184] PMAA-I macroinitiators with three different DPs (5, 11, and 20) was used and the DP of the PMMA segment was varied from 0 to 193. A phase diagram depicting the morphologies of the various self-assembled polymers with various DP is as shown in
[0185] Using the PMAA.sub.5-I macroinitiator with DP=5, a series of PISA experiments with varying of the DP of the PMMA segment (at DP of PMAA=5 in the horizontal axis in
[0186] The generated block copolymer was soluble for PMAA.sub.5-PMMA.sub.10 with a short PMMA segment of DP=10. As the DP of the PMMA segment increased, the block copolymer self-assembled to micelles (spheres) for PMAA.sub.5-PMMA.sub.22 (DP=22), worms for PMAA.sub.5-PMMA.sub.40 (DP=40), and vesicles for PMAA.sub.5-PMMA.sub.86 (DP=86) (
[0187] An increase in the DP of PMMA to 86 led to the assembly of vesicles with a larger hydrodynamic size of 184 nm (Table 2, entry 2). This size was much larger than twice of the contour length of PMAA.sub.5-PMMA.sub.86 (45 nm), which was consistent with the vesicle structure observed in the TEM image (
[0188] Using the PMAA.sub.11-I and PMAA.sub.20-I macroinitiators with DP=11 and 20, the DP of the PMMA segment (
TABLE-US-00002 TABLE 2 Synthesis of PMMA.sub.x-PMMA.sub.y by varying the DP of the PMAA-I macroinitiators, the concentrations of MMA monomers to PMAA-I macroinitiators, and the reaction time (t), in ethanol (90 wt %) at 60 C. [MMA].sub.0/ Hydro- DLS Size [PMAA-I].sub.0/ dynamic Distri- Code in DP of [NaI].sub.0/[V65].sub.0 Conv DP of Code of Block f.sub.PMMA Diameter.sup.c bution Assembled FIGS. Entry PMAA (mM).sup.a t (h) (%) PMMA.sup.b PDI.sup.b Copolymer inital final (nm) Index Structure.sup.d 2 and 3 1 5 8000/133/40/40 0.3 30 10 1.10 PMAA.sub.5-PMMA.sub.10 0.67 0.70 Soluble 0.6 50 22 1.10 PMAA.sub.5-PMMA.sub.22 0.81 0.84 28 0.100 S A 1 64 33 1.32 PMAA.sub.5-PMMA.sub.33 0.87 0.88 70 0.060 W 1.5 79 40 1.39 PMAA.sub.5-PMMA.sub.40 0.89 0.90 106 0.080 W B 2 5 8000/80/40/40 1.5 71 65 1.34 PMAA.sub.5-PMMA.sub.65 0.93 0.94 154 0.060 V 2.5 80 86 1.39 PMAA.sub.5-PMMA.sub.86 0.95 0.95 184 0.080 V C 3 5 8000/53/40/40 3 69 107 1.49 PMAA.sub.5-PMMA.sub.107 0.96 0.96 200 0.140 V 4 5 8000/40/40/40 3 82 177 1.45 PMAA.sub.5-PMMA.sub.177 0.98 0.98 440 0.220 V D 5 11 8000/160/40/40 1 48 20 1.18 PMAA.sub.11-PMMA.sub.20 0.65 0.68 Soluble 6 11 8000/80/40/40 1.5 51 42 1.20 PMAA.sub.11-PMMA.sub.42 0.79 0.82 43 0.105 S E 2 72 65 1.36 PMAA.sub.11-PMMA.sub.65 0.86 0.87 138 0.120 W F 2.3 80 77 1.35 PMAA.sub.11-PMMA.sub.77 0.88 0.89 159 0.176 W + V 7 11 8000/53/40/40 3 70 95 1.41 PMAA.sub.11-PMMA.sub.95 0.90 0.91 297 0.126 V G 6 83 186 1.40 PMAA.sub.11-PMMA.sub.186 0.94 0.95 375 0.360 V H 8 20 8000/80/40/40 1 34 30 1.10 PMAA.sub.20-PMMA.sub.30 0.60 0.64 Soluble 1.6 58 60 1.25 PMAA.sub.20-PMMA.sub.60 0.75 0.78 50 0.100 S I 2 68 70 1.34 PMAA.sub.20-PMMA.sub.70 0.78 0.80 80 0.106 S 9 20 8000/53/40/40 3.5 70 85 1.30 PMAA.sub.20-PMMA.sub.85 0.81 0.83 110 0.268 W J 4 76 95 1.36 PMAA.sub.20-PMMA.sub.95 0.83 0.85 121 0.200 W K 4.8 80 134 1.45 PMAA.sub.20-PMMA.sub.134 0.87 0.89 150 0.215 W + V 10 20 8000/40/40/40 5 73 150 1.43 PMAA.sub.20-PMMA.sub.150 0.88 0.90 211 0.168 V L 5.2 82 160 1.44 PMAA.sub.20-PMMA.sub.160 0.89 0.90 380 0.300 V M 11 20 8000/27/40/40 10 68 170 1.39 PMAA.sub.20-PMMA.sub.170 0.89 0.91 390 0.369 V 14 75 180 1.40 PMAA.sub.20-PMMA.sub.180 0.90 0.91 465 0.450 V N .sup.aThe mixture of MMA, PMAA-I, NaI, and V65 at the described concentration was diluted with ethanol (ethanol content = 90 wt %). .sup.bDP and PDI were determined by THF-GPC after methylation of the PMAA segment. .sup.cThe DLS peak top value. .sup.dS = sphere, W = worm, and V = vesicle.
Example 3. Synthesis of Fixed PMAA.SUB.x.-(PMMA/EGDMA).SUB.y .Block Copolymer, and Comparison of its Stability in Basic Conditions with PMAA.SUB.x.-PMMA.SUB.y
[0189] Synthesis of PMAA.sub.x-(PMMA/EGDMA).sub.y
[0190] In Examples 1 and 2, a non-crosslinkable monomer MMA was used in the second block, which gave assembly structures that were not fixed. To fix the assembly structures, a cross-linkable divinyl monomer, i.e. ethylene glycol dimethacrylate (EGDMA), was used as a co-monomer with MMA (instead of MMA alone) in the second block in this example.
[0191] With that, the synthesis of PMAA.sub.x-(PMMA/EGDMA).sub.y block copolymer with various x and y values was carried out following the method described in Examples 1 and 2, and as listed in Table 3. Relatively small molar fractions (2.5-4.8% in initial studies, or 4.8-9.1% in optimised studies) of EGDMA were used in order for the crosslinking to take place after the assembly structures are generated. The EGDMA fraction was set smaller in the order of spheres (4.8% in initial studies, or 9.1% in optimised studies), worms (3.4% in initial studies, or 6.5% in optimised studies), and vesicles (2.5% in initial studies, or 4.8% in optimised studies) to delay the crosslinking point at a larger DP of the second segment.
Comparison of the Stability of PMAA.sub.x-(PMMA/EGDMA).sub.y with PMAA.sub.x-PMMA.sub.y in Basic Condition
[0192] In Example 2, using the PMAA.sub.20-I macroinitiator with DP=20, spheres, worms and vesicles were obtained for PMAA.sub.20-PMMA.sub.60, PMAA.sub.20-PMMA.sub.85 and PMAA.sub.20-PMMA.sub.160, respectively. These assemblies decomposed in a strongly basic condition (pH>12) with sodium hydroxide (NaOH). The DLS analysis (
[0193] The crosslinked assemblies were treated in a basic condition (pH>12) with NaOH. Unlike the non-crosslinked assemblies, the crosslinked assemblies did not decompose in the basic condition, as shown in the DLS analysis (
[0194] Importantly, the morphologies (sphere, worm, and vesicle) observed from the TEM images were the same with (
TABLE-US-00003 TABLE 3 Synthesis of PMAA.sub.x-(PMMA/PEGDMA).sub.y in ethanol (90 wt %) at 60 C. [MMA].sub.0/[EGDMA].sub.0/ [PMAA.sub.20-I].sub.0/[V65].sub.0/ DLS [NaI].sub.0 (mM).sup.a Hydrodynamic DLS Size (subsequent, Code of Block Diameter Distribution Assembled Code in Entry optimised values) t (h) Copolymer.sup.6 (nm).sup.c Index Structure.sup.d FIG. 6 1 7620/380/80/40/40 1.5 PMAA.sub.20- 73 0.100 S O (7270/730/80/40/40) (PMMA/PEGDMA).sub.60 after adding 79 0.164 S R aqueous NaOH 7730/270/53/40/40 3.5 PMAA.sub.20- 102 0.143 W P (7480/520/53/40/40) (PMMA/PEGDMA).sub.85 2 after adding 106 0.108 W S aqueous NaOH 7800/200/40/40/40 5.2 PMAA.sub.20- 400 0.400 V Q (7620/380/40/40/40) (PMMA/PEGDMA).sub.160 3 after adding 470 0.414 V T aqueous NaOH .sup.aThe mixture of MMA, EGDMA, PMAA20-I, NaI, and V65 at the described concentration was diluted with ethanol (ethanol content = 90 wt %). The subsequent, optimised concentrations are as shown in the brackets. .sup.bDP of (PMMA/PEGDMA) in entries 1, 2, and 3 in Table 3 corresponds to DP of PMMA in entries 8 (1.6 h), 9 (3.5 h), and 10 (5.2 h) in Table 2, respectively. .sup.cThe DLS peak top value. .sup.dS = sphere, W = worm, and V = vesicle.
Example 4. Synthesis and Characterisation of PMPC.SUB.x.-PLMA.SUB.y .Block Copolymer by NTMC-CRP and PISA (via NTMC-CRP)
[0195] The synthesis of PMPC.sub.x-PLMA.sub.y block copolymer with various x and y values was carried out following the method described in Example 1.
[0196] PMPC-I macroinitiator with a DP of 24 was first synthesised using MPC monomers, CP-I (as initiating dormant species), V65 (azo initiator) and tetrabutylammonium iodide (BNI, as catalyst) in ethanol (60 wt %) at 60 C. (
TABLE-US-00004 TABLE 4 Synthesis of PMPC-I macroinitiators. [MPC].sub.0/[CP-I].sub.0/ [V65].sub.0/[BNI].sub.0 T t Conv. Entry (mM) ( C.) (h) (%) M.sub.n PDI 1 8000/160/80/80 60 2.5 20 7000 1.11 (DP = 24)
[0197] The synthesis of PMPC.sub.x-PLMA.sub.y block copolymer was then carried out using the as-synthesised PMPC-I (as the macroinitiators), CP-I, V65 and BNI in ethanol (90 wt %) at 60 C. via the PISA process (
[0198] The DP of PMPC-I was calculated by the molecular weight obtained from GPC, using water as eluent. As the block polymers were not soluble in water, GPC was not performed and the DP of the block polymers was calculated using proton NMR.
TABLE-US-00005 TABLE 5a Synthesis of PMPC.sub.x-PLMA.sub.y block copolymer [MPC].sub.0/[CP-I].sub.0/ [V65].sub.0/[BNI].sub.0 T t Conv. Size Code in (mM) ( C.) (h) (%) M.sub.n PDI (nm) Structure FIG. 8 8000/160/80/80 60 3 20 150 sphere + A vesicle 18 88 128000 350 vesicle B (DP = 24 + 480)
Example 5. Synthesis and Characterisation of PMMA.SUB.y.-PMAA-PMMA.SUB.y .Block Copolymer by NTMC-CRP and PISA
[0199] The synthesis of the block copolymer was extended to using a bi-functional initiator to give the PMMA.sub.y-PMAA.sub.x-PMMA.sub.y block copolymer, following the method described in Example 1.
[0200] I-PMAA-1 macroinitiator with a DP of 30 was first synthesised using MAA monomers, PhE-II (as initiating dormant species), NaI as a catalyst, water as a solvent (50 wt %), at 45 C. for 1.3 h (
[0201] It was observed that the DP of the PMMA block can lead to the formation of self-assemblies with different morphologies. As the DP of the PMMA segments (20) increased, the morphology of the self-assemblies changed from spheres to worms to vesicles, as shown in
[0202] The presence of two chain ends with similar solubility property can allow self-assembling to occur such that no chain ends of the block copolymer chain are outside the periphery of the structures. This produces polymeric structures with low viscosity and high lubrication, with better penetration through the phospholipid bilayers of cells.
TABLE-US-00006 TABLE 5b Synthesis of PMMA.sub.y-PMAA.sub.x-PMMA.sub.y block copolymer [MMA].sub.0/[I-PMAA-I].sub.0/ DP of [V65].sub.0/[NaI].sub.0 t Conv. Size Code in I-PMAA-I (mM) (h) (%) M.sub.n PDI (nm) Structure Fig. 11 30 8000/20/10/40 2.5 22 6700 1.18 Soluble (DP = 30 + 37) 4 25 11200 1.20 50 Spheres A (DP = 30 + 82) 5.5 33 16000 1.21 120 Worms B (DP = 30 + 134) 7.5 57 18900 1.21 179 Vesicles (DP = 30 + 163) 9 64 20000 1.24 250 Vesicles C (DP = 30 + 170) 20 80 24000 1.24 300 Vesicles (DP = 30 + 210)
Example 6. Synthesis and Characterisation of Block Copolymer Synthesised Using Stimuli-Responsive Initiators
[0203] The currently claimed invention can be extended to the use of stimuli-responsive initiators to produce responsive block copolymer or assemblies. Such stimuli-responsive polymeric assemblies can respond to external stimuli like reducing agents (e.g. NaBH.sub.4) or heat to result in structural changes in the morphologies (i.e. by cleavage of SS bond or structural changes), which can potentially be use in releasing and delivery of materials encapsulated within the polymeric assemblies. Some examples of stimuli-responsive initiators are the redox-responsive initiator and thermos-responsive initiators as shown in
[0204] In this example, the redox-responsive initiator (SPHE-Br)2 was used to synthesise the redox-responsive block copolymer (
[0205] The I-PEGMA-1 macroinitiator was synthesised using PEGMA as a monomer, (SPHE-Br)2 as an initiator, BNI as a catalyst and NaI for in situ halogen exchange and methyl ethyl ketone (MEK) as a solvent at 60 C. for 3.5 h (Table 7). The as-synthesised I-PPEGMA-1 was purified by reprecipitation from a mixture of hexane and diethyl ether (1:1, v/v) as a non-solvent. The obtained macroinitiator was used in PISA to generate self-assemblies and the obtained block copolymer was cleaved using NaBH.sub.4. The cleaving of SS bond was indicated by the GPC chromatographs as shown in
TABLE-US-00007 TABLE 6 Synthesis of I-PEGMA-I macroinitiators using the redox-responsive initiator (SPHE-Br)2 [PEGMA].sub.0/[Initiator].sub.0/ [V65].sub.0/[BNI].sub.0/[NaI].sub.0 T t Conv. (mM) ( C.) (h) (%) M.sub.n PDI 8000/40/80/80/90 60 3.5 75 15000 1.31 in MEK (60 wt %) (DP = 50)
TABLE-US-00008 TABLE 7 Synthesis of redox-responsive PMMA-PEGMA-PMMA with (SPHE-Br)2 as the initiator [MMA].sub.0/[I-EGMA-].sub.0/ [V65].sub.0/[NaI].sub.0/] T t Conv. Size (mM) ( C.) (h) (%) M.sub.n PDI.sup.a (nm) PDI.sup.b Structure 8000/20/20/160 60 16 60 22000 1.45 200 0.212 (DP = 50 + 70) .sup.aObtained from GPC (molecular weight distribution) .sup.bObtained from DLS (assembly size distribution)
Example 7. Synthesis and Characterisation of PPEGMA.SUB.x.-PMMA.SUB.y .Block Copolymer by NTMC-CRP and PISA (Via NTMC-CRP, in Water or Ethanol)
Synthesis of PPEGMA-1 Macroinitiators
[0206] PPEGMA-1 macroinitiators were prepared using tetrabutylammonium iodide (BNI) as a catalyst. An in situ generated alkyl iodide (RI) was utilised as an initiator instead of an isolated RI. Typically, iodine (I.sub.2) and an azo compound, i.e., 2,2-azobis(2,4-dimethylvaleronitrile) (an azo initiator, V65)) were used to generate an RI in situ. V65 generated the alkyl radical (R) which reacted with I.sub.2 to form RI.
[0207] In a typical reaction, a mixture of poly(ethylene glycol) methyl ether methacrylate (PEGMA) (average molecular weight=300, 8 M, monomer), I.sub.2 (40 mM), V65 (160 mM), BNI (80 mM, catalyst), and ethanol (20 wt %, solvent) was heated at 60 C. for 3.5 h (Table 8, entry 1). At 3.5 h, the monomer conversion reached 75%. The as-synthesised polymer was purified by reprecipitation using a mixture of hexane and diethyl ether (1:1, v/v) as a non-solvent to give macroinitiators with DPs 90, 52, 46, 33, and 27 (Table 8).
TABLE-US-00009 TABLE 8 Synthesis of PPEGMA-I macroinitiators using PEGMA, I.sub.2, V65, and BNI in 20 wt % ethanol. [PEGMA].sub.0/[I.sub.2].sub.0/ [V65].sub.0/[BNI].sub.0 T t Conv..sup.b Entry (mM).sup.a ( C.) (h) (%) M.sub.n.sup.c DP.sup.c .sup.c 1 8000/40/160/80 60 3.5 75 27000 90 1.31 2 8000/80/320/80 60 3.5 73 13800 46 1.21 3.6 15600 52 1.24 3 8000/160/640/80 60 4 70 9900 33 1.16 3.7 8100 27 1.16 .sup.aSolution polymerisation in 20 wt % ethanol (solvent). .sup.bMonomer conversions were calculated from .sup.1H NMR analyses. .sup.cThe M.sub.n, DP, and values of PPEGMA-I were PMMA-calibrated GPC values after purification (reprecipitation).
PISA in Water
[0208] Typically, a mixture of MMA (8 M, monomer), PPEGMA.sub.90-I (20 mM, macroinitiator), 4,4-azobis(4-cyanovaleric acid) (V501) (40 mM, azo initiator), NaI (160 mM, catalyst), and water (90 wt %, solvent) was heated at 60 C. (Table 9, entry 3). The pH of the solution was adjusted to 7 by adding sodium bicarbonate (NaHCO.sub.3). Different PPEGMA.sub.90-PMMA.sub.y block copolymers at different polymerisation times (up to 4 h) were obtained (with monomer conversion=83%, where y is the DP of PMMA). At each sampling time, a small portion of the reaction mixture was taken out from the reactor vessel, divided in three parts. The first part was dried and subjected to GPC analysis. The second part was diluted with DMSO-d.sub.6 and analysed by .sup.1H NMR. The third part was diluted by 50 times with water and was used as the stock solution for the subsequent dynamic light scattering (DLS) and transmission electron microscope (TEM) studies. The reaction was repeated using PPEGMA-1 macroinitiators with DP of 33 and 46, with different conditions as summarised in Table 9. The as-synthesised polymers were characterised by TEM as shown in
PISA in Ethanol
[0209] Typically, a mixture of MMA (8 M, monomer), PPEGMA.sub.27-I (20 mM, macroinitiator), V65 (20 mM, azo initiator), NaI (160 mM, catalyst), and ethanol (90 wt %, solvent) was heated at 60 C. (Table 10, entry 1). Different PPEGMA.sub.27-PMMA.sub.y block copolymers were obtained at different polymerisation times. The reaction was also repeated using PPEGMA-1 with DP of 52 with different conditions as summarised in Table 10. The as-synthesised block polymers were characterised by TEM (
TABLE-US-00010 TABLE 9 Synthesis of PPEGMA.sub.x-PMMA.sub.y via PISA in water, using MMA, PPEGMA-I, V501, and NaI in 90 wt % water at 60 C. Size [MMA].sub.0/ Hydro- Distri- [PPEGMA-I].sub.0/ dynamic bution Code in DP of [NaI].sub.0/[V501].sub.0 t Conv DP of Symbol of Block Diameter.sup.c Index Assembly FIGS. 17 Entry PPEGMA (mM).sup.a (h) (%) PMMA.sup.b .sup.b Copolymer f.sub.PMMA in DLS (nm) in DLS Structure.sup.d and 18 1 33 8000/20/160/40 1.2 35 21 1.17 PPEGMA.sub.33-PMMA.sub.21 0.18 30 0.124 S 1.8 43 31 1.21 PPEGMA.sub.33-PMMA.sub.31 0.24 39 0.134 S A 2.3 50 49 1.21 PPEGMA.sub.33-PMMA.sub.49 0.33 60 0.284 S 2.8 57 61 1.21 PPEGMA.sub.33-PMMA.sub.61 0.38 110 0.352 S + V B 3.8 67 91 1.24 PPEGMA.sub.33-PMMA.sub.91 0.48 158 0.366 V C 2 46 8000/20/160/40 1 20 16 1.31 PPEGMA.sub.46-PMMA.sub.16 0.13 60 0.113 S 1.5 30 26 1.32 PPEGMA.sub.46-PMMA.sub.26 0.16 75 0.137 S D 2 35 34 1.31 PPEGMA.sub.46-PMMA.sub.34 0.20 85 0.143 S 2.5 41 42 1.32 PPEGMA.sub.46-PMMA.sub.42 0.23 93 0.127 S 3 54 58 1.28 PPEGMA.sub.46-PMMA.sub.58 0.30 100 0.210 S 3.5 66 78 1.26 PPEGMA.sub.46-PMMA.sub.78 0.36 135 0.329 S + V E 5 75 140 1.35 PPEGMA.sub.46-PMMA.sub.140 0.50 165 0.284 V F 3 90 8000/20/160/40 1.2 20 15 1.27 PPEGMA.sub.90-PMMA.sub.15 0.05 35 0.243 S 1.8 28 25 1.27 PPEGMA.sub.90-PMMA.sub.25 0.08 45 0.203 S G 2.3 35 35 1.27 PPEGMA.sub.90-PMMA.sub.35 0.12 65 0.196 S 2.8 60 110 1.42 PPEGMA.sub.90-PMMA.sub.110 0.30 100 0.139 S + V H 4 83 480 1.50 PPEGMA.sub.90-PMMA.sub.480 0.64 370 0.590 V I .sup.aThe mixture of PPEGMA-I, NaI, and V501 was diluted with water (water content = 90 wt %) and mixed with MMA at the described concentration. .sup.bDP and were recorded using DMF-GPC after drying. .sup.cThe size was the DLS peak-top value. .sup.dS = sphere and V = vesicle.
TABLE-US-00011 TABLE 10 Synthesis of PPEGMA.sub.x-PMMA.sub.y via PISA in ethanol, using MMA, PPEGMA-I, V65, and NaI in 90 wt % ethanol at 60 C. [MMA].sub.0/ Hydro- [PPEGMA-I].sub.0/ dynamic Code in DP of [NaI].sub.0/[V65].sub.0 t Conv DP of Symbol of Block Diameter.sup.c Assembly FIGS. 15b Entry PPEGMA (mM).sup.a (h) (%) PMMA.sup.b .sup.b Copolymer f.sub.PMMA in DLS (nm) Structure.sup.d and 16 1 27 8000/20/20/80 1.7 32 38 1.17 PPEGMA.sub.27-PMMA.sub.38 0.31 Soluble 2.5 38 49 1.21 PPEGMA.sub.27-PMMA.sub.49 0.38 35 S A 4 46 88 1.21 PPEGMA.sub.27-PMMA.sub.88 0.52 91 W B 7 52 119 1.21 PPEGMA.sub.27-PMMA.sub.119 0.60 154 V 17 72 159 1.24 PPEGMA.sub.27-PMMA.sub.159 0.66 201 V C 2 52 8000/20/20/80 2.5 42 110 1.21 PPEGMA.sub.52-PMMA.sub.110 0.41 30 S D 5 55 131 1.21 PPEGMA.sub.52-PMMA.sub.131 0.46 80 W E 15 70 230 1.23 PPEGMA.sub.52-PMMA.sub.230 0.61 215 V F .sup.aThe mixture of PPEGMA-I, NaI, and V65 was diluted with ethanol (ethanol content = 90 wt %) and mixed with MMA at the described concentration. .sup.bDP and were recorded using DMF-GPC after drying. .sup.cThe size was the DLS peak-top value. .sup.dS = sphere, W = worm, and V = vesicle.