FUNCTIONALIZED A- ANGELICA LACTONE MONOMERS AND POLYMERS OBTAINED THEREFROM

Abstract

The present invention is directed to a monomer for chain growth polymerization, in particular anionic polymerization, said monomer having the general formula (EFL)

##STR00001##

wherein: R.sup.a is a C.sub.1-C.sub.30 alkyl, C.sub.3-C.sub.30 cycloalkyl, C.sub.6-C.sub.18 aryl or C.sub.2-C.sub.12 alkenyl group. The present invention is further directed to a process for the anionic polymerization of at least one compound (EFL) as defined above, wherein said anionic polymerization is conducted in the presence of an initiator selected from the group consisting of: alkali metal organyls; alkali metal alkoxides; alkali metal thiolate; alkali metal amides; and compounds of an element of group 3a of the Periodic Table of the Elements. The process of anionic polymerization yields a homo- or co-polymer (p-EFL) having pendant lactone functional groups in its repeating units.

Claims

1. A monomer for chain-growth polymerization, preferably anionic polymerization, having the general formula (EFL) ##STR00014##  wherein: R.sup.a is a C.sub.1-C.sub.30 alkyl, C.sub.3-C.sub.30 cycloalkyl, C.sub.6-C.sub.18 aryl or C.sub.2-C.sub.12 alkenyl group.

2. The monomer according to claim 1 having the general formula: ##STR00015## wherein: R.sup.a is a C.sub.1-C.sub.18 alkyl, C.sub.3-C.sub.18 cycloalkyl, C.sub.6-C.sub.18 aryl or C.sub.2-C.sub.10 alkenyl group.

3. The monomer according to claim 1, wherein R.sup.a is a C.sub.1-C.sub.12 alkyl or C.sub.2-C.sub.8 alkenyl group.

4. A process for the synthesis of a compound as defined in claim 1, said process comprising the step of reacting in the presence of an acid anhydride and an antioxidant: a) α-angelica lactone; and, b) an orthoester having the general formula (1) ##STR00016##  in which: R.sup.1, R.sup.2 and R.sup.3 are independently selected from C.sub.1-C.sub.30 alkyl, C.sub.3-C.sub.30 cycloalkyl, C.sub.6-C.sub.18 aryl and C.sub.2-C.sub.12 alkenyl groups.

5. The process according to claim 4, wherein the acid anhydride is one of acetic anhydride, propionic anhydride, butyric anhydride or succinic anhydride and further wherein said acid anhydride is present in a catalytically sufficient amount based on the total number of moles of reactants (a), b)).

6. The process according to claim 4, wherein said antioxidant comprises or consists of at least one sterically hindered phenol and wherein said antioxidant is present in an amount of up to 10 wt. % based on the total weight of the reactants (a), b)).

7. A process for the chain growth polymerization of at least one monomer (EFL) as defined in claim 1.

8. A process according to claim 7 for the anionic polymerization of at least one monomer (EFL), wherein said anionic polymerization is conducted in the presence of an initiator selected from the group consisting of: alkali metal organyls; alkali metal alkoxides; alkali metal thiolate; alkali metal amides; and compounds of an element of group 3a of the Periodic Table of the Elements.

9. The process according to claim 8, wherein said initiator is present in an amount of from 0.0001 to 5 wt. %, based on the total weight of monomers.

10. The process according to claim 8, wherein said initiator comprises an aliphatic alkoxide of sodium, potassium or lithium.

11. The process according to claim 8, wherein said initiator comprises an organolithium compounds selected from the group consisting of: ethyllithium; propyllithium; isopropyllithium; n-butyllithium; sec-butyllithium; tert-butyllithium; phenyllithium; diphenylhexyllithium; hexamethylenedilithium; butadienyllithium; isoprenyllithium; polystyryllithium; 1,4-dilithiobutane; 1,4-dilithio-2-butene; and 1,4-dilithiobenzene.

12. The process according to claim 8, wherein said initiator comprises an aluminum alkyl compound selected from the group consisting of: trimethylaluminum; triethylaluminum; triisopropylaluminum; triisobutylaluminum; tri-n-butylaluminum; tri-n-hexylaluminum; diethylaluminum hydride; diisobutylaluminum hydride; and, isoprenylaluminum.

13. The process according to claim 8 comprising the anionic polymerization of a monomer mixture comprising, based on the total weight of said monomers: a) from 15 to 75 wt. %; and, b) from 25 to 85 wt%,  wherein, wherein said at least one co-monomer is providing, olefinically unsaturated monomer selected from the group consisting of: (meth)acrylonitrile; alkyl (meth)acrylate esters; (meth)acrylic acids; vinyl esters; and, vinyl monomers, more preferably said at least one co-monomer comprises a vinyl monomer selected from the group consisting of: 1,3-butadiene; isoprene; styrene; divinyl benzene; heterocyclic vinyl compounds; and vinyl halides.

14. A homo- or co-polymer (p-EFL) having pendant lactone functional groups and which is obtainable or obtained by the process as defined in claim 8, said polymer (p-EFL) having the general formula: ##STR00017##  wherein: R.sup.a is a C.sub.1-C.sub.30 alkyl, C.sub.3-C.sub.30 cycloalkyl, C.sub.6-C.sub.18 aryl or C.sub.2-C.sub.12 alkenyl group; and,  n is an integer greater than 20.

15. A polymer (p-EFL) having pendant lactone functional groups which is obtainable or obtained by the process as defined in claim 8, said polymer being further characterized by at least one of: i) a number-average molecular weight (Mn), as determined as measured by gel permeation chromatography (GPC) in tetrahydrofuran using a polystyrene standard, of at least 2500 g/mol, preferably from 10000 to 150000 g/mol; ii) a glass transition temperature (Tg) of from 50 to 200° C.; and, iii) a polydispersity index (PDI) of from 1.1 to 2.0.

16. A composition having two separate, reactive components that when mixed together form a reactive mixture that undergoes curing or hardening, said two-component composition comprising: i) in a first component, said homo- or co-polymer (p-EFL) as defined in claim 14; and, ii) in a second component, an un-substituted or hydroxyl-substituted mono-, di- or trialkylamine.

Description

DETAILED DESCRIPTION OF THE INVENTION

Synthesis of the Functionalized α-Angelica Lactone (EFL)

[0052] The synthesis of the functionalized α-angelica lactone (EFL) is most broadly characterized by the following reaction scheme:

##STR00008##

[0053] There is no particular intention to limit the means by which the reactant alpha-angelica lactone (a)) is obtained: aside from said compound being commercially available, it may also be synthesised via a multiplicity of synthesis routes known to the skilled artisan. Reference in this regard might be made to http://www.molbase.com/en/synthesis_591-12-8-moldata-4778.html. When expedient based on the synthesis route employed, the alpha-angelica lactone may be isolated and purified using methods known in the art. Mention in this regard may be made of extraction, evaporation, distillation and chromatography as suitable techniques.

[0054] The orthoester reactants having utility in the above described reaction scheme have the general formula (b)) herein below:

##STR00009##

 in which: R.sup.1, R.sup.2 and R.sup.3 are independently selected from C.sub.1-C.sub.30 alkyl, C.sub.3-C.sub.30 cycloalkyl, C.sub.6-C.sub.18 aryl and C.sub.2-C.sub.12 alkenyl groups.

[0055] In a preferred embodiment of the orthoesters of Formula (b)), R.sup.1, R.sup.2 and R.sup.3 are independently selected from C.sub.1-C.sub.18 alkyl and C.sub.2-C.sub.12 alkenyl groups; R.sup.1, R.sup.2 and R.sup.3 may for instance be independently selected from C.sub.1-C.sub.12 alkyl groups and C.sub.2-C.sub.8 alkenyl groups or independently selected from C.sub.1-C.sub.6 alkyl or C.sub.2-C.sub.4 alkenyl groups. Alternatively or additionally to the aforementioned embodiment, it is preferred that at least two of R.sup.1, R.sup.2 and R.sup.3 in Formula (1) are the same.

[0056] Examples of suitable orthoesters (b)) for use in the present invention include but are not limited to: triethyl orthoformate (R.sup.1═R.sup.2═R.sup.3=Et); trimethyl orthoformate (R.sup.1═R.sup.2═R.sup.3=Me); tributyl orthoformate (R.sup.1═R.sup.2═R.sup.3=Bu); tripropoxy orthoformate (R.sup.1═R.sup.2═R.sup.3=nPr); diethyl vinyl orthoformate (R.sup.1═R.sup.2=Et, R.sup.3═CH.sub.2═CH.sub.2); trioctadecyl orthoformate (R.sup.1═R.sup.2═R.sup.3═C.sub.18H.sub.37); and, tripentyl orthoformate (R.sup.1═R.sup.2═R.sup.3═C.sub.5H.sub.11).

[0057] As noted in the above scheme, the reaction is performed in the presence of an acid anhydride. Typically said acid anhydride is one of acetic anhydride, propionic anhydride, butyric anhydride or succinic anhydride. A preference for acetic anhydride is noted. That aside, the acid anhydride should be present in a catalytic amount which, in this regard, may include sub-stoichiometric amounts of said acid anhydride relative to the total number of moles of reactants (a), b)) but does not preclude the acid anhydride being present in molar excess—for instance up to a 20% molar excess—to the total number of moles of reactants (a), b)).

[0058] The reaction is also performed in the presence of a suitable antioxidant which will typically constitute up to 10 wt. % or up to 5 wt. %, based on the total weight of the reactants (a), b)) The use of one or more sterically hindered phenol—including but not limited to 2,6-di-tert-butyl-4-methylphenol (BHT) and/or butylated hydroxyanisole (BHA)—is preferred herein.

[0059] Whilst the presence of a co-catalyst is not required, it is also not precluded. The reaction between the orthoester and the alpha-angelica lactone may, in an embodiment, be performed in the presence of a catalytic amount of a strong protic acid selected from a group consisting of H.sub.2SO.sub.4, HNO.sub.3, HCl, HBr, HI, trifluoroacetic acid (TFA), H.sub.3PO.sub.4, p-toluene sulfonic acid (p-TSA) and methanesulfonic acid (MSA).

[0060] The above reaction should be performed under anhydrous conditions. Exposure to atmospheric moisture may be avoided by providing the reaction vessel with an inert, dry gaseous blanket. Whilst dry nitrogen, helium and argon may be used as blanket gases, precaution should be used when common nitrogen gases are used as a blanket, because such nitrogen may not be dry enough on account of its susceptibility to moisture entrainment; the nitrogen may require an additional drying step before use herein.

[0061] The above described reaction may be carried out in the presence of a solvent. Inert solvents are preferred as solvents; these contain no reactive groups that react with the starting compounds. Inert, polar, aprotic solvents are particularly preferred. Named as such are, e.g., cyclic ether compounds, in particular tetrahydrofuran (THF).

[0062] The reaction temperature is typically at least 40° C. and preferably at least 60° C. Whilst the reaction temperature may be 200° C. or higher, it is preferred that the temperature does not exceed 190° C. or even 180° C. in order inter alia: to maintain workable reactor pressures; and, where applicable, to maintain adequate catalyst activity without deactivating or decomposing the catalyst. As the reaction is generally exothermic, some cooling might be required as it progresses.

[0063] The process pressure is not critical: as such, the reaction can be run at sub-atmospheric, atmospheric, or super-atmospheric pressures but pressures at or slightly above atmospheric pressure are preferred. Mention in this regard may be made of pressures of from 100 to 500 MPa or from 100 to 200 MPa.

[0064] The progress of the above reaction can be monitored by known tecchniques. For example, samples may be withdrawn from the reaction vessel and tested using Gas Chromatography (GC) with Flame Ionization Detection (FID).

[0065] The reaction product may be isolated and purified using methods known in the art. Whilst mention in this regard may be made of extraction, filtration, evaporation, distillation and chromatography as suitable techniques it is most convenient that the product of the reaction be isolated by distilling off the solvent and any unreacted starting materials.

The Formation of Exo-Methylene Functionalized Polymers

[0066] The second aspect of the present invention provides for the polymerization of the above defined monomeric compounds (EFL). Broadly, the polymerization is performed by means of chain growth polymerization but may, in particular, be performed under anionic conditions: the skilled artisan will select appropriate conditions so that the vinyl-addition pathway of polymerization predominates over the competing ring-opening polymerization pathway. The resultant homo- or copolymer (p-EFL) thus retains the lactone structure in its repeating unit.

Co-Monomers

[0067] As mentioned previously, the aforementioned monomers (EFL) may be incorporated into co-polymers (p-EFL). Most broadly, viable co-monomers are those that provide reasonable polymerization reaction rates under suitable, pragmatic anionic polymerization conditions.

[0068] In a non-limiting and illustrative embodiment of the present invention, there is provided a copolymer (p-EFL) comprising:

[0069] from 15 to 75 wt. %, preferably from 15 to 60 wt. % of at least one monomer as defined in Formula (EFL) hereinabove; and,

[0070] from 25 to 85 wt%, preferably from 40 to 85 wt. % of at least one co-monomer.

[0071] In a further exemplary embodiment—which is not intended to be mutually exclusive of the above illustrative embodiment—a copolymer is derived from the above defined monomer (EFL) and at least one further monomer, wherein said at least one further monomer is a non-carbonyl-providing, olefinically unsaturated monomer selected from the group consisting of: (meth)acrylonitrile; alkyl (meth)acrylate esters; (meth)acrylic acids; vinyl esters; and vinyl monomers.

[0072] Suitable vinyl monomers include: 1,3-butadiene; isoprene; styrene; divinyl benzene; heterocyclic vinyl compounds; and vinyl halides such as chloroprene. Preferably the vinyl monomers include ethylene, styrene, butadiene and isoprene. Suitable vinyl esters include vinyl acetate, vinyl propionate, vinyl versatate and vinyl laurate.

[0073] Suitable alkyl esters of acrylic acid and methacrylic acid are those derived from C.sub.1 to C.sub.14 alcohols and thereby include as non-limiting examples: methyl acrylate; methyl methacrylate; ethyl acrylate; ethyl methacrylate; n-butyl acrylate; n-butyl methacrylate; 2-ethylhexyl acrylate; 2-ethylhexyl methacrylate; isopropyl acrylate; hydroxyethyl methacrylate; hydroxypropyl methacrylate; isopropyl methacrylate; n-propyl acrylate; n-propyl methacrylate; and, di(meth)acrylate esters of alkane diols such as 1,6-hexane diol diacrylate.

Polymerization Processes

[0074] The anionic polymerization of the monomers (EFL) and any co-monomers present is conducted in the presence of an initiator selected from the group consisting of: alkali metal organyls; alkali metal alkoxides; alkali metal thiolate; alkali metal amides; and, compounds of an element of group 3a of the Periodic Table of the Elements, preferably an aluminum or boron organyl.

[0075] Alkali metal organyls which may be used are mono-, bi- or multifunctional alkali metal alkyls, aryls or aralkyls. It is advantageous to use organolithium compounds including but not limited to: ethyllithium; propyllithium; isopropyllithium; n-butyllithium; sec-butyllithium; tert-butyllithium; phenyllithium; diphenylhexyllithium; hexamethylenedilithium; butadienyllithium; isoprenyllithium; polystyryllithium; 1,4-dilithiobutane; 1,4-dilithio-2-butene; and, 1,4-dilithiobenzene.

[0076] Alkali metal alkoxides which may be used, either alone or in admixture, are aliphatic, aromatic or araliphatic alkoxides of lithium, sodium or potassium. Examples are lithium, sodium or potassium methoxide, ethoxide, n-propoxide, isopropoxide, n-butoxide, sec-butoxide, tert-butoxide, n-pentoxide, isopentoxide, hexoxide, amyl alkoxide, 3,7-dimethyl-3-octoxide, phenoxide, 2,4-di-tert-butylphenoxide, 2,6-di-tert-butylphenoxide, 3,5-di-tert-butylphenoxide, 2,4-di-tert-butyl-4-methylphenoxide and trimethylsilanoate. Preference is given to using the aliphatic alkoxides in particular methoxides, ethoxides, n-propoxides, isopropoxides, n-butoxides, sec-butoxides and tert-butoxides of sodium, potassium or lithium.

[0077] Alkali metal thiolates which may be used, either alone or in admixture, are aliphatic, aromatic or araliphatic thiolates of lithium, sodium or potassium. Examples are lithium, sodium or potassium methyl sulfide, ethyl sulfide, butyl sulfide, hexyl sulfide, decyl sulfide, dodecyl sulfide, stearyl sulfide, thiophenoxide, tolyl sulfide, cyclohexyl sulfide or dilithium 1,2-dimercaptoethane. Preference is given to aliphatic thiolates having from 8 to 18 carbon atoms in the alkyl chain.

[0078] Alkali metal amides which may be used, either alone or in admixture, are lithium, sodium or potassium salts of ammonia or primary or secondary amines having aliphatic, aromatic or araliphatic substituents. Examples of suitable amides are lithiumamide, N-lithiummethylamide, N-lithiumethylamide, N-lithiumpropylamide, N-lithiumbutylam ide, N-lithiumamylamide, N-lithiumphenylamide or the corresponding sodium or potassium salts; N-lithiumdimethylamide, N-lithiumdiethylamide, N-lithiumdipropylamide, N-lithiumdibutylamide, N-lithiumdiamylamide, N-lithium-(N,N-bis-trimethylsilyl)amide, N-lithiumdicyclohexylamide, N-lithium-N-methylanilide, N-lithium-N-ethylanilide, N-lithiummorpholide, N-lithiumdiphenylamide, N-lithiumpiperidide or N-lithiumimidazolide. Particular preference is given to salts of secondary aliphatic amines, with very particular preference being given to N-lithiumdiisopropylamide.

[0079] Aluminum or boron organyls which may be used are those of the formula R.sub.3Al or R.sub.3B, wherein the radicals R are each, independently of one another, hydrogen, halogen, C1-C18-alkyl or C6-C18-aryl. Preferred aluminum organyls are aluminum trialkyls such as trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-butylaluminum, triisopropylaluminum, tri-n-hexylaluminum, diethylaluminum hydride, diisobutylaluminum hydride or isoprenylaluminum. Particular preference is given to using triisobutylaluminum.

[0080] It is envisaged that it may be possible to use aluminum organyls which are formed by the partial or complete hydrolysis, alcoholysis, aminolysis, thiolysis, phosphinolysis or oxidation of alkyl- or arylaluminum compounds or those which are complexed with alkoxides, thiolates, sulfides, amides, imides, nitrides or phosphides. Examples of such compounds carrying hetero substituents include but are not limited to: diethylaluminum N,N-dibutylamide; diethylaluminum ethoxide; diisobutylaluminum ethoxide; diisobutyl-(2,6-di-tert-butyl-4-methyl-phenoxy)aluminum; methylaluminoxane; isobutylated methylaluminoxane; isobutylaluminoxane; tetraisobutyldialuminoxane; bis(diisobutyl)aluminum oxide; diethylboron methoxide; trimethylboroxine; and, 2-phenyl-1,3,2-dioxaborinane.

[0081] Further examples of suitable initiators include: aluminum alkoxides, such as aluminum trimethoxide, aluminum triethoxide, aluminum tripropoxide, and, aluminum tributoxide; and, boric acid trialkyl esters. Preference is given to using the aluminum compounds, especially those having oxo or alkoxide groups. Very particular preference is given to using diethylaluminum ethoxide, diisobutylaluminum ethoxide, methyl aluminoxane, aluminum propoxide and aluminum tri-sec-butoxide.

[0082] There is no particular limitation on the amount of initiator used but it will be typically be from 0.0001 to 5 parts by weight, and preferably from 0.05 to 1 part by weight, based on 100 parts by weight of the monomers.

[0083] Furthermore, the polymerization may be performed in solution or in the melt without a solvent. When used, suitable solvents for the polymerization should be non-reactive, organic liquids capable of dissolving at least 1 wt. % and preferably over 10 wt. % polymers at 25° C. Dichloromethane and tetrahydrofuran (THF) may be mentioned as exemplary solvents.

[0084] In certain embodiments, the anionic polymerization process is performed in the presence of a Lewis acid. The preferred Lewis acids for use in the polymerization processes of the present invention are characterized as being “non-protic”: they are Lewis acids which are not capable of functioning as a source of a proton (H+). Particularly preferred Lewis acids for the purposes of this invention include halides of elements selected from the group consisting of aluminum, manganese, iron, cobalt, boron, iron, titanium, tin, chromium, magnesium, vanadium, hafnium, zirconium and zinc.

[0085] In the homo- and co-polymerization processes of the present invention, the amount of (non-protic) Lewis acid should be adjusted such that the activity of the catalyst, as measured by the weight of monomer reacted per unit of time at a given temperature, does not decrease more than 20% as compared to the catalyst activity under the same conditions in the absence of Lewis acid: in this regard it will often be advantageous to utilize a Lewis acid: catalyst weight ratio in the range of from 0.1 to 1.0.

[0086] Whilst there is certainly no intention to preclude either batch-wise or continuous performance of the polymerization—as described in U.S. Pat. Nos. 5,777,177 and 5,689,012—the polymerization reactions are most suitably performed as semi-batch processes.

[0087] The polymerization reaction can be performed in any type of vessel that is suitable for the pressures and temperatures described below. In the preferred semi-batch process, the vessel should have one or more inlets through which monomer(s) can be introduced during the reaction. In the less desired continuous process, a reactor vessel should contain at least one outlet through which a portion of the partially polymerized reaction mixture could be withdrawn. That aside, exemplary vessels for continuous or semi-batch operations include but are not limited to: tubular reactors; loop reactors; and, continuous stirred tank reactors (CTSR). Any reactor should, of course, be equipped with a means for providing or removing heat so that the temperature of the polymerization mixture can be maintained within the desired range: there is no intention to limit such means but examples include jacketing for thermal fluids and internal and/or external heaters.

[0088] At the commencement of the polymerization process, the initiator and, optionally, a Lewis acid are charged into the reaction vessel. In the preferred semi-batch process, the initiator may undergo a preliminary heating step, in the absence of monomer(s), at a temperature of from 50 to 220° C., for instance from 75 to 180° C. That preliminary heating step is conducted in an inert atmosphere and is typically but, not necessarily, conducted under sub-atmospheric pressure. The preliminary heating is, moreover, usually conducted for a period of at least 10 minutes: a period of from 10 to 30 minutes might be mentioned for illustrative purposes.

[0089] The homo-polymerization of monomers (EFL), the copolymerization of two or more monomers meeting the general formula (EFL), and the co-polymerization of monomers (EFL) with co-monomers should be performed under anhydrous conditions and in the absence of any compound having an active hydrogen atom, save for the deliberate inclusion of the initiating compound. Exposure to atmospheric moisture may be avoided by providing the reaction vessel with an inert, dry gaseous blanket. Whilst dry nitrogen, helium and argon may be used as blanket gases, precaution should be used when common nitrogen gases are used as a blanket, because such nitrogen may not be dry enough on account of its susceptibility to moisture entrainment; the nitrogen may require an additional drying step before use herein.

[0090] The polymerization temperature is typically at least 25° C. and preferably at least 50° C. Whilst the reaction temperature may be 200° C. or higher, it is preferred that the temperature does not exceed 200° C., 175° C. or even 150° C. in order inter alia: to maintain workable reactor pressures; to minimize the rate of polymer degradation and the concomitant formation of volatile impurities or other by-products; and, if applicable, to maintain adequate catalyst activity without deactivating or decomposing the catalyst. Within the typically desired polymerization temperature range of from 50 to 150° C., the solvent type, agitation rate and pressure will be determinative of the reaction times but times of from 1 to 100 hours will be standard.

[0091] The process pressure is not critical: as such, the polymerization reaction can be run at sub-atmospheric, atmospheric, or super-atmospheric pressures but pressures at or slightly above atmospheric pressure are preferred. Mention in this regard may be made of pressures of from 100 to 500 MPa or from 100 to 200 MPa.

[0092] The reaction product may be isolated and purified using methods known in the art. Whilst mention in this context may be made of extraction, evaporation, distillation and chromatography as suitable techniques, it is most convenient that the product of the reaction be isolated by distilling off the solvent and any un-reacted starting materials under reduced pressure.

[0093] Where it is intended that the (optionally purified) reaction product be stored upon production, the polymers should be disposed in a vessel with an airtight and moisture-tight seal.

[0094] The homo- or copolymers (p-EFL) derived in the above described polymerization processes may possess: i) a number-average molecular weight (Mn), as determined by gel permeation chromatography (GPC) in tetrahydrofuran using a polystyrene standard, of at least 2500 g/mol, for instance from 10000 to 150000 g/mol and preferably from 10000 to 100000 g/mol; ii) a glass transition temperature (Tg) of from 50 to 200° C., for example from 100 to 200° C.; and, iii) a polydispersity index (PDI) of from 1.1 to 2.0, for example from 1.10 to 1.90, and preferably from 1.10 to 1.80.

Polymer Derivatives of the Homo- And Co-Polymers (P-EFL)

i) Ring-Opening Polymerization

[0095] The lactone functional group in the polymers (p-EFL) of the present invention can be used to regulate the ring opening polymerization of at least one monomer selected from the group consisting of: cyclic carbonates; cyclic anhydrides; oxalates; and, cyclic esters having 5-, 6-, and/or 7-member rings. In particular, the polymers (p-EFL) may be present as a reactant macro-monomer in a ring open polymerization with at least one monomer selected from the group consisting of: lactide; glycolide; ε-caprolactone; para-dioxanone; trimethylene carbonate; 1,4-dioxepan-2-one; 1,5 dioxepan-2-one; γ-butyrolactone; α-methylene-γ-butyrolactone; γ-methyl-α-methylene-γ-butyrolactone; α-bromo-γ-butyrolactone; α-hydroxy-γ-butyrolactone; α-acetyl-γ-butyrolactone; spirocyclic-γ-butyrolactone; γ-valerolactone; α-angelica lactone; and β-angelica lactone. The derived copolymer may be a block copoly(ester) or a random copoly(ester).

[0096] Whilst there is no specific intention to limit the mechanism of ring opening polymerization employed in the present invention and whilst therefore ring opening polymerization of cyclic monomers by the anionic route, via basic catalysts is not strictly precluded, it is preferred herein for said polymerization to proceed by a cationic route, via acid catalysis. Broadly, any suitable acidic ring opening polymerization catalyst may be utilized herein and, equally, mixtures of catalysts may be employed. Both Lewis and Brönsted acids may be suitable in this context, but the latter are preferred as they tend to be effective at temperatures of less than 150° C. and are usually effective at temperatures of from 50 to 100° C.

[0097] Examples of suitable Lewis acids include but are not limited to: BF.sub.3; AlCl.sub.3; t-BuCl/Et.sub.2AlCl; Cl.sub.2/BCl.sub.3; AlBr.sub.3; AlBr.sub.3.TiCl.sub.4; I.sub.2; SbCl.sub.5; WCl.sub.6; AlEt.sub.2Cl; PF.sub.5; VCl.sub.4; AlEtCl.sub.2; BF.sub.3Et.sub.2O; PCl.sub.5; PCl.sub.3; POCl.sub.3; TiCl.sub.6; and, SnCl.sub.4.

[0098] Examples of Brönsted acid or proton acid type catalysts—which may optionally be disposed on solid, inorganic supports—include, but are not limited to: HCl; HBr; HI; H.sub.2SO.sub.4; HClO.sub.4; para-toluenesulfonic acid; trifluoroacetic acid; and, perfluoroalkane sulfonic acids, such as trifluoromethane sulfonic acid (or triflic acid, CF.sub.3SO.sub.3H), C.sub.2F.sub.5SO.sub.3H, C.sub.4F.sub.9SO.sub.3H, C.sub.5F.sub.11SO.sub.3H, C.sub.6F.sub.13SO.sub.3H and C.sub.8F.sub.17SO.sub.3H. The most preferred of these strong acids is trifluoromethane sulfonic acid (triflic acid, CF.sub.3SO.sub.3H).

[0099] The catalysts for said ring opening polymerization may usually be employed at a concentration of from 1 to 1000 ppm by weight based on the total weight of the monomers to be polymerized. Preferably from 5 to 150 ppm by weight are used, most preferably from 5 to 50 ppm. The catalytic amount may be reduced when the temperature at which the monomers and the catalyst are contacted is increased.

[0100] The ring opening polymerization may conveniently be carried out at a temperature in the range from 10 to 150° C. Preferably, however, the temperature range is from 20 or 50 to 100° C. as obviating high temperatures can limit the loss of volatile monomers from the reaction mixture due to their lower boiling point.

[0101] The process pressure is not critical. As such, the polymerization reaction can be run at sub-atmospheric, atmospheric, or super-atmospheric pressures but pressures at or above atmospheric pressure are preferred.

[0102] Importantly, the reaction should be performed under anhydrous conditions and in the absence of any compound having an active hydrogen atom. Exposure to atmospheric moisture may be avoided by providing the reaction vessel with an inert, dry gaseous blanket. Whilst dry nitrogen, helium and argon may be used as blanket gases, precaution should be used when common nitrogen gases are used as a blanket, because such nitrogen may not be dry enough on account of its susceptibility to moisture entrainment; the nitrogen may require an additional drying step before use herein.

[0103] The duration of the reaction is dependent on the time taken for the system to reach equilibrium. Equally, however, it is understood that the desired product can be obtained by stopping the equilibration at exactly the desired time: for example, the reaction can be monitored by analyzing viscosity over time or by analyzing monomer conversion using gas chromatography and the reaction stopped when the desired viscosity or monomer conversion is attained. These considerations aside, the polymerization reaction generally takes place for from 0.5 to 72 hours and more commonly from 1 to 30 or 1 to 20 hours. Acid catalysts present in the reaction mixture at the end of the polymerization reaction can easily be neutralized in order to stabilize the reaction product.

[0104] Upon completion of the polymerization, it is possible to remove any solid, suspended compounds by, for example, filtration, crossflow filtration or centrifugation. Further, the output of the polymerization may be worked up, using methods known in the art, to isolate and purify the hydroxyl-functionalized polyesters. Mention in this regard may be made of extraction, evaporation, distillation and chromatography as suitable techniques. Upon isolation, it has been found that typical yields of the hydroxyl-functionalized polyesters are at least 40% and often at least 60%.

The polyesters derived by this ring opening polymerization process may possess a molecular weight (Mn) as determined as measured by gel permeation chromatography (GPC) in tetrahydrofuran using a polystyrene standard, of at least 5000, preferably from 10000 to 200000 g/mol. Moreover, the polymers may be characterized by a polydispersity index in the range from 1.0 to 2.5, preferably from 1.0 to 2.0.

ii) Polyester Formation

[0105] In a second exemplary embodiment, the polymer (p-EFL) of the present invention may be used as a macro-monomer in an esterification, wherein the resultant copolymer comprises non-lactoyl units derived from at least two co-monomers which are capable of forming an ester bond. More particularly, those co-monomers comprise: i) at least one diol; and (ii) at least one dicarboxylic acid or its ester forming derivative.

[0106] Suitable diols (i) for use in this context include saturated and unsaturated aliphatic and cycloaliphatic dihydroxy compounds as well as aromatic dihydroxy compounds. These diols preferably have a molecular weight of 250 daltons or less. When used herein, the term “diol” should be construed to include equivalent ester forming derivatives thereof, provided, however, that the molecular weight requirement pertains to the diol only and not to its derivative. Exemplary ester forming derivatives include the acetates of the diols as well as, for example, ethylene oxide or ethylene carbonate for ethylene glycol.

[0107] Preferred diols are those having from 2 to 10 carbon atoms. As examples of these diols there might be mentioned: ethylene glycol; propylene glycol; 1,3-propane diol; 1,2-butane diol; 2-methyl propanediol; 1,3-butane diol; 1,4-butane diol; 2,3-butane diol; neopentyl glycol; hexanediol; decanediol; hexamethylene glycol; cyclohexane dimethanol; resorcinol; and hydroquinone. Mixtures of such diols may be employed, but in this regard, it is generally preferred that at least about 60 mol. % and preferably at least 80 mol. %, based on the total diol content, be the same diol.

[0108] In a preferred embodiment, the diol is selected from: ethylene glycol; propylene glycol; 1,3-propane diol; 1,2-butane diol; 1,3-butane diol; 1,4-butane diol; 2,3-butane diol; neopentyl glycol; hexamethylene glycol; cyclohexane dimethanol; and mixtures thereof. Most preferably, the diol is either ethylene glycol or neopentyl glycol.

[0109] Dicarboxylic acids (ii) which are suitable for use in the above context include aliphatic, cycloaliphatic, and/or aromatic dicarboxylic acids. These acids should preferably have molecular weight of less than 300 daltons. The term “dicarboxylic acids” as used herein includes equivalents of dicarboxylic acids having two functional carboxyl groups which perform substantially like dicarboxylic acids in reaction with glycols and diols in forming polyesters. These equivalents include esters and ester forming reactive derivatives, such as acid halides and anhydrides, provided however that the molecular weight preference mentioned above pertains to the acid and not to its equivalent ester or ester-forming derivatives. Thus, an ester of a dicarboxylic acid having a molecular weight greater than 300 daltons or an acid equivalent of a dicarboxylic acid having a molecular weight greater than 300 daltons are included provided the acid has a molecular weight below 300 daltons. Additionally, the dicarboxylic acids may contain any substituent groups(s) or combinations which do not substantially interfere with the polymer formation and use of the polymer of this invention.

[0110] Preferred dicarboxylic acids are those selected from the group comprising alkyl dicarboxylic acids having a total of 2 to 16 carbons atoms and aryl dicarboxylic acids having a total of from 8 to 16 carbon atoms. Representative alkyl dicarboxylic acids include: glutaric acid; adipic acid; pimelic acid; succinic acid; sebacic acid; azelaic acid; and malonic acid. A preference for adipic acid might be mentioned here.

Representative aryl dicarboxylic acids include: terephthalic acid; phthalic acid; isophthalic acid; the dimethyl derivatives of said acids; and mixtures thereof.

Compositions Containing the Homo- and Co-Polymers (P-EFL) of the Present Invention

[0111] The polymers (p-EFL) of the present invention are considered to be versatile and thereby have a plethora of uses. For example, the lactone bearing polymers can be used to prepare ionic complexes with agents—including therapeutic agents such as a peptide—having a cationic moiety. The lactone ring(s) present in these polymers can also be opened by an alkali hydroxide to form an alkali metal salt of the corresponding hydroxycarboxylic acid. Furthermore, polymers containing lactone groups can be crosslinked by means of multifunctional compounds that can react with lactone. Multifunctional amines are particularly desirable in this regard.

[0112] It is anticipated that the functionalized polymers of the present invention per se may find utility as a curable, crosslinkable or otherwise reactive component of a coating composition, a sealant composition or an adhesive composition.

[0113] In an important embodiment of the present invention, there is provided a composition having two separate, reactive components that when mixed together form a reactive mixture that undergoes curing or hardening, said two-component composition comprising:

[0114] in a first component, said polymer (p-EFL); and,

[0115] in a second component, an un-substituted or hydroxyl-substituted mono-, di- or trialkylamines.

[0116] Preferably, the alkylamines are at least one of a primary amine and a secondary amine. More preferably the alkylamine is a primary amine. Independently or additionally, it is preferred that the said second component comprises an un-substituted or hydroxyl-substituted mono-, di- or tri-(C.sub.1-C.sub.12) alkylamine. Further, again independently of or additionally to these preferred conditions, the composition may be characterized in that the molar ratio of lactone groups in component (i) to amine groups in component (ii) is in the range from 0.8:1 to 2.5:1.

[0117] Suitable examples of alkylamines in component (ii) include but are limited to: methyl-, dimethyl- or trimethylamine; ethyl-, diethyl- or triethyl-amine; ethanol-, diethanol- or triethanol-amine; tris-(hydroxymethyl)-methylamine; 2-hydroxy-tert-butylamines; N,N-dimethyl-N-(2-hydroxyethyl)-amine; N-methyl-D-glucamine; diisopropylethylamine; and ethyldiisopropylamine.

[0118] Said compositions—such as a coating, sealant or adhesive composition—comprising homo- or copolymers (p-EFL) obtained in the present invention will typically further comprise adjuvants and additives that can impart improved properties to these compositions. For instance, the adjuvants and additives may impart one or more of: improved elastic properties; improved elastic recovery; longer enabled processing time; faster curing time; and lower residual tack. Included among such adjuvants and additives are catalysts, plasticizers, stabilizers, antioxidants, fillers, reactive diluents, drying agents, adhesion promoters and UV stabilizers, fungicides, flame retardants, rheological adjuvants, color pigments or color pastes, and/or optionally also, to a small extent, solvents.

[0119] A “plasticizer” for the purposes of this invention is a substance that decreases the viscosity of the composition and thus facilitates its processability. Herein the plasticizer may constitute up to 40 wt. % or up to 20 wt. %, based on the total weight of the composition, and is preferably selected from the group consisting of: polydimethylsiloxanes (PDMS); diurethanes; ethers of monofunctional, linear or branched C4-C16 alcohols, such as Cetiol OE (obtainable from Cognis Deutschland GmbH, Düsseldorf); esters of abietic acid, butyric acid, thiobutyric acid, acetic acid, propionic acid esters and citric acid; esters based on nitrocellulose and polyvinyl acetate; fatty acid esters; dicarboxylic acid esters; esters of OH-group-carrying or epoxidized fatty acids; glycolic acid esters; benzoic acid esters; phosphoric acid esters; sulfonic acid esters; trimellitic acid esters; epoxidized plasticizers; polyether plasticizers, such as end-capped polyethylene or polypropylene glycols; polystyrene; hydrocarbon plasticizers; chlorinated paraffin; and, mixtures thereof. It is noted that, in principle, phthalic acid esters can be used as the plasticizer but these are not preferred due to their toxicological potential. It is preferred that the plasticizer comprises or consists of one or more polydimethylsiloxane (PDMS).

[0120] “Stabilizers” for purposes of this invention are to be understood as antioxidants, UV stabilizers or hydrolysis stabilizers. Herein stabilizers may constitute in toto up to 10 wt. % or up to 5 wt. %, based on the total weight of the composition. Standard commercial examples of stabilizers suitable for use herein include: sterically hindered phenols; thioethers; benzotriazoles; benzophenones; benzoates; cyanoacrylates; acrylates; amines of the hindered amine light stabilizer (HALS) type; phosphorus; sulfur; and, mixtures thereof.

[0121] As noted, the compositions according to the present invention can additionally contain fillers. Suitable here are, for example, chalk, lime powder, precipitated and/or pyrogenic silicic acid, zeolites, bentonites, magnesium carbonate, diatomite, alumina, clay, talc, titanium oxide, iron oxide, zinc oxide, sand, quartz, flint, mica, glass powder, and other ground mineral substances. Organic fillers can also be used, in particular carbon black, graphite, wood fibers, wood flour, sawdust, cellulose, cotton, pulp, cotton, wood chips, chopped straw, chaff, ground walnut shells, and other chopped fibers. Short fibers such as glass fibers, glass filament, polyacrylonitrile, carbon fibers, Kevlar fibers, or polyethylene fibers can also be added. Aluminum powder is likewise suitable as a filler.

[0122] The pyrogenic and/or precipitated silicic acids advantageously have a BET surface area from 10 to 90 m.sup.2/g. When they are used, they do not cause any additional increase in the viscosity of the composition according to the present invention but do contribute to strengthening the cured composition.

[0123] It is likewise conceivable to use pyrogenic and/or precipitated silicic acids having a higher BET surface area, advantageously from 100 to 250 m.sup.2/g, in particular from 110 to 170 m.sup.2/g, as a filler: because of the greater BET surface area, the effect of strengthening the cured composition is achieved with a smaller proportion by weight of silicic acid.

[0124] Also suitable as fillers are hollow spheres having a mineral shell or a plastic shell. These can be, for example, hollow glass spheres that are obtainable commercially under the trade names Glass Bubbles®. Plastic-based hollow spheres, such as Expancel® or Dualite®, may be used and are described in EP 0 520 426 B1: they are made up of inorganic or organic substances and each have a diameter of 1 mm or less, preferably 500 μm or less.

[0125] Fillers which impart thixotropy to the composition may be preferred for many applications: such fillers are also described as rheological adjuvants, e.g., hydrogenated castor oil, fatty acid amides, or swellable plastics such as PVC.

[0126] The total amount of fillers present in the compositions of the present invention will preferably be from 1 to 80 wt. %, and more preferably from 5 to 60 wt. %, based on the total weight of the composition. The desired viscosity of the curable composition will typically be determinative of the total amount of filler added and it is submitted that in order to be readily extrudable out of a suitable dispensing apparatus—such as a tube—the curable compositions should possess a viscosity of from 3000 to 150,000, preferably from 40,000 to 80,000 mPas, or even from 50,000 to 60,000 mPas.

[0127] Examples of suitable pigments are titanium dioxide, iron oxides, or carbon black.

[0128] In order to enhance shelf life even further, it is often advisable to further stabilize the compositions of the present invention with respect to moisture penetration through using drying agents. A need also occasionally exists to lower the viscosity of an adhesive or sealant composition according to the present invention for specific applications, by using reactive diluent(s). The total amount of reactive diluents present will typically be up to 15 wt. %, and preferably from 1 and 5 wt. %, based on the total weight of the composition.

[0129] The following examples are illustrative of the present invention and are not intended to limit the scope of the invention in any way.

EXAMPLES

[0130] The following materials were employed in the Examples:

α-angelica lactone: 4-Hydroxy-3-pentenoic acid γ-lactone, available from Sigma Aldrich
Triisopropyl orthoformate: CAS Number 4447-60-3, available from Sigma
AldrichTriethyl orthoformate: CAS Number 122-51-0, available from Sigma Aldrich
Trimethyl orthoformate: CAS Number 149-73-5, available from Sigma Aldrich
Tributyl orthoformate: CAS Number 588-43-2, available from Sigma Aldrich
Tripropoxy orthoformate: CAS Number 621-76-1, available from Sigma Aldrich
Diethyl vinyl orthoformate: CAS Number 34712-46-4, available from Sigma Aldrich
Trioctadecyl orthoformate: CAS Number 17671-28-2, available from Sigma Aldrich
Tripentyl orthoformate: CAS Number 637-42-3, available from Sigma Aldrich

Example 1: Synthesis of 2-ethoxymethylene-α-angelica Lactone (EtOMAL)

[0131] 179 mL of triethyl orthoformate (1.07 mol) were firstly added to 203 mL of acetic anhydride (2.15 mol) into a 1 L round bottom flask under argon atmosphere and under stirring. 64.4 mL of α-angelica lactone (0.72 mol) and 150 mg of 2,6-di-tert-butyl-p-cresol (BHT) were then added into the flask under argon atmosphere. The mixture was stirred under reflux conditions (T=110° C.-130° C.) and under an argon atmosphere for around 7 hours.

[0132] Five samples were withdrawn during the reaction at respectively 0, 60, 120, 260 and 410 minutes. Between 100 and 250 μL of these samples were added into chromatography (GC) vials containing 30 μL of dodecane used as the internal standard; 1.6 mL of toluene was added into all GC vials and the obtained solutions were analyzed by GC-FID. The relative amount of α-angelica lactone was calculated by the ratio between the integration areas normalized with respect to the internal standard and with respect to the amount of reaction mixture used for GC analysis.

[0133] Upon completion of the reaction, the mixture was brought to room temperature and it was stored overnight under argon atmosphere. Subsequently the mixture was distilled under vacuum.

[0134] 77.25 g of a fraction containing the desired product EtOMAL were collected—at a temperature of approximately 120° C. and a pressure of 0.4 mbar—as a yellow liquid. GC-FID analysis indicated that this fraction contained around 90% of EtOMAL (Yield=61%). 25 mL of diethyl ether and 20 mL of hexane were added to the collected fraction under an argon atmosphere. The mixture was immersed in an ethanol bath and the temperature was slowly decreased by addition of dry ice into the bath. A white crystalline material precipitated and the latter was filtered under atmospheric conditions and washed several times with pentane. Finally, the product was dried overnight under vacuum and stored under inert conditions. The overall yield was about 40%.

[0135] The product was characterized by Nuclear Magnetic Resonance (NMR) as follows:

##STR00010##

[0136] .sup.1H NMR (300 MHz, CD.sub.2Cl.sub.2, δ): =7.18 (q, .sup.6J=0.75 Hz, H6, 1H), 5.80 (m, H3, 1H), 4.16 (q, .sup.3J=7.05 Hz, H7, 2H), 2.04 (dd, .sup.4J=1.44 Hz, .sup.6J=0.75 Hz, H5, 3H), 1.34 (t, .sup.3J=7.07 Hz, H8, 3H) ppm.

[0137] .sup.13C NMR (100 MHz, CD.sub.2Cl.sub.2, δ): 171.06 (C1), 154.17 (C6), 151.54 (C4), 107.86 (C2), 99.22 (C3), 71.93 (C7), 15.42 (C8), 14.31 (C5) ppm.

Example 2: Anionic Polymerization of EtOMAL

[0138] ##STR00011##

Example 2.1: Synthesis and Characterization of Poly-EtOMAL Using Sodium Isopropoxide (NaiPrO) as the Catalyst

[0139] 2.1.1 Synthesis

[0140] 800 mg of EtOMAL was dissolved in 1 mL of toluene under inert conditions. The solution was added to a mixture of 4 mg of NaiPrO and 1 mL of toluene at 60° C. under an inert atmosphere. Additional toluene (1 mL) was used to quantitatively transfer EtOMAL into the reaction mixture.

[0141] Shortly after the addition of EtOMAL a solid material in the form of a gel started to precipitate. The reaction was left for 2 hours at 60° C. Afterwards around 1 mL of an aqueous HCl (0.1 M) solution was added into the reaction Schlenk vessel. The solid was then washed several times with toluene. Afterwards the washed solid was dissolved in dichloromethane and filtered through a short column of SiO.sub.2. Finally, it was dried overnight under vacuum. Overall yield was typically higher than 90%.

[0142] 2.1.2 NMR Characterization of Poly-EtOMAL

[0143] The product was characterized by Nuclear Magnetic Resonance (NMR) as follows:

##STR00012##

[0144] .sup.1H NMR (300 MHz, CD.sub.2Cl.sub.2, δ): =7.43 (bs, H.sub.3, 1H), 4.29 (bs, H.sub.6, 1H), 3.43 (bs, H.sub.7, 2H), 1.45 (bs, H.sub.5, 3H), 1.13 (bs, H.sub.8, 3H) ppm.

[0145] .sup.13C NMR (75 MHz, CD.sub.2Cl.sub.2, δ): 171.35 (C.sub.1), 156.22 (C.sub.3), 131.78 (C.sub.2), 88.17 (C.sub.4), 76.80 (C.sub.6), 66.77 (C.sub.7), 20.79 (C.sub.5), 15.27 (C.sub.8) ppm.

[0146] 2.1.3 Molecular Weight Characterization of poly-EtOMAL

[0147] FIG. 1 appended hereto illustrates a bi-modal molecular weight distribution obtained when the molecular weight of the polymer of this Example was analyzed in tetrahydrofuran (THF) by gel permeation chromatography (GPC) using polystyrene calibration standards.

Example 2.2: Synthesis of Poly-EtOMAL by Using aluminum Isopropoxide [Al[iPrO).SUB.3.] as the Catalyst

[0148] 900 mg of EtOMAL were dissolved in 1 mL of toluene under inert conditions. The solution was added to Al(iPrO).sub.3 (1o mol. %) in 1 mL of toluene at 60° C. under an inert atmosphere. Additional toluene (1-3 mL) was used to quantitatively transfer EtOMAL into the reaction mixture.

[0149] Shortly after the addition of EtOMAL a solid material in the form of a gel started to precipitate. The reaction was left for 2 h at 60 ° C. Afterwards aqueous HCl (0.1 M) solutions were used to quench the reactions. The solid was washed on a Bruckner filter several times with toluene, dichloromethane and diethyl ether. Finally, it was dried overnight under vacuum. Overall yield was typically higher than 80%. Polymer formation was identified by NMR analysis.

Example 2.3: Synthesis of Poly-EtOMAL by Using Butyl Lithium as the Catalyst

[0150] 170 mg of EtOMAL was dissolved in 2 mL of THF under inert conditions. The solution was heated to reach 60° C. under an inert atmosphere. A volume of BuLi 1.6 M solution in hexane corresponding to 1 mol % vs. EtOMAL was then added under stirring to the monomer solution. The reaction was quenched after 1 hour with aqueous HCl (1 M) solutions. Afterwards dichloromethane was added to the mixture and the obtained solution was filtered through celite. Finally, it was dried overnight under vacuum. Polymer formation was identified by NMR analysis.

Example 3: Synthesis of 2-isopropoxymethylene-α-angelica Lactone (.SUP.i.PrOMAL)

[0151] Triisopropyl orthoformate (61.1 g, 321 mmol) was reacted with α-angelica lactone (21.2 g, 216 mmol) under reflux conditions for 7 hours in the presence of acetic anhydride (65.8 g, 645 mmol) and 2,6-di-tert-butyl-p-cresol (BHT, 0.060 g, 0.27 mmol).

##STR00013##

[0152] Five fractional samples of the reaction mixture were withdrawn during the reaction and added into gas chromatography (GC) vials containing 30 μL of dodecane used as the internal standard; 1.6 mL of toluene was added into all GC vials and the obtained solutions were analyzed by GC-FID. The relative amount of α-angelica lactone was calculated by the ratio between the integration areas normalized with respect to the internal standard and with respect to the amount of reaction mixture used for GC analysis.

[0153] Upon completion of the reaction, the reaction mixture was distilled under reduced pressure to obtain .sup.iPrOMAL as a light-yellow oil (12.1 g, 33.3% yield), which product was characterized as follows:

[0154] .sup.1H NMR (400 MHz, CDCl.sub.3) δ 7.22 (s, 1H), 5.78 (s, 1H), 4.28 (sep, J=4 Hz, 1H), 2.03 (s, 3H), 1.31 (d, 6H) ppm.

[0155] .sup.13C NMR (100 MHz, CDCl.sub.3) δ 171.5, 153.3, 151.2, 107.9, 33.5, 79.5, 22.1, 14.5 ppm.

Example 4: Further Syntheses

[0156] The above method for the synthesis of 2-isopropoxymethylene-α-angelica lactone (.sup.iPrOMAL) was viably repeated at yields≥25% using the following orthoformates ((XO).sub.3CH): trimethyl orthoformate (R.sup.1═R.sup.2═R.sup.3=Me); tributyl orthoformate (R.sup.1═R.sup.2═R.sup.3=Bu); tripropyl orthoformate (R.sup.1═R.sup.2═R.sup.3=nPr); diethyl vinyl orthoformate (R.sup.1═R.sup.2=Et, R.sup.3═CH.sub.2═CH.sub.2); trioctadecyl orthoformate (R.sup.1═R.sup.2═R.sup.3═C.sub.18H.sub.37); and, tripentyl orthoformate (R.sup.1═R.sup.2═R.sup.3═C.sub.5H.sub.11).

[0157] In view of the foregoing description and examples, it will be apparent to those skilled in the art that equivalent modifications thereof can be made without departing from the scope of the claims.