High molecular weight polyisobutylenes and polyisobutylene networks from liquid polyisobutylenes by thiol-ene clicking

Abstract

A polyisobutylene-based polymer network comprising the thiol-ene reaction product of at least two thiol-terminated polyisobutylene precursor polymers and at least one multi-functional allyl-containing precursor moiety or polymer in the presence of light or heat. The at least two thiol-terminated polyisobutylene precursor polymers have at least two thiol end groups. When each polyisobutylene precursor polymer has only two thiol end groups then the allyl-containing precursor moiety or polymer has at least three functional groups, and wherein when the allyl-containing precursor moiety or polymer has two functional groups then each polyisobutylene precursor polymer has at least three thiol end groups.

Claims

1. A polyisobutylene-based polymer network comprising the thiol-ene reaction product of: at least two thiol-terminated polyisobutylene precursor polymers, each polyisobutylene precursor polymer having at least two thiol end groups; and at least one multi-functional allyl-containing precursor moiety or polymer, in the presence of light or heat; wherein when each polyisobutylene precursor polymer has only two thiol end groups then the allyl-containing precursor moiety or polymer has at least three functional groups, and wherein when the allyl-containing precursor moiety or polymer has two functional groups then each polyisobutylene precursor polymer has at least three thiol end groups.

2. The polyisobutylene-based polymer network of claim 1 wherein each polyisobutylene precursor polymer comprises a core and at least two polyisobutylene chains extending from the core, wherein each of the at least two polyisobutylene chains have a thiol end group.

3. The polyisobutylene-based polymer network of claim 1, wherein each polyisobutylene precursor polymer has a formula selected from: ##STR00015## wherein m and m′ are each an integer from 2 to 5,000, and when present, m″ is an integer from 2 to 5,000.

4. The polyisobutylene-based polymer network of claim 1, wherein the at least one multi-functional allyl-containing precursor moiety or polymer has a formula selected from: ##STR00016## wherein A represents an allyl group, M is a moiety and P is polymer.

5. The polyisobutylene-based polymer network of claim 4 wherein the at least one multi-functional allyl-containing precursor moiety is an ##STR00017## moiety represented by the specific formula ##STR00018##

6. The polyisobutylene-based polymer network of claim 4 wherein the polymer is polyisobutylene.

7. A polyisobutylene-based polymer network comprising at least two sulfur containing polyisobutylene polymer segments and at least one residue of an allyl-containing moiety or polymer, wherein the at least two sulfur containing polyisobutylene polymer segments each include a core and at least two polyisobutylene polymer chains extending therefrom and including at least one sulfur atom being attached to the residue of the allyl-containing moiety or polymer, the residue of the allyl-containing moiety or polymer connecting the at least two sulfur containing polyisobutylene polymer segments together.

8. The polyisobutylene-based polymer network of claim 7 having the formula: ##STR00019## wherein n, n′, n″, and n′″ are each an integer from 2 to 5,000 and wherein each represents a polyisobutylene chain.

9. A method for creating a polyisobutylene-based polymer network, the method comprising: providing at least two thiol-terminated polyisobutylene precursor polymers, each polyisobutylene precursor polymer having at least two thiol end groups; adding at least one multi-functional allyl-containing precursor moiety or polymer with the at least two polyisobutylene precursor polymers to form a mixture; wherein when each polyisobutylene precursor polymer has only two thiol end groups then the allyl-containing precursor moiety or polymer has at least three functional groups, and wherein when the allyl-containing precursor moiety or polymer has two functional groups then each polyisobutylene precursor polymer has at least three thiol end groups; and irradiating the mixture with light or heating the mixture, so as to provide a thiol-ene reaction, thereby producing the polyisobutylene-based polymer network.

10. The method of claim 9, wherein each polyisobutylene precursor polymer comprises an initiator core and at least two polyisobutylene chains extending from the initiator core, wherein each of the at least two polyisobutylene chains have a thiol end group.

11. The method of claim 9, wherein each polyisobutylene precursor polymer has a formula selected from: ##STR00020## wherein m and m′ are each an integer from 2 to 5,000, and when present, m″ is an integer from 2 to 5,000.

12. The method of claim 9, wherein the at least one multi-functional allyl-containing precursor moiety or polymer is selected from a formula selected from: ##STR00021## wherein A represents an allyl group, M is a moiety and P is polymer.

13. The method of claim 12 wherein the at least one multi-functional allyl-containing precursor moiety is an ##STR00022## moiety represented by the specific formula ##STR00023##

14. The method of claim 12 wherein the polymer is polyisobutylene.

15. The method of claim 9, wherein the step of irradiating includes heating the mixture in the presence of a free radical initiator to produce the polymer network.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures in which:

(2) FIG. 1. is graph of the swelling ratio versus time for a) PIB-AXS and b) PIB-SXA.

(3) FIG. 2A is a .sup.jH NMR spectrum of a hydroxyl terminated polyisobutylene.

(4) FIG. 2B is a .sup.1H NMR spectrum of a thiol terminated polyisobutylene.

(5) FIG. 3 shows the GPC traces of a) a hydroxyl terminated polyisobutylene and b) a thiol terminated polyisobutylene.

(6) FIG. 4 is a graph of a creep experiment showing strain percentage versus time for PIB-SXA.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

(7) The present invention generally relates to polyisobutylene (PIB) networks. It will be appreciated that it is an important aspect of the present invention that the sulfur containing segments of the formed polyisobutylene networks are introduced by the use of sulfur terminated linear PIBs or sulfur terminated star PIBs. The preparation of these PIB networks is also provided. Such a polyisobutylene network can be used, for example, for making corrosion resistant coatings for metal surfaces and water-repellent wound dressings on living skin.

(8) Under carefully controlled conditions, the thiol-ene “click” reaction, as shown below in Scheme 1 will proceed to essentially quantitative conversions under mild conditions.

(9) ##STR00010##

(10) In one embodiment of the present invention, thiol-terminated polyisobutylene precursor polymers must be prepared. The preparation and characterization of hydroxyl telechelic polyisobutylene (HO-PIB-OH) have been previously described in International Patent Publication No. WO2010039986 by Kennedy et al., the contents of which are herein incorporated by reference.

(11) Once prepared, the HO—PIB-OH must be end-capped with a thiol. In one or more embodiments of the present invention, the thiol is 3-mercaptopropionic acid (MPA). The HO-PIB-OH is end-capped by the addition of the HO-PIB-OH and the thiol in a solvent such as toluene. The solution is then heated to a temperature of about 50° C. The next step in the process is to add a sulfonic acid into the system and then heat the system to a temperature of about 130° C. overnight in a distillation device such as a Dean and Stark apparatus. In one or more embodiments of the present invention, the sulfonic acid is p-toluenesulfonic acid. The next day the formed polymer is precipitated in 0.5 L of a solvent such as methanol, the solvent is decanted, and then dried in vacuum at a temperature of about 30° C.

(12) In some embodiments, the thiol-terminated polyisobutylene precursor polymer formed from the process above has the formula:

(13) ##STR00011##
wherein m and m′ are each an integer from 2 to 5,000.

(14) In some embodiments, the thiol-terminated polyisobutylene precursor polymer formed from the process above has the formula:

(15) ##STR00012##
wherein m, m′ n″ are each an integer from 2 to 5,000.

(16) Once the thiol-terminated polyisobutylene precursor polymers have been formed, in one embodiment of the present invention, the next step in the process is to take the thiol-terminated polyisobutylene precursor polymer and form a polyisobutylene-based polymer network. This is done by adding an allyl-containing precursor moiety or polymer to the already formed thiol-terminated polyisobutylene precursor polymer and then either irradiated with ultra violet light in the presence of a catalyst or heating in the presence of a radical initiator.

(17) In one embodiment of the present invention, the allyl-containing precursor moiety or polymer has a formula selected from:

(18) ##STR00013##
wherein A represents an allyl group, M is a moiety and P is polymer. In one embodiment of the present invention, the allyl-containing precursor moiety is 1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (TATA). In one embodiment of the present invention, the polymer segment in the allyl-containing precursor polymer is a polyisobutylene polymer.

(19) As will be appreciated by those of skill in the art, the thiol-ene “click” reactions used herein may be initiated in at least two ways. In some embodiments, a photochemical reaction is used. In these embodiments, a suitable catalyst is added to the solution, and then the solution is irradiated with ultraviolet light to initiate the reaction. Any catalyst known in the art for use with UV light-activated thiol-ene reactions may be used and one of ordinary skill in the art will be able to select a suitable catalyst without undue experimentation. In some embodiments, the catalyst is 2,2-dimethoxy-2-phenyl acetophenone (DMPA).

(20) Next the solution is irradiated with ultraviolet (UV) light to activate the thiol-ene reaction. In some embodiments, the solution may be irradiated with UV light using a medium pressure Hg lamp as the UV source. The exact reaction parameters will depend upon the particular materials being reacted and is well within the ability of one of ordinary skill in the art to determine without undue experimentation. In some embodiments, solution may be irradiated with UV light using a medium pressure Hg lamp for 60 min at from about 0° C. to about 5° C. to complete the reaction.

(21) Alternatively, a radical initiator is added to the solution, and then the solution is heated to initiate the reaction. Any radical initiator known in the art for use with UV light-activated thiol-ene reactions may be used and one of ordinary skill in the art will be able to select a suitable radical initiator without undue experimentation. The exact reaction parameters will depend upon the particular materials being reacted and is well within the ability of one of ordinary skill in the art to determine without undue experimentation. In some embodiments, the solution may be heated to initiate the reaction.

(22) By way of example, Scheme 2 below shows the structures of the starting materials and the network obtained when a thiol-terminated polyisobutylene precursor polymer is crosslinked with at least one multi-functional allyl-containing precursor moiety and exposed to UV radiation (or heat in the presence of a radical initiator) according to at least one embodiment of the present invention.

(23) ##STR00014##

(24) In one or more embodiments of the present invention, it is important to note that although it is envisioned that the polyisobutylene-based polymer networks of the present invention can be made with at least two thiol-terminated polyisobutylene precursor polymers each having at least two thiol end groups and at least one multi-functional allyl-containing precursor moiety or polymer, there are some limits to the number of thiol end groups on the thiol-terminated polyisobutylene precursor polymers and the number of functional groups on the at least one multi-functional allyl-containing precursor moiety or polymer used to make the networks. For example, when each polyisobutylene precursor polymer has only two thiol end groups, then the allyl-containing precursor moiety or polymer has to have at least three functional groups. Additionally, when the allyl-containing precursor moiety or polymer has exactly two functional groups, then each polyisobutylene precursor polymer has to have at least three thiol end groups. The limitations on the number of thiol end groups on the thiol-terminated polyisobutylene precursor polymers and the number of functional groups on the at least one multi-functional allyl-containing precursor moiety or polymer used to make the networks is in place to ensure that no linear polymer networks are formed.

(25) Experiments were also done so as to compare the polyisobutylene-based polymer networks of the present invention made with the at least two thiol-terminated polyisobutylene precursor polymers each having at least two thiol end groups and the at least one multi-functional allyl-containing precursor moiety or polymer, symbolized as PIB-SXA with prior art polyisobutylene-based polymer networks prepared with allyl-terminated polyisobutylene precursor moieties and at least one multi-functional thiol, symbolized as PIB-AXS.

(26) Swelling experiments yield valuable information of network characteristics. FIG. 1 shows swelling of PIB-AXS and PIB-SXA in cyclohexane, which is a good solvent for polyisobutylene as a function of time, and Table 1 below summarizes average molecular weight between crosslinks (M.sub.e), equilibrium swelling ratio (q.sub.w), crosslink density (ρ.sub.c), mesh size (ξ), and extractables %.

(27) TABLE-US-00001 TABLE 1 Extract- M.sub.c ρ.sub.c ξ ables Visual Network (g/mol) q.sub.w (×10.sup.−4) (nm) (%) observations PIB-AXS 1141 5.35 7.96 5.28 17.8 Optically clear, tacky, weak film PIB-SXA 890 4.00 10 4.15 10.0 Optically clear, Non-tacky, strong film

(28) Figure FIG. 1 shows that PIB-AXS swells to about 535% and that PIB-SXA swells to about 400% within an 1 hour and 25 minutes. This data indicates about 4 grams of cyclohexane per one gram of the network gel which indicates rather tightly crosslinked networks. The higher crosslink density, ρ.sub.c, lower swelling ratio, q.sub.w, and lower mesh size, ξ, indicate higher crosslinking efficiency of PIB-SXA as compared to PIB-AXS. It is believed that this occurs because the thiol-ene click reaction occurs easily and efficiently between the polyisobutylene precursor polymers and the multi-functional allyl-containing precursor moiety or polymer. The absence of tackiness and unpleasant odor after crosslinking is likely due to complete thiol conversion. PIB-AXS and PIB-SXA produced 17.8 and 10.0 wt. % extractables (i.e., 82.2 and 90% gel), respectively. This data also indicates high thiol-ene conversions.

(29) It has been discovered that the preparation of polyisobutylene networks synthesized with thiol-terminated polyisobutylene precursor polymers and multi-functional allyl-containing precursor moieties or polymers will produce optically clear odorless non-tacky strong network films exhibiting essentially no creep (less than 1% permanent set.

EXAMPLES

(30) The following examples are offered to more fully illustrate the invention, but are not to be construed as limiting the scope thereof. Further, while some of examples may include conclusions about the way the invention may function, the inventors do not intend to be bound by those conclusions, but put them forth only as possible explanations. Moreover, unless noted by use of past tense, presentation of an example does not imply that an experiment or procedure was, or was not, conducted, or that results were, or were not actually obtained. Efforts have been made to ensure accuracy with respect to numbers used (e.g., amounts, temperature), but some experimental errors and deviations may be present. Unless indicated otherwise, parts are parts by weight, molecular weight is weight average molecular weight, temperature is in degrees Centigrade, and pressure is at or near atmospheric.

Example 1

Synthesis of Thiol Telechelic PIB (HS-PIB-SH)

(31) Hydroxyl terminated polyisobutylene (HO-PIB-OH) is first end capped with 3-mercaptopropionic acid (MPA). Thus, HO-PIB-OH (7.5 g, 2.4 mmol) and MPA (2.7 g, 23 mmol) were dissolved in 120 ml of toluene and the solution was heated to 50° C. Then, 0.033 g (0.17 mmol) of p-toluenesulfonic acid (p-TSA) was added, and then the system was stirred at 130° C. overnight in a Dean and Stark apparatus. The formed polymer was precipitated in 0.5 L of methanol, the solvent was then decanted, and then dried in a vacuum at 30° C. The product was characterized by .sup.1H NMR spectroscopy and GPC.

(32) As shown in FIG. 2A, .sup.1H NMR spectroscopy indicated essentially complete functionalization. Thus, the resonance at 3.6 ppm associated with the —CH.sub.2OH proton of the starting material disappeared, while a resonance at 4.2 ppm indicating the ester of the target product appeared as shown in FIG. 2B. FIG. 3 shows the GPC traces of the starting material and that of the product were monomodal and indicated a Mn of HO-PIB-OH of 3180 g/mol and the Mn of SH-PIB-SH was 3750 g/mol, with a Mw/Mn of 1.06 for the HO-PIB-OH and a Mw/Mn of 1.1 for the SH-PIB-SH.

Example 2

Crosslinking of HS-PIB-SH with Triallyl Triazine

(33) 1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (TATA) (0.039 g, 1.56×10.sup.−4 mol) was added to HS-PIB-SH (0.583 g, 1.56×10.sup.−4 mol) along with 2,2-dimethoxy-2-phenylacetophenone (DMPA) initiator (0.04 g, 1.6×10.sup.−4 mol) dissolved in THF under vigorous mixing and the solution was quickly poured into a Teflon mold. The void-free solution was illuminated with UV light for one hour. Subsequently, network films were dried overnight in vacuum at 30° C. and postcured for 30 additional minutes.

(34) PIB-SXA prepared with HS-PIB-SH and TATA produced an odorless non-tacky strong film on manual examination. A deformation experiment also indicated behavior typical of a strong elastomer. FIG. 4 shows the result of a representative creep experiment. Thus, after 15 minutes of force applied at room temperature, deformation was ˜22%; after removing the force the sample recovered very rapidly with less than 1% permanent deformation. This is a characteristic of a strong rubber.

(35) In light of the foregoing, it should be appreciated that the present invention significantly advances the art by providing polyisobutylene networks synthesized with thiol-terminated polyisobutylene precursor polymers and multi-functional allyl-containing precursor moieties or polymers that are structurally and functionally improved in a number of ways. While particular embodiments of the invention have been disclosed in detail herein, it should be appreciated that the invention is not limited thereto or thereby inasmuch as variations on the invention herein will be readily appreciated by those of ordinary skill in the art. The scope of the invention shall be appreciated from the claims that follow.