Rubber Functionalization by Diels–Alder Chemistry: From Cross-Linking to Multifunctional Graft Copolymer Synthesis

Abstract

The functionalization of polyisobutylene-co-isoprene, commonly referred to as butyl rubber, was investigated with the aim of preparing multifunctional materials. First, the acid catalyzed ring-opening of epoxidized butyl rubber was investigated. Ring-opening followed by elimination resulted in the formation of different dienes depending on the reaction conditions. It was possible to cleanly isolate the exo-diene, which readily undergoes Diels–Alder [4 + 2] cycloaddition reactions and it was demonstrated that this chemistry could be used to prepare multifunctional graft copolymers. For example, poly(ethylene oxide) (PEO) or polystyrene (PS) could be grafted while at the same time introducing carboxylic acid moieties along the polymer backbone, and both polymers could be simultaneously grafted to form mixed graft copolymers with tunable tensile properties. Furthermore, it was demonstrated that reaction with a dimaleimide led to efficient cross-linking of the rubber and this cross-linking could be reversed upon heating due to the thermoreversible nature of the Diels–Alder reaction. Thus, this chemistry allows for clean and facile synthesis of new rubber derivatives, opening possibilities for new rubber applications.

Polyisobutylene‐paclitaxel conjugates with pendant carboxylic acids and polystyrene chains: Towards multifunctional stent coatings with slow drug release

“…40 Briefly, as shown in Scheme 1A, butyl rubber containing 2 mol % of isoprene units was epoxidized to afford PIB-EPOX, 31 and the epoxide was opened with HCl in CHCl 3 . 40 The resulting allylic alcohol PIB-OH was activated by treatment with methanesulfonyl chloride in the presence of K 2 CO 3 and NEt 3 to provide PIB-OMs. Heating the mesylate (PIB-OMs) in the presence of DIPEA provided exo-diene PIB-DIENE, which underwent a Diels-Alder reaction at ambient temperature with maleic anhydride to afford PIB-MA.…”

“…Heating the mesylate (PIB-OMs) in the presence of DIPEA provided exo-diene PIB-DIENE, which underwent a Diels-Alder reaction at ambient temperature with maleic anhydride to afford PIB-MA. 40 The opening of these anhydrides with PTX was then investigated (Scheme 1B). Nucleophilic ring opening of the anhydride with 2.5 equiv.…”

“…Gel formation was also previously observed when hydroxyl-terminated PEO was reacted with PIB-MA under similar conditions. 40 However, increasing the PTX excess to 5 equiv. greatly suppressed the gel formation and provided the first target conjugate PIB-PTX-COOH.…”

“…58 As previously reported, PIB-MA can also be opened by hydroxyl-terminated polymers such as PS (PS-OH) and PEO. 40 While PIB-PEO graft copolymers have been extensively reported by our group and others, [28][29][30]32,59,65,66 PS was of particular interest due to the use of SIBS in stent coatings. Linear block copolymers of PIB with PS or polyalloocimene have been found to exhibit thermoplastic elastomeric (TPE) properties that are conducive to their application in stent coatings.…”

“…40 As described earlier, because of its favorable chemical and biological properties, PIB-based materials are of significant interest for application as coatings for drug-eluting stents. 1,3 The current generation of stents incorporates physically encapsulated drug within a polymeric coating.…”