DMR-0804878 Special Creativity Extension 2014-2016
Summary. During this Special Creativity Extension we propose to synthesize and characterize biodegradable polyisobutylene (PIB) using “green polymer chemistry” and a newly discovered two-phase thiol oxidative living polymerization system. Specifically, PIBs containing ester and disulfide bonds will be synthesized from low molecular weight telechelic SH-functionalized PIB precursors. The precursors will be synthesized by reacting first low molecular weight liquid HO-PIB-OH with divinyl-adipate, followed by reacting the vinyl-PIB-vinyl with mercaptoethanol to produce SH-adipate-PIB-adipate-SH (SH-A-PIB-A-SH). Both reactions will be catalyzed by Candida antarctica lipase BCALB, without the use of solvents. The SH-A-PIB-A-SH precursor will then be polymerized using an environmentally friendly oxidative polymerization process discovered in our laboratory. The precursors and polymers will be characterized by NMR spectroscopy, high resolution SEC, mass spectrometry, TEM, DSC, DTA, tensile testing and other appropriate techniques. The degradation behavior of the polymers will also be investigated.
Merit. Poly(styrene-b-isobutylene-b-styrene) SIBS, a biostable polymer is in clinical practice since 2004 as the drug-eluting coating of the Taxus coronary stent. PIB has extraordinary biocompatibility and biostability. However, recent trends in the pharmaceutical and medical device industries favor biodegradable polymers. Biodegradable PIBs will be synthesized and characterized for the first time, using “green polymer chemistry”. Our group reported the first example of quantitative polymer functionalization using Candida antarctica lipase B CALBunder solventless conditions. We have precision synthesized telechelic acrylate- and methacrylate functionalized PIBs using CALB. Mass spectrometry verified the structures. We have also developed new, greener chemistry for the synthesis of disulfide polymers via dithiol oxidation using water, H2O2, air and triethylamine as a catalyst. While this latter is not “green”, it can be recycled leading to more sustainable processes. The oxidative polymerization of 2-[2-(2-sulfanylethoxy)ethoxy]ethanethiol (DODT) yielded high molecular weight elastomers under living conditions.1,2 In addition, we discovered that the polymerization involved rings. We have proposed a mechanism that needs to be verified. Studying the oxidative polymerization of SH-PIB-SH will help to verify the polymerization mechanism. We will attempt to visualize high molecular weight rings by chemical attenuation and AFM. In addition, we expect to find unique material properties. Thus the proposed project, a continuation of our PIB-related research, has both theoretical and practical importance.