Synthesis and extension of diallyl telechelic polyisobutylenes to higher molecular weights and networks by thiol-ene chemistry

Abstract

In this research, the focus is on the use of the thiol-ene click chemistry for the preparation of high molecular weight linear rubbery or crosslinked polyisobutylenes from lower molecular weight liquid polyisobutylene precursors for the first time. Radical thiol-ene addition reactions were found to successfully connect polymer blocks together with the purpose of chain extension. The synthetic strategy followed comprises three stages: (i) synthesis of a difunctional carbocationic initiator,5-tert-butyl-1,3-bis(2-chloro-2-propyl)benzene (t-Bu-m-DiCumCl) from 5-tert-butyl-1,3-dicarboxybenzene in three steps; (ii) synthesis of well-defined polyisobutylenes via quasiliving carbocationic polymerization and following in-situ end-capping reactions with allyltrimethylsilane; (iii) utilization of UV light initiated thiol-ene reactions in order to obtain high molecular weight products and networks in the presence of 2,2-dimethoxy-2-phenyl acetophenone (DMPA) as photoinitiator in dichloromethane under inert atmosphere. In a complementary study, the effect of thermal initiation on the efficiency of radical thiol-ene addition reactions in chain extension reactions was also investigated. The intermediates and the final products were characterized by 1H NMR spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR) and Size Exclusion Chromatography (SEC) in terms of molecular structure and molecular weight, respectively. Increase in the molecular weight of the chain extended linear polymers was monitored by SEC. The crosslinked networks were characterized by Raman spectroscopy which confirmed the formation of C-S bonds. The network properties were evaluated by swelling and extraction studies.