Living cationic polymerization of poly(isobutylene) based linear and multiarm star block copolymers used in the development of water-permeable thermoplastic elastomers

Stacy J. Taylor


The research described herein is focused on the study and development of linear A-B-A and multiarm block copolymers displaying thermoplastic elastomeric behavior. These materials consisted of poly(isobutylene) (PIB) center blocks and styrnic end blocks and were synthesized using a living cationic polymerization method in which the styrenic monomer was added sequentially to living PIB chains to form block copolymers (BCPs). In the first part of this study, the synthesis of PIB-based BCPs having copolymer end blocks containing styrene and p -methylstyrene (p MSt) repeat units was investigated in an attempt to minimize a chain-coupling reaction that occurs at the 4position on styrene repeat units during end block polymerization. Model end block copolymerizations using varying feed ratios of styrene and p MSt were conducted, and aliquots taken at various conversions were analyzed via 1 H NMR to investigate the relative incorporation of the two monomers throughout the polymer chains. P(styrene-co-p MSt)-PIB-P(styrene-co-p MSt) triblock copolymers were synthesized using varying feed ratios of styrene and p MSt. It was found that rate of end block propagation increased with increasing p MSt in the feed. The second portion of this research investigated the initiation of styrene polymerization from TMPCl capped with 1,1-diphenylehtylene (DPE). This initiating species was expected to increase the efficiency of crossover to styrene during block copolymerization. To investigate this behavior, TMPCl was capped with DPE using a [DPE]/[TMPCl] ratio that ranged from 0 to 9 and then used to initiate the polymerization of styrene. It was found via in situ FTIR that chain-end capping caused an increase in the positive y-intercept of the first-order plot of styrene propagation, indicating the occurrence of a rapid monomer consumption (RMC) event caused by the higher equilibrium constant for the initiating species as compared to the propagating species. In the final portion of this research, multifunctional initiators were synthesized having two, three and four initiation sites per molecule. Block copolymerizations initiated by 5-tert -Butyl-1,3-di(2-chloro-2-propyl)benzene (blocked-dicumyl chloride, bDCC) and 1,3,5-tris(2-chloro-2-propyl)benzene(tricumyl chloride, TCC) and 3,3' ,5,5' -tetra(2-chloro-2-propyl)-biphenyl (tetracumyl chloride biphenyl, TCCBP)yielded two, three and four-arm star block copolymers, respectively, having PIB centerblocks and PS end blocks. The synthesis of four-arm stars was also attempted using TCCDPP as an initiator. (Abstract shortened by UMI.)