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New block copolymers of Isobutylene by combination of cationic and anionic polymerizations
(2004)
- The studies presented in this thesis deal with the new block copolymers of isobutylene by combination of cationic and anionic polymerizations, which are new materials with numerous promising potential applications. A new method for the synthesis of tailored polyisobutylene(PIB)-based block copolymer by combination of controlled / living cationic and anionic polymerizations has been developed. In addition and parallel to these subjects, new synthetic routes for preparation of telechelic PIBs and conductive polymers have been investigated. The PIB precursors used for subsequent anionic polymerization and other processes were prepared by controlled / living cationic polymerization of isobutylene followed by quenching with thiophene under selected conditions. Quantitative functionalization of living PIB with thiophene (T) has been achieved. The process is complicated by coupling between living PIB and PIB-T formed by in situ deprotonation. By lithiation of PIB-T a new, convenient method has been demonstrated for the synthesis of PIB-based block copolymers, involving anionic initiation of tert-butyl methacrylate. A major improvement is that for an industrial process, lithiation by n-BuLi is much more convenient than metalation by Na/K alloy, which had to be used in former processes. Block copolymers with narrow and unimodal molecular weight distribution (MWD) were synthesized under well-controlled conditions. The lithiated thiophene-capped PIB was also used to prepare four-armed star PIB via chlorosilane coupling. Using the same method, new amphiphilic block copolymers, namely PIB-b-poly(N,N-dimethylacrylamide) and PIB-b-poly(ethylene oxide) were synthesized. The anionic polymerization of N,N-dimethylacrylamide (DMAAm) was carried out with a binary initiator system prepared from thienyllithium and the Lewis acids triethylaluminium (Et3Al), diethylzinc (Et2Zn) or triethylborane (Et3B) in THF. Polymerizations proceeded in a homogeneous manner and gave polymers having controlled molecular weights. However, in presence of alkoxides the polymerization results in polymers insoluble in THF, even using Et3Al. Finally, lithiated PIB-T, in conjunction with Lewis acids, was used to initiate the living anionic polymerization of DMAAm, resulting in the new amphiphilic block copolymer PIB-b-PDMAAm. The anionic polymerization of ethylene oxide (EO) was carried out with a binary initiator system prepared from thienyllithium and the polyiminophosphazene base tBu-P4 in THF. Lithilated PIB-T- in conjunction with tBu-P4 was used to initiate the living anionic polymerization of ethylene oxide. In a second method, PIB-b-PEO was synthesized using hydroxyl end-capped PIB as macroinitiator in conjunction with tBu-P4. The aggregation behavior in dilute aqueous solutions of a PIB-b-PEO copolymer, produced from the combination of cationic and anionic polymerizations, was investigated by dynamic light scattering in aqueous solution. The monoaddition of ethylene oxide to lithiated PIB-T is demonstrated as a new pathway for the synthesis of hydroxy-functional PIB (PIB-OH). This is a useful alternative to the tedious procedures used in the literature so far. PIB-OH was successfully used as a macroinitiator for the ring-opening polymerizations of L-lactide and epsilon-caprolactone catalyzed by stannous octoate. Combination of chromatographic methods and MALDI-TOF ass spectrometry gave information about the side reactions during polymerization. Quantitative functionalization of living PIB with 2-bromothiophene has been achieved. Using various coupling methods, this polymer was convertet to a macromonomer with a pendant thiophene group, which is accessible in the 1- and 5-position. Oxidative copolymerization with thiophene led to graft copolymers consisting of polythiophene-graft-PIB.
