Amphiphilic model conetworks of polyisobutylene methacrylate and 2-(dimethylamino)ethyl methacrylate prepared by the combination of quasiliving carbocationic and group transfer polymerizations
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A series of amphiphilic polymer conetworks (APCN) of the hydrophobic polyisobutylene methacrylate macromonomer (PIBMA) and the ionizable hydrophilic 2-(dimethylamino)ethyl methacrylate (DMAEMA) were synthesized by combining, for the first time, two controlled polymerization methods, quasiliving carbocationic polymerization (QLCCP) and group transfer polymerization (GTP). First, isobutylene (IB) was polymerized by QLCCP, and the resulting IB 7-mer (PIB) was modified to yield PIBMA with exact chain end-functionality of 1.0. Subsequently, PIBMA was successfully polymerized sequentially by GTP with DMAEMA (comonomer) and ethylene glycol dimethacrylate (EGDMA, cross-linker) using a bifunctional GTP initiator, 1,4-bis(methoxytrimethylsiloxymethylene)cyclohexane. Amphiphilic conetworks with linear segments of well-defined molecular weights (model conetworks) and a randomly cross-linked conetwork with linear segments characterized by a broad size distribution between the cross-links were prepared. Four of the model conetworks were based on poly(PIBMA-b-DMAEMA-b- PIBMA) triblock copolymers and two were based on poly(DMAEMA-b-PIBMA-b-DMAEMA) triblock copolymers of different degrees of polymerization (DP). Another conetwork was prepared from statistical copolymer chains. For comparison, four more networks, two of them based on DMAEMA homopolymers and two others based on copolymers of DMAEMA and methyl methacrylate, were also synthesized in the course of this study. Gel permeation chromatography and 1H NMR analyses indicated that the precursors to all the networks had the desired molecular weights and compositions. The degrees of swelling (DS) of the conetworks in tetrahydrofuran, n-hexane, and acidic water depended on the DP and the composition of the polymer chains between the EGDMA cross-links, while the DSs in neutral water were very low and almost constant because of the low degree of ionization of DMAEMA units in the conetworks in this solvent. These results show that the swelling behavior of the DMAEMA-PIBMA and DMAEMA-MMA conetworks can be controlled by the length and the composition of the chains between the cross-links, by the solvent polarity and the pH in a broad range. © 2007 American Chemical Society.