Self-Assembly of Poly(vinylpyridine-b-oligo(ethylene glycol) methyl ether methacrylate) Diblock Copolymers

摘要

Poly(oligoethylene glycol)-poly(2-vinylpyridine) is a model diblock for studying the effect of block-localized charge on block copolymer self-assembly because in the absence of charge the polymers are perfectly miscible, and upon protonation of the vinylpyridine block the polymer undergoes an order-disorder transition. Seven model block copolymers with molecular weights of approximately 60 kDa containing poly(2-vinylpyridine) volume fractions spanning 0.069-0.700 were synthesized using reversible addition fragmentation transfer polymerization and then studied to understand the effect of protonation level, diblock composition, and temperature on the location of the ordering transition and the type of nanostructures formed in a charge asymmetric system. All of the polymers displayed lower critical solution-type behavior, with the order-disorder transition temperature decreasing with increasing acid content. Polymers with symmetric compositions showed the highest degree of incompatibility for a given degree of protonation, and the observed morphologies for all polymers were consistent with those observed at similar compositions for classical hydrophobic block copolymers. The observed protonation-induced phase transition can be explained by the shift of the Flory-Huggins parameter due to the alternation of the identity of monomers, consistent with the prediction of Nakamura and Wang's theory. The use of polyvalent ions promotes self-assembly at lower concentrations, consistent with ionic crosslinking effects between polymer chains that are promoted at high concentration due to exchange entropy in crosslinked polymers. (c) 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1181-1190