Synthesis and Characterization of Zwitterionic Block Copolymers

Zwitterionic poly(2-(dimethylamino)ethyl methacrylate-block-methacrylic acid) (PDMAEMA-block-PMAA) copolymers are synthesized by group transfer polymerization using 2-tetrahydropyranyl methacrylate (THPMA) as a protected monomer for the acid block. Subsequent thermolysis led to quantitative removal of the tetrahydropyranyl groups, but control experiments indicated significant broadening of the molecular weight distribution (MWD) of a PDMAEMA homopolymer under the same conditions. Hence this deprotection route was considered unsatisfactory. Acid hydrolysis of the block copolymers under mild conditions also led to quantitative removal of the THP groups, as judged by 1H NMR spectroscopy. This deprotection chemistry was adopted as our preferred route, since it did not lead to MWD broadening of the same PDMAEMA homopolymer. A series of zwitterionic blocks were synthesized with good control over both molecular weight and copolymer composition. The aqueous solubility vs. pH behavior of these copolymers was determined by acid titration. Finally, the reversible micellization of these copolymers in aqueous media was examined using dynamic light scattering and variable temperature 1H NMR spectroscopy.