Post-polymerization modification enabling library synthesis of highly isotactic polyacrylamides carrying different pendant groups.

Abstract

The tacticity of vinyl polymers, i.e., the regularity of the side-chain stereochemistry, plays a crucial role in determining their physical properties. For example, the crystalline properties of isotactic polypropylene endow it with outstanding mechanical properties. In general, stereo-regulation during polymerization is greatly affected by even slight differences in the steric demand and/or position of the polar groups of the monomer side chains. In other words, no universal strategy to precisely control the tacticity for a given monomer with different pendant groups has been developed so far. Here, we provide a ground-breaking method for a library synthesis of highly isotactic polyacrylamides (99% meso dyad) with various pendant groups, including polar structures and di-substituted motifs. For that purpose, we designed an acrylamide monomer with a pendant that is sufficiently bulky to control the polymer tacticity that can be replaced by another pendant after polymerization. The transformable bulky monomer underwent iso-specific radical polymerization and subsequent aminolysis with a primary or secondary amine afforded a series of isotactic polyacrylamides derived from the added amine. Moreover, we clarified the isotacticity-dependent physical properties of the resulting polymers, such as their glass-transition temperature, crystalline properties, and solubility/thermo-responsibility in water, through a comparison with the corresponding atactic polyacrylamides.