Syndiotactic- and heterotactic-specific radical polymerizations of N-n-propyl-α-fluoroacrylamide and phase-transition behaviors of aqueous solutions of poly(N-n-propyl-α-fluoroacrylamide)

Abstract

Radical polymerization of N-n-propyl-α-fluoroacrylamide (NNPFAAm) was investigated in several solvents at low temperatures in the presence or absence of Lewis bases, Lewis acids, alkyl alcohols, silyl alcohols, or fluorinated alcohols. Different effects of solvents and additives on stereospecificity were observed in the radical polymerizations of NNPFAAm and its hydrocarbon analogs such as N-isopropylacrylamide (NIPAAm) and N-n-propylacrylamide (NNPAAm); for instance, syndiotactic (and heterotactic) specificities were induced in radical polymerization of NNPFAAm in polar solvents (and in toluene in the presence of alkyl and silyl alcohols), whereas isotactic (and syndiotactic) specificities were induced in radical polymerizations of the hydrocarbon analogs under the corresponding conditions. In contrast, heterotactic specificity induced by fluorinated alcohols was further enhanced in radical polymerization of NNPFAAm. The effects of stereoregularity on the phase-transition behaviors of aqueous solutions of poly(NNPFAAm) were also investigated. Different tendencies in stereoregularity were observed in aqueous solutions of poly(NNPFAAm)s from those in solutions of the hydrocarbon analogs such as poly(NIPAAm) and poly(NNPAAm). The polymerization behavior of NNPFAAm and the phase-transition behavior of aqueous poly(NNPFAAm) are discussed based on possible fluorine–fluorine repulsion between the monomer and propagating chain-end, and neighboring monomeric units.