Effect of the composition of methanol-water mixtures on tacticity of poly(N-ethylacrylamide) gel

摘要

Two series of macroporous poly(N-ethylacrylamide) (PNEAM) gels are synthesized in different composition of methanol-water mixtures (x(m)=0, 0.06, 0.13, 0.21, 0.31, and 0.43; where x(m)=mole fraction of methanol) in presence as well as in the absence of 0.1M Y(OTf)(3) Lewis acid as additive. The gels synthesized in the absence of Lewis acid are atactic and in the presence of the same are isotactic. Synthesis of the corresponding linear PNEAM homopolymers shows that, the isotacticity (meso dyad, %) of the resulted polymers increases for the gels prepared in the presence of Lewis acid (LA) and remains constant for the gel prepared in the absence of LA, respectively, with the increase in the concentration of the synthesis solvent methanol. SEM micrographs reveal that, the hydrogels synthesized in the presence of LA are more porous than the gels prepared in the absence of LA. Swelling ratio of all the hydrogels decreases with the increase in the temperature and LA gels show higher swelling ratio values than non LA gels (NLA). Deswelling rate of the hydrogels prepared in methanol-water mixture in presence of LA is faster than the hydrogels prepared in absence of LA. Moreover, reswelling rate increases with increase in the isotacticity of the PNEAM segment in the gel. All these results have been explained on the basis of the formation of highly porous hydrogels with higher isotactic PNEAM chain segment in the presence of LA in methanol-water mixtures. (c) 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41668.