Steric Hindrance Effect On Thermoresponsive Behaviors Of Polymers

In recent years, thermoresponsive polymers have attracted increasing attention.Numerous papers reported the chemical factors and physical factors controling overthe thermoresponsive behaviors of polymers. Less work has appeared, however,regarding steric hindrance effect on thermoresponsive behaviors of polymers.Therefore, the research of steric hindrance effect on thermoresponsive behaviors ofpolymers is a foresight work.This paper gave a careful description on the synthesis and characterization of twokinds of monomers and corresponding polymers. One kind of polymers was flexiblepolymers based on acry acid. The other was semirigid polymers based on2-vinylterephthalic acid. The research results were declared as follows:1. Two kinds of new pyrrolidone-based monomers were designed and synthesized.One was based on acry acid （i.e., N-（1-meth-2-acryloyloxyethyl） pyrrolidone （M1）and N-（2-acryloyloxypropyl） pyrrolidone （M2））. The other was based on2-vinylterephthalic acid （i.e., bis （N-（1-meth-2-hydroxyethyl） pyrrolidone）2-vinylterephthalate （M3） and bis （N-（2-hydroxypropyl） pyrrolidone）2-vinylterephthalate （M4））.2. The flexible polymers P1and P2were synthesized from M1and M2via freeradical polymerization, respectively. Both P1and P2exhibited a thermoresponsivephase transition behavior in light water （H2O）. The cloud point （CP） of P1and P2both decreased with increasing concentration. Yet the CP of P1which has the strongerhindrance effect was lower than P2at the same concentration.3. Well-definited semirigid polymers P3and P4from M1and M2weresynthesized via RAFT polymerization, respectively. P3and P4exhibited the liquidcrystal property, when the molecular weight reached2.12×10⁴g mol^-1,1.95×10⁴gmol^-1, respectively. The CP of P3and P4aqueous solution remarkably increased withincreasing molecular weight. On the whole, for polymers P3and P4with theapproximate MWs and polydisperisties, the CP of P3which has the strongerhindrance effect was lower than that of P4at5.0mg mL^-1.