Effect of synthesis method and buffer composition on the LCST of a smart copolymer of N-isopropylacrylamide and acrylic acid

Responsive polymers have been the focus of many studies during the past decade because of their ability to change according to environmental stimuli. In this paper, we report on the development of a method to synthesize a pH/temperature-sensitive linear copolymer, poly(N-isopropylacrylamide-co-acrylic acid) (poly(NIPAAm-co-AAc)), with a molecular weight of about 10(6)-10(5) Da in water using azobisisobutyronitrile (AIBN) as the initiator. The effects of the following on the lower critical solution temperature (LCST) of the copolymer and homopolymer of NIPAAm were investigated: the type of buffer salts and pH changes of test solutions, molecular weight and concentration of homopolymer/copolymer solutions, and AAc monomer molar feed ratio (mol%). The effects of different synthesis methods on the molecular weight and on the AAc content were also evaluated. The mechanism of action in environments with different pH values is discussed. Copyright (c) 2007 John Wiley & Sons, Ltd.