Investigation of the LCST of polyacrylamides as a function of molecular parameters and the solvent composition

The paper investigates the thermoprecipitation of two macromolecule structu res, poly(N-isopropylacrylamide) (poly-NIPA) and poly(N,N-diethylacrylamide ) (poly-DEA) from aqueous solution. The majority of the data are collected for small (M-w < 5000 g/mol) homogeneous (D ( 1.3) molecules of the indicat ed type synthesized by anionic, group transfer, and radical polymerization in the presence of a chain transfer agent. Conventional radical polymers (M -w < 200,000 g/mol) are also synthesized and used for comparison. Turbidity curves (photometry) and transition enthalpies thigh sensitivity differenti al scanning calorimetry) are measured to investigate the phase transition a s a function of the molecular size and the tacticity as well as the concent ration of certain solution additives (simple salts, glucose, and the surfac tant tetrabutylammonium acetate) and mixtures thereof. Where applicable, th e results are interpreted on the basis of a two-state model to gain insight in the cooperativity of the transition. (C) 1999 John Wiley & Sons, Inc.