Light-scattering studies of poly( N-isopropylacrylamide) in tetrahydrofuran and aqueous solution

Abstract

Poly( N-isopropylacrylamide) (PNIPAM) was synthesized by free-radical polymerization. High resolution n.m.r. was used to confirm its chain composition and linear chain configuration. The solution properties of both unfractionated and fractionated PNIPAM samples in THF and water at 20°C were investigated by laser light scattering (LLS). Owing to its polyelectrolyte nature, it is extremely difficult, or nearly impossible, to obtain a set of narrowly distributed PNIPAM fractions with M w/ M n < 1.3. Therefore, a scaling relationship between the translational diffusion coefficient ( D) and the molar mass ( M) has not yet been established. In this study, a combination of M w from static LLS and the translational diffusion coefficient distribution ( G( D)) from dynamic LLS results enabled us to establish D (cm 2 s −1)= 2.49 × 10 −4 M −0.540 for PNIPAM in THF at 20°C. Using this scaling relationship, we successfully calculated the molar mass distributions of a series of PNIPAM samples. For a given PNIPAM sample, the molar mass distributions obtained in different solvents are fairly comparable.