Dynamic light scattering studies of poly(4-chlorostyrene) and poly(2-chlorostyrene) in theta solvents

Abstract

Most studies of coil-to-globule transitions of macromolecules have dealt exclusively with the standard polystyrene–cyclohexane system. In this work we aim to extend such investigations to halogenated polystyrenes, namely poly(4-chlorostyrene)(PPCS), poly(2-chlorostyrene)(POCS) and poly(chlorostyrene)(PCS),a mixture of 2- and 4- isomers. Changes in R h of these polymers with temperature in their respective theta solvents were investigated by dynamic light scattering. The hydrodynamic size of PPCS in n-propyl benzene( M w: 2.25×10 6 g mol −1, M w/ M n: 1.16) decreases to 75% of that in the unperturbed state at 22.2°C. POCS ( M w: 10.32×10 6 and M w: 4.30×10 6, M w/ M n: 1.10) in 2-butanone exhibited LCST behaviour and a limited chain collapse was observed with increasing temperature above theta point. The parameters α h= R h/ R h( θ) for POCS with two different molecular weights, (10.32 M and 4.30 M) were found to be 0.67 and 0.77, respectively at 37.0°C. A smooth and continuous contraction was also observed for the mixture of 2- and 4- isomers, PCS ( M w: 2.32×10 6 g mol −1, M w/ M n: 1.06).