STUDY OF THE DISSOLUTION PROCESS OF POLYSTYRENE IN CONCENTRATED CYCLOHEXANE SOLUTION BY MNR RELAXATION

C-13-NMR relaxation times of polystyrene (PS) chains in its theta solv ent, cyclohexane, have been measured at different temperatures. It was found that relaxation of carbon nuclei of the side-chain-phenyl group s and those of main chains have remarkably different temperature-depen dent relaxation behaviors in the solvent. A two-step model for the dis solution process is proposed. According to the model, swelling of the polymer below theta temperature corresponds mainly to the gradual disp ersion of the side-chain phenyl groups; while the complete dissolution above theta temperature corresponds mainly to the gradual dispersion of the main chains at a molecular level. These dispersions reflect the fact that cohesional interaction among sidechain-phenyl rings or main chains are weakened by solvent molecules, which shows the existence o f the cohesional entanglements among polymer chains. The results of T- 1(C) are confirmed by the biexponential dependence of H-1-NMR spin-spi n relaxation on temperature.