THERMODYNAMICS OF ISOTOPIC MIXTURES OF SYNDIOTACTIC POLY(METHYL METHACRYLATE) FROM SMALL-ANGLE NEUTRON-SCATTERING

Mixtures of high-molecular-weight hydrogenous, syndiotactic poly(methy l methacrylate) with two lower-molecular-weight deutero poly(methyl me thacrylate)s have been investigated over a range of temperatures and c ompositions using small-angle neutron scattering. Effective interactio n parameters have been obtained which have been used to estimate the F lory-Huggins interaction parameter. Spinodal temperatures have been de fined from the temperature dependence of these effective interaction p arameters and other parameters of the mixtures. The conclusion is that these isotopic mixtures are incompatible at ambient temperatures and have an upper critical solution temperature. The influence of local st ereochemistry on the polymer configuration is evident in the scatterin g cross-section variation with scattering vector. This variation is co mpared with the scattering obtained from Monte Carlo rotational isomer ic state calculations.