POLY(METHYL METHACRYLATE) 1,2-DICHLOROETHANE SYSTEM - FREEZING OF CONFORMATIONAL MOBILITY IN THE LOW-MOLECULAR COMPONENT/

The conformational dynamics in 1,2-dichloroethane (DCE)/poly(methyl me thacrylate) (PMMA) mixtures has been studied at different concentratio ns of DCE. The intensities of the infrared absorption bands belonging to the trans and gauche conformers have been measured in the 77-300 K temperature range. Besides, the glass transition temperatures of the m ixtures T-g were determined by the differential scanning calorimetry. For all the systems under investigation the freezing of the conformati onal transitions has been found: below a certain temperature T-f the t rans/gauche ratio becomes temperature independent. The T-f value for t he lowest volume fraction of DCE (C = 0.01) was found to be close to t he temperature of one of the secondary relaxation transitions of pure PMMA (195 K). At this temperature the free volume entities in PMMA sho uld have the volume close to that of the conformationally mobile group s of DCE (similar to 25 Angstrom(3). The concentration dependence of T -f consists of two branches. At low concentrations of the diluent (C < 0.6) T-f slowly decreases with the concentration of DCE, reflecting t he concentration behaviour of the relaxation transition temperature. A t the higher concentrations the freezing of the conformational equilib rium in DCE occurs at the glass transition of the mixtures, and the T- f values are close to the T-g ones. Copyright (C) 1996 Elsevier Scienc e Ltd.