J. Podešva

The effect of sequence distribution on glass transition in the theory of the cooperative Behaviour of random copolymers

SummaryThe description of the cooperative behaviour of polymers in the glass transition region according to ADAM and GIBBS (1965) has been extended to comprise the dependence of glass transition temperature, Tg, on the chemical composition of random copolymers if the distribution of dyads of comonomer units is included. The compositional dependence of Tg is expressed in terms of (i) differences between the isobaric heat capacities in the liquid and glassy states, and of (ii) the equilibrium T2 temperatures of the parent homopolymers and of the alternating copolymer. Validity of this theory was verified by comparison with data on styrene/methyl methacrylate and styrene/n-octyl methacrylate copolymers; the results indicate that the relations derived agree quantitatively with the experiment similarly to the equations suggested earlier by JOHNSTON (1976) and BARTON (1970). Moreover, these relations are based on a physically better justified approach to the glass transition phenomenon.