Enthalpy relaxation in poly(ethylene terephthalate) and related polyesters

Enthalpic relaxation data are presented on poly(ethylene terephthalate), po ly(ethylene naphthalate) and their copolymers. Analysis of these data allow s the determination of the amount of energy absorbed at the glass transitio n, Q(t), and the location of the enthalpic recovery peak, T-max, as a funct ion of the time of ageing of the samples. Ageing measurements were carried out for periods of up to 2016h and at temperatures between 40 degreesC and 110 degreesC, depending upon the chemical composition of the system being i nvestigated. The enthalpic relaxation rates are influenced by the chemical structure and reflect the effects of local order pinning the chains and inf luencing the rate of enthalpic recovery. (C) 2000 Society of Chemical Indus try.