RELAXATION PROCESSES IN HYPERBRANCHED POLYESTERS - INFLUENCE OF TERMINAL GROUPS

Three hyperbranched polyesters with the same backbone structure but wi th different terminal groups: hydroxyl, benzoate or acetate groups, we re studied by dielectric spectroscopy, differential scanning calorimet ry and dynamic mechanical analysis. The benzoate-and acetate-terminate d polymers exhibited only one subglass process (beta), originating fro m reorientation of the eater groups, distinct from the glass transitio n (alpha). The hydroxyl-terminated sample exhibited a low-temperature subglass process (gamma), due to motions of the hydroxyl groups, in ad dition to the beta and alpha processes. The relaxation strengths of th e hyperbranched polymers were found to be considerably lower than for those of linear analogues. The activation energies of the beta process in the polymers studied increased in the order of hydroxyl, acetate a nd benzoate, indicating that the benzoate-terminated polymer is the mo st constrained. (C) 1997 Elsevier Science Ltd.