Relaxation processes in hyperbranched polyesters: Influence of terminal groups

Three hyperbranched polyesters with the same backbone structure but with different terminal groups: hydroxyl, benzoate or acetate groups, were studied by dielectric spectroscopy, differential scanning calorimetry and dynamic mechanical analysis. The benzoate-and acetate-terminated polymers exhibited only one subglass process (beta), originating from reorientation of the eater groups, distinct from the glass transition (alpha). The hydroxyl-terminated sample exhibited a low-temperature subglass process (gamma), due to motions of the hydroxyl groups, in addition to the beta and alpha processes. The relaxation strengths of the 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 and benzoate, indicating that the benzoate-terminated polymer is the most constrained. (C) 1997 Elsevier Science Ltd.