RELAXATION PROCESSES IN HYPERBRANCHED POLYESTERS

Dielectric permittivity and loss have been measured over the frequency range 10(-2) Hz - 10 kHz between 100 K and 350 K for samples of 50/50 mixtures of each of two hyperbranched polyesters, one five-generation hydroxy functional (5G-OH) and one three-generation alkyl-terminated polymer (3G), with dielectrically inactive linear polyethylene. The th ermal transitions of the hyperbranched polymers were studied with diff erential scanning calorimetry. Three relaxation transitions were found in 5G-OH: alpha, the glass-rubber transition and two subglass process es denoted beta and gamma showing Arrhenius temperature dependence bot h with an activation energy of 96+/-2 kJ mol-1. The low temperature pr ocess could be assigned to motions of the terminal hydroxyl groups whe reas beta is due to reorientation of the ester groups. Sample 3G showe d only a glass transition and one subglass process being assigned to r eorientation of the ester groups. The high activation energy (202 kJ m ol-1) of this process indicates that the ester groups are highly const rained in this polymer.