Thermal stability of some self-assembling hydrogen-bonded polymers and related model complexes

The thermal stability of polymers is of fundamental importance both in processing and in many applications, eg, injection moulding, hot melts. As part of an investigation to determine the suitability of supramolecular polymers for novel applications in materials science, the thermal behaviour of two model compounds representing the principal classes of supramolecular polymer has been studied in some detail. p-Methoxybenzoic acid was complexed with 1,2-di(4-pyridyl)ethylene in 2:1 ratio as a model compound representing liquid-crystal association chain supramolecular polymers. It is proposed that the model compound degrades as a single species obeying first-order kinetics; the activation energy (E_act) of the degradation process was calculated to be 127 kJ mol^-1. A model ureido-pyrimidinone dimer degraded in two steps, also following first order kinetics, with E_act = 71.5 kJ mol^-1. The dimer was unaffected by annealing, suggesting that related polymers may be used at elevated temperatures. Polymer analogues of both model compounds were synthesized and their thermal behaviour was found to parallel that of the models. In light of these results, the implications for processing both supramolecular polymers are also considered.