Effect of Local Conformational Transition on Craze Initiation in Polyestercarbonates Containing Cyclohexylene Linkages

Measurements of craze stresses and impact strengths have been performed on specially designed polyestercarbonates with 1,4-cyclohexylene linkages synthesized in our laboratory. The copolymers became more craze resistant as the cyclohexylene content was increased. On the other hand, the activation volumes of these copolymers, as calculated from the Eyring model for plastic yielding, greatly increased with increasing cyclohexylene ring content. We hypothesize that the conformational transition of cyclohexylene rings can enhance polymer chain mobility and therefore distribute strain over a larger volume. A mechanism is proposed for craze initiation:  high chain mobility due to conformational transitions helps to collapse nanovoids that are precursors to stable craze nuclei and increases the stress necessary for the formation of stable nuclei in craze initiation.