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 synt hesized in our laboratory. The copolymers became more craze resistant as th e cyclohexylene content was increased. On the other hand, the activation vo lumes 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 e nhance 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 prec ursors to stable craze nuclei and increases the stress necessary for the fo rmation of stable nuclei in craze initiation.