THERMALLY STIMULATED SHRINKAGE FORCES IN ORIENTED POLYMERS .2. TIME-DEPENDENCE

The four-state model proposed in a previous paper to describe thermal shrinkage in oriented polymers is solved to describe the time dependences of shrinkage forces under constant temperature conditions. The time dependences of shrinkage forces have been recorded for polycarbonate and polyethylene terephthalate at temperatures below the glass transition. It is shown that experimentally recorded time dependences of shrinkage forces can be satisfactorily fitted by dependences predicted by the model, and the comparison leads to reasonable values of activation energy and activation volume for the shrinkage process.