Observation of a transient structure prior to strain-induced crystallization in poly(ethylene terephthalate)

Using time-resolved X-ray diffraction at the European Synchrotron Radiation Facility we have observed a highly oriented weak transient diffraction pea k which persists for about 0.2 s prior to strain-induced crystallization du ring the uniaxial drawing of poly(ethylene terephthalate) (PET) under indus trial processing conditions. This structure may be identified with the meso phase structure proposed by a number of workers to occur during drawing of PET, poly(ethylene naphthalate) (PEN) and random copolymers of PET and PEN. In our studies, the transient structure was not observed at draw temperatu res greater than 90 degrees C nor when the draw conditions resulted in a de gree of polymer orientation below a critical level. The possibility that th is transient structure is a precursor of strain-induced crystallization is suggested by our observation of a correlation between the decay of the diff raction associated with it and an increase in the intensity of diffraction peaks associated with the development of crystallistion. (C) 1999 Elsevier Science Ltd. All rights reserved.