Polymer Communication Observation of a transient structure prior to strain-induced crystallization in poly(ethylene terephthalate) A. Mahendrasingam a, * , C. Martin a , W. Fuller a , D.J. Blundell b , R.J. Oldman b , D.H. MacKerron c , J.L. Harvie c , C. Riekel d a Department of Physics, Keele University, Staffordshire ST5 5BG, UK b ICI Technology, PO Box 90, Wilton, Middlesbrough, Cleveland TS90 8JE, UK c DuPont UK Ltd, PO Box 2002, Wilton, Middlesbrough, Cleveland TS90 8JF, UK d ESRF, BP 220, F-38043 Grenoble Cedex, France Received 4 February 1999; received in revised form 23 June 1999; accepted 5 July 1999 Abstract Using time-resolved X-ray diffraction at the European Synchrotron Radiation Facility we have observed a highly oriented weak transient diffraction peak which persists for about 0.2 s prior to strain-induced crystallization during the uniaxial drawing of poly(ethylene terephtha- late) (PET) under industrial processing conditions. This structure may be identified with the mesophase 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 temperatures greater than 90°C nor when the draw conditions resulted in a degree of polymer orientation below a critical level. The possibility that this transient structure is a precursor of strain-induced crystallization is suggested by our observation of a correlation between the decay of the diffraction associated with it and an increase in the intensity of diffraction peaks associated with the development of crystallistion.  1999 Elsevier Science Ltd. All rights reserved. Keywords: Mesophase; PET; Crystallization 1. Introduction The exploitation of PET as a polymer material for bottles typically involves mechanical deformation at elevated temperatures close to its glass transition temperature (T g ). Such processing can have major effects on the degree of polymer orientation and crystallinity and hence on the physical properties of the material. X-ray diffraction provides one of the most powerful techniques for character- izing polymer orientation and crystallinity and hence for exploring the relationship between the industrial processing conditions and the properties of the finished artefact. The increasing availability of synchrotron radiation sources during the last decade, with a brilliance in the X-ray region many orders of magnitude greater than conventional labora- tory rotating anode sources, has dramatically extended the power of diffraction techniques for investigating polymer conformation and organization and, in particular, for following the development and decay of transient structures on very short time-scales. The information obtainable from these techniques has been of fundamental importance for developing an understanding of strain-induced crystal- lization processes which occur when polymers such as PET are oriented close to their T g [1]. In this communication we report the observation of a highly oriented weak transient diffraction peak which occurs immediately prior to strain- induced crystallization in PET when sheets of the polymer are drawn close to T g . This peak may be identified with the mesophase proposed by Bonart [2–4], Asano and Seto [5], Nicholson et al. [6] and Carr et al. [7] following the drawing of PET and PEN. This oriented transient diffraction has recently been reported and briefly analysed as a mesophase by Welsh et al. [8] for a series of random copolymers of PET and PEN units, as well as for the two parent homopolymers. In their study the transient structure was stabilized by quenching during or immediately after drawing. 2. Experimental Wide angle X-ray diffraction data were recorded on beamline ID13 at the European Synchrotron Radiation Polymer 41 (2000) 1217–1221 JPOL 4167 0032-3861/00/$ - see front matter  1999 Elsevier Science Ltd. All rights reserved. PII: S0032-3861(99)00461-9 * Corresponding author. Tel.: +44-1782-583326; fax: +44-1782-711093. E-mail address: a.mahendrasingam@keele.ac.uk (A. Mahendrasingam)