AbstractThe procedure of Southern and Porter has been used to prepare poly(ethylene terephthalate) segments by high‐pressure extrusion in an Instron capillary rheometer at temperatures from 245° to 265°C. X‐Ray measurements of crystalline orientation along the axis of long‐growth segments showed that segment properties were controlled by the time‐dependent crystallization of polymer melt in the rheometer reservoir. During the initial stage of extrusion, a highly oriented, translucent segment was generated by flow‐induced crystallization. However, formation of the translucent morphology eventually stopped, and thereafter a poorly oriented, opaque segment was generated by solid‐state extrusion. From wide‐ and small‐angle x‐ray scattering, differential scanning calorimetry, and density measurements, it was determined that the most perfect morphologies were prepared at an extrusion temperature of 265°C. In addition to having the highest degree of crystalline orientation, translucent segments extruded at 265°C have a peak melting point of 267°C and a crystallinity value of 62. Hot‐stage optical microscopy showed that the translucent segments contained axially aligned fibrous crystals whose birefringence persisted to 290°C. The exceptional thermal stability of the segments was corroborated by the results of shrinkage tests at temperatures near the melting point; even after 1 hr at 260°C, the shrinkage did not exceed 7. The accumulated evidence suggests that the translucent segments contain a
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