Poly(ethylene terephthalate)–poly(caprolactone) block copolymer. I. Synthesis,reactive extrusion,and fiber morphology

A novel poly(ethylene terephthalate)–poly(caprolactone) block copolymer (PET–PCL) is synthesized in a reactive twin‐screw extrusion process. In the presence of stannous octoate, ring‐opening polymerization of ϵ‐caprolactone is initiated by the hydroxyl end groups of molten PET to form polycaprolactone blocks. A block copolymer with minimal transesterification is obtained in a twin‐screw extruder as a consequence of the fast distributive mixing of ϵ‐caprolactone into high melt viscosity PET and the short reaction time. The PET–PCL structure is characterized by IV, GPC, ¹H‐NMR, and DSC. Fully drawn and partially relaxed fibers spun from PET–PCL are characterized by WAXD and SAXS. A substantial decrease in the oriented amorphous fraction appears to be the major structural change in the relaxed fiber that provides the fiber with the desired stress–strain characteristics. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1858–1867, 1999