The structure change of crystalline PET．which were crystallized from amorphous species isothermally at various temperatures

was investigated in the course of tempe-rature eIavation by means of DSC，WAXD，SAXS， density measurement and TEM The result shows that besides there are partial melting and reerysta]lization in the pro-cess，its morphology is modified at the salne time including the thickening and enlarge-ment of Iamella，crystals changing from nodular paetdng to typical lamella packing，enlargement and perfeetivn of the crystallite and increasing of regular folding on fold surface．Thus，the morphology formed at isothermal crystallization turns to be more stable which is the cause of the appearence of double melting peaks on DSC curves．