Crystallization of poly(ethylene terephthatalate-co-isophthalate)

Melt crystallization behaviors of poly(ethylene terephthalate) (PET) and po ly(ethylene terephthalate-co-isophthalate) (PETI) containing 2 and 12 mol % of noncrystallizable isophthalate components were investigated. Differenti al scanning calorimetry (DSC) isothermal results revealed that the introduc tion of 2 mol % isophthalate into PET caused a change of the crystal growth process from a two-dimensional to a three-dimensional spherulitic growth. The addition of more isophthalate up to 12 mol % into the PET structure ind uced a change in the crystal growth from a three-dimensional to a two-dimen sional crystal growth. DSC heating scans after completion of isothermal cry stallization at various T-c's showed three melting endotherms for PET and f our melting endotherms for PETI-2 and PETI-12. The presence of an additiona l melting endotherm is attributed to the melting of copolyester crystallite composed of ethylene glycol, tere-phthalate, and isophthalate (IPA) or the melting of molecular chains near IPA formed by melting the secondary cryst allite T-m(I) and then recrystallizing during heating. Analyses of both Avr ami and Lauritzen-Hoffman equations revealed that PETI containing 2 mol % o f isophthalate had the highest Avrami exponent n, growth rate constant G(o) , and product of lateral and end surface free energies sigma sigma(e). (C) 2000 John Wiley & Sons, Inc.