Melting behavior and crystallization kinetics of poly(butylene terephthalate-co-diethylene terephthalate) and poly(butylene terephthalate-co-triethylene terephthalate) copolyesters

The melting behavior of poly(butylene terephthalate-co-diethylene terephtha late) and poly(butylene terephthalate-co-triethylene terephthalate) copolym ers was investigated by differential scanning calorimetry after isothermal crystallization from the melt. Multiple endotherms were found for all the s amples, and attributed to the melting and recrystallization processes. By a pplying the Hoffman-Weeks' method, the equilibrium melting temperatures of the copolymers under investigation were obtained. Two distinct peaks in the crystallization exothermic curve were observed for all the samples. Both o f them appeared at higher times than that of PET, indicating that the intro duction of a comonomer decreased the crystallization rate. The observed dep endence of this latter on composition was explained on the basis of the con tent of ether-oxygen atoms in diethylene and triethylene terephthalate unit s, and of the different sizes of these units. (C) 2001 John Wiley & Sons, I nc.