Synthesis and characterization of poly(butylene terephthalate-co-triethylene terephthalate) copolyesters

Poly(butylene terephthalate-co-triethylene terephthalate) random copolymers of various compositions and molecular weights were synthesized in bulk and characterized in terms of their chemical structure and thermal and rheolog ical properties. At; room temperature all the copolymers were partially cry stalline and showed good thermal stability. The main effect of copolymeriza tion was a decrease in the melting and glass-transition temperatures with r espect to the poly(butylene terephthalate) homopolymer. The fusion temperat ures were well correlated with the composition by the Baur equation and the equilibrium melting temperature and the heat of fusion extrapolated values for poly(butylene terephthalate) were in good agreement with those reporte d elsewhere. Triethylene terephthalate units were found to influence the th eological behavior in the melt, the viscosity being significantly higher th an that of the poly(butylene terephthalate-co-diethylene terephthalate) cop olymers investigated previously. (C) 2001 John Wiley & Sons, Inc.