DILUTE-SOLUTION AND THERMAL-BEHAVIOR OF RANDOM POLY(BUTYLENE ISOPHTHALATE TEREPHTHALATE) COPOLYMERS

Random poly(butylene isophthalate/terephthalate) (PBI/PBT) copolymers of various compositions and different molecular weights were synthesized and characterized by vapour pressure osmometry and viscosity measurements in CHCl3. The Stockmayer-Fixman procedure was applied to viscometric data in order to obtain information on the composition dependence of the unperturbed dimensions. The extrapolated K(THETA) values were found to decrease with increasing content of isophthalate units. Thermal characterization in the solid state was carried out by means of a differential scanning calorimeter on PBI/PBT copolymers as well as on PBI and PBT homopolymers. Minima for melting temperature and heat of fusion were observed for the copolymer with 60/40 PBI/PBT molar composition. Amorphous samples in the 40-100% PBI concentration range were obtained by quenching from the melt, characterized by a monotonic decrease of the glass transition temperature T(g) and by a constant value of the specific heat increment DELTAc(p). The Fox equation was found to describe quite well the T(g)-composition data and permitted calculation of the T(g) of wholly amorphous PBT.