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 synthesiz ed and characterized by vapour pressure osmometry and viscosity measur ements in CHCl3. The Stockmayer-Fixman procedure was applied to viscom etric data in order to obtain information on the composition dependenc e of the unperturbed dimensions. The extrapolated K(THETA) values were found to decrease with increasing content of isophthalate units. Ther mal 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 f usion were observed for the copolymer with 60/40 PBI/PBT molar composi tion. Amorphous samples in the 40-100% PBI concentration range were ob tained by quenching from the melt, characterized by a monotonic decrea se 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 calculatio n of the T(g) of wholly amorphous PBT.