Toughening of in situ polymerized cyclic butylene terephthalate by addition of tetrahydrofuran

A new method of toughening polymerized cyclic butylene terephthalate (pCBT) with tetrahydrofuran (THF) is proposed. The pCBT was prepared by in situ ring-opening polymerization of a commercial cyclic butylene terephthalate, a cyclic form of poly(butylene terephthalate), in the presence of THF. In comparison to conventionally polymerized pCBT, the resultant material was found to be ductile, showing a strain at break of well above 100% in tensile tests. Other matrix properties, such as tensile modulus, tensile strength and glass transition temperature, were not significantly altered by the addition of THF. It was found that the presence of THF enhanced the polymerization reaction, resulting in an increased molecular weight and a narrowed molecular weight distribution. Moreover, remaining oligomers after polymerization were extracted by the THF and a toughened oligomer-free pCBT was obtained. The influence of time and temperature on the long-time toughening action of THF was studied. The results showed that samples became brittle after 3 months when subjected to a temperature of 80 degrees C, resulting in a reduction of the toughening action. (C) 2010 Society of Chemical Industry