| 摘要 |
A copolyetherester comprising a random head-to-tail copolymer of 25-55 percent by weight of short-chain ester units; at least 75 mole percent is composed of 1,4-butylene terephthalate units, and long-chain ester units derived from ethylene oxide-capped poly(propylene oxide) glycol having an ethylene oxide content of from 15-35 percent by weight and a number average molecular weight ranging from 1500-2800. The copolyetherester displays improved physical properties, such as a higher elongation at rupture, notched tensile impact energy and tearing energy, if its relative viscosity (1 g of polymer in 100 g m-cresol at 25 DEG C.) is in the range of 2,45 to 5,0 and the melt index MFI is between <IMAGE> and <IMAGE> It may be prepared by melt condensation of a copolyetherester having a relative viscosity of 1,8 to 2,5 and subsequently subjecting it to post-condensation in the solid phase for a sufficient period to obtain a polymer corresponding to said viscosity and melt index. |
