Some block copolymers illustrating the effects of siloxane and silane units on the properties of terephthalate-glycol thermoplastics

Modified poly(butylene terephthalate)-poly(tetramethylene glycol) multibloc k copolymers were prepared by including either siloxane or silane units wit hin the terephthalate hard blocks or the glycol soft blocks. These material s were characterized in terms of their dynamic-mechanical properties, glass transition temperatures T-g, and morphology las obtained from small-angle X-ray scattering measurements. One interesting result was the finding that putting siloxane units into the terephthalate hard blocks significantly dec reased the storage modulus, whereas placing them into the glycol soft block s somewhat increased it. Other interesting results were the observation tha t the T-g of the soft segments increased if the siloxane units were placed into the hard blocks but slightly decreased if they were placed into the so ft blocks, while the hard-segment T-g was not observed at all. Some of thes e results could be explained in terms of the phase separation suggested by the X-ray scattering results. (C) 1999 Elsevier Science Ltd. All rights res erved.