EFFECTS OF COPOLYMERIZATION AND TEMPERATU RE ON DOUBLE YIELD POINTS IN POLY(BUTYLENE TEREPHTHALATE)

Poly(butylene terephthalate) (PBT) shows double yield points under ten sile deformation. Copolymerization of poly(tetramethylene glycol) (PTM G) as soft segments in amorphous regions reduces the first yield point in PBT. Higher temperatures soften the amorphous region and reduce th e first yield point in PBT. At lower temperatures the first yield poin t in PBT and a PTMG/PBT copolymer becomes more apparent. These results suggest that amorphous regions in injection molded specimens are resp onsible for the first yield point.