Solid-state condensation polymerization of PBT/PET blends are studied. The experimen tal results of reaction kinetics show that reaction rate of PBT/PET blends are quicker than that of the PBT or PET
and molecular weight (characterized by [η]) of reaction product of PBT/PET blends increase in ultra-addition. The ultra-additive effect has been discoursed by theory of solid-state condensation polymerization and ester interchange
and it is show that ultra-additive effect is related to the increase of reaction rate and the formtion of block polymer.