Rubber toughening of poly(ether imide) by modification with poly(butylene terephthalate)

Rubber toughening of poly(ether imide) (PEI) has been elusive up to now due to the high processing temperature of PEI, which leads to degradation of the rubber. In this study, by profiting from the miscibility between PEI and poly(butylene terephthalate) (PBT), and the low T_g of PBT, we prepared a blend by melt extrusion with 20 wt% PBT in an attempt to render it toughenable by decreasing its T_g and processing temperature. The PEI-rich blend was subsequently mixed with maleic anhydride (0.9 wt%) grafted poly(ethylene-octene) copolymer (mPEO) up to 30 wt%. The decrease in T_g and processing temperature resulted in no observable degradation of the mPEO, and to the formation of a homogeneous morphology of rubber particles with a fine particle size, indicating that compatibilization was achieved. Upon rubber addition, stiffness decreased, while a very large toughness increase occurred with only 15% mPEO (impact strength more than 10-fold that of the PEI-PBT matrix). Upon observation of the fracture surface, the increase in impact strength was attributed partially to the cavitation and debonding of the rubber particles, and mostly to the deformation and yielding of the PEI-PBT matrix.