Decreasing the CTE of Thermoplastic Polyimide by Blending with a Thermosetting System

A series of thermoplastic polyimide resins with a low coefficient of thermal expansion(CTE)were prepared by blending a rigid resin system 3,3’,4,4’-biphenyltetracarboxylic dianhydride(BPDA)/p-phenylenediamine(PDA)with a flexible resin system 4,4’-[isopropylidenebis(pphenyleneoxy)]diphthalic anhydride(BPADA)/PDA.The effects of the blending ratio on the macromolecular coil size,free volume,and CTE of the mixed system were studied.The mixing is carried out in the prepolymer poly(amide acid)(PAA)stage,which makes the two systems more compatible and is conducive to the formation of a semi-interpenetrating network structure between the rigid molecular chains and flexible molecular chains.The flexible structure of the BPADA/PDA system is used to ensure the melt processing performance.The rigid characteristics of the BPDA/PDA system can inhibit the movement of molecular chains and reduce the free volume fraction,thereby reducing the CTE value.When the rigid system content reaches 30%,the CTE can be reduced to 38 ppm/K.This method provides a new approach for studying low CTE thermoplastic polyimide resins.