Thermal degradation kinetics of 6FDA/durene diamine/pPDA copolyimides

Abstract

Aromatic copolyimides have been synthesised from 2,2-bis (3,4-dicarboxyphenyl)-hexafluoropropane dianhydride (6FDA) with various mol-% of 2,3,5,6-tetramethyl-1,4-phenylene diamine (durene diamine (DDA)) and 1,4-phenylene diamine (pPDA) in N-methyl-2-pyrrolidone (NMP). Copolyimides were characterised by inherent viscosity, GPC, DSC, DMA, XRD, and TGA. Inherent viscosity and molecular weight increased with increase in DDA content in copolyimides. This was attributed to higher basicity of DDA than pPDA, which resulted in higher reactivity towards dianhydride. They were found to be soluble in all common solvents except CCl4 and methanol. The glass transition temperature Tg of these amorphous copolymers increased with increase in DDA content; Tgs determined by DSC and DMA were comparable and Tg calculated using the Fox equation was compared with the experimental value. Thermal degradation of these copolyimides was found to follow second order kinetics in air. The activation energy Ea for the thermal degradation of these copolyimides in air was determined by both the Coats-Redfern and Chang methods and the result was comparable. Both Ea and In A were found to decrease with increase in DDA content; CO2 and trace amounts of CHF3 were the decomposition products. The mechanism of thermal degradation is unique and is not affected by a change in the copolymer composition because all copolyimides display the kinetic compensation effect. © 2002 IoM Communications Ltd.