Kinetics of thermal degradation of 6FDA based copolyimides - I

Two series of linear aromatic copolyimides containing hexafluoro isopropylidine moieties (i.e. 6F) were synthesized by reacting 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) with various mole percents of 2,3,5,6-tetramethyl-1,4-phenylene diamine (Durene diamine) and 2,6-diamino toluene (DAT) or m-phenylene diamine (mPDA) in N-methyl-2-pyrrolidone (NMP). These copolyimides were characterised by GPC, XRD, DSC, TMA, DMA and TGA. Copolymer composition of these copolyimides was determined using ¹H-NMR. T_g calculated using Fox equation was compared with experimentally found values. All copolyimides were found to be amorphous. Activation energy was determined for the thermal degradation of these copolyimides using Coats-Redfern and Chang equations and were found to follow first order kinetics in air and in nitrogen. Inherent viscosity and T_g, decreased with decrease in mole ratio of durene diamine whereas activation energy and frequency factor [ln (A)] were found to increase with decrease in mole ratio of durene diamine in [6FDA + Durene diamine + mPDA] and [6FDA + Durene diamine + DAT] copolyimide series. CO₂ was the main decomposition product in air and CHF₃ in nitrogen atmosphere. Amount of CHF₃ evolved increased with increase in durene content in copolyimide series.