Bis propargyl ether resins: synthesis and structure-thermal property correlations

Bis propargyl ethers of bisphenol-A, (BPA), bisphenol ketone (BPK) and bisphenol sulfone (BPS) were synthesised and characterised. These monomers were thermally polymerised to the corresponding poly (bischromenes). The cure behaviour, as monitored by differential scanning calorimetry, depended on the structure of the monomer. The non isothermal kinetic analysis of the cure reaction using four integral methods revealed that the presence of electron-withdrawing group did not favour the cyclisation reaction leading to formation of chromene, which precedes the polymerisation and this is in conformation to the proposed mechanism of polymerisation. Thus, the cure temperature and activation energy for the reaction increased in the order BPA < BPK < BPS. The cure profile under isothermal and nonisothermal conditions could be simulated from the kinetic parameters. The substituent group bridging the two phenyl rings also influenced the thermal stability of the resultant polymers. Thus, sulfone and ketone-containing polymers were stabler than the isopropylidene-containing one. Kinetic analysis of thermal decomposition of the major step involving the chromene moieties revealed a two-stage degradation mechanism. The computed activation energies implied that the initiation of the degradation reaction was disfavoured by the electron-withdrawing nature of the bridge unit, probably destabilisation of the intermediate radical. (C) 1998 Elsevier Science Ltd. All rights reserved.