Phase transfer catalysis in polycondensation processes XXIV. On the thermal stability of some aromatic polyethers containing a propylenic spacer

We have studied the correlation between thermal stability and molecular str ucture, for some copolyethers. Thermal stability was evaluated from thermog ravimetric analyses and molecular modeling. The oligomers were synthesized by a phase transfer catalysis technique, starting from 1,3-dibromopropane a nd various bisphenols, 4,4'-dihydroxyazobenzene, 4,4'-dihydroxydiphenyl, bi sphenol A and 4,4'-dihydroxybenzophenone. Use of bisphenols with different geometry or polarity permitted us to modify chain conformation and polarity and to correlate these factors with thermal stability. The study demonstra ted that the presence of azobenzene groups in the chain induces lower stabi lity: the weight loss starts around 260-300 degrees C. The most stable prod uct was that based on biphenyl and bezophenone. Chain polarity is less impo rtant than chain periodicity, the most stable products being those with an equimolecular ratio between the bisphenols. The presence of bent bisphenol in the chain decreases thermal stability, but this effect can be compensate d by an increase of chain polarity. Two heating rates were used, the compen sation effect calculated demonstrating that the degradation mechanism is si milar for both rates. (C) 2000 Elsevier Science Ltd. All rights reserved.