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 structure, for some copolyethers. Thermal stability was evaluated from thermogravimetric analyses and molecular modeling. The oligomers were synthesized by a phase transfer catalysis technique, starting from 1,3-dibromopropane and various bisphenols, 4,4'-dihydroxyazobenzene, 4,4'-dihydroxydiphenyl, bisphenol 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 demonstrated that the presence of azobenzene groups in the chain induces lower stability: the weight loss starts around 260-300 degrees C. The most stable product was that based on biphenyl and bezophenone. Chain polarity is less important 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 compensated by an increase of chain polarity. Two heating rates were used, the compensation effect calculated demonstrating that the degradation mechanism is similar for both rates. (C) 2000 Elsevier Science Ltd. All rights reserved.