Thermal behavior and primary degradation mechanism of some aromatic polyethers with semi-flexible chain

The present paper describes a thermogravimetric study combined with mass spectrometry of some aromatic polyethers and copolyethers in order to obtain information on the degradation mechanism. The investigated polymers were synthesized starting from 3,3-bis(chloromethyl) oxetane and various bisphenols: 4,4'-dihydroxyazobenzene, 4,4'-dihydroxydiphenyl, bisphenol A and 4,4'-dihydroxydiphenylether. The presence of an oxetanic spacer in the structure, permitting the opening of the cycle, induces more complications in the characterization procedure. But, due to the possibilities relative to the modification of polymers or cross-linking reactions, the presence of the oxetanic moiety may offer some advantages. Out of all the investigated polymers, those containing azobenzenic moieties have the lower thermo stability. If the chain flexibility is augmented, the degradation mechanism is based on chain transfer reactions. All polymers present higher thermostability in an argon atmosphere. Based on mass spectra, a degradation mechanism sustained with the assumption that the oxetanic unit is the most labile was proposed. The opening of the oxetanic cycle begins with the most tensioned bond (-C-CH2-) and generates a cross-linking process, which is more evident if the polymer melts below 200degreesC.