Thermal characteristics of addition-cure phenolic resins

The thermal and pyrolysis characteristics of four different types of additi on-cure phenolic resins were compared as a function of their structure. Whe reas the propargyl ether resins and phenyl azo functional phenolics underwe nt easy curing, the phenyl ethynyl-and maleimide-functional ones required h igher thermal activation to achieve cure. All addition-cure phenolics exhib ited improved thermal stability and char-yielding property in comparison to conventional phenolic resole resin. The maleimide-functional resins exhibi ted lowest thermal stability and those crosslinked via ethynyl phenyl azo g roups were the most thermally stable systems. Propargylated novolac and phe nyl ethynyl functional phenolics showed intermediate thermal stability. The maximum char yield was also given by ethynyl phenyl azo system. Non-isothe rmal kinetic analysis of the degradation reaction implied that all the poly mers undergo degradation in at least two steps, except in the case of ethyn yl phenyl azo resin, which showed an apparent single step degradation. The very low pre-exponential factor common to all polymers implied the signific ance of volatilisation process in the kinetics of degradation. Isothermal p yrolysis studies led to the conclusion that in the case of nitrogen-contain ing polymer, the pyrolysis occurs via loss of nitrogenous products, which i s conducive for enhancing the carbon-content of the resultant char. FTIR sp ectra of the pyrolysed samples confirmed the presence of C-O groups in the char. XRD analysis of the partially carbonised polymers did not give any in dication of crystallites except in the case of ethynyl phenyl azo system. ( C) 2001 Elsevier Science Ltd. All rights reserved.