Thermal degradation kinetics and flame retardancy of phosphorus-containing dicyclopentadiene epoxy resins

The 2,6-dimethylphenol-dicyclopentadiene epoxy resin (MDE) was obtained by epoxidation of the intermediate 2,6-dimethylphenol-dicyclopentadiene novolac (MDN) which was synthesized from the reaction between dicyclopentadiene (DCPD) and 2,6-dimethylphenol. Subsequently, the 2,6-dimethylphenol-dicyclopentadiene advanced epoxy resin (MDAE) were prepared by reactions of 2-(6-oxido-6-H-dibenzo[c,e][1,2]oxaphosphorin-6-yl)-1,4-benzenediol (ODOPB) with MDE. The structure of MDN, MDE and ODOPB was confirmed by 1H NMR, Fourier transform infrared (FTIR), elemental analyses (EA), mass spectroscopy (MS) and epoxy equivalent weight titration. Curing and thermal degradation kinetics of MDAE cured with diaminodiphenyl sulfone (DDS) were studied by the dynamic differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA), respectively. The activation energies of dynamic curing and thermal degradation were calculated by using the Kissinger and Ozawa's methods, respectively. The dynamic model gives a good description of curing kinetics up to a much wider temperature range. The relations concerning the activation energy of curing and phosphorous content of epoxy resins were discussed. The char yields and thermal stabilities of cured ODOPB-modified epoxy networks uniquely increase with ODOPB contents. The degradation temperatures (Td, 5%) in nitrogen at a heating rate of 20 °C/min ranged from 344 to 401 °C, and the char yields at 800 °C are 11-24%. The activation energies of degradation ranged from 190 to 268 kJ/mol. High LOI value (found 33.8) could be achieved with a low phosphorus content around 1.0%, which implied that the flame retardancy was improved by the incorporation of ODOPB.