Heat stability and degradation of thermally stable prepolymers in a controlled atmosphere. III. Thermal homopolymerization cycle of dicyanate monomers and physicochemical characterization of the crosslinked system

Monitoring the homopolymerization of cyanate monomers during heat treatment shows that triazine rings formed during the 180°C step. Oligomers were composed of 1 to 15 triazine rings. Analysis of compounds formed before the gel point revealed the presence of side products containing terminal phenolic functions: the phenol-cyanate (M 0 -OH) and oligomers with one or two hydroxyl functions (M 1,2 , -OH). Kinetic and mechanistic monitoring during treatment at 210°C in the solid state allowed the determination of the structure of the final system and the detection and quantification of unreacted cyanate functions. Kinetic and thermal studies in the temperature range of 100 to 220°C showed that the homopolymerization of hexafluorobisphenol A dicyanate starts at a lower temperature and is slower than that of bisphenol A dicyanate. Thermogravimetric data showed that residual monomers volatilized between 150 and 300°C, while the degradation of crosslinked products occurred between 400 and 600°C and involved two distinct steps.