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 degreesC step. Oligomers w ere composed of 1 to 15 triazine rings. Analysis of compounds formed before the gel point revealed the presence of side products containing terminal p henolic functions: the phenol-cyanate (M-0-OH) and oligomers with one or tw o hydroxyl functions (M-1.2,...-OH). Kinetic and mechanistic monitoring dur ing treatment at 210 degreesC in the solid state allowed the determination of the structure of the final system and the detection and quantification o f unreacted cyanate functions. Kinetic and thermal studies in the temperatu re range of 100 to 220 degreesC showed that the homopolymerization of hexaf luorobisphenol 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 degreesC, while the degradation o f crosslinked products occurred between 400 and 600 degreesC and involved t wo distinct steps.