Hydrolysis and blistering of cyanate ester networks

The hydrolysis of a cyanate ester network made from the monomer 2,2′-bis(4-cyanatophenyl)isopropylidene (bisphenol A dicyanate homopolymer) was studied. Hydrolysis reactions were performed isothermally at temperatures from 150 to 180°C under conditions of excess water. The kinetics of the reaction were characterized by the decrease in T_g as measured by differential scanning calorimetry. The rate of change of T_g was found to be adequately described as first order in T_g, which is an indirect measure of the concentration of crosslink junctions. The activation energy of the reaction was found to be 115 kJ/mol. In addition, moisture-conditioned, glass-reinforced laminate samples were heated and the time to delamination or blistering was recorded as a function of temperature. The blister time at solder temperatures (T = 220-260°C) was modeled using the above kinetic results. Heat transfer to the laminate was considered and the criteria used for blister time was the time at T = T_g of the sample. At lower temperatures (T < 220°C), loss of water from the laminate is sufficiently fast to prevent blistering.