Mechanistic and kinetic aspects of the curing of phthalonitrile monomers in the presence of propargyl groups

The influence of propargyl groups on the thermal polymerization of phthalonitrile groups has been examined through reaction of a blend of a bisphthalonitrile viz. 2,2-bis(4-phthalonitrile oxy phenyl)propane and a bispropargyl ether viz. 2,2-bis(4-proparyloxy phenyl)propane (BPhPR). The possibilities for co-reaction of the propargyl and phthalonitrile moieties and/or the catalytic nature of the cure reaction prevailing in their blends were indicated by multiple exotherms in differential scanning calorimetry and dynamic rheological experiments. These have been attributed to homopolymerization of propargyl, hydroxyl and chromene mediated nitrile polymerization. FT-IR and fluorescence emission spectroscopic investigations on model compounds confirmed that nitrile polymerization was favoured by the chromene and hydroxyl groups formed by Claisen rearrangement. Activation energy of the reaction step involving chromene mediated phthalonitrile crosslinking was found to be 89 kJ/mol which was close to the value of phenol catalysed phthalonitrile curing.