Synthesis and characterization of low temperature curable phthalonitrile containing propargyl- novolacs through click-chemistry approach

Low temperature curable propargyl novolac resin containing phthalonitrile moieties was realized through click chemistry approach. Towards this, propargylated novolac phthalonitrile and azide novolac functionalized resins were coupled through click reaction leading to triazole linked networks. The Cu₂I₂ catalyzed reaction was initiated at 80 °C and the click coupled products showed excellent thermal stability up to 400 °C. The kinetics of click reaction was monitored using FT-IR spectroscopy and click coupling has been assumed to be second order with activation energy of 50 kJ mol⁻¹. The possibility of formation of coupled products were theoretically evaluated using Density Functional Theory (DFT/B3LYP) method with 6-311G (d,p) basis set. Activation energy for the triazole ring formation was found to be 67 kJ mol⁻¹ which was closely matching with kinetic studies. The click cured samples found to form firm coating on glass substrates capable of withstanding elevated temperature without property deterioration unlike the generally used epoxies and silicones. The attempts through click-coupling may ease the sluggish curing restrictions of phthalonitriles that limits its potential applications.