Synthesis of Triazole-functionalized Phenolic Resin and its Inherent Flame Retardant Property

Abstract

A novel triazole-functionalized phenolic resin was developed, and its thermal and flame-retardant properties were investigated. The triazole group was incorporated as a pendant unit on the phenolic resin via copper- mediated click chemistry between propargylated phenolic resin and benzyl azide. The newly-developed triazole-functionalized phenolic resin showed higher thermal stability and char yield, together with a reduced total heat release (THR), than the non-functionalized bare phenolic resin, indicating enhanced flame retardancy for the triazole-functionalized phenolic resin. and superior mechanical and ablative properties. 1,2 Phenolic resins are generally prepared by reactions bet- ween formaldehyde and phenol in the presence of acid or base. When prepared by acid catalysis, they are normally called novolac-type resins. In these resins, the molar ratio of formaldehyde to phenol is less than 1, and substitution occurs mostly at the ortho position of the phenol. In contrast, base-catalyzed pathways produce more cross-linked struc- tures, and are called resole-type phenolic resins, with sub- stitutions at both ortho- and para-positions. Phenolic resins with improved thermal and pyrolysis characteristics are desirable for producing composites for thermo-structural applications. 3,4 Although conventional phenolic resins are already considered to be temperature- resistant polymers and are currently in use for the above- mentioned applications, some of the properties of phenolic resins need further improvement for meeting the ever- increasing performance requirements. With sufficient heat and oxygen, most organic polymers will burn. Fundamentally, four processes are involved in the polymer combustion cycle: heating, decomposition, ignition, and combustion. In order to increase its flame resistance, the polymer system should function to interrupt this cycle. 5 A