Side- and end-chain benzoxazine functional polymers

This chapter describes synthetic pathways for the synthesis of side- and end-chain benzoxazine functional polymers by using controlled and conventional polymerization methods involving free radical and rhodium catalysts. It presents numerous synthetic methods to combine benzoxazines with polymers and contribute to increase the performance and property characteristics of these resins. These approaches may serve a valuable guideline for preparing polybenzoxazines with desired properties to fulfill industrial demands. The synthesis of the polybenzoxazine by cross-linking bifunctional benzoxazine monomer through a ring-opening reaction is reported and the benefits of this family of compounds are identified. Polybenzoxazines can offer various superior properties compared to the conventional novolac or resole or epoxy type resins. Though benzoxazine based materials possess several advantages, they are not very attractive to the chemical industry because of problems of processability, brittleness, and high curing temperatures. Recently a new type of addition-cure phenolic system, polybenzoxazine is developed. These materials offer low water absorption, high char yield, resistance against flame, high modulus, high strength, high glass transition temperatures, chemical resistance, and long shelf life; they have very limited volumetric change upon curing; and strong acid catalysts are not required for curing. Though polybenzoxazines have such superior properties, pure benzoxazine based thermosettings suffer from high curing temperatures (200 °C or higher), difficulty in processing, and brittleness. Another encouraging approach is the synthesis of novel polymeric benzoxazine precursors, designed to impart flexibility and processability. Incorporation of benzoxazine groups into a polymer backbone as a side chain is an important way to obtain a dense network. Various synthetic methods can be used to obtain such kinds of precursors. © 2011