Chapter 25 - Morphology and Properties of Polybenzoxazine Blends

Abstract

Polybenzoxazines are a class of attractive alternatives to some traditional thermosets such as epoxies, phenolic resins, and bismaleimides owing to their excellent thermal, mechanical, and electrical properties. The thermosets can be prepared via thermally activated ring-opening polymerization of benzoxazine monomers and no hardeners are required in the polymerization process. The unique chemistry of polymerization endows the materials with excellent processing properties through a very wide range of molecular design. Over the past few decades, considerable progress is made in the synthesis of a variety of precursors to improve the properties of this class of thermosets. It is recognized that besides the development of new polybenzoxazine materials through the chemical syntheses of a series f new benzoxazine monomers, benzoxazine resins can alternatively be modified via a blending approach. The polybenzoxazines can be modified by incorporating a variety of thermoplastics or elastomers into the thermosets. The control over the miscibility and morphology of polybenzoxazine blends is important for the optimization of the intercomponent interactions, thereby endowing the materials with improved properties. It is identified that the morphological structures of polybenzoxazine blends are quite dependent on the intermolecular specific interactions and the competitive kinetics between polymerization and phase separation. As a proton-donating polymer, polybenzoxazine can be miscible with some proton-accepting polymers such as poly(N-vinylpyrrolidone) because of the formation of the favorable intermolecular hydrogen bonding interactions. The formation of fine heterogeneous morphology in polybenzoxazine thermosets has a profound impact on the thermal, mechanical, optical, and processing properties of the materials. For elastomer-modified polybenzoxazine thermosets, the improvement of fracture toughness follows several known toughening mechanisms such as shear yielding, particle bridging, crack-pinning, and microcracking mechanisms.