Chapter 34 - HCl-Catalyzed Polymerization of Benzoxazine and Chemical Transformations Along Pyrolysis to Microporous Carbons

Abstract

This chapter describes a room-temperature HCl-catalyzed synthesis of polybenzoxazine aerogels from bisphenol A, formaldehyde, and aniline that cuts the typical multiday, high-temperature (≥130°C) route to a few hours. In addition to the ortho-position of the phenol, the HCl-process engages the para-position of the aniline moieties leading to a higher degree of cross-linking, which, in turn, leads to smaller particles, higher mesoporosity, higher surface areas, and lower thermal conductivity than the thermal route. The carbonization efficiency (up to 61% w/w), as well as the nanomorphology and the pore structure of pyrolytically derived C-aerogels depend critically on a curing step of as-prepared polybenzoxazine aerogels at 200°C in air, which oxidizes the –CH2– bridges along the polymeric backbone and subsequently fuses the rings of phenol and aniline. C-aerogels from cured polybenzoxazine aerogels are microscopically similar to their respective parent aerogels, however, they have greatly enhanced surface areas, up to 520m2g−1 (from ≤70m2g−1 in the parent aerogel) with up to 83% of that new surface area attributed to newly created micropores. The applications reviewed are specific to those findings and include the synthesis of iron oxide/polybenzoxazine interpenetrating networks as precursors of iron(0) aerogels, and the use of microporous carbons for CO2 sequestration.