Regioselectivity of the ring-opening polymerization of monofunctional alkyl-substituted aromatic amine-based benzoxazines

The reaction site of the ring-opening polymerization in monofunctional aromatic amine-based benzoxazines has been investigated through systematic manipulation of the monomer chemistry. Selective protection or activation of sites on the arylamine ring towards electrophilic aromatic substitution has allowed a series of materials to be developed, which contain varying amounts of phenolic Mannich base bridges, arylamine Mannich base bridges, and methylene bridges. Electron-donating alkyl substituent groups at one or both meta positions on the arylamine ring facilitate ring opening/degradation at lower temperatures. This opening of rings in a step other than the polymerization reaction greatly increases the numbers of methylene linkages. Confirmation of the reaction sites was obtained via 1H and 13C NMR spectroscopy of oligomeric species.