Preparation and properties of poly(urethane-benzoxazine)s based on monofunctional benzoxazine monomer

Abstract

Poly(urethane-benzoxazine) films were prepared by blending a monofunctional benzoxazine monomer, 3-phenyl-3,4-dihydro-2H-1,3-benzoxazine (Pa), and polyurethane (PU) prepolymer that was synthesized from 2,4-tolylene diisocyanate and polyethylene adipate polyol (Mw ca. 1000) in 2:1 molar ratio, followed by casting as films and thermal curing of the films. The poly(urethane-benzoxazine) films obtained by the thermal cure at 190°C were yellow and transparent. All the films had only one glass transition temperature (Tg) from viscoelastic measurements, indicating good miscibility between PU and polybenzoxazine due to the in-situ copolymerization of Pa and PU prepolymer. The Tg shifted increasingly with the increase of Pa content. The films containing less than 50% of Pa had characteristics of elastomer, with elongation at break more than 200%. These elastic films exhibited good resilience with excellent reinstating behavior. The films containing more than 60% of Pa had char acteristics of plastics. The poly(urethane-benzoxazine) films showed excellent resistance to the solvents such as tetrahydrofuran, N,N-dimethyl formamide, N-methyl-2-pyrrolidinone and DMSO.