Recent Progress of High Performance Thermosets Based on Norbornene Functional Benzoxazine Resins

With the growing demand for high performance polymeric materials in industry, several types of thermosets such as bismaleimides, advanced epoxy resins, cyanate esters, and phenolic resins have been widely investigated to improve the performance of thermosetting products. Among them, benzoxazine resins have received wide attention due to their extraordinarily rich molecular design flexibility, which can customize our needs and adapt increasing requirements. To further improve the properties of polybenzoxiazines, researchers have found that the introduction of a norbornene functional group into the benzoxazine moiety can effectively improve the comprehensive performance of polybenzoxazine thermosets. This article focused on reviewing the recent development of high-performance thermosets based on norbornene functional benzoxazine thermosetting resins.

A high performance polybenzoxazine via smart ortho-norbornene functional benzoxazine monomer based on ring-opening metathesis polymerization

Monofunctional benzoxazine with ortho-norbornene functionality ( oHPNI-a) has been synthesized via Mannich condensation. The benzoxazine monomer containing norbornene group can be polymerized by ring-opening metathesis polymerization (ROMP) to form a side-chain benzoxazine functionalized polynorbornene (poly( oHPNI-a)side) with number-average molecular weight 3840 and weight-average molecular weight 7290. The structures of synthesized monomer and side-chain functionalized linear polymer have been confirmed by 1H nuclear magnetic resonance spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The further thermal curing polymerization mechanisms of poly( oHPNI-a)side are monitored by in situ FTIR and differential scanning calorimetry (DSC). Activation energy of polymerization for poly( oHPNI-a)side is also studied by DSC. The polybenzoxazine obtained by ROMP and further thermally activated ring-opening polymerization exhibits much higher thermal stability than the polybenzoxazine directly formed by traditional thermal curing.