Synthesis And Performance Study Of Bisphenol AP-based Polybenzoxazines

Polybenzoxazines, as a novel class of thermosetting phenolic resins, have been shown many advantiages such as no need for harsh catalysts to initiate polymerization, no release of volatiles during cure, near zero shrinkage, high glass transition temperature (Tg),thermal stability and mechanical properties.Six benzoxazine monomers were synthesized using 4,4'-(1-phenylethylidene) bisphenol (bisphenol AP), formaldehyde and primary amines (aniline, o-toluidine,3,5-xylidine, n-butyamine, n-octy amine and allylamine) as starting materials by solution method in this paper. The chemical structures of benzoxazine monomers were identified by Fourier transform infrared (FT-IR), proton and carbon nuclear magnetic resonances ('H NMR and 13C NMR). The polymerization behavior and thermal stability of benzoxazines and the blends system were characterized by differential scanning calorimetry (DSC), FT-IR. dynamic themomechanical analyzer (DMA) and thermogravimetric analysis (TGA). The results show that the molar ratio of bisphenol AP, formaldehyde and primary amine is 1:4:2,1,4-dixane and ethanol as solvent, which the quality ratio is 1:1, formaldehyde and primary amine were mixed for 2h at low temperature, then reacted with bisphenol AP for 6h at higher temperature (85℃). The yield of benzoxazine monomers were around 65%-75%.The polymerization of bisphenol AP based-benzoxazines followed the thermal ring-opening polymerization of 1,3-benzoxazines. The polymer chains were connected by phenolic Mannich bridge, arylamine Mannich bridge, methylene linkages, intermolecular and intramolecular hydrogen bonding. The cross-linking opportunity was increased and the cross-link density was improved corresponds to the side reaction on the para position of 3,5-xylidine. The curing temperature was decreased for other polymersable group in the structure of allylamine, and cross-linking density was improved. The curing kinetics of bisphenol AP-based benzoxazine monomers were measured by isothermal and non-isothermal methods (Kissinger and Ozawa methods), the obtained activation energy were around 99-156kJ/mol. Meanwhile, the activation energy obtained in the B-AP-a and B-AP-o monomers was similar to that of non-isothermal method.The thermal property of polybenzoxazines shows that the glass transition temperature (Tg) and thermal stability are highly improved by the introduction of special structure of bisphenol AP in to the benzoxazine monomers. The thermal stability of aromatic-based benzoxazines is superior to aliphatic-based benzoxazines. The other polymeric group in the allyl-based benzoxazine improves the cross-linking, To and thermal stability of polybenzoxazine.The toughness properties of benzoxazine resins were modified with the epoxy resin and 2-ethyl-4-methyl-imidazole (EMI). Epoxy resin and EMI can cataylse the ring-opening of oxazine ring, make the curing temperature decreased, at the same time, epoxy resin and benzoxazine can copolymerize, which is good for the improvement of cross-linking density and thermal degradation temperature of blending resins. The char yield is closey correlated with the amount of benzoxazine. The polymerization reaction of benzoxazine-epoxy resin-EMI system will undergo three stages. EMI has prfit to the formation of homogeneous copolymers and improvement of cross-linking density and compatibility of blending resins. The comprehensive performance of the ternary blending resins is better than those of neat benzoxazines and the duality blending resins, which may be a good candidate for electronic encapsulation materials, composite materials, etc.