Syntheses And Properties Of Bio-Based Benzoxazine Monomers And Polymers

Polybenzoxazine is a kind of thermosetting resin, compared with phenolic resins, with excellent properties such as near-zero shrinkage, low water uptake, high char yield and high glass transition temperature. Therefore, benzoxazine resins can be applied in the field of electronic device packaging and halogen-free flame retardant in the replacement of phenolic resins. With the gradual strictness of environmental protection policy, more and more people shift their attention to the high performance materials made by natural product.4-(2-hydroxyethyl)phenol, which can be used as raw material to synthesize benzoxazine monomer(abbreviated as B1), is a natural product extracted from Syringa oblata Lindl. The structure of B1 monomer was characterized by FT-IR, 1H NMR and 13 C NMR and the thermal curing property and thermal stability of cross-linked polymer were studied by TG-DSC. The hydroxyethyl group of B1 monomer not only can accelerates the ring-opening polymerization, but also can goes through condensation reaction and electrophilic substitution reaction, which can improve the crosslinking density of PB1 polymer. In addition, the curing reaction of B1 was investigated by non-isothermal differential scanning calorimetry(DSC). The apparent activation energy(Ea) of B1 was 79.58 KJ mol-1, 83.76 KJ mol-1 and 94.90 KJ mol-1 calculated by Kissinger, Ozawa and Flynn-Wall-Ozawa method.The three kinds of polyether polyol type benzoxazine monomers(B2) are synthetized from the B1 monomer and polyurethane prepolymers which can be obtained from the reaction of toluene diisocyanate(TDI) and polyether polyol such as polyethylene glycol-400, polyethylene glycol-2000 and glycerol polyether 3010. The structure of B2 monomers were characterized by FT-IR and 1H NMR and the thermal curing behavior was studied by FT-IR. The three kinds of polymers are in possession of good thermodynamic properties with the weight loss temperature of P(B2-01) at 10% is 319.1 oC, the char yield at 600 oC is 16.1% and the glass transition temperature is 123.0 oC.A novel benzoxazine monomer equipped with epoxy group(B3) is synthetized from the B1 monomer and epoxy soybean oil methyl ester(3b) which can be obtained from soybean oil after go through transesterification and epoxidation reaction. A bifunctional benzoxazine monomer(B4) is synthetized from the B1 monomer and TDI. The structure of B3 and B4 were characterized by FT-IR, 1H NMR and 13 C NMR and the thermal curing behavior was studied by FT-IR. The copolymers, which are prepared by the mixture composed of 3b, B3 and B4 monomer via ring-opening polymerization, are in possession of good thermodynamic properties with the weight loss temperature of P(B-b/B4 8:2) at 10% is 327.8 oC, the char yield at 850 oC is 23.4%, the glass transition temperature is 117.9 oC and storage modulus at 25 oC is 3.30 GPa. The influence of catalysts, namely 2-ethyl-4-methylimidazolen, p-toluenesulfonic acid and methyl p-toluenesulfonate, was studied by differential scanning calorimetry. With the addition of methyl p-toluenesulfonate, the copolymers are still in possession of good thermal stability with the the char yield of P(B-b/B4 10:0)-MeOTs, P(B-b/B4 8:2)-MeOTs and P(B-b/B4 6:4)-MeOTs at 850 oC is 19.4%, 21.6% and 21.1% respectively.