Synthesis of new biobased benzoxazine through green strategy and its polybenzoxazine resin with high thermal resistance and mechanical strength

Abstract

Benzoxazine resins from benzoxazine monomers synthesized with green strategies often do not have high thermal resistance and mechanical strength. Herein, starting from renewable resources citraconic anhydride, furfurylamine and tyramine, a new benzoxazine monomer (CT‐fa) was synthesized and purified in green solvents (ethanol and ethyl acetate), which has excellent molding processability reflected by low melting point (84.9 °C) and low curing temperature (207–245 °C). More attractively, the cured CT‐fa resin (poly(CT‐fa)) has both high glass transition temperature (281 °C) and high initial thermal decomposition temperature (407 °C), the former is higher than those of all monofunctional benzoxazine resins synthesized though green strategies in literature, and the latter is even higher than those of all benzoxazine resins synthesized by green strategies (SCI database). In addition, poly(CT‐fa) also has high storage modulus (3955 MPa) and good tensile strength (51.60 MPa). These attractive properties demonstrate that poly(CT‐fa) is a promising green high performance resins.

Preparation of Thermally Resistant and Mechanically Strong Biomass Benzoxazine Resins via Green Strategy

“…The DSC curves of DPTA-f and DPTR-f are provided in Figure a; there is a melting peak in each plot, suggesting that DPTA-f or DPTR-f has a melting point ( T m ) of 61 or 49 °C, and both of them are far lower than those (84.9–152 °C) of GreenBenz monomers synthesized from furfurylamine as amine source in the SCI database. − ,− In actual applications, T m is an important indicator for assessing the processability of a resin; a lower T m usually suggests better processability. In addition, there is an exothermic peak in the DSC curve of DPTA-f or DPTR-f, suggesting the occurrence of curing, of which the peak temperature ( T p ) is 227 or 224 °C.…”

“…The T g data of all cured GreenBenz resins included in the SCI database are provided in Figure b. Obviously, P­(DPTA-f) has higher T g than all cured GreenBenz resins ( T g : 82–310 °C). − This superior advantage on T g is attributed to the special structures of P­(DPTA-f) and P­(DPTR-f), such as high cross-linking density, high rigid structure, and a large number of hydrogen bonds.…”

“…The high tensile properties of P­(DPTA-f) and P­(DPTR-f) resulted from the synergistic effects of high cross-linking density and the flexible chain segments. Among reported GreenBenz resins in the literature, only four of them were reported tensile properties (Table S2) ,, ; however, the three GreenBenz resins do not have good enough T g ( T g ≤ 281 °C).…”

“…Generally, the cured benzoxazine resin from a benzoxazine monomer with more oxazine rings (functional groups) tends to have high heat-resistance − ; however, reported tri- or multifunctional benzoxazine monomers (SCI database) were not synthesized through green strategy. To the best of our knowledge, about 30 GreenBenz resins were reported (SCI database), − but only one of them has a glass transition temperature ( T g ) higher than 300 °C; moreover, the static mechanical properties of only four GreenBenz resins were reported. ,, Therefore, it is a meaningful project to develop a new high-performance biobased benzoxazine resin by synthesizing a unique trifunctional GreenBenz.…”