The chemical effect of furfuryl amide on the enhanced performance of the diphenolic acid derived bio‐polybenzoxazine resin

Abstract

As a renewable chemical, diphenolic acid (DPA) has attracted immense interest in bio-based polymer science. However, its application for polybenzoxazines is limited due to decarboxylation, that is, the release of CO 2 during the curing reaction of benzoxazine. In this study, the amidation strategy of converting DPA to diphenolic amides (DPAM) was demonstrated to solve this problem while simultaneously improving the thermal properties of polybenzoxazine. DPA was amidated by separately using four amines (hexamine, cyclohexylamine, furfurylamine, and aniline), then reacted with furfurylamine and paraformaldehyde to synthesize their benzoxazine monomers. By using TGA and DMA, all amide-containing polybenzoxazines were found to exhibit excellent thermal stabilities. Among all of the benzoxazine resins, poly(DFA-fa), which was obtained from amidation with furfurylamine, exhibited the highest glass transition temperature (T g ) of 310 C and a decomposition temperature (T d10 ) of 406 C. Furthermore, a possible post-curing reaction mechanism was proposed to explain the outstanding thermal performance of poly(DFA-fa) resin. This study proposes an innovative strategy to solve the decarboxylation of DPA-based polymers, which is of significance for high-performance bio-based polymers.

Bio‐basedbenzoxazine from renewableL‐tyrosine: Synthesis, polymerization, and properties

“…It was observed that the storage modulus ( E ′) for PTCDPF gradually decreased from 1650 MPa at 30 °C to 940 MPa at 250 °C, indicating that the polymer retained good mechanical properties upon raising temperature. The T g value of PTCDPF was as high as 322 °C, which exceeded those of most known amide‐containing polybenzoxazines 37,38 . This result confirmed that the thermomechanical property of polymer could be improved significantly by introducing diketopiperazine units into the molecular backbone.…”

“…The estimated cross‐linking density value of PTCDPF was 23 mol dm −3 , which was higher than those of the reported polybenzoxazines 38,41,42 …”

“…The accurate value of the exothermic onset temperature ( T onset ) was unavailable because of the partial overlap of the endothermic and the exothermic peaks. The exothermic peak temperature ( T p ) of TCDPF was 220 °C, which was lower than those of the commercially available benzoxazines 35,36 and the amide‐containing benzoxazines 37,38 …”

“…It was reported that the cross‐linking density of polybnzoxazine could be increased by introducing additional hydrogen bond acceptors (C═O in this work) 40 . The cross‐linking density of the polybenzoxazine was estimated using the following equation 38 : where is the storage modulus at T g + 30 K, R is the gas constant, T is the absolute temperature at T g + 30 K, and θ c is the cross‐linking density.…”

“…During cure, a new signal was found at 3362 cm −1 which might corresponded to the free NH generated after the dissociation of hydrogen bonds or the phenolic hydroxyls produced during cure 28 . Besides, the trisubstituted benzene ring band at 1508 cm −1 and the furan ring band at 742 cm −1 were significantly weakened with elevating temperature, indicating that the benzene and furan rings participated in the polymerization 37,38 . The possible chemical structure of the thermoset is presented in Scheme 2.…”