The Design, Preparation, Structure And Properties Of New Bio-based Benzoxazine Molecules

In recent years,research hotspots in countries around the world have been shifting toward bio-based materials,which are a kind of sustainable materials prepared by reacting renewable raw materials.Benzoxazine is a thermosetting compound containing a benzene ring and an O,N six-membered heterocyclic ring in its molecular structure.It has a very excellent thermal stability,mechanical properties,low dielectric properties,zero curing shrinkage and flexible molecular design,etc.,it is very suitable for the electronics,aerospace,and other high-tech communication field.The development of bio-based benzoxazines is at an early stage.There are many raw materials that can be used for bio-based benzoxazines,such as cardanol,eugenol,vanillin,guanamine,guaiacol,etc.It is a new type of benzoxazine which is very developmental.In this paper,three kinds of vinyl-containing benzoxazine monomers were designed and synthesized by using vanillin,p-hydroxybenzaldehyde,salicylaldehyde,2-Furfurylamine and other raw materials.And these three monomers were characterized to study the mechanism of cure,UV and thermal effect performance test.The thermal curing mechanism of the three monomers were studied by in situ FTIR.Among them,the curing of the vanillin bio-based benzoxazine(FVBZ)is mainly through the oxazine ring opening and cross-linking with the furan ring.The curing of the p-hydroxybenzaldehyde bio-based benzoxazine(FHBZ)and the salicylaldehyde bio-based benzoxazine(FSBZ)mainly through the oxazine ring ring and benzene ring ortho and para crosslinking.At the same time,the UV light effects of three benzoxazine monomers are also different.The UV light effect of FVBZ is the most obvious,followed by FHBZ,and FSBZ has no obvious response.The nuclear magnetic resonance(1H NMR)characterization showed that the vinyl group in FVBZ reacted under UV light.Differential scanning calorimetry(DSC)tests showed that the melting points of FVBZ,FHBZ and FSBZ are all higher than those of bisphenol-A benzoxazine(FBBZ).This is because the contained vinyl structure has a conjugate effect with the benzene ring,which reduced their conformational capacity and improved the melting point.In thermal curing process,the vinyl and oxazine ring cross-linked almost simultaneously.The functional groups interacted with each other,and reduced the curing peak temperature.Thermogravimetric analysis(TGA)tests showed that FVBZ has the best thermal stability.Although the FVBZ 5%weight loss temperature is 327.2 ?.Compared with FHBZ and FSBZ,FVBZ has a lower decomposition rate,and the char yeild at 800 ? is 60.7%.After Py-GC/MS testing,the thermal cracking of FVBZ was first cracked to produce amine compounds and phenol compounds that are still in a cross-linked state,and the phenol compounds were again cleaved to produce small molecule phenol compounds.The thermal stability of the heat-cured FVBZ resin after UV irradiation has decreased,due to the reaction of the vinyl group under UV conditions to generate an unstable cyclobutane structure.The thermal stability of the cross-linking reaction between the vinyl molecules under heat curing is better.