Preparation And Properties Of High-performance Bio-based Benzoxazine Resins

Benzoxazine overcomes many shortcomings of traditional phenolic resins,such as forming a microporous structure during the curing process.The volume shrinkage rate of benzoxazine during polymerization is close to zero.Benzoxazine resin also possesses low hygroscopicity,low dielectric,low expansion coefficient,high T_g,good mechanical strength and excellent flame retardant performance.In addition,in the actual experimental design,benzoxazines with specific functions can be prepared by changing the functional groups of phenols,amines and other compound components to meet the different needs of various fields?With the rising of green chemistry and the changing of people's ideology on environmental protection,the research prospects of traditional organic chemistry have been limited.Compared with the single functional groups and limited reserves of petroleum-based raw materials,bio-based materials exhibit complex and diverse functional systems and sustainable supply,which are not available for petroleum-based raw materials.In addition,the current reports on bio-based benzoxazines are very rare,and most bio-benzoxazine are designed as mono-oxazine ring ones,showing slightly insufficient performance in thermal stability,flame retardant and mechanical properties.The systematic studies on bio-based multi-functionalized benzoxazines and optimization of secondary molecular design have not been reported so far.In this paper,a series of bifunctional and trifunctional new benzoxazine monomers were synthesized based on guaiacol,resveratrol and other low-cost bio-based raw materials,and their comprehensive properties have been improved by functional group modification.As a result,high-performance bio-based benzoxazine resins have been achieved as our expectations.This paper will mainly discuss from the following three aspects:(1)A bifunctional bio-based benzoxazine containing trifuran group was synthesized for the first time by a solvent-free method.The detailed chemical structure of this newly obtained bis-benzoxazine monomer has been identified by NMR and FT-IR spectroscopies and elemental analysis.The polymerization behaviors of benzoxazines are investigated by DSC and in situ FT-IR,and the thermal and fire-related performances of resulting thermosets are investigated by TGA and micro-scale combustion calorimetry(MCC).Notably,the corresponding polybenzoxazine derived from the newly developed tri-furan functional bis-benzoxazine shows very excellent thermal stability with a T_g of 290?and a T_d10of 375?in nitrogen atmosphere.Moreover,a non-ignitable polybenzoxazine has also been achieved as shown by the very low heat release capacity(30.4 J g^-1K^-1)and total heat release value(5.8 KJg^-1).(2)A new type of all-bio-based trifunctional Benzoxazine Resin is reported.The raw materials resveratrol,furan amine,etc.are all from natural renewable resources.It is also the first known report on the synthesis of trifunctional benzoxazine using natural renewable resources.The structure of benzoxazine was characterized by ¹H NMR,¹³C NMR,2D nuclear magnetic resonance(HMQC and NOSEY),and FT-IR.The polymerization behaviors of benzoxazines are investigated by DSC and in situ FT-IR.In addition,the thermal and flame retardant properties of polybenzoxazine were evaluated.The newly prepared RES-fa benzoxazine monomer exhibits a lower melting temperature(126?)and a lower ring-opening polymerization temperature(229?),and has good processing properties.The T_g of polybenzoxazine obtained by direct thermal activation polymerization was 312?,and T_d5and T_d10 were 346?and403?,the residual carbon rate is as high as 65%,respectively.Additionally,it also showed self-extinguishing and non-flammability,with HRC of 54Jg^-1K^-1 and THR of9.3KJg^-1.(3)A series of trifunctional benzoxazine monomers based on resveratrol were synthesized-(RES-a,RES-ac,RES-ch).The structure of benzoxazine was characterized by ¹H NMR,¹³C NMR and Fourier transform infrared spectroscopy(FT-IR).Differential scanning calorimetry(DSC)and in-situ FT-IR,thermal weight loss analysis(TGA),and micro-burn calorimetry(MCC)were used to study the thermal curing process of benzoxazine monomers and the thermosets after curing.And the performance of ethynyl functionalized poly(RES-ac)is particularly outstanding,the newly prepared RES-ac benzoxazine monomer exhibits a lower ring-opening polymerization temperature(189?),and has good processing properties.The T_g of polybenzoxazine obtained by direct thermal activation polymerization was higher than 35?,and T_d5 and T_d10 were 417?(N₂)/414?(air)and465?(N₂)/471?(air),the residual carbon rate is as high as65%,respectively.Additionally,it also showed self-extinguishing and non-flammability,with HRC of 30.7Jg^-1K^-1 and THR of 6.0KJg^-1.