Synthesis Of Fluorinated Benzoxazines And Their Application In Coating Field

In recent years,due to the rapid development of electronic industry and aerospace technology,the demand for high-performance materials is increasing.As a new thermosetting resin,benzoxazine has the characteristics of flexible molecular design,near zero shrinkage of curing,no small molecule release during curing,excellent thermal stability and flame retardant performance,and has been applied in the fields of electronics,electronics,aerospace and machinery manufacturing.However,the traditional polybenzoxazine has been unable to meet the requirements of resin for the rapid development of industry.In order to solve this problem,it is feasible to use the good molecular design of benzoxazine to dope heteroatoms into the molecular structure of benzoxazine through synthesis,so as to provide more active sites to improve the properties of cured products.Chemical reaction with it as raw material or intermediate is a hot topic in chemical analysis and synthesis research nowadays.Pyridine functional group is a six membered heterocyclic structure containing one nitrogen heteroatom.Due to the existence of negative nitrogen atom in pyridine ring,the intramolecular and intermolecular hydrogen bonds of the resin increase;Moreover,the flame retardancy of the polymer will be significantly improved due to the increase of nitrogen content.At the same time,fluorine-containing heterocyclic structure has always been a hot spot in the research and development of resin field.It accounts for a large proportion in the structural system and has a wide range of applications.Fluoropyridine structure is an excellent active group,introducing fluorine atoms into pyridine ring structure,is expected to prepare a high carbon residue,hydrophobic benzoxazine.This is because fluorine atoms and hydrogen atoms have great similarity,and have greater electronegativity and higher C-F bond energy than hydrogen atoms.Therefore,fluorine-containing polymers have higher structural stability,higher flame retardancy and hydrophobicity.In this paper,a series of benzoxazine monomers with high heat resistance and flame retardancy were designed and synthesized.By introducing fluorine atom and pyridine group into the molecule,the structure and curing kinetics of different monomers were studied,and the properties of cured products and coatings were explored.Finally,the catalytic reaction mechanism of benzoxazine was further studied by introducing transition metal ions into the synthesized benzoxazine.The main research contents and conclusions are as follows:1.A series of Fluoroaniline benzoxazines were successfully synthesized from bisphenol A,m-fluoroaniline,o-fluoroaniline,p-fluoroaniline and paraformaldehyde.Based on the experimental and theoretical analysis,the effects of fluorine atom substitution position on the curing mechanism,thermal stability and surface properties of polybenzoxazine were discussed in detail.The structural and geometrical parameters were investigated by NMR(~1H,¹⁹F)and FTIR spectroscopy.The curing peak temperature of fluorine substituted benzoxazines was found to be in order of meta-fluoroaniline benzoxazine(m-Bf,235.9°C)13C NMR,¹⁹F NMR and FTIR.The curing behavior of the resin was studied by DSC and FTIR.The results show that the curing temperature of benzoxazine can be significantly reduced by introducing fluorine atom and pyridine group into benzoxazine.On the one hand,due to the electron absorption effect of fluorine atom,on the other hand,due to the electron effect of pyridine ring,the C-O bond energy of oxazine ring in oxazine ring is lower than that in bisphenol A aniline benzoxazine,and the C-O bond is easier to break during heating,which reduces its solidification temperature.According to thermogravimetric analysis(TG),the10%weight loss temperature of fluoropyridine polybenzoxazine was 370.8?,and the carbon residue was 69.4%at 800?,which were much higher than that of bisphenol A aniline polybenzoxazine.The flame retardancy of fluoropyridine polybenzoxazine was studied by MCC test and LOI calculation.The results showed that the flame retardancy of Benzoxazine Resin was significantly improved by the addition of fluorine atom and pyridine group.The flame retardant mechanism was analyzed by TG-IR and SEM.Due to the existence of pyridine heterocyclic structure in the material,the thermal stability of heterocyclic structure was better than that of polybenzoxazine,and pyridine heterocyclic structure was more conducive to the formation of final carbon residue than that of crosslinked structure.The static water contact Angle of fluoropyridine benzoxazine coating is about 123.5°,which is about 32°higher than that of bisphenol A aniline polybenzoxazine coating.Reduce the interaction of phenolic hydroxyl groups with water,thus reducing their water absorption.The mechanical properties of the coating were tested.The results showed that the hardness of fluorinated pyridine type benzoxazine coating was 6h and the adhesion was 5b,which was much higher than that of bisphenol a type benzoxazine(the hardness was 2H and the adhesion was 1b);At the same time,the electrochemical workstation is used to test its anti-corrosion performance.The results show that the anti-corrosion performance of fluorinated pyridine benzoxazine is much higher than that of bisphenol A benzoxazine.