Preparation And Properties Of Bio-Benzoxazines Based On Furan-Containing Diamines

Polybenzoxazines are high performance thermosets which find numerous applications in electronics,matrix resins for fibrous composites,high temperature resistant adhesives,aerogels and membranes for separation etc.There are several advantages of these resins including high thermal stability,high glass transition temperature,good mechanical properties,attractive flame retardancy,minimum curing shrinkage,no curing byproducts,and no need of acid or base catalyst during curing process.Benzooxazine also has molecular design flexibility,and the structure and performance regulation of benzoxazine can be easily achieved by changing the type of phenol or amine.In order to improve the overall performance of benzoxazine resins,a lot of research has been done on diamine benzoxazines.At the same time,due to the increasing concern about environmental protection,the use of natural products to prepare high-performance materials has attracted wide attention.In this paper,two bio-based diamines 2,2-bis（5-amino-2-furyl）propane（FA-a）and4,4-bis（5-amino-2-furyl）pentanoic acid hydrochloride（FA-b）were synthesized by molecular design principles using the furanmethylamine,levulinic acid,etc,and characterized by infrared（FT-IR）,nuclear magnetism（NMR）and mass spectrum（MS）.Three factors including reaction temperature,reaction time and hydrochloric acid dosage were selected as the research objects.The effect of three factors on the yield was studied by orthogonal experiment with L9（3³）.The primary and secondary order of the three factors affecting the experimental results was reaction time>The amount of hydrochloric acid>reaction temperature.The optimum conditions were a reaction temperature of 50°C,a reaction time of 24 h,and a hydrochloric acid dosage of 20 mL.Two diamine benzoxazines2,2-bis（5-benzoxazin-2-furanyl）propane（a-BOZ）and 4,4-bis（5-benzoxazin-2-furanyl）pentanoic acid（b-BOZ）were synthesized from these two diamines and salicylaldehyde,and their structures were characterized by infrared and nuclear magnetic properties.The curing behavior of a-BOZ was studied by measuring the infrared spectrum of the samples obtained at different temperatures.It was found that the sample was completely ring-opened at 180°C for 30 min,and O,N-acetal form was also present.The curing kinetics of a-BOZ monomer was studied by non-isothermal DSC method.The activation energies were calculated by Kissinger method,Ozawa method and Flynn-Wall-Ozawa method,which is 110.7 kJ/mol,113.4 kJ/mol and 113.7 kJ/mol.The curing mechanism was verified by Friedman method as autocatalytic reaction.The thermal stability of polybenzoxazine P（a-BOZ）was studied by TGA test.The results showed that the T_5%was 372.2°C,the T_10%was 422.4°C,and the carbon residue rate at 800°C was 56.8%,which has better thermal stability than bisphenol A-furanylamine diphenol type benzoxazine.The curing behavior of b-BOZ at different temperatures was studied by FT-IR.The method behavior of b-BOZ monomer was studied by non-isothermal DSC curve.The combination of the two found that b-BOZ decarboxylation occurred during the curing process.Through the DMA test,the change of storage modulus and loss factor with temperature was studied.The results show that P（b-BOZ）can maintain high storage modulus（2GPa-3.5GPa）over a wide temperature range（room temperature-300℃）and has high vitrification temperature（360℃and 397℃）.By TGA test,T_10%was 347°C,T_maxax was 426°C,and the carbon residue rate at 800°C was 58%,which showed better thermal stability than bisphenolic acid-aniline diphenol type benzoxazine.