Copolymerization Of Benzoxazine-based Maleimide With Styrene And The Curing Kinetics Of The Resultant Copolymer

As a universal linear polymer, polystyrene (PS) has been widely used in theproduction and life because of its excellent physical and chemical properties and goodprocessing properties. But the shortage of thermal properties of polystyrene limits itsapplication on special conditions. So how to improve the performance of polystyreneto expand its application areas has aroused extensive attention.In this thesis, a novel maleimide containing oxazine ring was synthesized and itscopolymerization with styrene was also investigated. The brief contents are shown asfollows:Firstly, a novel maleimide monomer (HPM-Bz-Me) containing oxazine ring wassynthesized by solution method with self-made HPM as a phenol source andp-toluidine as an amine source. General free radical polymerization was employed toprepare the nearly alternating copolymer of HPM-Bz-Me with styrene (St) using2,2-azobis (isobutyronitrile)(AIBN) as an initiator. The structures of the monomer andthe copolymer were identified by1H-NMR, FTIR and13C-NMR. TGA results showedthat, when using DMSO as a solvent, the copolymer emerged the best thermalproperties. The10%weight loss temperature was about442°C and char yield was44.5%at800°C, which showed that the copolymers could be used as high thermalresistance materials.Secondly, the mechanism of alternate complex and the effect of solvent polarityon the copolymer stereochemistry, which further affected the thermal performance ofthe copolymers, were discussed. The higher thermal properties should be attributed tothe more incorporation of HPM-Bz-Me unit that contains both rigid imide and oxazinerings into the copolymer and formation of the crosslinking copolymers when solventpolarity emerges an upward trend.Thirdly, the curing reaction was also investigated under non-isothermaldifferential scanning calorimetry (DSC) at different heating rates. The averageactivation energy of the curing reaction was determined to be134.1kJ/mol and135.9kJ/mol, respectively, according to Kissinger and Ozawa methods. TheFlynn–Wall–Ozawa method provided the change of activation energy Ea values as afunction of the degree of conversion. The autocatalytic kinetic model was found to bethe best description of the investigated curing reactions according to Friedman method. The reaction order m and n are0.49and1.44, respectively. Non-isothermal DSCcurves obtained from the experimental data showed a good agreement with thattheoretically calculated. In addition, the curing process of poly (HPM-Bz-Me-co-St)was also investigated in detail.