Property enhancement of polybenzoxazine modified with maleic anhydride
One seemingly shortcoming of polybenzoxazine is its relatively high rigidity. Therefore, various efforts have been attempted to toughen polybenzoxazine such as by alloying with more flexible monomers or polymers e.g. urethane elastomers or flexible epoxy. The alloying of polybenzoxazine with those resins or polymers has been reported to show synergy in some properties thus economically provide a novel class of resin systems with superior performance. In this work, polybenzoxazine alloys were prepared from bisphenol-A-aniline based benzoxazine resin (BA-a) and maleic anhydride (MA) in N, N-Dimethyformamide (DMF) solvent. The miscible monomer mixture was easily transformed into transparent polymer alloys by thermal cure. Fourier transform infrared spectroscopy showed that the chemical interaction between hydroxyl groups of poly(BA-a) and the carbonyl group of MA occurred and generated ester linkages, resulting in a more flexibility in poly(BA-a):MA alloys. The thermomechanical properties of poly(BA-a):MA alloys and the neat poly(BA-a) were characterized by dynamic mechanical analysis (DMA). The result revealed that storage modulus (E’) at room temperature of the polymeric alloy films exhibited a value of 3.91 GPa at poly(BA-a):MA of 1:1 mole ratio. The value is significantly higher than that of the neat poly(BA-a) i.e. 2.57 GPa. Interestingly, glass transition temperature (Tg) of the monoanhydride-modified poly(BA-a), obtained from the maximum peak of the loss modulus, increased with an increase in MA content. The maximum value of 200°C was obtained in poly(BA-a):MA=1:1 and is higher than that of the neat poly(BA-a) i.e. 178°C. Moreover, only single Tg .was observed in these alloy systems, indicating no phase separation in poly(BA-a):MA samples. From thermogravimetric analysis, it was found that the incorporation of MA in poly(BA-a) could raise its degradation temperature as well as the char content. The modification is highly simple and of practical use for polybenzoxazines which are currently commercialized for applications such as aerospace composites, or electronic packaging materials.
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