Copolymerization of methyl methacrylate (MMA) with flame retardant monomer is considered to be the most promising method for the preparation of transparent flame retardant poly (methyl methacrylate) (PMMA). However, the mechanical strength and heat resistance of the obtained flame retardant copolymers aren't satisfactory. In this work, the organic-inorganic hybrid PMMA copolymer is designed and synthesized by the ternary copolymerization of MMA, octavinyl silsesquioxane (V-POSS) and phosphorus-containing flame retardant monomer (DEP). V-POSS hardly affects the transparency and flame retardancy of the copolymer, but can significantly improve the thermal stability and mechanical properties. When 0.4 mol% V-POSS is copolymerized, the hybrid copolymer shows limiting oxygen index, heat release rate and visible light transmittance equivalent to the copolymer containing only DEP unit, and the initial decomposition temperature, storage modulus, flexural strength and impact strength are increased by 13 C, 21%, 11% and 23% respectively because of the cross-linking structure and the enhancement of inorganic nanoparticles. This study illustrates the reinforcing and flame retardant effects of hybrid copolymers, and provides a novel strategy for the preparation of high-performance flame retardant plexiglass.
The synthesis of intrinsic flame retardant copolymer by copolymerization with reactive flame retardants is the most potential method to prepare transparent and flame retardant poly (methyl methacrylate) (PMMA) at present,but the main challenge of this method is that the copolymer usually has poor mechanical properties and heat resistance. In this work, the hydrogen bond enhancement strategy is adopted, and the flame retardant PMMA with excellent comprehensive properties is obtained by ternary copolymerization with methyl methacrylate (MMA) as matrix unit, diethyl (methacryloyloxymethyl) phosphonate (DEP) as flame retardant unit and methacrylamide (MAA) as hydrogen bond unit. Due to the formation of intermolecular hydrogen bond via MAA unit, the storage modulus, flexural strength and impact strength of the terpolymer containing 15 mol% MAA are 48%, 19%, and 24% higher than those of the copolymer of MMA and DEP, and its hardness, glass transition temperature and load thermal deformation temperature (increased by 7°C) are also superior. Moreover, owing to the gas‐phase dilution and charring flame retardancy of MAA unit, the terpolymer shows increased limiting oxygen index (24.3%) and UL94 rating (V‐1). This work not only provides a promising flame retardant PMMA for practical application, but also offers a new strategy to design flame retardant polymers with good mechanical properties.
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