Synthesis of poly(styrene-co-methyl methacrylate)/SiO₂ and polyisoprene/SiO₂ nanoparticles via differential microemulsion polymerization

Nanosized ethylene-propylene rubber (EPM) latex with a particle size of 47 nm was synthesized via an alternative route consisting of isoprene polymerization followed by hydrogenation. EPM yield of 94% produced from nanosized polyisoprene had high thermal stability and high storage modulus due to the saturated carbons domains of the ethylene segments in the polymer chains. Differential microemulsion polymerization was proposed for the synthesis of poly(styrene-co-methyl methacrylate) (ST-co-MMA)-SiO₂ and polyisoprene (PIP)-SiO₂ nanocomposites. To achieve the monodispersion and reduce nano-SiO₂ aggregation, core-shell morphology was designed, consisting of silica as the nano-core encapsulated by polymer as the nano-shell. Poly(ST-co-MMA)-SiO₂ with a particle size of 40 nm having a narrow size distribution could be synthesized using a low surfactant amount (surfactant/monomer weight ratio of 1/57). PIP-SiO₂ with a particle size of 20-60 nm and high polymer grafting efficiency of 78% was obtained. An approach of diimide hydrogenation was applied to synthesize hydrogenated polyisoprene (HPIP)-SiO₂ as new nanocomposite. The highest hydrogenation degree of 98% was achieved using a ratio of hydrogen peroxide to hydrazine at 1.5:1 and HPIP-SiO₂ nanocomposites showed the maximum degradation temperature of 521ºC resulting in an excellent thermal stability. PIP-SiO₂ and HPIP-SiO₂ nanocomposites could be used as new nanofiller in natural rubber (NR) latex due to a dramatic improvement in the storage modulus, tensile strength, tensile modulus, and anti-ageing properties and ozone resistance.