Thesis (M.Sc.)--Chulalongkorn University, 2006

The copolymer sheets of styrene (ST) and methyl methacrylate (MMA) containing modified natural rubber (NR) prepared by bulk copolymerization using benzoyl peroxide and 2,2'-azobis-(2,4-dimethylvaleronitrile) as initiators were studied. The modified NRs were prepared by graft copolymerization and hydrogenate reactions. The grafted NR prepared by emulsion copolymerization using redox initiator consisted of 66.1 wt% NR-g-(MMA-co-ST), 26.9 wt% free rubber and 7.0 wt% free copolymers. The hydrogenation of NR catalyzed by OsHCl(CO)(O[subscript 2])(PCy [subscript 3]) was carried out at 140 ํC and 400 psig, the degree of hydrogenation was 56.5. The effect of styrene and rubber monomer content on the mechanical properties, physical properties and morphology of modified acrylic sheet were investigated. The results show that mechanical properties were evaluated as a function of modified NR and ST content. The appropriate mechanical properties of modified acrylic sheet were obtained at 2 wt% of grafted NR and 1 wt% of hydrogenated NR. The optimum content of ST in modified acrylic sheet for improving the mechanical properties was 20% by weight. Moreover, the HNR modified acrylic sheet present the superior thermal resistance. The tensile fracture surface examined by scanning electron microscope showed the relatively smooth surface with few relatively small cracks. It implied that the modified NR can be used as an impact modifier for acrylic cast sheet.