INDEX styrene-butadiene rubbers

Transparency. Standard ABS grades are opaque because of the refractive index mismatch between the dispersed rubber phase and the continuous SAN matrix. However, ABS-type systems are available as transparent grades for clear applications, with transparency achieved by the matching of the refractive index of the rubber and matrix phases through the incorporation of comonomers. Typically, refractive index of the rubber phase is increased through the use of styrene-butadiene rubber and the matrix phase reduced and matched to the rubber phase through terpolymerization with methylmethacrylate. 

Figure 4. Swelling index of butadiene-styrene copolymers vs. 1,2 content in the rubber...

Other Impact-Modified Commercial Grafting-Based Polymers Typical HIPS and ABS polymers are opaque materials however, MABS (methyl methacrylate-acrylonitrile-butadiene-styrene) polymers, which are produced by processes similar to those used in the production of ABS, are transparent materials. This property is obtained by the addition of methyl methacrylate (MMA) to the recipe in order to impart transparency to the polymer by equalizing the refracting index of the rubber particles to that of the matrix. These materials find applications... 

Properties Water-wh. to pale yel. liq. sol. in ether, alcohol insol. in water m.w. 202.44 dens. 0.849 (15.5/15.5 C) m.p. -7 C b.p. 274-278 C flash pt. (OC) 127 C ref. index 1.4589 Toxicology Irritant avoid contact and inh. strong sensitizer mutagenic data TSCA listed Precaution Combustible Hazardous Decomp. Prods. Heated to decomp., emits toxic fumes of SOx Uses Catalyst accelerator for unsat. polyester resins modifier in polymerization reactions, esp. for SBR reducing initiator chain transfer agent for styrene-butadiene/chloroprene rubber prod. In food-pkg. adhesives adjuvant in food pkg. 

The importance of the graft handle on a 62/38 butadiene-methyl methacrylate rubber can be illustrated by its effect on the optical properties of the polyblend. From Table II it can be seen that the reduction in percent haze is dramatic for an increase of methyl methacrylate graft from 0 to 27% by weight, while there is no apparent change in the light transmission. The blend resin in this polyblend system was an 88-12 methyl methacrylate-styrene copolymer, and the total resin to backbone rubber ratio was kept at 2.5-1.0. The measured refractive indices are included for each component (the graft rubber and the blend resin). The difference in refractive index amounts to no more than 0.004 unit for any of the components. 

Clarity of Graft Polymers with Varying Methyl Methacrylate/ Styrene Ratios. Refractive index considerations 7,8) and general state of the art considerations (8) favor methyl methacrylate (MMA) over styrene (St) as the major monomer portion of the matrix. With this in mind, we selected MMA/St ratios from 62/38 to 80/20 (wt %). Using a commercial Firestone butadiene latex (2004) to supply the 15% rubber graft, polymerization runs were made as outlined in Table I. 

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