Compounds of Formula I ##STR1## wherein Z is an aromatic group, each R is individually selected from the group consisting of alkyl groups of from 1 to about 12 carbon atoms, thioalkyl groups of from 1 to about 12 carbon atoms, and halogen atoms, n is from 1 to about 6, and x is from 0 to 7, are suitable for use in preparing rubber latex particles. The rubbers are useful as substrates in graft copolymers and the resulting graft copolymers are suitable for use in thermoplastic blend compositions, particularly with transparent polymers. The rubber materials are advantageous in that they exhibit low glass transition temperatures and high refractive indices.