Abstract: The invention relates to a thio(meth)acrylic acid bisester of formula I ##STR1## where R.sub.1 represents hydrogen or methyl;r represents the number 0 or 1; ands, m, and n independently represent an integer from 2 to 6, with the proviso thatwhen r=0, s+n>4; andwhen r=1, s+m+n>6 useful as or monomer for high refractive index plastics.

Abstract: The invention relates to a method of producing (meth)acryloylthio esters of general formula I ##STR1## where R represents hydrogen or methyl, and R.sup.1 represents a phenyl group, a substituted phenyl group, a C.sub.1-24 alkyl group, a substituted C.sub.1-24 alkyl group, a cyclic C.sub.3-24 alkyl group;comprising reacting (meth)acrylic acid anhydride (formula II) ##STR2## where R represents hydrogen or methyl, with at least the stoichiometric amount with a thiol or thiolate of formula IIIR.sub.1 --S--M, (III)where M represents hydrogen or a metal cation, andR.sub.1 is defined as above.

Abstract: The invention relates to a high refractive index plastic produced by reaction of an alkylthiol with a multiply unsaturated monomer, wherein said alkylthiol (A) has at least 2, and up to 20 carbon atoms in the alkyl group, and contains at least 2 thiol groups in the molecule, is reacted with an alkylpolythiol ester (B) having at least 2, and up to 24, preferably up to 12, carbon atoms in the alkyl group, which ester contains at least 2 thiol groups esterified with (meth)acrylic acid in the molecule, said reaction being under conditions of radical polymerization, with the limitation that the numerical ratio of the mercapto groups to the available double bonds is .ltoreq.1, preferably <0.5.

Abstract: The invention relates to sulfur-containing polymethacrylates P produced by radical polymerization of monomers of formula I: ##STR1## where Y represents a C.sub.2-12 alkyl group, a C.sub.2-12 branched alkyl group, a C.sub.3-12 cyclic alkyl group, a C.sub.6-14 aryl group, or a C.sub.7-26 alkaryl group, wherein the carbon chains of Y may be interrupted by one or more ether or thioether groups; andR represents hydrogen or methyl; andwherewith the polymer P contains, in addition to units of monomer(s) of formula I, units of at least one monomer of formula II: ##STR2## where R and Y have the same meanings as above; and n is an integer in the range 1 to 6.