priori further we have found that synthesis and measurement are required to determine the exact refractive index and reactivity of these highly halogenated monomers and that copolymers must be prepared in order to determine their precise refractive index and melting point calculations and predictions are insufficient table 1 below shows the disparity between calculated and observed refractive indices for a number of homopolymers of the invention halogenated acrylates of the present invention have the general formula str6 wherein m a and z are as defined above the portion of the molecule other than the z moiety defines a typical acrylate when a is oxygen and a thioacrylate when a is sulfur as those skilled in the art of polymer science are well aware acrylates are a broad class of polymerizable materials the chemistry of which is well defined although m typically is h other substituents such as ch 3 f cl br i or cf 3 can be used in place of hydrogen however any such substitution should be done while keeping in mind the desired performance characteristic s of the material e g polymer index of refraction ease of polymerization liquidity at the temperature s of use very little absorption in the critical infrared regions monomer availability and cost etc many acrylates meet.