Optical plastics have been the priority area of research for material scientists worldwide, mainly, to find alternative materials to glass, a conceptual optical material in use over the years. There are numerous advantages of using plastics for optical applications, in particular for ophthalmic applications over glass. Recently, the researchers have been putting their efforts to develop novel plastic materials to meet requirements of ophthalmic industries. The present review compiles the recent developments in the area of optical plastics. The aim is to present the current state-of-the-art in the field, besides analyzing the various aspects of developing optical plastics. The review presents various possible approaches to achieve the desired properties e.g. high refractive index of the optical plastic materials.
Plastics produced from the sulfur-based monomer are excellent materials with many optical applications such as ophthalmic lenses, fiber optics and non- linear optics. High refractive index plastic materials are able to reduce the curvature, edge and center thickness of lenses. Sulfur containing plastics such as sulfide, polysulfide, and sulfur containing vinyl compound, thioacrylate, polythiol and isocyanate/isothiocyanate based monomers have demonstrated high refractive index, high Abbe number, good impact strength, excellent machinability, good tintability and good transmittance. In the present article, various sulfur containing plastics with different types of monomers for ophthalmic lens applications are reviewed.
Sulfur and chlorine containing bifunctional diols with C-S bond has been prepared starting from chloroepoxy alkane and thioalcohol. The studies of FTIR, TLC, HPLC and NMR have been used to understand the reaction mechanism, as well as for optimization of the reaction parameters. The reaction is highly exothermic and the effect of temperature, rate of addition of reagents and reaction time are important factors affecting the formation of diol. Viscosity studies, HPLC, FTIR, NMR and acid number studies have shown that, these parameters could be used as process control parameters for the synthesis of diol. Refractive index of the synthesized diol is found to be higher than that of the reactants used.
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