Synthesis And Properties Of Polyurethane Optical Plastics

Compared with optical glass, optical plastics have the advantages of light weight, good transparency, impact-resistance, processability, cutting and dyeability. Ordinary optical plastics such as PMMA, PC and CR-39 have been widely used in many fields. However, the disadvantages of the ordinary plastics, such as lower refractive index and large dispersivity, have restricted their applications for high precision elements. Therefore, it is of great importance to create new kinds of optical resins, especially with properties of higher index, lower dispersivity.First, according to molecule design principle, the S element has higher mole refractive index. Based on the results in literature, several new type monomers containing S were designed and synthesized in the present work: (1) 2,3-dimercaptoethylthiopropanethiol (BES) was synthesized easily from epoxy chloropropane and thioethanol, followed by reaction with HCl/thiocarbamide; (2) p-and m-a,a'-benzyl isothiocyanate(XDTI) were synthesized easily from p- and o-a,a'-benzyl chloride through group replacement, respectively. The best synthesizing conditions were studied and optimized.Utilizing the above synthesized monomers, two kinds of new structure and high quality resins were obtained: polythiourethane and HEMA-XDI resins. The former one, synthesized from BES and XDI (xylene diisocyanate) through condensation -polymerization, has good optical and mechanical properties: good transmittance, weatherability, high refractive index (1.659), excellent impact resistance (izod impact strength 25-~30kgcm/cm2), low density (1.34g/cm3) and dispersivity. The homopolymer resin of BES- XDTI and the copolymer resins of BES-XDTI-XDI were prepared as well. Their refractive indices were improved further. However, the resins were not colorless. The last one, based on the reaction of OH and NCO groups, double alkene monomer containing N element was prepared in situ. Then a new kind optical resin with higher surface hardness, good heat-resistance, and excellent optical properties was made from HEMA-XDI. Modification of this-ii-resin with BES put forward a new method to prepare optical resins.Resins containing sulfur, especially the polythiourethane resin synthesized from BES and XDI, have the properties of high refractive index, low dispersivity, good heat-resistance, and excellent impact resistance. Meanwhile, the cost is still very low and the processing is easily to control. In conclusion, the polythiourethane is a very prospective optical plastic.