distortion, ghosting And other phenomena; high refractive index to minimize the thickness of the lens; surface hardness, can be repeatedly scrub; impact resistance is good, not broken; The most suitable hard lenses for transparent plastic materials are CR-39 and J. D two, and to CR-39-based. In the United States, 70% of the optical material for the CR-39, in China can reach 30% to 40%. The common characteristics of these two materials are good transparency, high refractive index, low birefringence, impact resistance, high surface hardness. CR-39 is a diallyl diethylene glycol carbonate polymer, which is thermosetting and can be cast. It has high transmittance, good hardness, impact resistance, heat resistance, low birefringence, suitable for the production of lenses. The main drawback is the wear resistance, the refractive index is slightly smaller. CR-39 and high refractive monomer such as diallyl phthalate copolymer, the refractive index can be increased to 1. 546. CR-39 surface coating, can improve its wear resistance. J. D series PES derived copolymer, the composition of diene polyphenylene ether sulfone, styrene, methyl methacrylate; it is also a thermosetting resin, can be cast molding. J. D has a maximum refractive index of 1.62 and a maximum hardness of 6H (Rockwell hardness of 332) at a cost of only 1/2 of PMMA and 1/6 of CR-39, which is comparable to CR-39 Optical materials. Hard mirror products are generally produced by casting method, which can avoid the orientation of processing to prevent birefringence increases. (2) contact lens contact lenses with the performance requirements of the material is more demanding than the hard mirror, the specific requirements are as follows: high transmittance, should be more than 90%, low haze; low birefringence to prevent image skew, Distortion, ghosting and other phenomena; high refractive index to minimize the thickness of the lens; high water absorption, the general physiological saline absorption rate of not less than 30%; soft and flexible; oxygen permeability is good, in order to facilitate the eye Physiological respiration; good physical compatibility, and eye contact without adverse reactions. Health, non-toxic The most suitable contact lens material is poly (hydroxyethyl methacrylate) (HEMA), its light transmittance up to 97%, the refractive index of 1. 43 ~ 1.45, water absorption of 39% to 60%. HEIx4 polymerization method is: ethylene glycol dimethacrylate (EGDMA) as a cross-linking agent, the HEMA polymerization into a hydrogel-like material, then add polyvinylpyrrolidone, so that the water absorption from 40% to 60 %.