Preparation And Properties Of Hetero Atom-containing Optical Resins

Optical material, an organic polymeric resin material of highly practicability, develops rapidly in recent years. Compared with inorganic glass, optical material is of several qualities, namely light weight, compact resistance, dye-ability, easy processing and excellent optical performance. However, traditional optical resin can hardly meet people’s requirement of high precision, high performance on optical components. The ordinary optical epoxy resins can be applied to most optical fields because of its high mechanical strength, elastic modulus and good solvent resistance, but some special-purpose optical components require higher precision and performance. Sulfur atom has a relatively lower density, less dispersion and higher molar refraction index, and thus can be introduced into optical epoxy resins to produce optical resins with higher refractive index and better performance.In this article, a sulfur-containing epoxy resin is synthesized with 4, 4’-thiodiphenol and epichlorohydrin as raw materials, and Na OH as catalyst. Then a sulfur-containing epoxy acrylic resin(EA) can be synthesized by the ring-opening polymerization between this sulfur-containing epoxy resin and crylic acid. Therefore, optical resin materials with higher refractive index and better performance can be synthesized by the separate copolymerization of sulfur-containing epoxy acrylic resin(EA) with styrene(St) and methyl methacrylate(MMA).Orthogonal experimental design method is employed to optimize the synthesis of sulfur-containing epoxy resin and epoxy acrylate resin. The optimal conditions for synthesis of sulfur-containing epoxy resin are: 4 hours’ etherification reaction time, 2 hours’ close-ring reaction time, n(Na OH)/n(4,4’-thiodiphenol) = 1.2:1, 90 ℃ reaction temperature. The epoxy value and productivity of the sulfur-containing epoxy resin under these conditions are 4.599mmol/g and 87.79% respectively. The optimal conditions for synthesis of epoxy acrylic resin are: amount of catalyst was 3% of the total weight of the raw material, temperature dropping was 70 ℃, the reaction temperature was 95 ℃, and reaction time was 4h. The epoxy value and acid value of EA under these conditions are 0.0797mmol/g and 2.2468 mg KOH/g respectively. The molecular structure of the resin is characterized by Fourier transform infrared spectroscopy(FTIR), nuclear magnetic resonance hydrogen spectrum(1H-NMR) and nuclear magnetic resonance carbon spectrum(13C-NMR).The light transmittance of curable resins copolymerized by EA with St and MMA is over 80% and its refractive index and surface hardness are proportional to the content of EA in copolymer composition, which is much higher than the corresponding homopolymer, such as PS or PMMA. When the mass fraction of EA in the copolymer composition is 75%, the refractive index of EA/St copolymer resins can reach 1.60, and that of EA/MMA copolymer resins is 1.57. The water absorption of the cured resin increases with the increasing EA content in the copolymer composition, while the heat resistance decreases.