Study On Stereocontrol In Photopolymerization Of Methyl Methacrylate

Tacticity of polymers closely related to their mechanical, optical, dielectric and other properties. A high degree of isotactic or high syndiotactic polymers are easy to form more properties characteristics of spiral patterns which demonstrate the great unique optical activity. It may have a valuable application on bio-medicine, asymmetric reactions, optical information material areas,etc. Radical polymerization as the mainstream method which can obtain high molecular weight polymer can be easy to carry out a variety of structural modification of polymers to obtain the relevant property.Photopolymerization has become a well-accepted technology in polymerization because of its unique advantages, such as moderate, efficient, enabling, economical, energy-vironmental friendly, etc. Efficient free-radical polymerization under the low temperature can be realized by photopolymerization, so as to control the tacticity of polmers. In this paper,the moderate and fast synthesis of polymethyl methacrylate (PMMA) with high tacticity was studied through photopolymerization, making use of high efficiency of low-temperature photopolymerization, asymmetry of monomers, introduction of polar solvents, asymmetric chelation of Transition Metal Salts to form polymers with high tacticity.In present research, the photopolymerization of MMA and the influences of solvent, additives and temperature on the polymerization yield and PMMA tacticity were investigated. The research outcome can be described as following:1,Photopolymerization was proved more favorable for improving PMMA tacticity than thermal polymerization. For the photopolymerization of MMA at room temperature, the presence of Lewis acid (yttrium trifluoromethysulfonate Y(OTf)3, ytterbium trifluoromethysulfonate Yb(OTf)3, ZnBr2 ), hexamethyl phosphoric triamide (HMPA) and L-(+)-tartaric acid was found slightly impact on the PMMA tacticity. The triad syndiotacticity (rr) of PMMA was appreciably improved, but the triad isotacticity (mm) kept the same as the controlled.2,The photopolymerization efficiency of MMA at low temperature was very low in common organic solvents, i.e. methanol, isopropanol, ethanol and toluene, etc. With hexafluoroisopropanol (HFIP) as distinct solvent for the low temperature photopolymerization of MMA, the polymerization efficiency and polymer syndiotacticity increased moderately. A higher syndiotacticty (r 95 %) and yield (14.8 %) were obtained for the photopolymerization product of MMA at -78℃. In most cases of low temperature photopolymerization, the polymerization yield slightly increased with the aid of Lewis acid, but no remarkable tacticity regularization effect on the produced PMMA.3,Fortunately, efficient photopolymerization at low temperature was acquired for MMA while using polyethylene glycol (diethylene glycol, triethylene glycol and PEG 200) or propylene glycol as slovent. In the condensed polymerization solution at -60℃, PMMA yield more than 60 % and high syndiotacticity could be facily reached after 3 hours ultraviolet irradiation. The addition of HFIP to the glycol/MMA system was favorable for enhancing the PMMA syndiotacticity and polymerization yield.