The Synthesis Of Heat-resistant Poly(Methyl Methacrylate)

Poly(methyl methacrylate)(PMMA)is a transparent polymeric material possessing many excellent properties,such as light weight,high light transmittance,chemical resistance,colorlessness,resistance to weathering corrosion,and good insulating properties.The glass transition temperature of PMMA,however,is relatively low,which limits its applications in the optical-electronic industry,such as compact discs(CD),optical glasses,light guide plate and optical fibers.In order to improve the heat resistance of the PMMA resin,it was reported that many modified ways were investigated by some national scholars.Recently,the copolymerization of N-cyclohexyl maleimide(ChMI)or N-phenyl maleimide(PMI)with MMA has been known as one of the best ways to improve the heat resistance of PMMA.The incorporation of rigid polar maleimide structure in the macromolecular chain increase both the T_g and the degradation temperature of the modified PMMA.The coloration of these copolymers at high temperature,however,has been pointed as an undesirable characteristic because of the monomeric the unreacted monomers in the copolymers and decrease the transpancy of PMMA resin,which limits its application in the field of optical materials.Therefore,it is necessary to modify the heat resistance of PMMA resin through other new ways.Two ways were adopted to improve heat resistance of PMMA resin in this study:on the one hand,incorporating bulky and hydrophobic isobornyl methacrylate(IBMA)into the chain of PMMA enhanced the rigid of PMMA chains in order to improve its heat resistance.On the other hand,the heat resistant Poly(MMA-co-MAAM)copolymers was prepared by post-polymerized cyclization using the monomers of MMA and MAAM.Meanwhile,it is very crucial that the PMMA resin prepared by two approaches above-mentioned can retain its excellent transmittancy,heat resistance,thermal stability,the water absorption and the structures of PMMA were measured by these test methods of DSC,TGA,NMR,FTIR,GPC.(1)The heat resistance of PMMA resin can be enhanced by incorporating bulky and hydrophobic isobornyl methacrylate(IBMA)into the chains of PMMA and the glass transition temperature of Poly(MMA-co-IBMA)copolymers with the 30wt%content of IBMA is up to 132.2~oC.The thermal stability of its copolymers,however,was deteriorated due to the incorporation of IBMA in the PMMA chains and the initial thermal degradation temperature was decreased.(2)Introducing a small amount of the third comonomer of MAAM not only maintains the heat resistance of Poly(MMA-co-IBMA)copolymers,but also improve the thermal stability and then the initial thermal degradation temperature is increased.When the ratio of MMA/IBMA/MAAM was 80/14/6,the initial thermal decomposition temperature of Poly(MMA-co-IBMA-co-MAAM)terpolymer was 299.2~oC,its glass transition temperature was 143~oC,water absorption was 0.37wt%.(3)It can prepare high heat resistant PMMA resin by the intramolecular cyclization of post-polymerization.In the conditions of cyclization temperature of 230~oC,the degree of vacuum of-0.0095Mpa,cyclization time of 2min,the high heat resistance cycliczation PMMA resin can be prepared and its initial thermal decomposition temperatures,glass transition temperature and water absorption were 340~oC,154~oC and 0.35wt%,respectively.(4)In the continuous cyclization process of vacuum,the intramolecular cycliztion reaction occurred in the polymers chains of the high heat resistant PMMA resin,which can maintain the excellent transmittancy of PMMA resin without cross-linking reaction.