Study On Synthesis And Thermal Properties Of Heat-Resistant PMMA Resin

Polymethyl methacrylate?PMMA?is one of the best translucent resin materials.It has a lot of advantages,such as low density,light weight,high light transmittance,chemical resistance,weather resistance and easy processing.It has been widely used in the fields of optics,communication,construction,aerospace and other fields.However,its heat resistance is unsatisfactory,the glass transition temperature?T_g?of PMMA is about 105 ?,the heat distortion temperature is only 85 ?,and the use temperature is lower than 80 ?.The shortcoming had severely limited its application range.AMS is a by-product of production of phenol and acetone by oxidizing cumene.Therefore,it is cheap and obtained easily.Due to the electron-withdrawing action of?-methyl?-CH₃?and the steric hindrance effect of the benzene ring,AMS is difficult to homopolymerize and its homopolymer has a lower molecular weigth.But it can easily copolymerize with others vinyl monomer.The copolymer of AMS has usually higher heat resistance with its steric hindrance effect.For this reason,AMS is frequently used as the heat-resistant modified monomer to pruduct some polymer with a higher heat-resistance,such as the heat-resistant ABS,PS and PVC.The feasibility to enhance the heat resistance PMMA resin by using AMS as the heat-resistant modified monomer were studied by invesigating the effect of the copolymerization behavior and copolymerization composition in this work.The resuls confirm that the addition of AMS can raise the heat resistance of PMMA and the copolymer with higher molecular weight can be prepared by high temperature solution polymerization.The thermo stability of copolymer of MMA and AMS can be enhanced by the additon of third monomer to inhibit the unzipping depolymerization.Finally,the polymerization recipe and condition for synthesizing the heat resistance PMMA were obtained.The main results are as follow:?1?The conversion of high temperature solution polymerization,the molecular weight and copolymerization composition of Poly?MMA-co-AMS?copolymer are mainly affected by the polymerization temperature,AMS and solvent dosage.The copolyner with higher molecular weight copolymer can be synthesized under conditions that the polymerization temperature of 130 ?,the MMA/AMS ratio is 85/15,and the solvent porpotion is 20 wt%.under the mention aboved conditions,the polymerization conversion was 72%,the number average molecular weight of PMMA was 8.84?10⁴,the molecular weight distribution was1.51,and the copolymerization composition of AMS in this copolymer was 8.89 wt%.?2?The addition of comonomer AMS can significantly improve the heat resistance of PMMA resin.However,the addition of comonomer AMS will introduce the thermal instabiliy structure into the polymer chain,which will lead to the thermal stability of PMMA becomes worse.As the content of AMS in the copolymer is 10.7 wt%,the glass transition temperature of PMMA resin is as high as 132.6 ?,which is 8.1 ? higher than of PMMA homopolymer.?3?The thermal stability of Poly?MMA-co-AMS?copolymer can be improved by introducing the third monomer AM.Meanwhile,it is also of better heat resistance.Under the conditon of the ratio of MMA/AMS/AM for 80/15/5,the glass transition temperature and initial thermal decomposition temperature Poly?MMA-co-AMS-co-AM?copolymer is as high as 135.6 ? and 262.7 ?,respectivly.