聚甲基丙烯酸甲酯热氧化降解的化学动力学研究

使用质谱、热分析手段研究了PMMA热解反应.结果表明,在氮气中,PMMA-CH=CH2有两个失重阶段,分别对应于主链末端双键引发的断链和主链无规则断链反应,转折点的失重率约为26%.其中,第一阶段的失重速率受扩散过程控制,平均表观活化能E为158.5 kJ/mol, lnA为27.69;第二失重阶段为1.5级化学反应,平均表观活化能E为214.79 kJ/mol, lnA为40.46.在空气中, PMMA也有两个失重阶段,反应机理为1级化学反应,转折点处的失重率约为70%.其中在第一失重阶段平均表观活化能E为130.32 kJ/mol, lnA为24.81,在此阶段中, 过氧化基团的分解反应对PMMA的失重速率有重要影响; 在空气中第二失重阶段平均表观活化能E为 78.25 kJ/mol, lnA为13.97.

Chemical Kinetics on Thermal Oxidative Degradation of PMMA

Effect of oxygen on the thermal degradation of PMMA was studied by mass spectrometry and thermal analysis with TG and DTA. For radical polymeric PMMA, there were two main degradation models in N2: the end-chain scission model and the random chain-breaking model. The conversion rate at turning point was about 26%. Kinetic analysis results indicated the end-chain scission was controlled by diffusion process and the average activation energy E was 158.5 kJ/mol and lnA was 27.69. The random chain-breaking reaction was 1.5 order chemical reaction. The average activation energy E and lnA was 214.79 kJ/mol and 40.46, respectively. In air, there were also two stages of mass loss and the turning point conversion rate was about 70%. In the first stage, the decomposition of peroxy radicals has a notable effect on the overall degradation rate. The associated kinetic mechanism was first order chemical reaction and the average activation energy E was 130.32 kJ/mol and lnA was 24.81. In the second stage of mass loss, PMMA had already burnt and the reaction was also first order chemical reaction. The average activation energy and lnA were 78.25 kJ/mol and 13.97, respectively.