Chemical kinetics on thermal oxidative degradation of PMMA

Abstract

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 2 6 % .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 15 8.5kJ/mol,lnA为 2 7.6 9;第二失重阶段为 1.5级化学反应 ,平均表观活化能E为 2 14 .79kJ/mol,lnA为 4 0 .4 6 .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 .32kJ/mol,lnA为 2 4 .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 78.2 5kJ/mol,lnA为 13.97. Effect of oxygen on the thermal degradation of PMM A was studied by mass spectrometry and thermal analysis with TG and DTA. For radic al polymeric PMMA, there were two main degradation models in N 2: the end chai n scission model and the random chain breaking model. The conversion rate at tu rning point was about 26%. Kinetic analysis results indicated the end chain sci ssion was controlled by diffusion process and the average activation energy E was 158.5 kJ/mol and ln A was 27.69. The random chain breaking reaction w as 1.5 order chemical reaction. The average activation energy E and ln A 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 sta ge, the decomposition of peroxy radicals has a notable effect on the overall deg radation rate. The associated kinetic mechanism was first order chemical reactio n and the average activation energy E was 130.32 kJ/mol and ln A was 24.8 1. 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 ln A w ere 78.25 kJ/mol and 13.97, respectively.