真空恒温热处理对PMMA热稳定性的影响

Effect of Vacuum-predecomposition on Thermal Stability of PMMA

通过热重分析研究了270℃真空热处理条件下,不同热处理时间后聚甲基丙烯酸甲酯(PMMA)的热降解行为,并通过Flynn和Flynn-Wall-Ozawa法求取了这些PMMA样品的起始热分解活化能和热降解过程中不同质量损失率时的活化能。结果表明,在真空热处理过程中,只有具有不饱和末端的PMMA能被降解,而具有饱和末端的PMMA是热稳定的,热处理时间对PMMA的相对分子质量没有影响;通过热处理降解了PMMA中具有不饱和末端的分子链能够提高PMMA的低温热稳定性,热处理时间越长,PMMA中具有不饱和末端分子链的相对比例越低,PMMA的热稳定性越好;降低具有末端不饱和结构PMMA分子链的相对比例能够提高PMMA的起始热降解活化能和低温热降解活化能,但对热降解后期的热降解活化能没有影响。

The thermal degradation behavior of PMMA, which was predeeomposed with different time under vacuum condition, was investigated by thermogravimetry （TG）, and the initiation activation energy and activation energy at different weight loss stages were calculated by the methods of Flynn and Flynn-Wall-Ozawa. It showed that, only the PMMA chains with unsaturated ends decomposed during vaeuum-predeeomposition, and the predecomposing time had not any effect on the molecular weight of them. Those PMMA after predecomposing were much more thermal stable than original ones, and the less the unsaturated ends on the chain, the better its thermal stability. The reduction of unsaturated ends in the chain could increase the activation energy of the mass loss near 50 %, but had no effect on that at subsequent stages.