N-十六烷基马来酰胺酸根合镧(Ⅲ)对聚氯乙烯的热稳定机理

Heat Stabilizing Mechanism of Complexes of lanthanum(Ⅲ) with N-Hexadecyl Maleamic Acid Radical for Polyvinyl Chloride

利用已经成功制备的N-十六烷基马来酰胺酸根合镧(Ⅲ)配合物(LaL3)作为聚氯乙烯(PVC)热稳定剂,通过热重分析、热重-红外联用技术和热动力学分析方法对LaL3热稳定PVC的作用机理进行了分析研究。结果表明,添加LaL3前后PVC样品热解过程及气体释放顺序不变;但LaL3的添加会延迟并减少HCl及氯代烃气体的产生,并且有一定量的酰氯类物质生成,从而证明了LaL3可稳定PVC长链中的活泼Cl原子。LaL3对HCl气体有一定的吸收作用,使HCl气体的析出量明显减少;LaL3还可以与PVC降解生成的顺式共轭二烯通过Diels-Alder反应遏制共轭多烯结构的生成。LaL3可改变PVC热氧化脱氯化氢反应机理,Flynn-Wall-Ozawa法计算表明,LaL3使其活化能从纯PVC的107.7 kJ/mol提高到130.6 kJ/mol;MacCallum-tanner法计算表明,LaL3使PVC热氧化脱氯化氢反应动力学方程由一级反应的f(α)=1-α转化为二级反应的f(α)=(1-α)2,活化能也由纯PVC的97.41 kJ/mol大幅提升到132.9 kJ/mol。

The complex of lanthanum(Ⅲ) with N-hexadecyl maleamic acid radical(LaL3) was successfully synthesized and proved that it can be a heat stabilizer for polyvinyl chloride(PVC). The stabilizing mechanism of the complex on PVC degradation was investigated by TGA and TG-FT-IR. The result show that the PVC degradation process and gas release sequence don’t change. However the release of HCl and chlorohydrocarbon gas is delayed and a kind of acyl chloride appears due to the use of LaL3 by the qualitative and quantitative analysis of the gas released from the PVC decomposition. These prove that LaL3 can replace the unstable Cl atom in PVC chains. The results also show that the quantity of HCl gas decreases due to the use of LaL3, proving that LaL3 can react with HCl;the Diels-Alder reaction of LaL3 with CIS conjugated diene generated by PVC degradation can also inhibit the formation of conjugated polyene structures. LaL3 can change the reaction mechanism of PVC thermal oxidative dehydrochlorination. The Flynn-Wall-Ozawa method indicates that with the addition of LaL3, the activation energy increases from pure PVC 107.7 kJ/mol to 130.6 kJ/mol;MacCallum-tanner method indicates that the reaction order of PVC thermal oxidative dehydrochlorination changes from 1 to 2.