聚氯乙烯热降解过程中HCl脱除机理的理论研究

使用B3LYP/6-311++G(d,p)方法对聚氯乙烯(PVC)几种可能模型化合物在热降解过程中HCl的脱除机理进行了理论计算.计算结果表明:PVC在第一阶段热降解过程中脱氯形成HCl时主要进行的是协同反应;缺陷结构的支链(如—CH2CH2Cl,—CHClCH3和—CH3)能显著降低邻近碳位脱除HCl的反应能垒;热降解产物HCl对热降解反应有催化作用;更为显著的是脱除HCl之后形成的氯丙烯基(-CH-CH-CHCl—)能降低HCl形成的反应能垒,而氯丁烯基(-CH=CH-CH2—CHCl—)对HCl的脱除几乎没有影响.

Theoretical studies on mechanism of HCl removal during thermal degradation of polyvinyl chloride

The mechanism of HCl removal during thermal degradation of several possible polyvinyl chloride(PVC) model compounds were theoretically calculated by B3 LYP/6-311++G(d,p) method. The results showed that the main reaction of PVC in the first stage of thermal degradation during dechlorination and form HCl was synergistic reaction. The branched-chains of defect structure(such as —CH3,—CH2CH2Cl and —CHClCH3) significantly reduced the activation energy of HCl removal from their adjacent carbon sites. Product HCl has catalytic effect on the thermal degradation reaction. What’s more remarkable was that allyl group(-CH-CH-CHCl-) generated after a HCl elimination can obviously reduce the activation energy of HCl elimination, however, butenyl group(—CHCH—CH2—CHCl—) had little influence on the activation energy of HCl elimination.