新型氯乙烯非均相聚合动力学和成粒机理

对以正丁烷（But)为反应介质的新型氯乙烯（VC）非均相聚合动力学和成粒机理进行了研究，根据VC-But二元体系气液平衡方程，由聚合过程气相压力或组成变化计算VC聚合转化率，VC非均相聚合的诱导期不明显，自动加速现象一般发生在聚合前、中期，后期聚合速率较小，新型VC非均相聚合PVC树脂的体粒径与悬浮PVC树脂相当，数均粒径较小，PVC颗粒由基本不熔结的初级粒子组成，颗粒内部初级粒子分布密度大，粒径大，孔隙率高；而在颗粒表层初级粒子分布密度高，粒径小，孔隙率低；树脂的增塑剂吸收率远大于悬浮PVC树脂，根据PVC树脂的颗粒特性和PVC与VC／But混合液的溶解度参数差异，推断聚合成粒机理为：PVC分子链在很低转化率时就从聚合介质中沉析出来并聚集形成微区，初级粒子和颗粒；后期成粒过程包括颗粒内部初级粒子的增长和向表层的离心聚集，颗粒对新形成的大分子链及其初级聚集体的捕捉等。

Kinetics and Particle Formation Mechanism of a New Vinyl Chloride Heterogeneous Polymerization

The kinetics and particle formation mechanism of vinyl chloride (VC) heterogeneous polymerization using n-butane (But) as the reaction medium were studied. VC conversions were calculated from the vapor pressure or composition based on the vapor-liquid equilibrium equations of VC-But system. The polymerization induction period was not obvious and the self-acceleration phenomenon was occurred in the early and mid stages of the polymerization process. The volume average particle size of resulting poly(vinyl chloride) (PVC) resins produced by the proposed heterogeneous polymerization were close to that of conventional suspension PVC, while the number average particle size was much smaller. The PVC particles were constructed by primary particles, which were almost not fused together. The particle size of primary particles and porosity in the center of PVC particles were greater than that in the top layer of the particles. The cold plasticizer absorption of obtained PVC resin was much higher than that of conventional suspension PVC. The particle formation mechanism was proposed as following: PVC chains precipitate from the reaction medium to form domains, primary particles and particles in the early stage of polymerization. The increment of primary particles and their aggregation to the top layer of particle, growth of particles by capturing new formed PVC chains and their primary aggregates occur in the later polymerization stage.