引发剂对氯乙烯微悬浮聚合转化率和聚氯乙烯粒径分布的影响

分别采用水溶性过硫酸铵(APS)和油溶性偶氮二异庚腈(ABVN)引发剂进行氯乙烯(VC)微悬浮聚合,并与APS引发的VC乳液聚合以及ABVN引发的VC悬浮聚合情况进行比较,考察了引发剂类型对聚氯乙烯(PVC)乳胶粒子粒径分布和增塑糊流变特性的影响。结果表明:引发剂浓度相同时,VC微悬浮聚合转化率大于悬浮聚合,而小于VC乳液聚合;APS引发微悬浮聚合得到的PVC乳胶粒子存在数目较多的纳米级粒子,而ABVN引发微悬浮聚合得到的PVC基本不存在纳米级粒子;引发剂和分解产生的初级自由基在水相/油相/胶束中的分配和成核机理不同是导致上述差异的主要原因。ABVN引发微悬浮聚合得到的PVC树脂成糊后呈剪切增稠特性,而APS引发微悬浮聚合得到的PVC树脂成糊后呈剪切变稀特性,且糊黏度较大。

Influences of Initiators on Conversions of Vinyl Chloride Micro-Suspension Polymerizations and Particle Size Distributions of Poly(vinyl chloride) Resins

Vinyl chloride(VC) micro-suspension polymerizations(MSP) were carried out using a water-soluble initiator of ammonia persulfate (APS) and an oil-soluble initiator of 2,2'-azobis-(2,4-dimethylvaleronitrile) (ABVN), respectively, and their performances were compared with those of VC suspension polymerization (SP) initiated by ABVN and VC emulsion polymerization (EP) initiated by APS. Influences of initiator types on the particles size distribution of the resulted PVC latexes and the rheological behavior of plasticized PVC pastes were also investigated. It was found that VC MSP exhibited a higher conversion than SP, and lower conversion than EP after the same polymerization time under the same initiation condition. PVC latex prepared by MSP using APS as the initiator contained a greater number nano scale particles (size smaller than 100 nm), while almost no nano scale PVC particles were observed in PVC latex prepared by MSP using ABVN as the initiator. The above kinetics and size distribution differences were attributed to the different partition of primary free-radicals in water/micelles/monomer (sub) droplets, and the different nucleation modes. The plasticized paste prepared from MSP PVC using APS as the initiator showed pseduoplastic behavior and greater apparent viscosity, while the plasticized paste prepared from MSP PVC using ABVN as the initiator showed dilatant behavior.