丙烯腈溶液共聚过程体系黏度变化的动态测定与理论分析

通过BrookField DV-Ⅲ Ultra可编程旋转流变仪实时测定了以偶氮二异丁腈为引发剂,二甲基亚砜为溶剂,丙烯腈-衣康酸二元溶液共聚合体系的零剪切黏度变化。同时设计相同条件的封管实验测定转化率,并利用Arrhenius-Frenkel-Eyring方程导出了适合描述丙烯腈溶液共聚合体系的零剪切黏度随固含量、温度及黏均分子量变化的经验关联式。结果表明,各工艺条件对体系黏度都有显著影响,原料配比细微的差别将导致最终原液黏度相差数百帕秒以上,调控黏度时需综合考虑。值得注意的是,所有实验条件下反应2～3 h后,体系黏度激增1000倍以上,即从约2 mPa·s的初始黏度迅速增加至2～3 Pa·s;而当总单体含量达到28%时体系产生凝胶效应,反应一定时间后黏度急剧增长。另外发现,当体系达到某一临界固含量时,溶液中大分子发生链缠结,固含量微小的增量就会导致体系黏度剧增。

Viscosity behavior of solution copolymerization of acrylonitrile and itaconic acid: on-line determination and theoretical analysis

A programmable torque rheometer was used for on-line determination of zero shear viscosity of solution copolymerization of acrylonitrile and itaconic acid in dimethylsulfoxide.The Arrhenius- Frenkel-Eyring equation was extended to identify the dependence of zero shear viscosity on polymer content, temperature and viscosity-average molecular weight of polyacrylonitrile.It was observed that under all of these process conditions, small differences in feed composition would give rise to a large variation on zero shear viscosity and ultimate viscosity to more than 100 Pa·s, so the control strategy for viscosity should be considered critically.The changes of reaction temperature seemed to be more effective than other methods.The viscosity increased quickly from about 2 mPa·s to 2—3 Pa·s in the first three hours under all experiment conditions which would greatly depress heat exchange and mixing efficiency.It was also found that viscosity increased dramatically as a result of gel effect when total overall monomer mass fraction was beyond 28% in feed.In addition, a small increase of polymer content could give rise to a great increase in viscosity when polymer content reached some critical values, which indicated that macromolecules were entangled severely in copolymerization solution.