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.