Rheological and Relaxational Properties of Mixed Solutions Based on Linear and Highly Branched Polyacrylonitrile

Branched polyacrylonitrile has been synthesized via anionic polymerization with the 1,4-diazabicyclo[2.2.2]octane–ethylene oxide initiating system. The degree of branching has been determined by means of NMR spectroscopy and indirectly confirmed by viscometry of the dilute solutions. Solutions of binary mixtures of the branched PAN with the industrial linear polymer in dimethyl sulfoxide with different ratio of the components have been prepared; their rheological behavior has been investigated. It has been shown that the introduction of the branched polymer in a solution of linear PAN allows significant decrease in the mixed solutions viscosity at equal total fraction of the polymer. The addition of branched PAN in a solution of the linear PAN has increased the total concentration of the polymer in the system favoring the increase in the viscosity of the mixed solution, but the viscosity has been significantly lower than this of the equally concentrated solution of the linear polymer. Investigation of the frequency dependences of the components of complex shear modulus of these solutions has revealed that the increase in the viscoelastic properties is mainly due to the increase in the elasticity modulus. Exponent of the frequency dependence of the loss modulus in the terminal zone has not been changed, whereas this of the elasticity modulus has been decreased to 0.4 over the entire range of the ratio between the branched and linear PAN. The specific relaxation time has been decreased with the increase in the fraction of linear PAN. Thermal behavior of linear and branched PAN has been investigated by means of DSC. The performed study has revealed the possibility of preparation of the mixed films and fibers based on linear and branched polyacrylonitrile.