Elastic behavior of concentrated solutions of acrylonitrile copolymers

The elastic behavior of concentrated solution of acrylonitrile copolymer was investigated by the capillary end correction method. The results were as follows. (1) The shear stress is proportional to recoverable shear strain in accordance with Hooke's law below critical concentration; above a critical concentration, however, the shear modulus depends on shear stress. (2) The log–log plots of zero shear modulus against polymer concentration and molecular weight fall on two straight lines with different slopes. The intersection of lines is considered to be the onset of elastically deformable entanglement network. We denote this inflection point as (Cc)e or (Mc)e. (3) The log–log plot of viscosity against polymer concentration does not show a change of slope at the critical concentration (Cc)e. (4) By the application of the kinetic theory of rubberlike elasticity to the pseudo‐network structure of concentrated polymer solution, in the range of Cc < C < (Cc)e or Mc < M < (Mc)e, the number of chain entanglement per molecule is kept one; moreover, in the range of C > (Cc)e, or M > (Mc)e, the number of chain entanglement increases to three.