On the rheological behaviour of low-molecular-mass comb-like nematic polyacrylates

• Published in: Polymer science USSR 1991, Vol.33 (8), p.1646-1652
• Main Authors: Plotnikova, Ye.P., Rogunova, M.A., Tal'roze, R.V., Kulichikhin, V.G., Shibayev, V.P.
• Format: Article
• Language: English
• ISSN: 0032-3950; 1878-268X
• DOI: 10.1016/0032-3950(91)90052-R

In a broad temperature range, the rheological properties were studied of nematic polyacrylates differing in the structure of their mesogenic side groups: the series of poly( ε-acryloyloxycaproyloxy)- p′-methoxyphenylbenzoates in the range of M = (0.496–4.96) × 10 4, and of poly-{1-[4(4-cyan-4′-biphenyloxy)-tetraoxycarbonyl]} ethylene of M = 1.8 × 10 5. The rheological behaviour of the liquid-crystalline (LC) melts of these systems is characterized by a nearly linear dependence of the first difference of normal stress on shear rate in the range of Newtonian flow, and by the absence of correlation between the stationary and dynamic characteristics of the material. The activation energy of viscous flow in the isotropic and LC ranges was calculated. The value of the activation energy is affected both by the degree of order of the mesogenic side groups, and by their nature. From the character of the temperature variation of the rheological parameters, a structural transition was discovered within the LC state. This transition is interpreted as corresponding to the formation of local layer structures connected with conformational transitions in the macromolecular chain.