Rigid backbone polymers, XV: Phase transitions in polyisocyanate solution

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Abstract
Experimental data on polyisocyanate systems are presented demonstrating that: (1) When solutions of the rodlike polymer were of such concentration that isotropic and anisotropic phases coexisted, the polymer partitioned such that its molecular weight and concentration in the anisotropic phase were substantially higher than in the isotropic phase. (2) Ternary systems containing two rigid polymers and a solvent had a concentration range in which a single anisotropic phase was obtained for all polymer/polymer ratios. This was not attainable for rigid polymer/flexible polymer/solvent systems. The viscosity behavior of mesogenic polyisocyanates over the three concentration regimes: isotropic, biphasic and anisotropic was treated theoretically. The profound effects of the molecular weight distribution and partition on the viscosity in the biphasic interval were discussed. The theoretical results are in good agreement with experimental data.

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