LIQUID-CRYSTALLINE POLYURETHANES STUDIED BY POSITRON-ANNIHILATION METHOD

A series of liquid crystalline polyurethanes of different both flexibl e spacer length and mesogenic group content was studied by means of po sitron annihilation method. The investigated polymers were targeted on the separation of aromatic hydrocarbons from their mixtures with alip hatic ones. The effect of modification of the liquid crystalline polyu rethane chain on the polyurethane free volume size and free volume dis tribution was determined on the basis of the positron annihilation lif etime spectra. In the positron annihilation lifetime spectra measured for the samples under study two long components of several nanoseconds , characteristic of o-Ps decaying by pick-off, occurred. The correlati on of the values of the o-Ps lifetime with the size of the free volume region allowed to recover the free volume distributions with the use of the method employing the numerical Laplace inversion technique. The obtained results were compared with the diffusion data on the mobilit y of liquid hydrocarbons in the liquid crystalline polyurethanes enabl ing the correlations between polymer structure and its transport prope rties to be evaluated.