Macromolecular Stereochemistry: The Effect of Pendant Group Structure on the Axial Dimension of Polyisocyanates

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The optically active and racemic forms of the 1,2 acetone ketal of propylene glycol were converted via the hydroxyl function to the derived isocyanates. These monomers were polymerized following Shashoua, using sodium cyanide in dimethylformamide at -65 degrees C. Light scattering determination in chloroform of the weight average molecular weight and the root mean square radius of gyration (Mw;1/2) shows, by estimates of the persistence lengths, that the optically active polymer (730,00; 1600 Angstrom) has a more extended chain than its racemic derived isomer (500,000; 850Angstrom) and, based on the literature, is also more extended than poly(n- butyl isocyanate).