Broken worm and worm-like models for polyisocyanates.

In the study of polymer solutions with experimental techniques sensitive to overall chain dimensions it is difficult to distinguish between worm-like polymers with equal persistence lengths but with different frequencies of specific breaks (e.g. helix reversals) along the chains. In this work we describe the differences in the spectroscopic properties of two polyisocyanates of comparable persistence length. The results indicate that microscopic probes, i.e. NMR and U. V., can distinguish between these worm-like polymers. The predominant mode of chain flexibility in each polymer can be assigned to either helix reversals or torsional motions, or to a combination of both. These spectroscopic methods provide a determination of the relative contributions of minor conformational fluctuations and specific breaks to the overall extension of relatively stiff polymer chains.