Side-chain crystallization in alkyl-substituted semiflexible polymers

A series of comblike semiflexible polymers, in which the alkyl side chains were located nonsymmetrically on the ring, were synthesized by reacting hydroxypropylcellulose (HPC) with hexyl, octyl, dodecyl, and octadecyl isocyanates. Side-chain melting was observed in DSC experiments for polymers with 12 and 18 carbons in the pendant groups (C12HPC and C18HPC). Wide-angle X-ray (WAXS) studies indicated that the alkyl groups in C12HPC crystallized in a form similar to the beta(T) crystal of hydrocarbons but multiple crystalline forms coexisted in C18HPC. However, reorganization of the alkyl side chains was observed as the polymers underwent thermal transitions. A better packing of the alkyl side chains could be induced by shearing the samples in the molten state followed immediately by slow cooling. Quenching and annealing studies suggested that side-chain crystallization and reorganization could influence the packing of the semiflexible backbone. The interplay between the main chain and the side chain in order development is described.