Complexing blends of flexible ionomers and rigid rod polymers by specific interactions

The objective of this work was to develop a molecular architecture involving a flexible polymer backbone grafted with rigid rod polymer chains. To accomplish this, blends of a helix-forming polypeptide, poly($\gamma$-benzyl-L-glutamate), PBLG, and lightly sulfonated polystyrene, SPS, were prepared in a common solvent. No covalent bonds were formed between the two polymers, however, strong interactions involving the acid or salt groups of SPS or neutralized SPS and the terminal amine group or the ester side groups of PBLG occurred. Evidence of these specific interactions was provided by FTIR and it was observed that the sulfonic acid species induced some helix-to-coil transition of the PBLG conformation. Intermolecular interactions can improve the miscibility of the two polymers, as demonstrated from thermal analysis by the shift of the T$\sb{\rm g}$s. At specific blend compositions, a single phase, i.e., miscible, blends of a flexible coil and rigid rod polymer were achieved. Those blends remained optically clear after melt processing. The addition of 10% PBLG to SPS resulted in a modulus increase from 2.27 GPa (pure PS fiber) to 3.38 GPa for the melt spun fibers. Those materials appeared to be melt processable molecular composites. Shear-thickening behavior was also observed for the blend solutions in selected solvents as a consequence of the intermolecular interactions and conformational transitions of PBLG, indicating the applicability as rheology modifiers.