Smectic Aggregates of Sheet-Like Side-Chain Liquid Crystalline Polyacetylenes Directly Formed During Solution Polymerization

We have successfully synthesized two side-chain liquid crystalline polyacetylenes (denoted as P3-5 and P2-5) with the mesogenic units based on a phenyl-ester-phenyl motif directly linked to the semirigid polyacetylene backbone in a terminal-on mode without flexible spacer During the polymerization catalyzed by Rh(nbd)[B(C6H5)(4)] in toluene, the resultant polymers (or oligomers) automatically precipitate out of the polymerization solution as red solids, which cannot be dissolved in common organic solvents Wide-angle X-ray diffraction results confirm that the polymer precipitates possess a smectic (or sanidic) structure, suggesting that the molecules without flexible spacers are sheet-like and can stack parallel to each other during polymerization We in situ monitored the solution polymerization and the aggregation processes using UV visible and H-1 NMR spectroscopy methods The experimental results indicate that after leaching a critical molecular weight the P3-5 and P2-5 molecules self-aggregate in solution and that the smectic aggregation proceeds during the solution polymerization An apparent first-order polymerization kinetics can be obtained after the polymerization and aggregation slowed down The resultant polymers are cis-rich with the main-chain absorption at similar to 455 nm This implies that a considerably long effective conjugation length is achieved in the sheet-like cis-rich polyacetylene derivatives