Synthesis of Functionalized Side-Chain Liquid Crystal Polymers: Polyphenolic Combs

This work studied the synthesis of self-ordering comb polymers containing functionalized side chains. The target polymers in the study had methacrylate backbones with hydroxy-functionalized side chains containing phenolic groups at their termini. The synthesis of the targeted polymers was accomplished in seven steps and involved identifying suitable protecting groups for the phenolic monomers before free-radical polymerization. The various protecting groups explored for this purpose were dimethylthexylsilyl ether (O∑), benzyl carbonate (OCOOBn), trimethylsilyl ether (OTMS), triethylsilyl ether (OTES), diphenylmethylsilyl ether (ODPMS), and tetrahydropyranyl ether (OTHP) groups. Our studies show that ODPMS and OTHP ether groups are best suited to synthesize the functionalized polymers. Deprotection of polymers protected with these groups after free-radical polymerization could be quantitatively accomplished under relatively mild conditions. One of the target polymers and its corresponding functionalized monomer were found to melt into liquid crystalline fluids which exhibited isotropization transitions at higher temperatures. The synthesis of these polymers is significant in the context that mesomorphic behavior is not considered common in organic molecules with functions that can form intermolecular hydrogen bonds. Also these comb polymers may exhibit interesting behavior at interfaces with solid surfaces given the presence of reactive or hydrogen-bond-forming functions in their self-assembling side chains. One example would be their behavior as coupling agents at a composite material interface.