Synthesis and chiroptical properties of vinyl polymers containing laterally attached 4,4″-digalactosyloxy-p-terphenyl side groups

The synthesis and chiroptical properties of two novel optically active helical glycopolymers, poly{2,5-bis[4′-(2,3,4,6-tetra-O-acetyl-beta-D- galactosyloxy)phenyl]styrene} (PTAGPS) and poly{2,5-bis[4′-(β-D- galactosyloxy)phenyl]styrene} (PGPS), were reported. The former was obtained via radical polymerization of 2,5-bis[4′-(2,3,4,6-tetra-O-acetyl-β-D- galactosyloxy)phenyl]styrene (TAGPS), while the later by either direct radical polymerization of deacetylized monomer, 2,5-bis[4′-(β-D- galactosyloxy)phenyl]styrene (GPS), or deacetylation of PTAGPS. PTAGPS had a thermodynamically controlled conformation (TCC) regardless of the nature of the solvent where it was polymerized. However, PGPS prepared via radical polymerization of GPS in dimethyl sulfoxide (DMSO) had TCC, and that in N,N-dimethylformamide (DMF) had a kinetically controlled conformation (KCC), which could undergo an irreversible evolution to TCC by annealing in DMSO. PGPS derived from PTAGPS showed the essential chiroptical characteristics of both its precursor and PGPS with KCC obtained in DMF. These results demonstrated that achiral acetyl groups in the monomer molecule had a remarkable effect on the formation of chiral secondary structure of the polymer.