Helix-sense-selective free radical polymerization of 1-phenyldibenzosuberyl methacrylate

The helix-sense-selective free radical polymerization of 1-phenyldibenzosuberyl methacrylate was carried out in toluene at 40 or 50 degrees C under chiral reaction conditions which involve (1) (-)-dimenthyl peroxydicarbonate and (-)-o-carbomenthoxybenzoyl peroxide as an initiator, (2) (-)- and (+)-menthol, (+)-neomenthol, and (+)-1-phenyl-1-butanol as a reaction solvent (additive), (3) (+)- and (-)-neomenthanethiol and (-)-menthanethiol as a chain transfer agent, and (4) (-)-phenyl-2-pyridyl-o-tolylmethyl methacrylate as a comonomer for copolymerization. Highly isotactic, optically active polymers having a helical conformation with excess light- or left-handed helicity were obtained, In the polymerization using an optically active initiator, helix-sense-selection appeared to lake place through primary radical termination. The helix-sense-selection in the polymerization in the presence of the optically active alcohols and thiols was found to involve chain transfer process. In polymerization using thiols, both hydrogen transfer reaction from a thiol to a growing radical and initiation by thio radical were suggested to be responsible for the selectivity. In the case of the copolymerization, the optically active monomeric unit incorporated into the polymer chain was found to induce excessive single handed helicity where the selected helicity reversed depending on the amount of the incorporated optically active monomeric units.