文摘
We report a series of cyclopolymerizations of bis(4-vinylbenzoate) monomers through an atomtransfer radical polymerization (ATRP) using chiral ligands. Cyclized polymers showing chiroptical propertieswere produced by polymerization of the racemic bifunctional monomer, rac-2,4-pentanediyl bis(4-vinylbenzoate)(rac-1), and enantiomerically unbalanced bifunctional monomers were recovered, providing substantial evidencefor the enantiomer-selective polymerization of rac-1 mediated through the ATRP with chiral ligands. A comparisonbetween the enantiomerically pure monomers, (2R,4R)-2,4-pentanediyl bis(4-vinylbenzoate) (RR-1) and (2S,4S)-2,4-pentanediyl bis(4-vinylbenzoate) (SS-1), revealed a drastic discrepancy in the rates of their homopolymerizationsduring the ATRP. The enantiomeric copolymerization of RR-1 and SS-1 indicated that the monomer reactivityratio of RR-1 was higher than that of SS-1 for the ATRP with chiral ligands. The results of bothhomopolymerizations and copolymerizations clearly demonstrate the propensity for incorporation of the RR-1enantiomer and thus the enantiomer-selective polymerization in this system. The monomer-structural effects onthe enantiomer-selectivity were examined, and it was concluded that the chirality in the monomer is also essentialfor the enantiomer-selective polymerization as well as the chiral ligands for ATRP. Finally, the viability of thecyclopolymerization in the enantiomer-selective polymerization was proved using mono(4-vinylbenzoate) monomersincapable of cyclizing through the polymerization.
