Enantiomer-Selective Radical Polymerization of Bis(4-vinylbenzoate)s with Chiral Atom Transfer Radical Polymerization Initiating Systems

• Published in: Macromolecules 2007-12, Vol.40 (26), p.9272-9278
• Main Authors: Narumi, Atsushi, Sakai, Ryosuke, Ishido, So, Sone, Masako, Satoh, Toshifumi, Kaga, Harumi, Nakade, Hiroshi, Kakuchi, Toyoji
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Polymerization; Preparation, kinetics, thermodynamics, mechanism and catalysts
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma071162j

We report a series of cyclopolymerizations of bis(4-vinylbenzoate) monomers through an atom transfer radical polymerization (ATRP) using chiral ligands. Cyclized polymers showing chiroptical properties were 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 evidence for the enantiomer-selective polymerization of rac-1 mediated through the ATRP with chiral ligands. A comparison between 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 homopolymerizations during the ATRP. The enantiomeric copolymerization of RR-1 and SS-1 indicated that the monomer reactivity ratio of RR-1 was higher than that of SS-1 for the ATRP with chiral ligands. The results of both homopolymerizations and copolymerizations clearly demonstrate the propensity for incorporation of the RR-1 enantiomer and thus the enantiomer-selective polymerization in this system. The monomer-structural effects on the enantiomer-selectivity were examined, and it was concluded that the chirality in the monomer is also essential for the enantiomer-selective polymerization as well as the chiral ligands for ATRP. Finally, the viability of the cyclopolymerization in the enantiomer-selective polymerization was proved using mono(4-vinylbenzoate) monomers incapable of cyclizing through the polymerization.