Chirality induction in cyclopolymerization XVI. Synthesis of optically active poly(methyl acrylate-co-dimethyl fumarate) by radical cyclopolymerization of asymmetrical nonconjugated diene having chiral pentanediol

Abstract

The molecular design and synthesis of asymmetric bifunctional monomers, 3-(S)-acryloyloxy-1-(S)-methyl-butyl methyl fumarate (1a) and 3-(R)-acryloyloxy-1-(R)-methyl-butyl methyl fumarate (1b), have been carried out in terms of a novel method of producing optically active polymers based on cyclopolymerization. The polymerization of 1 proceeded via the cyclopolymerization mechanism to yield the cyclopolymer 2 with the extent cyclization of 0.87-0.96 when the monomer concentration ([M]) in the feed was 0.3 mol L-1 or less. The number-average molecular weight (Mn) decreased with a decrease in the [M] from 8300 to 3300 for polymer 2a and from 4200 to 2400 for polymer 2b. The specific rotation ([α]43523, c 1.0, CHCl3) of the resulting polymers changed from +19.3° to +33.4° for 2a and from -26.2° to -34.9° for 2b. In order to confirm the chirality induction, the chiral pentanediyl moiety was removed from polymer 2 by saponification, and the hydrolyzed polymer was treated with diazomethane to give poly(methyl acrylate-co-dimethyl fumarate) (3). The Mn was 2200-2600 for 3a and 2300-5700 for 3b, and the template-free polymers showed an optical activity with a specific rotation that ranged from -1.4° to -9.3° for 3a and from +7.5° to +8.8° for 3b. The CD spectra of 3a showed a positive Cotton effect whereas 3b showed a negative Cotton effect which is the mirror image of 3a. The optical activity of polymer 3 should be attributed to the threo-erythro sequence of the methyl acrylate and dimethyl fumarate units.