Optically active hydrocarbon polymers with aromatic side chains, 7. Synthesis and properties of copolymers of vinyl aromatic monomers with chiral α-olefins

Optically active alkyl-α-olefins such as (R)-3,7-dimethyl-1-octene ( 1 ), (S)-4-methyl-1-hexene ( 2 ), and (S)-5-methyl-1-heptene ( 3 ) were copolymerized with styrene ( 4 ), 1-vinylnaphthalene ( 5 ) or 2-methylstyrene ( 6 ) by Ziegler-Natta catalysts based on VCl₄, TiCl₄ or TiCl₃ “ARA” and Al[CH₂CH(CH₃)₂]₃ or Al(C₂H₅)₃. Fractionation by solvent extraction as well as optical rotation and differential dichroic absorption (Δε) demonstrate unequivocally the formation of copolymer macromolecules. The isotactic enchainment of the units is supported by IR and X-ray spectra. A remarkable contribution to optical rotation by aromatic units is observed in the copolymers of 1. In addition circular dichroism data relative to the lowest energy π→π^* electronic transition of aromatic nuclei show that aromatic units, when inserted in optically active copolymer macromolecules, assume a preferential chiral conformation.