Chiroptical Properties of Graft Copolymers Containing Chiral Poly(n-hexyl isocyanate) as a Side Chain

Chiral poly(n-hexyl isocyanate) (PHIC) macromonomers were synthesized by living anionic polymerization of n-hexyl isocyanate (HIC) using the functional initiator sodium N-(4-vinylphenyl)benzamide (Na-4VPBA) in tetrahydrofuran (THF) at -98 degrees C. Polymerization was terminated by (S)-2-acetoxypropionyl chloride using pyridine as a catalyst. Initiator efficiency and aggregation behavior during polymerization were also studied. Chiral PHIC macromonomers with varying molecular weight (MW) were synthesized with a narrow molecular weight distribution (MWD). Graft copolymerization of the chiral PHIC macromonomers was performed in toluene at 80 degrees C under vacuum using free radical polymerization with a 2,2'-azobis(2-methylpropionitrile) (AIBN) initiator. Several experiments were performed to determine the optimum polymerization time for macromonomers and graft copolymers. Formation of the graft copolymer was confirmed using SEC MALLS, H-1 NMR, and circular dichroism (CD). CD spectra showed that graft copolymers adopted a conformation with opposite helical sense and a lower CD intensity as compared with chiral PHIC macromonomers.