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

Abstract

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 °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 °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, 1H 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.