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, 1 H 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.