Chiral copolymers of (R)‐N‐(1‐phenylethyl) methacrylamide and 2‐hydroxyethyl methacrylate: copolymerization characteristics and chiroptical properties

Abstract

AbstractThe aim of this investigation was the copolymerization of a chiral monomer, (R)‐N‐(1‐phenylethyl) methacrylamide, with an achiral monomer, 2‐hydroxyethyl methacrylate (HEMA). The copolymerization characteristics as well as the chiroptical properties (optical rotation and circular dichroism) and their variation with copolymer composition and temperature are discussed. The copolymers are statistical and enriched in HEMA. The monomer reactivity ratio of the chiral monomer (r1) is 0.133 whereas that of HEMA (r2) is 1.042 based on the Kelen–Tudos method. The sequence of consecutive chiral monomer units predominates for a feed composition between 0.5 and 0.9 (mole fraction). On the other hand, the sequence of HEMA is uniform and it predominates for a feed composition of around 0.5 (mole fraction). The chiroptical properties of the copolymers do not vary linearly with the content of chiral units in the copolymers. The optical rotation and circular dichroism attain optimum values above 30–40 mol% of chiral monomer units in the copolymers. However, the circular dichroism of the copolymers varies linearly with the temperature. The chiral monomer being a more bulky structure is less reactive than HEMA. The nonlinear variation of chiroptical properties of the copolymers with the content of chiral units may be due to the secondary interaction in the copolymers associated with the hydrogen bonding involving the amide linkage (CONH) present in the pendant chromophore of the chiral monomer as well as the hydroxyl pendant group of HEMA and also the aromatic π–π interaction. Copyright © 2009 Society of Chemical Industry