Fluorescence studies of the self‐organization of a cholesterol‐bearing polymethacrylate in n‐hexane solution

A copolymer of cholesteryl 6‐(methacryloyloxy)hexanoate and a small amount of (1‐pyrenylmethyl) 6‐(methacryloyloxy)hexanoate (Py‐C₅‐MA) was prepared by free radical copolymerization. A copolymer of 1‐eicosanylmethacrylate and a small amount of Py‐C₅‐MA was also prepared as a reference copolymer. A wide‐angle X‐ray diffraction pattern for an n‐hexane solution of the cholesterol(Chol)‐containing copolymer showed a peak corresponding to a spacing of 5.3 Å. In n‐hexane, the hydrodynamic radius (R_h) for the Chol‐containing copolymer (M_w = 7.8 × 10⁴) was 8.1 nm, while that of the eicosanyl‐containing copolymer (M_w = 4.9 × 10⁴) was 9.6 nm, R_h for the former being smaller than that for the latter, although M_w for the former was higher than that of the latter. ¹H‐NMR spectra of the Chol‐containing polymer in n‐hexane‐d₁₄ indicated a strong restriction of local motions of pendant Chol groups. Fluorescence spectra of the Chol‐containing copolymer in n‐hexane indicated that each pyrene group was isolated from others. In n‐hexane/benzene mixed solutions of the Chol‐containing polymer, the ratio of the intensity of the excimer relative to the monomer emission decreased with increasing the ratio of n‐hexane in the mixed solvent. Electron transfer from N,N‐dimethylaniline to singlet‐excited pyrene chromophores was suppressed in the Chol‐containing copolymer in n‐hexane. The pyrene chromophores exhibited a long triplet lifetime in n‐hexane. These observations led us to conclude that Chol groups formed stacks in n‐hexane, and that the pyrene chromophores were trapped in the Chol stacks, leading to the “protection” of pyrene from the bulk phase. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 47–58, 1999