Study of Poly(methyl methacrylate) Stereocomplex Formation by Nonradiative Energy Transfer and by Time-Resolved Fluorescence Spectroscopy

Abstract

Poly(methyl methacrylate)s labeled with a fluorophore donor, carbazole (C), or acceptor, anthracene (A), have been prepared by free radical, anionic, and coordination polymerization, yielding atactic (a), isotactic (i), and syndiotactic (s) polymers. Nonradiative energy transfer (NET) was used to study polymer association in solutions. The efficiency of NET for mixtures of labeled tactic poly(methyl methacrylate)s (CPOL = 5.00 g L-1; CC = 2.61 × 10-4 M; CA = 6.00 × 10-4 M) in dimethylformamide and dioxane was 0.20 and 0.10, respectively. For a mixture of atactic polymers, the efficiency of NET in the same solvents under similar conditions is much lower. The efficiency of NET for a mixture of labeled atactic poly(methyl methacrylate)s increases with increasing polymer concentration and is nearly independent of concentration for a mixture of labeled tactic polymers. The time-dependent decays of fluorescence anisotropy show that stereocomplexation causes an increase in rotational correlation times of carbazole and anthracene fluorophores. The rotational correlation time of carbazole fluorophore as a part of a stereocomplex is 25.5 and 19.1 ns in dimethylformamide and dioxane, respectively, and shorter than 2 ns in noncomplexing solvents.