Fluorescence Lifetime Distributions of Labeled Amorphous Polymers in Bulk

Abstract

Polystyrene, poly(methylmethacrylate), poly(cyclohexyl methacrylate) and poly(1-butylmethacrylate) were labeled with anthryl groups by copolymerization. Films of labeled polymers as well as blends of them with unlabeled polystyrene samples of different polydispersity and molecular weight, were prepared by solvent casting. The time resolved emission of anthryl groups in those films was measured by Single Photon Counting with front face excitation at the standard 30° incident angle and with much lower incident angles to photoselect chromophores on the polymer-air surface. Fluorescence decays were fitted with bimodal fluorescence lifetime distributions, which were analyzed taking into consideration some polymer characteristics and the compatibility of polymer blends. It was thus concluded that solid-like and liquid-like environments are both in the bulk and in the surface of the film although liquid-like domains are more frequent on the surface than in bulk. Polymer Tg determines the position of the two modes and polydispersity justify the broadness of the modes in the fluorescence lifetime distribution.