Determination of the rate constant for chain insertion into poly(methyl methacrylate)-block-poly(methacrylic acid) micelles by a fluorescence method

Poly(methyl methacrylate)-block-poly(methacrylic acid) (PMMA-b-PMAA) with and without pyrene labels attached to the end of the PMAA block have been synthesized and characterized. These polymers formed micelles with PMAA as the core in ethyl acetate/methanol mixtures when the ethyl acetate volume fraction was higher than 80%. After mixing a micelle solution of PMMA-b-PMAA without pyrene labels, i.e., polymer I, with a unimer solution of the sample with pyrene, i.e., polymer II, the fluorescence intensity I-Py(t) of pyrene increased with time. This was caused by the insertion of the pyrene group of polymer II chains into the rigid core of polymer I micelles. The pyrene fluorescence quantum yield is higher in a more rigid environment due to the reduced quenching of pyrene fluorescence by oxygen and the possible suppression of certain nonradiative deactivation pathways. A kinetic model has been proposed for describing the chain insertion process. Fitting the experimental fluorescence intensity data using the derived expression for I-Py(t) allowed the first determination of the rate constant k(n) for diblock copolymer chain insertion into micelles.