Study of a Polymeric Network by Dynamic Fluorescence Quenching Using a Blob Model

The association behavior of a maleic anhydride grafted and pyrene labeled ethylene−propylene random copolymer was studied using fluorescence spectroscopy. The labeling was achieved with 1-pyrenebutanoic acid hydrazide via the grafted anhydride groups. The resulting polar grafts induced intra- and intermolecular associations among the polymer chains in apolar solvents. This association process was studied using steady-state and time-resolved fluorescence spectroscopy as a function of polymer concentration. Due to the high complexity of the polymer system, an improved approach of handling the time-resolved fluorescence data had to be introduced. Thus, the quantitative analysis of the fluorescence decays was carried out using a novel model in which the polymer network is divided into blobs among which the chromophores distribute themselves randomly, according to a Poisson distribution. Results show that, as the polymer concentration is increased, the number of polar group aggregates increases. However, the local concentration of aggregated polar groups in the polymer network does not change. This indicates that as polymer concentration is increased, either that there are only a few polymer aggregates in the solution that increase in size and keep the concentration of polar junctions constant throughout the polymeric network or that more polymer aggregates are formed. This latter process would be reminiscent of micelle formation. This behavior is observed until the overlap concentration (c* = 10−20 g/L), above which newly formed polar aggregates contribute to increasing the local aggregate concentration.