Study of a polymeric network by dynamic fluorescence quenching using a blob model

The association behavior of a maleic anhydride grafted and pyrene labeled e thylene-propylene random copolymer was studied using fluorescence spectrosc opy. The labeling was achieved with 1-pyrenebutanoic acid hydrazide via the grafted anhydride groups. The resulting polar grafts induced intra- and in termolecular associations among the polymer chains in apolar solvents. This association process was studied using steady-state and time-resolved fluor escence spectroscopy as a function of polymer concentration. Due to the hig h complexity of the polymer system, an improved approach of handling the ti me-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 chromophore s distribute themselves randomly, according to a Poisson distribution. Resu lts show that, as the polymer concentration is increased, the number of pol ar group aggregates increases. However, the local concentration of aggregat ed polar groups in the polymer network does not change. This indicates that as polymer concentration is increased, either that there are only a few po lymer aggregates in the solution that increase in size and keep the concent ration of polar junctions constant throughout the polymeric network or that more polymer aggregates are formed. This latter process would be reminisce nt of micelle formation. This behavior is observed until the overlap concen tration (c* = 10-20 g/L), above which newly formed polar aggregates contrib ute to increasing the local aggregate concentration.