Maleated ethylene-propylene random copolymers: Determination of the microstructure and association level by fluorescence spectroscopy

A maleated ethylene-propylene (EP) random copolymer was labeled with the fl uorescent dye 1-pyrene-butanoicacid hydrazide to yield EP-Py. Fluorescence spectroscopy was used to determine the microstructure of EP-Py (i.e., the d istribution of the pendants along the chain) in THF where little associatio n is expected to occur between the polar pendants. In hexane, an apolar sol vent, associations take place between the polar pendants acid the associati on level of EP-Py (i.e., fractions of pendants, which are associated and un associated) was estimated by analyzing quantitatively both the monomer and the excimer fluorescence decays. The ability of pyrene to form an excimer w as used to carry out this study. The excimer formation process was monitore d by using a combination of two models, namely the sequential model and the blob model. Both monomer and excimer decays were analyzed in order to comp letely describe the distribution of pyrene groups. It was found that 70% of all pyrene groups are located at small distances from one another and form excimer readily. In apolar hexane, 87% of all pyrene groups are involved i nto loose pyrene aggregates, held together via polar interactions between t he succinic anhydride groups.