Long-Range, Polymer Chain Dynamics of a "Stiff" Polymer. Fluorescence from Poly(isobutylene-alt-maleic anhydride) with N-(1-Pyrenylmethyl)succinimide Groups

Abstract

The steady-state fluorescence (SSF) spectra and time resolved fluorescence (TRF) decays of five poly(isobutylene-alt-maleic anhydride) copolymers (PIMA), randomly labeled with N-(1-pyrenyl methyl)succinimide groups (Py-PIMA), have been analyzed in order to describe their long-range, polymer chain dynamics (LRPCD) and to assess the stiffness of the PIMA backbone compared to that of a series of poly(alkyl methacrylate)s whose LRPCD had already been investigated. The SSF spectra, recorded under dilute concentration conditions where only intrachain events are important, show that the intensity ratio of pyrenyl excimer to pyrenyl monomer emission (i.e., (I-E/I-m)(SSF)) increases linearly with increasing pyrenyl content as a result of increased pyrenyl pyrenyl contacts and diffusive encounters. The slope of the straight line, m(I-E/I-M), that reflected the efficiency of pyrenyl excimer formation for Py-PIMA, was found to be 60% smaller than for even poly(octadecyl methacrylate) (PC18MA), a polymer exhibiting slow LRPCD due to its long, bulky side chain. Analyses of the SSF spectra allowed separation of the averaged behavior of five different pyrenyl species in the Py-PIMA polymers, although only two of them were reflected in the LRPCD of PIMA. In addition, the fluorescence decays of the pyrenyl monomer and excimer, when fitted globally according to the model free analysis (MFA), yielded the average rate constant < k(MF)>(blob) of pyrenyl excimer formation that directly represents the LRPCD of Py-PIMA. After having conducted two tests that confirmed the validity of the parameters retrieved from the MFA of the TRF decays, < k(MF)>(blob) for Py-PIMA was compared to < k(MF)>(blob) of nine other polymers. The result of this comparison leads us to conclude that the PIMA backbone is extremely stiff in THF. This study demonstrates the ability of the MFA of fluorescence decays acquired from polymers randomly labeled with pyrenyl groups to characterize quantitatively the LRPCD of even extremely stiff polymers.