Flexibility of Poly(alkyl methacrylate)s Characterized by Their Persistence Length Determined through Pyrene Excimer Formation.

A series of poly(alkyl methacrylate)s and poly(oligo(ethylene glycol) methyl ether methacrylate)s labeled with 1-pyrenebutanol were referred to as the PyC 4 -PC n MA samples with n = 1, 4, 6, 8, 12, and 18 and the PyC 4 -PEG n MA samples with n = 0-5, 9, 16, and 19, respectively. Pyrene excimer formation (PEF) upon the encounter between an excited and a ground-state pyrenyl labels was employed to determine their persistence length ( l p ) in o -xylene. The fluorescence decays of the PyC 4 -PC n MA and PyC 4 -PEG n MA samples were acquired and analyzed with the fluorescence blob model to yield the number ( N blob ) of structural units in the volume probed by an excited pyrenyl label. N blob was found to decrease with an increasing number ( N S ) of non-hydrogen atoms in the side chain, reaching a plateau for the PyC 4 -PEG n MA samples with a longer side chain ( n = 16 and 19). The N blob values were used to determine l p . The l p values for the PyC 4 -PC n MA and PyC 4 -PEG n MA samples increased linearly with increasing N S 2 as predicted theoretically, which agreed with the l p values obtained by viscometry for a series of PC n MA samples. The good agreement between the l p values retrieved by PEF and viscometry served to validate the PEF-based methodology for determining l p for linear polymers.