Water-soluble copolymers: 26. Fluorescence probe studies of hydrophobically modified maleic acid-ethyl vinyl ether copolymers

Abstract

Pyrene fluorescence spectra and lifetimes have been employed to study the pH-induced conformational transitions of maleic acid-ethyl vinyl ether copolymers that have been hydrophobically modified with varying amounts of 4-butylaniline (4-BA). Results indicate that those copolymers containing up to 50 mol% 4-BA (relative to the total number of maleic acid groups) undergo a transition from a highly collapsed ‘hypercoil’ conformation at low degrees of ionization (α) to an open, hydrated conformation at high α. In contrast, a copolymer containing 70 mol% 4-BA moieties forms compact, hydrophobic microdomains over the entire range of α. Fluorescence quenching of the pyrene probe by Tl + and nitromethane indicates that the accessibility of these microdomains is related to α and/or the degree of hydrophobe incorporation. Diffusion coefficients and effective coil diameters of these polymers as determined via dynamic light scattering measurements indicate an increasing degree of intramolecular association with increasing hydrophobe content at high α, while fluorescence measurements indicate no such interactions. It is suggested that, though the pyrene probe may associate with the hydrophobic regions of these polymers, it is not adequately ‘protected’ from the bulk aqueous solution for fluorescence enhancement to occur.