On the Microenvironment of Soluble and Cross-Linked Polymers

The properties of the microenvironment of soluble synthetic polymers such as polymethacrylamide (PMA), poly(2-hydroxyethyl methacrylate) (PHEMA), poly(2-vinylpyridine) (P-2VP), poly(4-vinylpyridine) (P-4VP), poly(methyl methacrylate) (PMMA), poly(butyl methacrylate) (PBMA), polystyrene (PS), poly(4[5]-vinylimidazole) (PVIm), and poly(N-2- hydroxypropyl methacrylamide) (PHPMA) and cross-lined polymers were studied by the shift and shape of the band in electronic spectra of a solvatochromic “reporter” molecule embedded in polymer chains. Preferential interaction of parts of the polymer molecule with a reporter and the shielding of interactions between solvent molecules and a reporter molecule of a polymer causes a shift and broadening of its solvatochromic band. This shift is mechanistically interpreted as a change in the polarity of the microenvironment of a polymer in solution in comparison with polarity of the solvent used. 4-(4-Hydroxystyryl)-N-alkylpyridinium-betaine, spiropyran-merocyanine, and l-dimethylamino-5-sulfonamidonaphthalene (Dansyl) reporters were used. In almost all cases the polarity of the polymer microenvironment was lower than that of the solvent. At the same time, the dependence of the nature of the environment on the distance of the reporters from the polymer chain was studied.