Fluorescence Studies of Hydrophobic Association of Random Copolymers of Sodium 2-(Acrylamido)-2-methylpropanesulfonate and N-Dodecylmethacrylamide in Water

Abstract

Intrapolymer self-association of random copolymers of sodium 2-(acrylamido)-2-methylpropanesulfonate (AMPS) and N-dodecylmethacrylamide (DodMAm) with varying compositions in aqueous solution was investigated by various fluorescence techniques. The polymers were labeled with 1 mol % of naphthalene (Np) or pyrene (Py) or doubly labeled with Np (4 mol %) and Py (1 mol %). Vibronic fine structures of Py fluorescence, lifetimes of Np and Py fluorescence, intrapolymer nonradiative energy transfer (NRET) from singlet excited Np to ground-state Py labels, and fluorescence quenching by thallium cations were investigated as a function of the DodMAm content (f Dod) in the copolymers with or without added salt. Results from all these fluorescence studies indicate that with increasing f Dod, hydrophobic association commences at f Dod ≅ 20 mol % in pure water and at f Dod ≅ 10 mol % in 0.1 M NaCl, showing a saturation tendency near f Dod ≅ 40 mol % in the salt solution. In contrast, viscosity data show that the polymer size markedly decreases in the regime 5 < f Dod < 20 mol % owing to intrapolymer hydrophobic association of dodecyl groups. This decrease in the macroscopic size of the polymer in the low f Dod regime could not be detected by any fluorescence techniques employed. Although the viscosity data do not show any further contraction of the polymer chains at f Dod > 20 mol %, the NRET results indicate a considerable increase in the compactness of polymer chains at f Dod > 20 mol %. The combination of these fluorescence techniques proved to provide a sensitive tool to detect hydrophobic associations and conformational changes in the hydrophobically modified polymers, while viscosity reflects only global changes in the polymer size.

Micellar Synthesis and Properties of Hydrophobically Associating Polyampholytes

“…This behavior is in agreement with that previously reported for other hydrophobically modified water-soluble polymers with a high number of ionic sites, for which the degree of association is strongly lowered compared to that of neutral and low-charge homologues, [26,28,29] or which exhibit mainly intramolecular associations. [19,30,65,66] Although the associative behavior for this series is not much pronounced, the fluorescence measurements indicate the existence of hydrophobic microdomains ( Table 2). The I 1 /I 3 value in the 2 wt.-% 3-D4 aqueous solution is similar to that obtained for 1-D1 sample.…”

Quantifying the Level of Intermacromolecular Interactions in Ethylene–Propylene Copolymers by Using Pyrene Excimer Formation

“…2,12,19,20 Fischer-Scientific. Two ethylene-propylene copolymers were supplied by Afton Chemical Corporation.…”

Self-assembly of a series of random copolymers bearing amphiphilic side chains

“…So far, experimental results indicate that some architectural factors, such as the types of hydrophobic and ionic monomers [12][13][14][15][16][17], polymer composition [15][16][17][18][19][20][21], the degree of polymerization of polymer chains [22], and the type of spacer between hydrophobe and polymer backbone [17,[23][24][25][26][27] are important to determine the characteristics of side chain interaction of random polymers. The side chains may undergo intramolecular or intermolecular interaction, or both types of associations may take place synchronously to form various types of micelle-like assemblies.…”