Amphiphilic derivatives of carboxymethylcellulose: Evidence for intra-and intermolecular hydrophobic associations in aqueous solutions

The intra and/or intermolecular associations of CMC-g-poly(N,N-dihexylacrylamide) copolymers in aqueous systems were studied by static (SLS) and dynamic (DLS) light scattering, viscometry, and rheology. The copolymers containing 1 to 6 mol % of hydrophobic groups were synthesized by free radical micellar copolymerization. Their associations were evaluated in different solvents (0.5 M NaCl, synthetic formation water (SFW) and Milli-Q water), as a function of the polymer concentration, hydrophobicity, temperature, and ionic strength. Rheological behavior was investigated in SWF at 55 degrees C. The results indicated that polymer-polymer interactions increase with the increase of the hydrophobic group lengths grafted onto the CMC backbone. The copolymer with the highest concentration of hydrophobic groups (6 mol %) had the lowest values of intrinsic viscosity, weight-average molar mass (M-w), and hydrodynamic radius (RH), indicating a strongly compact structure due to intramolecular hydrophobic associations. The rheological behavior of the copolymers in SFW showed that the high polymer concentration and the high temperature together with the intermolecular hydrophobic interactions and the bridges formed between divalent cations and carboxilate groups were not enough to promote a significant increase in the size of the aggregates.