The synthesis and rheological behavior of hydrophobically modified copolymers based upon N,N‘-dimethylacrylamide (DMAM) containing dodecyl or octadecyl groups are described. The polymers were synthesized by free radical copolymerization in homogeneous solutions of toluene. This synthesis method ensured that the hydrophobic groups were incorporated individually into the copolymer, i.e., in a nonblocky fashion. This method contrasts with the more commonly produced hydrophobically modified polyacrylamides, synthesized by a micellar polymerization technique, resulting in multiblock structures. Associative behavior of the DMAM copolymers in water was investigated by viscosity measurements. Significant enhancement in viscosity was measured in the semidilute unentangled and entangled regimes. Viscosity enhancement was attributed to the formation of intermolecular hydrophobic aggregates, which act as transitory physical cross-links. While it is well established in the literature that blocky copolymers containing hydrophobic groups can significantly enhance solution viscosity, the same effect produced by hydrophobically modified acrylamide polymers based on randomly copolymerized hydrophobic and hydrophilic monomers is less well-known or understood. The results presented in this paper demonstrate that if long alkyl chains are used as stickers, then hydrophobic aggregation between neighboring chains can promote viscoelastic properties in the semidilute regime. The rheological behavior of these statistical copolymers can be described on the basis of recent theoretical models specially developed for solutions of associating polymers.

The modification of titanium alkoxides by chemical reactions with ligands yields complexes or molecular clusters that are substantially different from those of the parent alkoxides. In this study, we investigate the structural evolution of powders and thin films prepared from two titanium oxo‐alkoxyacylate clusters with different oxo‐core structures [Ti6(μ3‐O)2(μ2‐O)2](CH3COO)8(μ2‐OiPr)2(OiPr)6 and [Ti6(μ3‐O)6](μ‐RCOO)6(OiPr)6 ([6,4] and [6,6], respectively) as a function of annealing temperature. The structural evolution of powders and thin films prepared from the corresponding parent alkoxide Ti(OiPr)4 (TiP) were also investigated for comparison. In all powders, the amorphous‐to‐anatase transformation occurred upon heating to 400°C. In sharp contrast, the anatase‐to‐rutile transformation of the powder prepared from the [6,6] cluster was significantly inhibited compared with the conventionally derived powder, with no rutile being detected even after annealing at 800°C for 1 h. This was attributed to the small crystallite size in the [6,6]‐derived powder, which is lower than the critical size previously reported for the anatase‐to‐rutile transformation in similar sol–gel‐derived materials. In thin films, the amorphous‐to‐anatase phase transition also occurred at temperatures as low as 400°C for coatings deposited from conventional TiP precursor and [6,4] cluster solutions. However, in contrast to the corresponding powders no rutile nucleation occurred even at 800°C in either film.

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ABSTRACT:A cathodic, aqueous-based technique for producing uniform, thin, passive films of poly(methyl methacrylate) and poly(glycidylacrylate) on stainless steel electrodes was developed. The films were chemically characterized by Fourier transform infrared spectroscopy, NMR spectroscopy, and differential scanning calorimetry. The thickness (quantified by ellipsometry) and morphology of the films were dependent on the electrolysis time and potential and were also influenced by the individual monomer properties.

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