A new series of amphiphilic polymers (amphipols) with varied molecular characteristics was prepared, and their properties in aqueous media were examined by static and dynamic light scattering techniques. These polymers are short poly(sodium methacrylate) chains of various molecular weights and tacticities, modified with different degrees of n-octylamine as copolymers of two distinct hydrophobe distribution sequences (random vs multiblocky). To synthesize the parent poly(methacrylic acid) (PMAA) prior to hydrophobic modification, tert-butyl methacrylate was polymerized under the controlled conditions of atom transfer radical polymerization (ATRP) to yield after deprotection the syndiotactic-rich PMAA of targeted molar masses (12-28 kg mol -1 ) and low polydispersity indexes (1.08-1.19). Under similar conditions of ATRP and deprotection, a well-defined isotactic-rich PMAA was obtained from triphenylmethyl methacrylate. The amphipol carrying octyl side chains randomly distributed along the polymer main chain was produced by coupling the parent PMAA with n-octylamine in an organic medium (N-methylpyrrolidone). In contrast, the coupling reaction of PMAA in aqueous media, with the n-octylamine solubilized by sodium dodecyl sulfate, gave the amphipols bearing octyl groups distributed in a multiblocky fashion. The highly controlled hydrophobe distribution sequence and polymer tacticity were confirmed by 1 H and 13 C NMR spectroscopic techniques. All polymers in aqueous solutions form nanoparticles with the structure strongly determined by the polymer microstructure and composition. In the case of random graft amphipol, the polymer self-assembles and preferentially forms small aggregates of 1-2 polymer chains on average with a hydrodynamic radius of ∼3 nm. In cases of the multiblocky graft amphipols, well-defined nanoscaled self-assemblies are formed but from multiple polymer chains (aggregation number ) ∼17), with a drastic increase in the hydrodynamic radius (∼13 nm). Comparing to the effects due solely to the hydrophobe distribution sequence, the increments in structural parameters of the amphipol self-assemblies are only slightly enhanced when concurrently improving the polymer isotacticity or increasing the polymer molar mass. All results point to the critical impact of hydrophobe distribution sequence on the self-assembly of methacrylate-based amphipols in aqueous solutions.

The temperature-and pH-induced coil-globule transition has been studied in dilute aqueous solutions for different copolymers of N-isopropylacrylamide (NIPAM) and N-glycine acrylamide (Gly) using turbidimetry, scanning microcalorimetry, fluorescence spectroscopy, and dynamic light scattering. The four different samples prepared are a copolymer of NIPAM and Gly (PNIPAM-Gly), a copolymer of NIPAM, Gly, and N-(1-pyrenyl)methylacrylamide (PNIPAM-Gly-Py), and their hydrophobically modified (HM) derivatives, namely a copolymer of NIPAM, Gly, and N-(n-octadecylacrylamide) (PNIPAM-Gly-C 18) and a copolymer of NIPAM, Gly, and N-[4-(1-pyrenyl)butyl]-N-n-octadecylacrylamide (PNIPAM-Gly-C18Py). Polymeric micelles 16 ( 2 nm in diameter were detected in cold solutions of the hydrophobically modified polymers. All polymers underwent pH-dependent phase separation upon heating. Endotherms with enthalpies on the order of the strength of hydrogen bonds were observed at temperatures concurring, in the case of PNIPAM-Gly and PNIPAM-Gly-Py, with the transition temperatures detected by classical cloud-point measurements. Discrepancies between the two values were detected in the case of the hydrophobically modified polymers. Evidence from fluorescence spectroscopy, corroborated by dynamic light scattering and microcalorimetry data, suggests that the pH-or temperature-stimulated coil to globule collapse of the polymer main chain does not trigger the disruption of the hydrophobic core of HM-polymer micelles.

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The rheology of solutions of a cationic cellulose ether (JR400) and either sodium poly(2-acrylamido-2-methylpropanesulfonate) (PAMPS) or a copolymer of sodium 2-acrylamido-2-methylpropanesulfonate and N-n-dodecylmethacrylamide (PAMPS-Dod) has been examined over a wide composition range in the semidilute regime (10 g L-1) by steady shear and time-dependent steady shear measurements. Miscible combinations of pairs of oppositely charged polyelectrolytes form in two composition domains:  (1) a polyanion-poor region which exhibits shear thinning characteristics and (2) a polyanion-rich region which presents Newtonian behavior at low shear rates and, as the shear rate is increased, passes through a shear-thickening region before exhibiting a sharp decrease in viscosity. The latter fluids exhibit significant thixotropy, which is shown to depend on the delay time between measurements and on the composition of the fluids. Models based on electrostatically driven interactions between two oppositely charged polyelectrolytes poorly matched in terms of size, rigidity, and charge density are proposed to account for the unusual rheological behavior of the polyelectrolyte complexes under study.