Hydrophobically modified water-soluble polymers have been prepared by radial copolymerization of acrylamide and ethylphenylacrylamide as the hydrophobic comonomer.Three methods of synthesis in aqueous media have been investigated: (i) a "micellar" process in which the presence of a surfactant ensures the solubilization of the hydrophobic monomer; (ii) a "homogeneous" process wherein a miscible cosolvent is used; (iii) a "heterogeneous" process, without additive to solubilize the insoluble monomer. The properties of the copolymers in dilute and semidilute aqueous solutions strongly depend on the conditions of the synthesis.Copolymers prepared by the homogeneous and heterogeneous processes behave like homopolyacrylamide; i.e., hydrophobic interactions do not occur significantly. Copolymers obtained by micellar copolymerization exhibit improved thickening properties due to intermolecular hydrophobic associations. These differences can be directly related to the copolymer microstructure, i.e., to a random or blocky distribution of the hydrophobic units. The blockiness of the copolymer can be adjusted by varying the [hydrophobe]/[micelle] ratio at a constant hydrophobe level. Thus, it is possible to control the association degree and therefore the rheological properties. Fluorescence studies, using pyrene as a probe, reveal the formation of hydrophobic microdomains which corroborate the rheological results.
Polyaniline was synthesized in the presence of lignosulfonic acid to yield a product (LIGNO-PANI) that is water-dispersible. Several samples ranging from 0 to 70% lignosulfonate (LS) were prepared. These samples were then evaluated for differences in dispersibility and conductivity. As the percent of LS in the samples was increased, the water-dispersibility of the LIGNO-PANI also increased. The particle size of the samples as well as the conductivity of the samples decreased with increasing percentages of LS in the samples.After extensive washings, however, the conductivity remained fairly constant ($ 0.4 S/cm) regardless of the amount of LS in the samples. Additionally, elemental analysis, TGA, and IR data were used to demonstrate that the LS is grafted to polyaniline during the synthesis of LIGNO-PANI.
Dioctadecyldimethylammonium chloride (DODMAC) dispersions containing high concentrations of CaCl2 were stabilised using cationic polyelectrolytes with terminal hydrophobic anchors. The cationic polyelectrolytes were based on quarternised poly(vinyl‐2‐pyridine). The stability of the dispersions was dependent on the molecular weight of the polymer and the length of the hydrocarbon anchor. The amount of polyelectrolyte required to stabilise the dispersions was dependent on the type of polymer used and the concentration of salt in the dispersion. Some of the polymers were also capable of stabilising dispersions that were heated above the Lβ‐Lα phase transition temperature of the DODMAC vesicles. The polyelectrolytes that stabilised the dispersions most successfully in this study had molecular weights of about 10000‐20000 and hydrocarbon anchors containing 16 carbon atoms.
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