The peculiarities of physical network formation in carboxyl-containing poly(dimethylcarbosiloxane)

An unusual effect of physical network formation during heating or at room temperature alter previous heating was found for originally liquid poly(dimethylcarbosiloxane) containing 0.5 – 2.5 mol% of side carboxyl groups by means of the measurement of its Theological properties. The reason for this behaviour is supposed to be the predominance of intramolecular hydrogen bonding of COOH groups in original polymer and the intra– to Intermolecular bonds rearrangement during heating. The alternative reason can be the microphase separation with domains of COOH groups. The reversibility of the network is confirmed by the decrease in the elasticity modulus, development of irreversible deformation on further heating and by break-up of Junctions on the addition of small amounts of polar liquids.     

Hydrophobically associating water‐soluble polymers; a dramatic growth of solution viscosity and the specificity of physical gel formation

The rheological properties of dilute and semidilute solutions (viscosity) and physical gels (elasticity modulus) of hydrophobically modified self‐associated binary polymers (formed by micellar polymerization of acrylamide and methyl methacrylate with side hydrophobic groups (HG) containing 9, 12 and 18 C‐atoms), and terpolymers (the same monomers and a charged component — sodium acrylate) are studied. The dependences of properties on the length, form (linear or branched) and the number of HG and charges is established. It is shown that a very small number of linear HG leads to a considerably higher solution viscosity, starting at a smaller concentration compared with the effects of a larger number of branched HG. Solutions of terpolymers of concentration 2–3 wt % form physical gels that are thixotropic. After dilution, the polymers suddenly form gels at certain concentrations without the preliminary stage of viscosity growth     

Investigation of biodegradability of composites based on polyethylene and polysaccharides by independent methods

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EPR Spin Probe Study of New Micellar Systems

Molecular dynamics, structure, and phase state of two new micellar systems were investigated using spin-probe electron paramagnetic resonance spectroscopy. While the local mobility of the new cationic long-chain detergents varies in micelles in a minor way when the length of a chain increases from 16 to 22 carbon atoms, the order parameter increases noticeably. The latter is caused by gain of hydrophobic interactions. It is worthwhile to note that the incorporation of the two hydroxyl groups into the polar head group of the C22 detergent influences particularly on the molecular dynamics and phase state of an aqueous solution of the detergent. Furthermore, not only the local mobility decreases and ordering factor increases, but also the phase state of the system changes, being transited from the solid to the micellar (liquid) state. Addition of the KCl salt in an aqueous solution of the long-chain detergents results in a decrease of local mobility and increase of ordering factor. The phase transitions are found to be caused by the addition of the salt. The cationic monomer [2-(methacryloyloxy)ethyl]trimethylammonium methyl sulfate was shown to decrease the critical concentration of micelle formation of the anionic detergent sodium dodecyl sulfate (SDS). Most likely this is because, being the counterion, the cationic monomer forms a dense layer around the SDS micelle. Binding of SDS micelle with the monomer strongly reduces the local mobility of the detergent.