Polymer reversibility

Osmosis is the flow of solvent through a semipermeable membrane into a solution the osmotic pressure is proportional to the molar concentration of the solute. Osmometry is used to determine the molar masses of compounds with large molecules, such as polymers reverse osmosis is used in water purification. 

Phenomenex (see 2006 Catalog, SPE products) Strata-X Polar functionalized styrene-divinylbenzene polymer Reversed phase with weakly acidic, hydrogen bond donor, acceptor, and dipolar interactions Cetirizine (76) pyridoxine (77) omeprazole (78) mycophenolic acid (79) 25-hydroxy-vitamin D3 (80)... 

Irie, M., Hirano, Y., Flashimoto, S., and Hayashi, K. Photoresponsive Polymers. Reversible Solution Viscosity Change of Polyamides Having Azobenzene Residues in the Main Chain. Macromolecules 14, 262 (1981). 

The results shown in Fig. 6.11 not only support the reversibility of the strain-induced polymorphic transition (Boyle Overton, 1974) but also allow one to speak about reversibility of microhardness. This is feasible in cases in which, as a result of some treatment, it is possible to regenerate the starting structure of the polymer. Reversibility of the microhardness further emphasizes that this mechanical property depends primarily on the structure of material. 

Krebs JF, Borovik AS (1995) Metallo-network polymers Reversible CO binding to an immobilized copper(I) complex. J Am Chem Soc 117 10593... 

In some applications, the interaction of the polymer with a specific "solvent" and/or with certain molecules carried by that solvent is not a detrimental event, but an essential aspect of the operation of the polymer. Reverse osmosis membranes and swollen hydrogels used in applications such as the desalination of water, kidney dialysis, soft contact lenses and surgical implants [17] are among such polymers. 

In spite of its sustained high polymerization temperature ( 222°C), after eight minutes Polymer 8 torque remained quite steady during the last 8 minutes of the polymerization reaction with only a slight drop indicative of minor polymer reversion. 

Since 1-propanol is monofunctional and reacts with "matched dissociation isocyanate" (at internal urethane chain positions) as well as "unmatched isocyanate" (at polymer chain terminal positions) its effects include cleavage of some polyurethane chains in the process of generating more urethane groups. As a result, polymer DP, melt viscosity, and torque drop until the shortstop is consumed, or escapes the mixture by volatilizaton. Figure 9 shovjs that the more 1-propanol used to shortstop the polymerizations, the more pronounced the polymer reversion was. 

The behavior of Polymer 17 polymerization (0.24% SS at 8 minutes) showed less than complete shortstop action (+ AT 30/2) and a final torque of 470 meter-grams. Note the total absence of shortstop-induced polymer reversion even after 16 minutes of reaction time. 

Scheme 77.79 Synthesis and polymerization of optically active, helical poly(acetylenes). Esterification of the chiral alcohols in the polymer reverses the helicity.

Cationic Polymers., The relation between zeta potential and flocculation by a polymer has been studied by Rjes (3IS), who pointed out that as soon as a colloidal particle is coated with polymer it bears the same charge as the polymer and is redispersed. Similar studies by Ries and Meyers (316) involved the use of microphoresis and electron microscope observations of model colloids and polymeric flocculants. Polyamine type flocculants appeared to extend out from the particle surface for a distance of 20-300 A. Flocculation occurs simultaneously through charge neutralization and bridging of polymer chains from particle to particle then excess polymer reverses the potential and redispersion occurs. Adsorption of poly [(1,2-dimethylvinylpyridinium) methylsulfate] on silica was similarly studied by Shyluk (317), who concluded that the polymer chains lay flat along the surface when no excess polymer was present. 

The organic polymer reversed phases are often made by copolymerization of styrene and divinylbenzene (PS-DVB), but materials incorporating CIS chains in acrylate... 

Irie, M. (1986) Photoresponsive Polymers. Reversible Bending of Rod-Shaped Acrylamide Gels in an Electric Field, Macromolecules, 19, 2890-2. 

Conjugated polymers are very significant, smart, or responsive materials. Indeed, many properties (color, conductivity, volume, hydrophiHcity, permeability, etc.) depend on their oxidation state and can thus be reversibly controlled by the potential applied to the material. As an example, smart windows [2] are based on the electrochromism of these coatings, that is, the ability to switch these polymers reversibly between dark and colorless state by simple control of the polymer redox state. The intensity of Hght transmission through a window incorporating such a layer can thus be tuned at will by external electrical stimuli. 

The nomenclature of the poloxamers and the meroxapols (polyoxypropy-lene-polyoxyethylene-polyoxypropylene block co-polymers) reversed poloxamers is explained in Table 6.30. Another class of block co-polymers which has no generic name has the name Pluradot (Wyandotte). These have three block copolymer chains with the general formula,... 

Fig. 12.2 Thermoresponsive polymers reversible switch from a hydrophilic swollen state to a hydrophobic collapsed state...

Figures 45 and 46 shows response of PANI/Mn02/urease and PANFZnO/urease biosensor, respectively, with successive addition of 0.1 ml of 10-50 mM urea in 0.1 M PBS (pH 7.2) at potential of —0.3-0.6 V and at a scan rate of 50 mV/s. Urease hydrolyzes urea to ammonium and hydrogen carbonate anions. Ammonium ion interacts with polymer to induce a decrease in conductivity of the polymer. Reversible deprotonation of the polymer structure takes place, while increase in the...

The mechanism of thermal degradation is also directly related to the amount of oxygen present in the immediate environment as well as the presence of oils, chemicals or steam. When silicone elastomers are heated above 200 °C in close confinement, polymer reversion may result in softening and a loss of elastomeric properties. Usually this effect can be... 

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