Hydrophobized polymers

Aqueous dispersions are alternatives to solutions of Hquid and soHd resins. They are usuaUy offered in 50% soHds and may contain thickeners and cosolvents as stabilizers and to promote coalescence. Both heat-reactive (resole) and nonheat-reactive (novolak) systems exist that contain unsubstituted or substituted phenols or mixtures. A related technology produces large, stable particles that can be isolated as discrete particles (44). In aqueous dispersion, the resin stmcture is designed to produce a hydrophobic polymer, which is stabilized in water by an interfacial agent. 

Cellulose Deriva.tives, Cellulose can be derivatized to make both water-soluble gums and hydrophobic polymers. The preparation of the hydrophobic cellulose esters (qv), cellulose acetates and cellulose nitrates, has already been mentioned. The water-soluble cellulose derivatives are cellulose ethers (qv). 

Although current matrix diffusional systems are most suitable for small-molecule compounds, it has been demonstrated (84) that soHd hydrophobic polymers allow dispersed powdered macromolecules of nearly any size, for example, ethylene—vinyl acetate copolymers containing dispersed polypeptides, to be released for periods exceeding 100 days. 

Cationic, hydrophilic, and hydrophobic Chitosan, poly-2-vinyl pyridine 0.3-1.0 M salt/buffer, pH 2-7 with the addition of methanol for more hydrophobic polymers... 

We modified polyanionic polymers by use of a grafting reaction of hydrophobic groups onto the polymers. After an extensive evaluation for the affinity of the hy-drophobically modified (hydrophobized) polymers to cell membrane, the immuno-stimulating activity of polymers was investigated by in vitro or ex vivo experiments. Consequently, the increased biological activity was found in the hydrophobized polymer, indicating that... 

Two hydrophobized polymers, MA-DP-A20 (phenyl group grafted in 20 mol%) and MA-DP-H68 (hexyl group grafted in 68 mol%), were selected for the evaluation of the interaction between polymers and cell membranes... 

The in situ method using rat living intestine was simple and qualitative. However, it was difficult to evaluate the weak interaction between polymers and cell membranes quantitatively. Therefore, the lipid bilayer of liposome was used as a model of cell membranes for the quantitative evaluation for the affinity of the hydrophobized polymers (15). 

For additional evaluation of the effect of hydrophobization and the molecular weight of the polymers on the biological immuno-stimulating activity, we investigated the ex vivo cytokine (interIeukin-6 [IL-6], and tumor necrosis factor [TNFj-inducing activity from human peripheral whole blood cells of hydrophobized polymers by use of fractionated poly(M A-CDA) with narrow poly-dispersity. Since this assay uses the intact human cells, it shows more accurate results than in vitro assay using cultured cell line [25]. 

The hydrophobized polymers demonstrated higher activity than unmodified polymers. The molecular weight dependency on the activity was also found. In particular, MA-CDA-5K-A (MW 5,000) hydrophobized with 10 mol% aniline induced both cytokines remarkably higher than unmodified MA-CDA and modified MA-CDA with different molecular weights. 

The Limuius activity of hydrophobized polymers was measured by means of an Endospecy test , which is known to have the highest sensitivity for the detection of LPS. The MA-CDA-5K-A, which showed the highest... 

Strongly polarized cellulose fibers [38] inherently are rarely compatible with hydrophobic polymers [28, 39-41]. When two materials are incompatible, it is often possible to bring about compatibility by introducing a third material that has properties that are intermediate between those of the other two. There are several mechanisms [42] of coupling in materials ... 

This molecule is a copolymer with polymethyl methacrylate (PMMA) in acrylic latex paints, where the hydrophobic PMMA is surrounded by hydrophilic polyvinyl acetate molecules. Such a suspension of a hydrophobic polymer wrapped in a hydrophilic polymer is called a latex. 

Figure 8.23 Reduction of ketones with Geotrichum candidum in the presence of hydrophobic polymer XAD [19a],...

In the reduction of benzoyloxypropanone, the hydrophobic polymer XAD-7 was used to prevent product inhibition and increase substrate concentration [19b]. Thus, the reduction proceeded in 70 gl substrate concentration and afforded 87% (12.4 g) of (S)-l-benzoyloxy-2-propanol in >99% ee (Figure 8.24). Thebutanone derivative could be reduced with the same method and afforded (S)-alcohol in 72% yield and >99% ee, but the pentanone derivative could not be reduced. 

In disc form, when prepared by compression molding, the more hydrophobic polymers, PCPP and PCPP-SA, 85 15, displayed constant erosion kinetics over 8 months. By extrapolation, 1-mm-thick discs of PCPP will completely degrade in over 3 years. The degradation rates were increased by copolymerization with sebacic acid. An increase of 800 times was observed when the sebacic acid concentration reached 80%. By altering the CPP-SA ratio, nearly any degradation rate between 1 day and 3 years can be achieved (4). 

When a hydrophobic polymer with a physically dispersed acidic excipient is placed into an aqueous environment, water will diffuse into the polymer, dissolving the acidic excipient, and consequently the lowered pH will accelerate hydrolysis of the ortho ester bonds. The process is shown schematically in Fig. 6 (18). It is clear that the erosional behavior of the device will be determined by the relative movements of the hydration front Vj and that of the erosion front V2- If Vj > V2, the thickness of the reaction zone will gradually increase and at some point the matrix will be completely permeated with water, thus leading to an eventual bulk erosion process. On the other hand, if V2 = Vj, a surface erosion process wiU take place, and the rate of polymer erosion will be completely determined by the rate at which water intrudes into the matrix. 

Hilder, E.F. et al.. Separation of hydrophobic polymer additives by microemulsion electrokinetic chromatography, J. Chromatogr A, 922, 293, 2001. 

Hydrophobic polymers with some hydrophilic groups can be obtained with an emulsion polymerization technique. Suitable monomers are nitrogen-containing acrylics and methacrylics allyl monomers such as dimethylamino-ethyl methacrylate, dimethylaminopropyl methacrylamide, diethylamino-ethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate and nitrogen-containing allyl monomers (e.g., diallylamine and N,N-diallyl-cyclohexylamine) [225,226]. 

Membranes UF membranes consist primarily of polymeric structures (polyethersulfone, regenerated cellulose, polysulfone, polyamide, polyacrylonitrile, or various fluoropolymers) formed by immersion casting on a web or as a composite on a MF membrane. Hydrophobic polymers are surface-modified to render them hydrophilic and thereby reduce fouling, reduce product losses, and increase flux [Cabasso in Vltrafiltration Membranes and Applications, Cooper (ed.). Plenum Press, New York, 1980]. Some inorganic UF membranes (alumina, glass, zirconia) are available but only find use in corrosive applications due to their high cost. 

Figure 10.67 indicates the probable distribution of a silicone containing the optimum content of aminoethyliminopropyl groups when applied to a polyester fibre surface. In this case the attachment is through hydrophobic polymer-fibre interaction and the mobility of the silicone chain segments is increased by electrostatic repulsion between neighbouring cationic groups. Dependence of softness of the treated polyester fabric on the proportion of... 

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