Alcoholic gel

A process for the preparation of porous polyvinyl alcohol gels in three steps is (1) suspension polymerization of vinyl acetate with diethylene glycol dimethacrylate in the presence of a diluent as porogen, (2) saponifying of the resulting porous polyvinyl acetate gel with an alkali, and then (3) subjecting... 

A polyvinyl alcohol is obtained by suspension polymerization of vinyl acetate and the cross-linking agent, triallyl isocyanurate, with a triazine ring followed by alkali hydrolysis. The polyvinyl alcohol gel is used as packing for gel-... 

For the separation of D,L-leucine, Ding et al. [62] used poly(vinyl alcohol) gel-coated microporous polypropylene hollow fibers (Fig. 5-11). An octanol phase containing the chiral selector (A-n-dodecyl-L-hydroxyproline) is flowing countercur-rently with an aqueous phase. The gel in the pores of the membrane permits diffusion of the leucine molecules, but prevents convection of the aqueous and octanol phase. At a proper selection of the flow ratios it is possible to achieve almost complete resolution of the D,L-leucine (Fig. 5-12). 

Fang, L Brown, W, Decay Time Distributions from Dynamic Light Scattering for Aqueous Poly(vinyl alcohol) Gels and Semidilute Solutions, Macromolecules 23, 3284, 1990. 

NA Peppas, SR Stauffer. Reinforced uncrosslinked poly(vinyl alcohol) gels produced by cyclic freezing-thawing processes—A short review. J Controlled Release 16 305-310, 1991. 

Alcoholic gel systems, syneresis in, 23 64 Alcoholometry, 10 550 Alcohol oxidation, microwaves in, 16 567-570... 

Note 4 Examples of physically aggregated polymer gels are poly(vinyl alcohol) gel and agarose gel, which show reversible sol-gel transitions. 

Figure 1 A generalized diagram of the structure of the cetostearyl alcohol gel found in topical and vaginal creams. The bilayers are formed principally of cetostearyl alcohol. The hydrophilic poly(oxyethylene) chains attached to the 5-carbon sorbitan rings in Polysorbate 60 retard water drainage from the interlamellar space and keep the lamellae from collapsing into a dense crystalline structure.

A hydrogel placed in an excess of water will absorb the liquid until it reaches a maximum. This ability is typically reported as the percent water in a fully swollen gel. The hydrophilicity of the polymer and the degree of cross-linking determine the degree to which the gel will absorb. Some hydrogels contain as much as 99% water. An acrylic acid gel will have a higher equilibrium moisture than a polyvinyl alcohol gel. This characteristic is not unlike the hydrodynamic volume factor described above. 

Jackson, J. F., and S. J. Gill Elastic properties of crosslinked poly (vinyl alcohol) gels. Network topology. J. Polymer Sci. Pt A-2, 5, 663 (1967). 

Poly(vinyl alcohol)-Gel Spheres with Chitosan... 

Poly(vinyl alcohol)-gel spheres with chitosan (PVA-GS/Ch) or without chitosan (PVA-GS) were prepared to control the GI transit time of drugs, and their particles were 5-10 pm [26]. PVA-GS/Ch displayed a longer small-intestinal transit time than PVA-GS. The transit rate was considered to decrease by the adhesion of chitosan to the intestinal mucus layer. PVA-GS/Ch and PVA-GS were loaded with theophylline and ampicillin. These released the drugs in a similar manner. The drugs were released almost completely at 4 h after the start of the release test. Both the gel spheres containing theophylline exhibited a bioavailability similar to that of the theophylline solution. Also, the bioavailability of ampicillin was greater in PVA-GS/Ch than in the PVA-GS and ampicillin solution the bioavailability of PVA-GS/Ch was approximately 150% of that of ampicillin solution (Table 3.2). As theophylline is rapidly absorbed in... 

Sugimoto, K., et al. 1998. Evaluation of poly(vinyl alcohol)-gel spheres containing chitosan as dosage form to control gastrointestinal transit time of drugs. Biol Pharm Bull 21 1202. 

There are two classes of stationary phases in SEC, one type for GFC and the other for GPC. Stationary phases for GFC are hydrophilic and include polydextrans, polyvinyl alcohol gel, and silica gel those for GPC are hydrophobic, typically cross-linked, rigid polystyrene-divinylbenzene gels. Generally, columns of 15 to 50 cm length are used, packed with 7- to 10-/t,m particles and with an internal diameter between 0.6 and 0.8 cm. In SEC, unlike in other chromatographic modes, the stationary phase is the primary factor controlling retention. 

Uses of Gels Gels have found several applications. Silica gel is used in laboratory and in industry and is also used to support the platinum catalyst, when this is used in the contact process of H2S04 manufacture. It is resistant to catalytic poisoning. Solidified alcohol (gel) is used as fuel in picnic stoves and is made from alcohol and calcium acetate. 

Kimura T, Sato K, Sugimoto K, Tao R, Murakami T, Kurosaki Y, Nakayama T (1996) Oral administration of insulin as poly(vinyl alcohol)-gel spheres in diabetic rats. Biol Pharm Bull 19 897-900... 

Alcohol gel HPLC SPE, C OSD-2, MeOH-THF-0.025M 300 nm Retinoid stability... 

Fig. 26. Photo-effects on water permeation through a porous poly(vinj4 alcohol) gel with tri dmiyl-methane leucocyanide groups (content, 1.9 mol %). ( ) an unmodified membrane ( ) a coated membrane in the dark (O) a coated membraw under UV irradiation...

Benzoyl peroxide is available as creams, lotions, gels and washes (2.5, 5 and 10%, and a 4% cream). There is little difference in clinical response to these concentrations in terms of reducing the number of inflammatory lesions, but formulation appears to make a difference. The drying effect of an alcoholic gel base enhances the effectiveness of the active constituent, and it is more effective than a lotion of the same concentration. However, gels have a greater potential for causing skin dryness and irritation than preparations in aqueous bland bases, so water-based preparations may improve compliance. 

Formulations in alcohol gels dry out the skin, increase the penetration of the tretinoin and make the treatment more uncomfortable. Gels should only be used on thick and oily skins. 

A variety of materials are used in the drug reservoir, ranging from mineral oil to complex formulations, such as aqueous/alcoholic gels. A reservoir system should provide zero-order release of the drug over the entire delivery period which requires that the reservoir material remains saturated with the drug over the period of product application, which can usually be achieved by formulating the drug as a suspension. 

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