Water-insoluble polymers and polymer membranes

Polymers form perfect crystals with difficulty simply because of the low probability of 

In defining the properties of polymers for dmg formulation, certain characteristics are important. Obviously molecular weight and molecular weight distribution must be known, as these affect solvent penetration and crystallinity. The functionality of the polymer is best described by a series of parameters such as 

Crystallinity defines several features of polymers rigidity, fluidity, the resistance to diffusion of small molecules in the polymer, and degradation. 

In hydrogels can be measured and is a measure of polymer structure, crosslinking density, solvent content and polymer-solvent interactions, as can be seen from Table 8.6. 

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This subject can be considered in terms of five different types of molecules or materials (a) biologically inert, water-insoluble polymers (b) water-insoluble polymers that bear biologically active surface groups (c) water-swellable polymeric gels, or amphiphilic polymers that function as membranes (d) water-insoluble but bioerodable polymers that erode in aqueous media with concurrent release of a linked or entrapped bioactive molecule and (e) water-soluble polymers that bear bioactive agents as side groups. 

Materials that form a permeable membrane include fats, bee wax, carnauba wax, cetyl alcohol, cetylsteryl alcohol, zein, acrylic esters, silicone elastomers, and ethylcellulose (14). Aqueous dispersions of water-insoluble polymers are commonly used for sustained-release film coatings. Examples of commercially available aqueous polymer dispersions include Surelease-containing ethylcellulose, Aquacoat-containing... 

NC is a water-insoluble fibrous polymer. Consequently it is not absorbed thru the intestinal wall or cell membranes. This accounts for its total lack of oral toxicity to mammals. Subchronic and chronic feeding to rats and dogs at contents as high as 10% and to mice at 3% of the solid diet resulted in no effects other than those of fiber bulk, ie, as if they had been fed cotton linters. 

The use of ISEs with ion-selective membranes based on plasticized PVC, as well as glass pH electrodes, is limited to the analysis of aqueous solutions. On the other hand, sensors based on conducting polymer membranes are usually insoluble in organic solvents, which extends the range of possible applications. Electrosynthesized polypyrrole doped with calcion works as a Ca2+ sensor that can be applied as indicator electrode in the titration of Ca2+ with NaF in mixed solvents, such as water-methanol (1 1) and water-ethanol (1 1) [52], Another example is the use of polyaniline as indicator electrode in order to follow the acid-base precipitation titration of trimeprazine base with tartaric acid in isopropanol solution (see Procedure 5). 

Another important group of anisotropic composite membranes is formed by solution-coating a thin (0.5-2.0 xm) selective layer on a suitable microporous support. Membranes of this type were first prepared by Ward, Browall, and others at General Electric [52] and by Forester and Francis at North Star Research [17,53] using a type of Langmuir trough system. In this system, a dilute polymer solution in a volatile water-insoluble solvent is spread over the surface of a water-filled trough. 

Pennkinetic System Skye Pharma AG, Muttenz, Switzerland The system combines CR principles of ion exchange with membrane diffusion. The system is made up of an ion-exchange polymer-drug complex as a core material, which is subsequently coated with ethylcellulose to form a water insoluble but permeable coating. Release rates are relatively constant and unaffected by variable conditions of the GI tract. The system can be formulated in capsule form as well as suspensions. Delsym (Dextromethorphan), Corsym (Chlorpheniramine) and Cold Factor 12 (Phenylpropanolamine). 

Although there is no strict boundary line, we have divided polymers into water soluble polymers and water-insoluble systems, typified respectively by materials used to prepare viscous solutions and those which function as barrier membranes or containers, in the first case we have considered the factors controlling their properties the influence of molecular weight (distribution), branching, charge, flexibility, ionic strength and pH on solution properties, in the case of water-soluble polymers, the main concern has been with... 

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