Permeability of polymers

Hydrophobic polymers also play an important role in pharmacy. When these materials are used as membranes, containers or tubing material, their surfaces may come into contact 

Diffusion in nonporous solid polymer is of course a more difficult process than in a fluid because of the necessity for the movement of polymer chains to allow passage of the dmg molecule, and it is therefore slower. The equation which governs the process is Pick s first 

Permeation of drug molecules through the solid polymer, which may be acting as a dmg depot, is a function of the solubility of the drug in the polymer as 

The natural permeabilities of polymers vary over a wide range and this widens the choice, provided one can select a polymer which is compatible with the tissues with which it comes into contact. Once a polymer has been chosen that gives a flux of drug sufficient to provide adequate circulating levels, use of fillers and plasticisers can give fine control of permeability (Table 8.7). 

The method of preparation also influences the properties of the film. Cast films of varying properties can be prepared by variation inter alia of the solvent power of the casting solution containing the polymer, although the complex processes involved in film formation are not yet fully understood. It is clear, however, that the conformation of the polymer chains in concentrated solution just prior to solvent evaporation will determine the density of the film, and the number and size of pores and voids. Dmg flux through dense (nonporous) polymer membranes is by diffusion flux through porous membranes will be by diffusion and by transport in solvent through pores in the film. With 

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Permeability of Polymers to Gases and Vapors Brochure P302-335-79, The Dow Chemical Company, Midland, Mich., 1979. 

We test the permeability of polymer films or sheets to various vapors and gases by mounting the polymer between chambers that contain different concentrations of the migrant molecules. We can determine the permeability from pressure changes, volumetric changes, or by microanalytical techniques that measure the concentration of the migrant molecules in a stream of gas flowing across the low concentration side of the barrier. 

As mentioned earlier, high-speed separation is necessary to carry out fast, comprehensive 2D HPLC. The polymer monoliths have not been employed in such 2D HPLC, probably because permeability of polymer monoliths is not high enough to allow fast elution of the second dimension (2nd-D) in simple 2D operation, and the gradient cycle at the 2nd-D cannot be so fast to allow online 2D operation without reducing peak capacity at first dimension (lst-D). 

There is also a significant drawback the inherently higher fuel permeability of polymers. The strengthening of environmental regulations (PZEV Partial Zero Emission Vehicle) leads to severe requirements concerning fuel impermeability, needing modification of the techniques now in use. Moreover, some carmakers such as Ford and GM require higher mechanical and thermal resistance, and conductive materials. 

Gasa, J. V., Weiss, R. A. and Shaw, M. T. 2006. Influence of blend miscibility on the proton conductivity and methanol permeability of polymer electrolyte blends. Journal of Polymer Science Part B 44 2253-2266. 

Orientation. The effect of orientation on die permeability of polymers is difficult to assess because die words orientation and elongation or strain have been used interchangeably in the literature. Diffusion in some polymers is unaffected by orientation in others, increases or decreases... 

Many PSPs are composed of probe dyes, such as polycyclic aromatic hydrocarbons (e.g., pyrene) and coordination compounds (e.g., platinum por-phryins and ruthenium(II) polypyridyl complexes) immobilized in various gas permeable polymer films such as silicon polymer, organic glassy polymers (e.g., poly(methylmethacrylate), polystyrene), fluorinated polymers, or cellulose derivatives such as ethyl cellulose [9,10]. As probe molecules interact with polymer matrices directly, the properties of PSPs strongly depend on the properties of polymer matrices. The oxygen permeability of polymer matrix is an especially important factor for highly sensitive PSP. 

The most important techniques used to determine gas permeability of polymers are the ISO 2556, DIN 53 380 and ASTM D 1434 standard tests. 

The factors affecting the selectivity and permeability of polymer membranes to different gases are best discussed on the basis of Eqs. (12) and (14). As noted in Eq. (12), the permeability coefficient, P, of a penetrant gas in a polymer membrane is the product of a (concentration-averaged) diffusion coefficient, D, and of a solubility coefficient,... 

Stern SA, Krishnakumar B and Nadakatti SM, "Permeability of Polymers to Gases and Vapours", in Mark JE (Ed), "Physical Properties of Polymers Handbook", AIP Press, Woodbury, NY, 1996, Chap. 50. 

The permeability of polymers decreases with the increase in their glass transition temperature. This dependence becomes more pronounced with increasing kinetic diameter of penetrant molecules (Figure 9.9). 

Factors influencing the rate of monomer diffusion are surface tension distribution coefficient of monomers between the two phases rate of monomer transfer from phase to phase solvent power of organic phase for the polymer permeability of polymer film to monomers adsorption of monomers by the polymer film viscosity of the system. 

Permeability of Polymers to Gases, Vapors, and Liquids, Alexander Leborits, Modern... 

Table 1. Permeability of polymers and ideal separation factors for composite hollow fiber membranes (20 °C).

Since plasticizers are typically incorporated into film coating formulations in significant concentrations, their inclusion commonly affects the permeability of polymer films and consequently drug release from coated substrates. Therefore, plasticizer selection for film coating applications mu.st be carefully considered as plasticizers substantially... 

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