Poly methyl permeability

Fig. 15. Oxygen permeability versus 1/specific free volume at 25 °C (30). 1. Polybutadiene 2. polyethylene (density 0.922) 3. polycarbonate 4. polystyrene 5. styrene-acrylonitrile 6. poly(ethylene terephthalate) 7. acrylonitrile barrier polymer 8. poly(methyl methacrylate) 9. poly(vinyl chloride) 10. acrylonitrile barrier polymer 11. vinyUdene chloride copolymer 12. polymethacrylonitrile and 13. polyacrylonitrile. See Table 1 for unit conversions.

Hard lenses can be defined as plastic lenses that contain no water, have moduli in excess of 5 MPa (500 g/mm ), and have T well above the temperature of the ocular environment. Poly(methyl methacrylate) (PMMA) has excellent optical and mechanical properties and scratch resistance and was the first and only plastic used as a hard lens material before higher oxygen-permeable materials were developed. PMMA lenses also show excellent wetting in the ocular environment even though they are hydrophobic, eg, the contact angle is 66°. 

Hard contact lenses are composed of a polymer that repels water because the constituent repeating units (the monomers that link together to form the polymer) are nonpolar, hydrophobic segments. The first hard contact lens was constructed in 1948 from the monomer known as methyl methacrylate (MMA), yielding the polymer poly(methyl methacrylate) or PMMA. This material offers durability, optical transparency, and acceptable wettability for optimal comfort. Today the rigid lens material of hard contact lenses is often constructed by combining MMA with one or more additional hydrophobic monomers to provide better gas permeability. 

Pleated sheet conformation, 30,31 PLEDs (polymeric light-emitting diodes), 218 Plexiglas, 62 Plunkett, Roy, 65-66 PMMA. See Poly(methyl methacrylate) Polartec (Polar Fleece), 194 Poly(6-aminohexanoic acid), 25 Poly(a methyl styrene), 20 Polyacetylene, 72, 73 Polyacrylamide, 20 Polyamides, 22, 28, 61, 146 biodegradable, 185 Polyaramids, 77, 86 Polybutadiene, 70,109,148,155 Poly butyl acrylate), 20 Poly(butylene isophthalate), 25 Polycaprolactam, 21 Polycarbonate (PC), 17, 48, 86, 140 biodegradable, 185 density of, 247 impact strength of, 143 permeability of, 163 Polychloroprene, 65 Polycondensation, 85, 90-91 interfacial, 91-92... 

In order to avoid the infiltration of seeds in the support and to develop ultra-thin membranes (typically 500 nm thick) with a high permeability, a masking techniques has been recently developed in Lulea University [111]. A solution of poly methyl methacrylate (PMMA) in acetone was applied and dried on the support top surface. The interior of the support was subsequently filled with wax and the protective PMMA layer was dissolved in acetone. The masked support was then seeded with a monolayer of silicalite-1 crystals before being submitted to the classical hydrothermal and calcination steps. 

Contact lenses are the most common polymer product in ophthalmology. The basic requirements for this type of materials are (T)excellent optical properties with a refractive index similar to cornea good wettability and oxygen permeability ( ) biologically inert, degradation resistant and not chemically reactive to the transfer area ( ) with certain mechanical strength for intensive processing and stain and precipitation prevention. The common used contact lens material includes poly-P-hydroxy ethyl methacrylate, poly-P-hydroxy ethyl methacrylate-N-vinyl pyrrolidone, poly-P-hydroxy ethyl methacrylate, Poly-P-hydroxy ethyl methacrylate - methyl amyl acrylate and polymethyl methacrylate ester-N-vinyl pyrrolidone, etc. The artificial cornea can be prepared by silicon rubber, poly methyl... 

Yamamoto, Y., Maegawa, M. and Kumazawa, H. 2003. Gas permeability of NHj-plasma-treated poly(methyl methacrylate) membranes. 

Consistent with the preceding discussion concerning sorption and flux reductions by relatively noninteracting penetrants, the data shown in Fig. 20.4-11 clearly illustrate the progressive exclusion of CO2 from Langmuir soiption sites in poly(methyl methaciylate) (PMMA) as ethylene partial pressure (Pb) increased in the presence of an essentially constant CO2 partial pressure of 3-05 7 0.13 atm. The tendency of the CO2 soiption shown in Fig. 20.4-11 to decrease monotonically with ethylene pressure provides impressive support for the competition concept on which E. . 4-17) and (20.4-18) are based. Pemreation data are not available for this stem to determine if changes in the values of Dp and Dh occur in the mixed gas situation. If offsettiiig increases in these transport coefficients do not occur in the presence of ethylene, the CO2 permeability will be depressed in the mixed gas peimeation situations. 

At present, QDs are mainly used for cation detection and biosensing in solution-sensing assays (Costa-Fernandez 2006 Callan et al. 2007). However, it was established that the surrounding gas can also influence the fluorescence properties of QDs embedded in gas permeable polymer. In particular, Nazzal et al. (2003) found that the PL properties of the CdSe nanocrystals, stabilized by trioctylphos-phine oxide (TOPO) and incorporated in poly(methyl methacrylate) (PMMA) polymer films, can respond to the environment in a reversible and species-specific fashion (see Fig. 5.3). However, reversible response was observed in an oxygen-free atmosphere only. In oxygen, the CdSe was slowly oxidized, and therefore QDs have shorter lifetimes in air compared with those in an atmosphere of nitrogen. 

PHA solutions of various densities were used to prepare transparent flexible films. The surface properties of PHB and P(HB-co-HV) fllm scaffolds were similar to each other and to those of synthetic polyesters (polyethylene terephthalate, poly (methyl methacrylate), polyvinyl chloride, and polyethylene) (Shishatskaya 2(X)7X The scaffold s surface properties are important for cell attachment and proliferation. To enhance cell adhesion to the surface, improve the gas-dynamic properties of scaffolds, and increase their permeability for substrates and cell metabolites, the scaffolds can be treated by physical factors or by chemical reagents. Biocompatibility of PHA scaffolds has been enhanced by immobilizing collagen fllm matrices on the scaffold surface and coating with chitosan and chitosan/polysaccharides (Hu et al. 2003). 

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