Polycarbonate 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.

Stannett and Meyers have reported that crystallisation may reduce the nitrogen permeability by 50%. The moisture vapour permeability of the polycarbonate from l,l-bis-(4-hydroxyphenyl)cyclohexane has been quoted by Schneir as being somewhat below half that of the bis-phenol A polymer (1.7, c.f. 3.8 units). 

Aliphatic polycarbonates have few characteristics which make them potentially valuable materials but study of various aromatic polycarbonates is instructive even if not of immediate commercial significance. Although bisphenol A polycarbonates still show the best all-round properties other carbonic ester polymers have been prepared which are outstandingly good in one or two specific properties. For example, some materials have better heat resistance, some have better resistance to hydrolysis, some have greater solvent resistance whilst others are less permeable to gases. 

MV Shah, KL Audus, RT Borchardt. The application of bovine brain micro vessel endothelial-cell monolayers grown onto polycarbonate membranes in vitro to estimate the potential permeability of solutes through the blood-brain barrier. Pharm Res 6 624-627, 1989. 

For the AJL8/APC polymer, saturation was not achieved until 250 h of exposure to the DNT vapor. However, the sensing polymer produces a detectable amount of refractive index change within a few minutes of exposure to DNT vapor of 100 ppb concentration. The response rate is thought to be limited by the diffusion of DNT molecules into the polymer. In the initial experiments reported here PMMA and polycarbonate were used as the host polymers. These polymers are relatively less permeable to DNT. The response rate is expected to improve if a more permeable polymer host is used. 

Water vapour polycarbonate has a medium permeability, evaluated at 2.5 compared to a full range of 0.05 up to 400 for all tested plastics. 

In the same way, o-nitrophenyl octyl ether (o-NPOE) was immobilized on polycarbonate (PC) filters and the apparent permeability measured after 5 h incubation time was correlated to log Pnpoe for a series of reference compounds (log Pnpoe ranging from —1 to 3.6) [90]. Lipophilicity values in the alkane/water system were also determined using PAMPA with hexadecane-PC coated filters [89]. In this case, a correlation was found between intrinsic permeability (log Pq, permeability corrected for ionization and for unstirred water layer contribution, which particularly affects permeability of lipophilic compounds) and log P ik. However, log Pq is obtained from the knowledge of the pJC, value(s) and the permeability pH profile and therefore requires the full permeability pH profile to be measured for each compound, which negatively impacts the assay throughput. 

The data shown in Figure 8 illustrate the reduction in permeability of polycarbonate to CO2 caused by competition between isopentane and CO2 for Langmuir sorption sites (33) ... 

Figure 8. Permeability of Lexan polycarbonate to carbon dioxide at 35 °C as a function of C02 partial pressure.Qo, in the presence of 117 mm. Hg of isopentane in the feed , pure C02 Q...

In Section I we introduce the gas-polymer-matrix model for gas sorption and transport in polymers (10, LI), which is based on the experimental evidence that even permanent gases interact with the polymeric chains, resulting in changes in the solubility and diffusion coefficients. Just as the dynamic properties of the matrix depend on gas-polymer-matrix composition, the matrix model predicts that the solubility and diffusion coefficients depend on gas concentration in the polymer. We present a mathematical description of the sorption and transport of gases in polymers (10, 11) that is based on the thermodynamic analysis of solubility (12), on the statistical mechanical model of diffusion (13), and on the theory of corresponding states (14). In Section II we use the matrix model to analyze the sorption, permeability and time-lag data for carbon dioxide in polycarbonate, and compare this analysis with the dual-mode model analysis (15). In Section III we comment on the physical implication of the gas-polymer-matrix model. 

The solid line in Fig. 2 shows the permeability-pressure curve of C02 in polycarbonate calculated by fitting the simplified permeability expression, eq. (14), to experimental data of Wonders and Paul (15). The data fitting procedure, described elsewhere (1 1), gives Do = 1.09 x 10 8 cm2/sec and p = 0.065 cm3(polymer)/cm3(STP). Fig. 2 shows a good agreement between the experimental data and eq. (14) over the entire pressure range. 

Wonders and Paul (15) report that a nonlinear least-squares fit of the dual-mode expression [eq. (16) in the preceding chapter] to the permeability versus pressure data, for C02 in polycarbonate, gives and values of 4.78 x 10 8 and 7.11 x 10 9 cm2/sec, respectively. The broken curve in Fig. 2 was calculated from the dual-mode sorption coefficients of Fig. 1 and the values of the diffusion coefficients given above. 

Figure 2. Permeability of CO2 in conditioned polycarbonate at 35 °C. The experimental data are from Ref. 15. The solid curve is the calculated permeability based on the matrix model and the broken curve is calculated from the dual-mode model. Parameters used in the curves are given in the text.

Further, drug transport through epithelial cells has been studied. For instance, Madin-Darby canine kidney (MDCK) cells have been grown into tight mono-layers on a permeable polycarbonate membrane. This membrane (0.4-p.m pores,... 

Fig. 8.12. Sorption isotherms (a) and the permeability coefficients (b) for C02 sorption by (1) bisphenol A polycarbonate, (2) tetramethyl polycarbonate, (3) tetrachloropolycarbonate, and (4) tetrabromopolycarbonate at 35°C [189].

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... 

---