Polymeric material free volume

N.A. Plate and Y.P. Yampol skii, Relationship between Structure and Transport Properties for High Free Volume Polymeric Materials, in Polymeric Gas Separation Membranes, D.R. Paul and Y.P. Yampol skii (eds), CRC Press, Boca Raton, FL, pp. 155-208 (1994). 

N. Plate, Y. P. Yampol skii, Relationship between stmcture and transport properties for high free volume polymeric materials, Boca Raton CRC Press (1994). 

The sizes and concentration of the free-volume cells in a polyimide film can be measured by PALS. The positrons injected into polymeric material combine with electrons to form positroniums. The lifetime (nanoseconds) of the trapped positronium in the film is related to the free-volume radius (few angstroms) and the free-volume fraction in the polyimide can be calculated.136 This technique allows a calculation of the dielectric constant in good agreement with the experimental value.137 An interesting correlation was found between the lifetime of the positronium and the diffusion coefficient of gas in polyimide.138,139 High permeabilities are associated with high intensities and long lifetime for positron annihilation. 

Figure 2. Specific volume and "free volume" of polymeric material.

What can be seen from the foregoing examples is that one can use the photochemistry of small model compounds to predict the photochemistry of a polymeric material, provided that certain structural features are included and that one has some idea of the free volume required for the conformational or other motions necessary for the formation of the excited state and rearrangements or disproportionation into products. It can be concluded that... 

Materials and Film Preparation. The molecular structure of the polymerized lipid referred to as CO-1.5 is shown in Figure 1. The material is a co-polymer of a double 18-carbon alkyl chain lipid with a side-group spacer and five main-chain spacer groups. The purpose of the spacer chains is to allow more free volume for the lipid chains to orientationally order normal to the polymer backbone. The lipid chain contains an amide, and the main-chain spacer groups contain tertiary amines. The polymer was synthesized following the general procedures given by Laschewsky et al. (10). 

In this volume, we present five articles-two papers on the behavior of free radicals and active intermediates produced by irradiation in the polymeric matrix are studied one article is on radiation-induced polymerization as a process for biomedical application, and finally there are two papers concerned with the radiation effects on polymeric materials from ion beams and in relation to their use for fusion reactors. 

Appendix Free-volume Data in Polymeric Materials (R.T.)... 

Figure 4. Specific volume and free volume of polymeric material. (Reproduced with permission from Ref. 10. Copyright 1985 Cambridge University Press.)...

SC CO2 used as a carrier of drug molecules into a polymer matrix has a number of advantages such as the plasticizing ability of CO2 (based on specific interactions between CO2 and polymer moieties), which both enhances the diffusion rates of drug molecules into the polymer and facilitates solvent removal. Polymer plasticization is accompanied by the swelling of the polymer matrix, with a concomitant increase in the free volume of the polymer. Moreover, SC CO2 can reduce the melting temperature of semicrystalline polymers. These effects are crucial to the impregnation and modification of polymeric materials. 

The development of new polymeric structures for different technological applications usually requires knowledge about properties of this material. The prediction of properties using additive group contribution method is a valuable procedure adopted during the developments presented here. The group contribution method concept was applied to obtain viscosity data versus temperature, an intermediate step of the free-volume parameters estimation procedure (equation (2) inputs). Detailed concepts about prediction of polymer properties were studied and applied as presented in specific literature (Van Krevelen, 1992 Bicerano, 2002). Equations (4) and (5) are the key equations of the procedure to obtain zero shear viscosity predicted data. The references adopted in this section also allows to predict many others polymer properties. 

Positronium lifetime spectroscopy is particularly well suited for stud)hng defects in crystals and structural fluctuations in amorphous materials and can give an estimate of free volumes in condensed matter [116]. It is a useful technique to estimate the free volume of polymeric membranes [117]. In a study on silica gels, the decay lifetime has been found (Fig. 4.16) to be proportional to the pore diameters (measured by N2 adsorption) between 30 and 100 A [118]. Information on pore size distribution and surface area may also be obtained by means of calibration curves. 

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