Selected polymers

Table 10.4 Resistance of Selected Polymers and Rubbers to Various Chemicals...

R. E. Schawmm, A. E. Clark, and R. P. Reed,M Compilation and Evaluation of Mechanical, Thermal and Electrical Properties of Selected Polymers, NBS Report, A EC SAN-70-113, SANL 807 Task 7, SANL Task 6, National Technical Information Service, U.S. Dept, of Commerce, Springfield, Va., Sept. 1973, pp. 335-443. 

Because of the capacity to tailor select polymer properties by varying the ratio of two or more components, copolymers have found significant commercial appHcation in several product areas. In fiber-spinning, ie, with copolymers such as nylon-6 in nylon-6,6 or the reverse, where the second component is present in low (<10%) concentration, as well as in other comonomers with nylon-6,6 or nylon-6, the copolymers are often used to control the effect of sphemUtes by decreasing their number and probably their size and the rate of crystallization (190). At higher ratios, the semicrystalline polyamides become optically clear, amorphous polymers which find appHcations in packaging and barrier resins markets (191). 

Melt Viscosity. The study of the viscosity of polymer melts (43—55) is important for the manufacturer who must supply suitable materials and for the fabrication engineer who must select polymers and fabrication methods. Thus melt viscosity as a function of temperature, pressure, rate of flow, and polymer molecular weight and stmcture is of considerable practical importance. Polymer melts exhibit elastic as well as viscous properties. This is evident in the swell of the polymer melt upon emergence from an extmsion die, a behavior that results from the recovery of stored elastic energy plus normal stress effects. 

The diffusion and solubihty coefficients for oxygen and carbon dioxide in selected polymers have been collected in Table 5. Determination of these coefficients is neither common, nor difficult. Methods are discussed later. The values of S for a permeant gas do not vary much from polymer to polymer. The large differences that are found for permeabihty are due almost entirely to differences in D. 

Table 5. Diffusion and Solubility Coefficients for Oxygen and Carbon Dioxide in Selected Polymers at 23°C, Dry ...

Table 9. Water-vapor Transmission Rates of Selected Polymers ...

Table 10. Examples of Permeation of Flavor and Aroma Compounds in Selected Polymers at 25 C, Dry...

Ejfects of Thermal, Photochemical and High-energy Radiation 97 Table 5.9 Thermal degradation of selected polymers (Ref, 7)... 

Figure 9.2. Heal deflection temperatures under a load of 1.82 MPa for selected polymers. Note that incorporation of glass fibre has a much greater effect with crystalline polymers than with amorphous ones (after Whelan and Craft courtesy of British Plastics and Rubber)...

Another interesting applications area for fullerenes is based on materials that can be fabricated using fullerene-doped polymers. Polyvinylcarbazole (PVK) and other selected polymers, such as poly(paraphcnylene-vinylene) (PPV) and phenylmethylpolysilane (PMPS), doped with a mixture of Cgo and C70 have been reported to exhibit exceptionally good photoconductive properties [206, 207, 208] which may lead to the development of future polymeric photoconductive materials. Small concentrations of fullerenes (e.g., by weight) lead to charge transfer of the photo-excited electrons in the polymer to the fullerenes, thereby promoting the conduction of mobile holes in the polymer [209]. Fullerene-doped polymers also have significant potential for use in applications, such as photo-diodes, photo-voltaic devices and as photo-refractive materials. 

In the membrane process, the chlorine (at the anode) and the hydrogen (at the cathode) are kept apart by a selective polymer membrane that allows the sodium ions to pass into the cathodic compartment and react with the hydroxyl ions to form caustic soda. The depleted brine is dechlorinated and recycled to the input stage. As noted already, the membrane cell process is the preferred process for new plants. Diaphragm processes may be acceptable, in some circumstances, but only if nonasbestos diaphragms are used. The energy consumption in a membrane cell process is of the order of 2,200 to 2,500 kilowatt-hours per... 

Table 11 Comparison of the Proposed Integrated Approach with Traditional Graph Theory for Selective Polymers...

Equation (40) relates the lifetime of potential-dependent PMC transients to stationary PMC signals and thus interfacial rate constants [compare (18)]. In order to verify such a correlation and see whether the interfacial recombination rates can be controlled in the accumulation region via the applied electrode potentials, experiments with silicon/polymer junctions were performed.38 The selected polymer, poly(epichlorhydrine-co-ethylenoxide-co-allyl-glycylether, or technically (Hydrine-T), to which lithium perchlorate or potassium iodide were added as salt, should not chemically interact with silicon, but can provide a solid electrolyte contact able to polarize the silicon/electrode interface. 

Random copolymers usually exhibit properties which are intermediate between those of the specihc homopolymers. The fact that graft copolymers contain long sequences of two different monomer units indicates that it should be possible to select polymer combinations to give highly specihc properties which are characteristics of the homopolymers involved. 

The program has been useful in searching and summarizing all of the polymers, with specific vendor models, that have published chemical permeation data on a chemical class basis. The advantage of this is the increased the probability of selecting polymers and/or vendors models that may exhibit equal or better chemical permeation resistance to similar chemicals that have not yet been tested. Thus, fewer models may have to be tested with untested chemicals to find an acceptable garment. 

It was our intention in formulating this book to take selected polymers that have been widely studied and provide a comprehensive review of their properties, synthesis, and formulations. We hope that this will be useful to individuals who have been in the field for a long time and who would like to have all the information together in one place, as well as to individuals who are new to the field and would like to understand more about the various properties of biodegradable polymers. 

Typical compositions of polymeric GMs are depicted in Table 26.3. As the table shows, the membranes contain various admixtures such as oils and fillers that are added to aid the manufacturing of the FML but may affect future performance. In addition, many polymer FMLs will cure once installed, and the strength and elongation characteristics of certain FMLs will change with time. It is important therefore to select polymers for FML construction with care. Chemical compatibility, manufacturing considerations, stress-strain characteristics, survivability, and permeability are some of the key issues that must be considered. 

Table I lists the molecular weights and viscoelastic properties for the precursors and selected polymers produced in reaction (34). It also contains the ceramic yields obtained on pyrolysis to 900°C and the composition of the ceramic product.

We use a variant of flexural testing to measure a sample s heat distortion temperature. In this test, we place the sample in a three point bending fixture, as shown in Fig. 8.6 b), and apply a load sufficient to generate a standard stress within it. We then ramp the temperature of the sample at a fixed rate and note the temperature at which the beam deflects by a specified amount. This test is very useful when selecting polymers for engineering applications that are used under severe conditions, such as under the hoods of automobiles or as gears in many small appliances or inside power tools where heat tends to accumulate. 

When selecting polymers for use as insulators, in capacitors, and other electrical applications, we must consider factors other than their interaction with electric fields. The following examples illustrate some of the other factors that we must consider. 

Finally, a further unsolved problem should be mentioned. If we compare the plateau moduli of different polymer melts and relate them to the Kuhn length and to the density, this relation can also be adequately described with the scaling model, if an exponent a near 3 is chosen [73]. It is not known why this exponent is different if the contour length density is varied by dilution in concentrated solution or by selecting polymer chains of different volume. 

We have designed PBUILD, a new CHEMLAB module, for easy construction of random copolymers. A library of monomers has been developed from which the chemists can select a particular sequence to generate a polymeric model. PBUILD takes care of all the atom numbering, three dimensional coordinates, and knows about stereochemistry (tacticity) as well as positional isomerism (head to tail versus head to head attachment). The result is a model of the selected polymer (or more likely a polymer fragment) in an all trans conformation, inserted into the CHEMLAB molecular workspace in literally a few minutes. 

TABLE 2 Quantitative Considerations of Selected Polymer Pairs... 

T. Sokalski, A. Ceresa, T. Zwickl, and E. Pretsch, Large improvement of the lower detection limit of ion-selective polymer membrane electrodes. J. Am. Chem. Soc. 119, 11347-11348 (1997). 

Step 3 Biocompatibility. The biocompatibility of selected polymers, identified in Steps 1 and 2, were evaluated by implanting flat membranes into a C57/B16 mouse (Jackson Labs, Bar Harbor, ME). The membranes and capsules were implanted at various internal sites or in the back tissue under the skin. The results of these tests are not reported herein and will be discussed in a subsequent publication. They do, however, have important implications as to the ultimate selection of a polymeric system. 

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