Homogeneous Polymer Systems

Values of p, Cp, and k are presented for a number of commercially available polymers at 25 °C in Table 5.4 and at 150 C in Table 5.5. Here it is observed that the values 

FIGURE 5.6 Coefficient of thermal conductivity, heat capacity, thermal diffusivity, and density for polycarbonate, a glassy polymer. (Reprinted with permission of the publisher from Tadmor and Gogos, 1979, p. 132.) 

FIGURE 5.7 Thermal property data for a semicrystalline polymer, polypropylene (Data from Wanger, 1969.) 

TABLE 5.4 Density, Thermal Conductivity, and Heat Capacity of Some Polymers at Room Temperature 

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Consider in the first place homogeneous polymer systems in which all the linear polymers are of the same kind with respect to their main chain elements—some variety in side groups can be admitted— though necessarily of the same length. These fall into two categories ... 

In contrast to homogeneous polymer systems, the pendant ionic groups in ionomers interact or associate, forming ion-rich aggregates immersed in the nonpolar matrix of polymer backbone (Figure 15.10). The extent of ionic interactions and, hence, the properties of ionomers, are dictated by the ionic content, degree of neutralization, type of polymer backbone, and cation. 

Thus, the shifting of the data demonstrated in Fig. 7.3 should be represented by Eq. 7.4. The term thermorheologically simple refers to the key caveat that all relaxation times of the polymer must be affected by temperature in the same way. This assumption has been found to hold for a vast array of homogeneous polymer systems. Typically shift factors are found experimentally or by the WLF equation discussed in the next section. 

The fountain flow associated with the advancing front is extremely important to the properties of materials generated by means of injection molding. In the case of homogeneous polymer systems we have already seen how the molecular orientation is affected. For fiber-filled systems, the flow at the front can lead to highly oriented fibers at the surface of... 

In the Institut Fransais du Petrc le process (62), ethylene is dimerized into polymer-grade 1-butene (99.5% purity) suitable for the manufacture of linear low density polyethylene. It uses a homogeneous catalyst system that eliminates some of the drawbacks of heterogeneous catalysts. It also inhibits the isomerization of 1-butene to 2-butene, thus eliminating the need for superfractionation of the product (63,64). The process also uses low operating temperatures, 50—60°C, and pressures (65). 

Kuhn, W., Ramel,A., Walters, D. H. Ebner,G. and Kuhn, H. J. The Production of Mechanical Energy from Different Forms of Chemical Energy with Homogeneous and Cross-Striated High Polymer Systems. Vol. 1, pp. 540 — 592. 

Energy from Different Forms of Chemical Energy with Homogeneous and Cross-Striated High Polymer Systems. VoL 1, pp. 540-592. 

Values of Mw/M of 2 or less are common for the soluble catalyst systems whereas values of 4-8 are usual for ZNC systems. The soluble catalyst systems also are able to polymerize a larger number and greater variety of vinyl monomers to form homogeneous polymers and copolymers in comparison with solid catalyst systems. 

Consider now what occurs on the entry of a radical into a particle that already has a radical. For most reaction systems, the radical concentration in a polymer particle is 10-6 M or higher. This is a higher radical concentration than in the homogeneous polymerization systems and the radical lifetime here is only a few thousandths of a second. The entry of... 

Lactam polymerizations (nonassisted as well as assisted) are usually complicated by heterogeneity, usually when polymerization is carried out below the melting point of the polymer [Fries et al., 1987 Karger-Kocsis and Kiss, 1979 Malkin et al., 1982 Roda et al., 1979]. (This is probably the main reason why there are so few reliable kinetic studies of lactam polymerizations.) An initially homogeneous reaction system quickly becomes heterogeneous at low conversion, for example, 10-20% conversion (attained at a reaction time of no more than 1 min) for 2-pyrrolidinone polymerization initiated by potassium t-butoxide and A-benzoyl-2-pyrrolidinone. The (partially) crystalline polymer starts precipitating from solution (which may be molten monomer), and subsequent polymerization occurs at a lower rate as a result of decreased mobility of /V-acyl lactam propagating species. 

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