Other Representative Polymer Systems

For reasons of space it is not possible to give a comprehensive list of the various prepolymer commercial systems available. Instead, various representatives have been chosen to illustrate several commercial chemical combinations and their particular properties. Typical properties for a variety of commercial systems are given in Table 5.6-5.12. 

PHYSICAL PROPERTIES OF URETHANES OF POLYCAPROLACTONE/TDI (MOCA CHAIN 

60D indicates a Shore Hardness of 60 on the Shore Durometer scale D  

COMMON COMMERCIALLY AVAILABLE DIAMINE CURING AGENTS FOR LIQUID POLYURETHANE ELASTOMERS 

PROPERTIES OF URETHANE ELASTOMERS PREPARED FROM TWO TYPES OF PREPOLYMER CURED WITH 3,3 -DICHLORO-4,4 -DIAMINO- 

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Polymer products synthesized in laboratories and in industry represent a set of individual chemical compounds whose number is practically infinite. Macro-molecules of such products can differ in their degree of polymerization, tactici-ty, number of branchings and the lengths that connect their polymer chains, as well as in other characteristics which describe the configuration of the macromolecule. In the case of copolymers their macromolecules are known to also vary in composition and the character of the alternation of monomeric units of different types. As a rule, it is impossible to provide an exhaustive quantitative description of such a polymer system, i.e. to indicate concentrations of all individual compounds with a particular chemical (primary) structure. However, for many practical purposes it is often enough to define a polymer specimen only in terms of partial distributions of molecules for some of their main characteristics (such as, for instance, molecular weight or composition) avoiding completely a... 

The experimental results may be represented both by the titration curves or property-composition dependences. The extremums or bends on the titration curves indicate the formation of complexes and their composition. Thus, investigating the-possi-bility of complex formation in polyelectrolyte - nonionic polymer systems, one can use the methods of conductometric and potentiometric titration. The formation of interpolymer complexes in these systems, as some authors suggest18,211, is caused by a co-operative formation of hydrogen bonds between carboxy groups of the polyacid and oxygen atoms of nonionic polyvinylpyrrolidone or poly(ethylene glycol) and is therefore accompanied by an increase of pH of the solution. The typical titration curves for the system polyvinylpyrrolidone - copolymer maleic anhydride and acrylic add are shown in Fig. 1. The inflection points of the titration curves indicate the ratio at which the macromolecular components react with each other, i.e. the composition of the formed complexes. 

On close inspection the data of tables I and II show a number of inconsistencies with a three component model previously used to describe the excimer, quenched monomer and isolated monomer sites in other polymer systems (3 - 5.). For instance, if we consider the 25"C data for Poly(VBuPBD),Tj might be considered to represent the excimer, T2 the quenched monomer and T3 isolated monomer. However, B2 and B3 do not decrease proportionately as measurements are made at wavelengths further displaced from that dominated by monomer emission, though the high degree of monomer and excimer spectral overlap (Figure 1) means that B2 and B3 would not be expected to approach zero. In addition, the decay parameters clearly... 

The behavior of a polymer system is so complicated that we cannot represent it with the response time of a single Maxwell element. In other words, the simple model described above cannot approach the behavior of a real system. In 1893, Weichert showed that stress-relaxation experiments could be represented as a generalization of Maxwell s equation. The mechanical model according to Weichert s formulation is shown in Figure 3.11 it consists of a large number of Maxwell elements coupled in parallel. 

The adhesion properties of all types of polyolefins are not easy to explain because these properties are affected by different phenomena. Using of a single theory or mechanisms based on the physical and chemical adhesion manifestations is difiicult for the description of interdisciplinary nature and diversity. There is considerable information to discuss each of the adhesion mechanisms. Therefore, it is not possible to select only the thermodynamic theory of adhesion that is the best to describe the surface free energy of the polyolefin. All mechanisms and adhesion theories are implied by the diversity of polymer systems, which are embraced in combination with research for the analyses of adhesion properties. The physical and chemical composition in the first atomic layers dictates the adhesion and some other properties of the polymer materials. This layer represents underneath layer and this subsurface partially controls the outer layers. The double bonds and cross-linked stmctures limit the mobility macromolecules of polyolefins in the subsurface layers, which results in the functional group stabilization on the surface. Other basic research is necessary for an examination of the polymer subsurface layer and explanation of its effect changes of the surface properties. Moreover, for the improvement of quantitative measurements of adhesion, additional investigation is required. 

Figure 2.11. Models for two-phase polymer systems. Elements in (a) and (b) form the basic parallel and series models. Combinations shown in (c) and (d) represent two other possible models. Note the similarity to the spring and dashpot models often invoked in explaining homopolymer behavior. (After Takayanagi et ai, 1963.) Part (a) represents an isostrain model, (b) represents an isostress model, and (c) and (d) illustrate combinations of these limiting cases.

As with other three parameter systems, solvents are represented by points in a three dimensional model and polymer solubility by a volume. Solvents falling within this volume of solubility dissolve the polymer and those outside the volume do not. Hansen found that by doubling the scale of the d axis relative to the other axes, the volumes of solubility of most polymers were approximately spherical. This means that each polymer may be described in terms of the centre of this sphere having coordinates d o, po and and its radius (known as the radius of interaction), Rao- Values of the centre coordinates and radii of interaction for several polymers are given in Table 2.16. 

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