Solid macromolecular

These traps, (Fig. 6) and similar effects in the motion of holes and other charges through polymers, would eventually be correlated also with such structural probes as positron lifetimes in macromolecular solids. Extensive recent studies of positron lifetime are based on positronium decay. In this, the lifetime of o-positronium (bound positron-electron pair with total spin one) is reduced from about 140 nanoseconds to a few nanoseconds by "pick-off annihilation" in which some unpaired electron spins in the medium cause conversion quenching of orthopositronium to para-positronium. The speed of the t2 effect is supposed, among other things, to represent by pick-off annihilation the presence of defects in the crystalline lattice. In any case, what amounts to empty space between molecules can then be occupied by orthopositronium.(14,15,16) It is now found in linear polyethylene, by T. T. Wang and his co-workers of Bell Laboratories(17) that there is marked shift in positron lifetimes over the temperature range of 80°K to 300°K. For... 

Coals are considered macromolecular solids.(l) Although they are not polymers in the sense that they possess a repeating unit, they do possess several fundamental properties typical of synthetic crosslinked polymers.(2) One of these properties is the ability of coals to swell in organic solvents without dissolving. 

We shall conclude with some remarks on the structure of glassy polymers. If one frequently speaks of glass structures, this does not mean that there exists one definite glass structure similar to a crystal. In a macromolecular solid-e.g., the polystyrene-plasticizer system, entirely different glasses are obtainable, the macroscopic composition of which is always the same (8). In Figure 10 the full... 

Crystalline solids may be classified as (1) ionic solids, in which the repeating units are ions (2) network solids (or macromolecular solids), in which covalently bonded atoms are the repeating units (3) molecular solids, in which individual molecules are the repeating units and (4) metallic solids, in which individual metal atoms are held together by their loosely held valence electrons. 

Figure 14.2 Tiny Portions of Structures of Three Macromolecular Solids...

Although the mechanical response of macromolecular solids is complex, it is possible to gain an understanding of the broad principles that govern this behavior. Polymeric articles can be designed rationally, and polymers can be synthesized for... 

These theories are based on the classical theories of rubber elasticity of macromolecular solids, wherein permanent chemical crosslinks connect segments of molecules, forcing them to move together. This central idea can be applied to polymeric liquids. However in this case, the interactions between molecules are assumed to be localized at junctions and are supposed to be temporary. Whatever their nature, physical or topological, these crosslinks are continually created and destroyed but, at any time, they ensure sufficient connectivity between the molecules to give rise to a certain level of cooperative motion. 

Commonly applied polymeric supports are gels, loosely arranged and weakly structured macromolecular solids. A gel may swell to many times its collapsed volume when brought in contact with solvents for which it has a strong affinity. A swelled gel resembles a liquid in many ways, and catalytic groups bonded within a gel may act like catalytic groups in solution. 

As noted in the preceding section, IGC is an excellent tool for measurements of surface properties and of acid base interaction potentials of macromolecular solids (2,10,16). In this section the importance of acid-base interactions relative to the adhesion of PUs is considered in greater detail. IGC has been applied to a series of PU adhesives and to selected polymer substrates, allowing quantitative measurements to be made of the acid/base (electron donor-acceptor) interaction parameters applicable to the surfaces of these materials. Acid base pair-interaction parameters for substrate/PU combinations have been calculated. The bond characteristics of polymer/PU combinations have been measured, in part by conventional lap-shear procedures and in part, by the more recent constrained blister detachment method [11, 12]. Possible relationships between bond properties and acid base interactions have been considered, and a comparison of the two adhesion tests has been made. 

Of particular interest in connexion with our subject is the case of compound formation by a macromolecular solid e. g., the hydrate formation by cellulose and gelatin or the formation of an addition compound between nitrocellulose and acetone. Whereas in ordinary low molecular hydrates the composition of the successive compounds X, X. HgO, X. 2HaO etc. differs considerably as regards the percentage of water and, hence, the Gibbs potentials of these compounds differ by considerable jumps, the situation is different in macromolecular substances. If e.g., each monomeric residue R of a molecule consisting of a chain of n residues can bind one water molecule, the following hydrates are possible ... 

Figtire 16. Maximum draw ratio of dried gels of UHMW PE versus initial polymer volume fraction (0). The draw temperature was 130 C. This graph illustrates that upon simple reduction of the entanglement density in otherwise identical macromolecular solids, the draw ratio can be increased by more than an order of magnitude. 

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