Valence properties, polymer chains

Primary structure refers to the atomic composition and chemical structure of the monomer — the building block of the polymer chain. An appreciation of the nature of the monomer is fundamental to understanding the structure-property relationship of polymers. The chemical and electrical properties of a polymer are directly related to the chemistry of the constituent monomers. The physical and mechanical properties of polymers, on the other hand, are largely a consequence of the macromolecular size of the polymer, which in itself is related to the nature of the monomer. By definition, a polymer is a chain of atoms hooked together by primary valence bonds. Therefore, basic to understanding the structure of the monomer vis-a-vis the structure and properties of the resulting polymer is a fundamental understanding of ... 

The ideal, classical, rubbery properties are displayed by polymers cross-linked by valence bonds (main-chain bonds or sulphur bridges, see Introduction, Fig. 0.1) these are termed chemical cross-links. Physical cross-links are also important in many useful rubbery materials. In physical cross-linking the chains are not chemically attached one to another, but are effectively pinned together in one of three ways ... 

Just as the equilibrium conformational properties of macromolecules, the theory of which has been developed in well-known classical works by Kuhn, Flory, Volken-stein and others " the kinetic properties of polymer chains can be determined by two main mechanisms of intramolecular mobility. First, it is the discrete rotational isomeric (rotameric) mechanism of mobility caused by the jump of small-chain segments (kinetic units) from certain energically stable allowed conformers into others ° 1S4-16S) gg ond it is the continuous mechanism of motion determined by the accumulation of vibrational displacements of units owing to the twisting or bending vibrations (and librations) or valence angles and angles of internal rotation 45 i - ... 

Although VEH uses a set of parameterized one-electron orbitals, its accuracy approaches that of true ab initio methods. VEH gives ground-state properties, ionization potentials and energy gaps typically within 0.1 eV of the experimental values. The evolution of the band structure of poly(l,4-phenylene) (10 poly(p-phenylene), PPP) during inclusion of sodium is shown in Figure 3. The relaxation of the polymer chain in the vicinity of added electrons produces states in the band gap. These eventually fuse with the valence and conduction bands as Na content increases. These states and their relevance to the properties of real systems has been the focus of much excitement and debate. 

Carothers had already settled the controversy between Staudinger and his opponents. He had built Staudinger s macromolecules, and the properties of his macromolecules were identical to those of natural polymers. Even more, his path breaking technique of condensation polymerization had demonstrated that his macromolecules consisted of long chains held together by ordinary valence bonds. 

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