Chemical bonding in polymers

The enzyme then breaks chemical bonds in polymer chains such as ester, glycosidic, and peptide bonds by a hydrolysis reaction... 

Each chemical reaction requires a minimum amount of energy to activate the breaking of the first chemical bond. The energy of a quantum of ultraviolet radiation is sufficient to break many of the chemical bonds in polymers. Impurities, e.g. metal ions, and imperfections, e.g. oxygen incorporated into the polymer, are affected by visible hght. Visible Ught causes slow changes in polymer properties (Feller et al., 1981). Ultraviolet absorbers and stabilizers are used to increase the... 

Table 1 The characteristics of some single chemical bond in polymers...

This review has shown that the analogy between P=C and C=C bonds can indeed be extended to polymer chemistry. Two of the most common uses for C=C bonds in polymer science have successfully been applied to P=C bonds. In particular, the addition polymerization of phosphaalkenes affords functional poly(methylenephosphine)s the first examples of macromolecules with alternating phosphorus and carbon atoms. The chemical functionality of the phosphine center may lead to applications in areas such as polymer-supported catalysis. In addition, the first n-conjugated phosphorus analogs of poly(p-phenylenevinylene) have been prepared. Comparison of the electronic properties of the polymers with molecular model compounds is consistent with some degree of n-conjugation in the polymer backbone. 

For the most part, plastics are man-made since very few plcistlcs are natural, i.e.- nature-made. Natural plastics include large molecular-wei t proteins and similar molecules. Man-made plastics can be classified as either thermoplastic or thermosetting. Each class derives its physical properties from the effects of application of heat, the former becoming "plastic" (that is- it becomes soft and tends to flow) while the latter becomes less "plastic" and tends to remain in a softened state. This difference in change of state derives from the actual nature of the chemical bonds in the polymer. Thermoplastic polymers generally consist of molecules composed of many monomeric units. A good example is that of polyethylene where the monomeric unit is -(CH2-CH2)-. The molecule is linear... 

Track-Etched Track-etched membranes (Fig. 20-66) are now made by exposing a thin polymer film to a collimated beam of radiation strong enough to break chemical bonds in the polymer chains. The film is then etched in a bath which selectively attacks the damaged polymer. The technique produces a film with photogenic pores. 

Chemical bond in the main chain of a polymer molecule that is most susceptible to scission. 

Block copolymers have been obtained from polymeric radicals, which—unlike those employed for graft polymerization—have the radical centers at the ends of the polymer chains. This can be achieved by breaking chemical bonds in the polymer backbone by mastication (mixing) of the polymer [Ceresa, 1973, 1976, 1978 Sakaguchi and Sohma, 1978]. If... 

The molar cyclization equilibrium constants, Kx, of PDMS are measured. Using the Jacobson and Stockmayer equilibrium theory of macrocyclization, the dimensions of PDMS chains with 40-80 chemical bonds in the bulk polymer at 383 K are deduced. Dilution effects in the PDMS systems are contrasted with predictions of the Jacobson-Stockmayer theory, and the experimental molar cyclization equilibrium constants of the smallest siloxane rings are discussed in terms of the statistical properties of the corresponding oligomeric chains using tire RIS model of PDMS of Flory, Crescemi, and Mark [S 116]. 

In conventional organic nomenclature, a polymer is not considered to be an isomer of the repeating molecular unit, because the molecular formulas formally differ. This is a somewhat arbitrary distinction, however, because it is never really an isolated, single molecule of monomer that is compared with the polymer. In an aggregate of monomer molecules, intermolecular forces exist and the constitutional difference from an aggregate of polymer molecules is simply that some intermolecular forces have been converted into true chemical bonds. In any case, the term polymerization isomerism has had a long-standing use in coordination chemistry. It may refer... 

It became necessary to investigate the morphology of the cured adhesive and its changes. The changes occur owing to splitting of chemical bonds in the polymer network. 

A polymer chain has an enormous number of chemical bonds. For this, in the solution and amorphous states the NMR chemical shifts of polymers are often the averaged values for all of the possible conformations because of rapid interconversion by rotation about chemical bonds. In solids, however, chemical shifts are often characteristic of specific conformations because of strongly restricted rotation about the bonds. The NMR chemical shift is affected by a change of the electronic structure through the structural change(2). Solid state NMR chemical... 

---