Polymer chains, determination

Inter-chain attraction between the polymer chains determines the DP necessary to give the polymer the required toughness, strength, etc. For polymers containing heteroatoms, e.g., polyesters, polyamides, DP of 100-200 is adequate, whereas for polymers with little or no inter-chain attraction, e.g., PE and PP, then DP > 1,000 is recommended. 

The chemical structure of a polymer chain determines its statistical properties, such as its average dimensions in space and its flexibility. These parameters, in turn, affect various properties of a network consisting of these chains. A detailed understanding of the single chain is therefore important in this regard. 

Localization or delocalization of an excess electron (in anion radicals) and a hole (in cation radicals) along the polymer chain determines the electronic conductivity of the polymeric ion radicals. From this point of view, the cation radical of vinylene-bridged-oc-tithiophene oligomer should be mentioned. Quantum chemical calculation (Casado et al. 2000) indicates that the hole localizes in the middle of the molecule. The hole extends over the central part built from four thyenylene units. 

EPR-Spectroscopy of Spin-Marked Macromolecules as the Method of Polymer Chains Determination in Amorphous Solid Polymers... 

The cross-link density and the spacing of cross-links along the polymer chain determine the relative flexibility of the rigid network structures, which are naturally more resistant to heat, solvents, and chemical attack than uncross-linked polymers. Flexibilizing polymers or fillers are also added to thermosetting resins to improve toughness and reduce brittleness of the adhesive. 

Boyer, R. Determination of the packing density of solid polymer chains. Determination of the specific surface area of polymers by sorption of nitrogen vapor. Polym. Eng. Sci. 1968, 8 (3), 161. Bershtien, V. Egorov, V. Differential Scanning Calorimetery in the Physical Chemistry of Polymers] Ellis Horwood Chichester, 1993. 

Because the same molecular process, thermal excitation of segmental motion of the polymer chains, determines both the glass transition temperature and the tensile strength and extensibility of the polymer, it is not surprising to find a close correlation between the To and these mechanical properties of polymers (Table... 

Number of DC groups per one polymer chain, determined by UV absorption. 

The weakest bond in a polymer chain determines the overall thermal stability of the polymer molecule. The aliphatic carbon-carbon bond has a relatively low bond energy (see Table 5.1). Oxidation of alkylene groups is also observed during prolonged heating in air. Thus the weak links to be avoided are mostly those present in alkylene, alicyclic, unsaturated, and nonaromatic hydrocarbons. On the other hand, the functions proven to be desirable are aromatic (benzenoid or heterocyclic) ether, sulfone, and some carboxylic acid derivatives (amide, imide, etc.). Aromatic rings in the polymer chain also give intrinsically stiff backbone. 

Functionality refers to the moieties chemically distinct from the repeating units of polymer chains. It can be the terminal groups at chain ends or the functional groups deliberately added to a polymer chain. Determination of functionality type distribution of reactive oligomers (telechelics) is an old problem in polymer characterization. The classical method is the combination of SEC separation and functionality sensitive detection. Recent advances of the detection methods such as FT-NMR and MALDl-TOF MS have brought about big improvements in the precision of functionality characterization [12]. 

It is evident that the molecular weight of a polymer chain determines important properties such as viscosity and mechanical strength. Because synthetic polymers do not have a single chain length i and are instead polydisperse, any measure of molecular weight is an average. The chain length distribution is typically characterized by the first three moments of the distribution, where the Mi moment is described as follows ... 

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