Poly polymer motion

Vega AJ, English AD (1980) Multiple-pulse nuclear magnetic resonance of solid polymers. Polymer motion in crystalline and amorphous poly(tetrafluoroethylene). Macromolecules, 13 1635... 

Increa sing the bulkiness of the alkyl group from the esterifying alcohol in the ester also restricts the motion of backbone polymer chains past each other, as evidenced by an increase in the T within a series of isomers. In Table 1, note the increase in T of poly(isopropyl methacrylate) over the / -propyl ester and similar trends within the butyl series. The member of the butyl series with the bulkiest alcohol chain, poly(/-butyl methacrylate), has a T (107°C) almost identical to that of poly(methyl methacrylate) (Tg = 105° C), whereas the butyl isomer with the most flexible alcohol chain, poly( -butyl methaciylate), has a T of 20°C. Further increase in the rigidity and bulk of the side chain increases the T. An example is poly(isobomyl methacrylate)... 

In the case of polymer molecules where the dipoles are not directly attached to the main chain, segmental movement of the chain is not essential for dipole polarisation and dipole movement is possible at temperatures below the glass transition temperature. Such materials are less effective as electrical insulators at temperatures in the glassy range. With many of these polymers, e.g., poly(methyl methacrylate), there are two or more maxima in the power factor-temperature curve for a given frequency. The presence of two such maxima is due to the different orientation times of the dipoles with and without associated segmental motion of the main chain. 

Experimental values of the molar mass exponent close to 2 have been obtained. For example, for poly(methyl methacrylate), a value of 2.45 has found (see P. Prentice, Polymer, 1983, 24, 344—350). As with values of selfdiffusion coefficient, this has been regarded as close enough to 2 for reptation to be considered a good model of the molecular motion occurring at the crack tip. 

The classical example of a soUd organic polymer electrolyte and the first one found is the poly(ethylene oxide) (PEO)/salt system [593]. It has been studied extensively as an ionically conducting material and the PEO/hthium salt complexes are considered as reference polymer electrolytes. However, their ambient temperature ionic conductivity is poor, on the order of 10 S cm, due to the presence of crystalUne domains in the polymer which, by restricting polymer chain motions, inhibit the transport of ions. Consequently, they must be heated above about 80 °C to obtain isotropic molten polymers and a significant increase in ionic conductivity. 

In one example, the Tics of the non-crystalline methyl, methine and methylene carbons of iPP, 70% crystalline, were compared at room temperature with those of model atactic poly(propylene), hydrogenated poly(2-methyl-l,3-pentadiene) [163]. It was found that, within the experimental error, the Tic values of each of the carbons were the same in both polymers. The conclusion can then be reached that the fast segmental motion, at or near the Larmor frequency of... 

Very recently, however, two papers were published by the group of Fujiki which report successful solid-state CD studies of chiral polysilanes. In the first, a helix-coil transition was described for film samples of poly[(A)-3,7-dimethyloctyl- -propylsilylene)], 113.327 This polymer has a relatively low glass transition temperature, T, which was considered critical for the observation of a helix-helix transition in the solid state, since helical inversion would be precluded if the inversion temperature, Tc, were below Ts as the segmental motion of the chain,... 

The method is based on the fact that the rate of conformational change required for excimer formation depends on the free volume induced by the segmental motions of the polymer occurring above the glass transition. DIPHANT (compound 3 in Figure 8.3) was used as an excimer-forming probe of three polymer samples consisting of polybutadiene, polyisoprene and poly(dimethylsiloxane).a)... 

Many polymer-salt complexes based on PEO can be obtained as crystalline or amorphous phases depending on the composition, temperature and method of preparation. The crystalline polymer-salt complexes invariably exhibit inferior conductivity to the amorphous complexes above their glass transition temperatures, where segments of the polymer are in rapid motion. This indicates the importance of polymer segmental motion in ion transport. The high conductivity of the amorphous phase is vividly seen in the temperature-dependent conductivity of poly(ethylene oxide) complexes of metal salts. Fig. 5.3, for which a metastable amorphous phase can be prepared and compared with the corresponding crystalline material (Stainer, Hardy, Whitmore and Shriver, 1984). For systems where the amorphous and crystalline polymer-salt coexist, NMR also indicates that ion transport occurs predominantly in the amorphous phase. An early observation by Armand and later confirmed by others was that the... 

In the example above, a short-chain poly(ethylene glycol) was added to a rigid polyelectrolyte to plasticise the material and thereby increase polymer-solvent motion in the vicinity of mobile ions. This strategy has been widely explored as a means of improving ion transport in electrolytes. 

Fig. 4.13 Momentum transfer dependence of the characteristic time associated to the self-motion of protons in the a-relaxation regime Master curve (time exponentiated to p) constructed with results from six polymers polyisoprene (340 K, p=0.57) (filled square) [9] polybutadiene (280 K, p=0Al) (filled circle) [146] polyisobutylene (390 K, p=0.55) (empty circle) [147] poly (vinyl methyl ether) (375 K, f=0A4) (filled triangle) [148] phenoxy (480 K, p=0A0) (filled diamond) [148] and poly(vinyl ethylene) (340 K, p=0A3) (empty diamond) [ 146]. The data have been shifted by a polymer dependent factor Tp to obtain superposition. The solid line displays a Q -dependence corresponding to the Gaussian approximation (Eq. 4.11). (Reprinted with permission from [149]. Copyright 2003 Institute of Physics)...

These conclusions are further generalized by the more extensive data presented in Fig. 7 for polyethylene oxide and poly-trimethylene oxide. The continuous nature of the Ti function for both these polymers over a large temperature range is quite definite and is emphasized by the detailed data in the vicinity of the respective melting temperatures. This is true even for the polyethylene oxide samples where discontinuities in the linewidth are clearly indicated in Fig. 7. Obviously, the type of segmental motions which contribute to the two different relaxation pareim-eters are influenced quite differently by the presence of crystallinity. 

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