Temperature dependence poly segmental

V, is the molar volume of polymer or solvent, as appropriate, and the concentration is in mass per unit volume. It can be seen from Equation (2.42) that the interaction term changes with the square of the polymer concentration but more importantly for our discussion is the implications of the value of x- When x = 0.5 we are left with the van t Hoff expression which describes the osmotic pressure of an ideal polymer solution. A sol vent/temperature condition that yields this result is known as the 0-condition. For example, the 0-temperature for poly(styrene) in cyclohexane is 311.5 K. At this temperature, the poly(styrene) molecule is at its closest to a random coil configuration because its conformation is unperturbed by specific solvent effects. If x is greater than 0.5 we have a poor solvent for our polymer and the coil will collapse. At x values less than 0.5 we have the polymer in a good solvent and the conformation will be expanded in order to pack as many solvent molecules around each chain segment as possible. A 0-condition is often used when determining the molecular weight of a polymer by measurement of the concentration dependence of viscosity, for example, but solution polymers are invariably used in better than 0-conditions. 

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... 

Thus, the PEO segment actually becomes hydrophobic at higher temperatures. This temperature-dependent change converts the amphiphilic block copolymer to a water-insoluble hydrophobic polymer (Topp et al. 1997 Chung et al. 2000). The temperature at which the polymer exhibits this transition is called its lower critical solution temperature (LCST). In addition to PEO, substituted poly(A -isopropyl acrylamide) (PNIPAM Chart 2.1) exhibits temperature sensitivity, where the LCST can be tuned by varying the alkyl fimctionahty. The guest encapsulation combined with the temperature-sensitive precipitation of the polymers has been exploited to sequester and separate guest molecules from aqueous solutions (Fig. 2.4). 

The high rigidity of the catenane segments has been demonstrated by a temperature-dependent NMR spectroscopic study of the catenane monomers 44 and 46 [37, 52], Almost no temperature dependence was observed for the line shape of the spectra of the catenane monomers 44 and 46 whereas the temperature had a dramatic influence on the spectra of the unmethylated catenanes 41b,d and 42b,d [30, 37, 52, 56]. Therefore, the poly[2]catenanes 48 and 49 represent one extreme case where there is very little relative mobility of the macrocycles of the catenane segments. 

In the absence of solvent, the influence of the surface on the segmental mobility can be deduced by measuring the temperature dependence of the spectral line shape in the presence and absence of the surface. The temperature dependence of bulk poly(vinyl acetate) is shown in Figure 3, and of bulk polystyrene... 

Certain aspects of thermoplastic polyurethanes derived from poly(oxyethylene-oxypropylene)glycols have been described. Low temperature impact resistance and heat sag properties are dependent on segment length with 2000 molecular weight polyols being required for acceptable performance in automobile parts. 

The temperature dependence of the steric interaction between sterically stabilized particles mirrors the temperature dependence of [t x(7)]-Croucher and Hair (1978) have calculated the temperature dependence of the steric repulsion between two sterically stabilized particles of poly(acrylonitrile) stabilized by poly(a-methylstyrene) in n-butyl chloride. The particle radius was taken as 100 nm and each steric layer, assumed to be of constant segment density, was taken to be 12 nm thick. The parabolic nature of the repulsion as a function of temperature for two different distances of particle separation is obvious from Fig. 12.10. 

Since both the glass transition temperature and the melting temperature depend on the mobility of segments or molecules, a relationship between these two parameters should exist. If the cumulative frequencies of To / Tm ratios are plotted against these ratios, then a smooth curve is obtained for more than 70 homopolymers (Figure 10-20). Deviations are only found for low TgITm ratios and these belong to unsubstituted polymers such as poly(ethylene), poly(oxymethylene), poly(oxyethylene), etc. The median of the curve is independent of the constitution of the polymers, and corresponds to the empirical Beaman-Boyer rule ... 

Temperature dependence of dielectrically determined relaxation times "c of monomeric segments of poly(2-chlorostyrene) (P2CS) and poly(vinyl methyl ether) (PVME) in P2CS/PVME miscible blends with various P2CS volume fractions ( )p2cs as indicated. (Data taken, with permission, from Urakawa, O., Y. Fuse, H. Hori, Q. Tran-Cong, and O. Yano. 2001. A dielectric study on the local dynamics of miscible polymer blends Poly(2-chlorostyrene)/poly(vinyl methyl ether). Polymer 42 765-773.)... 

Haley, J. C., T. P. Lodge, Y. Y. He, M. D. Ediger, E. D. von Meerwall, and J. Mijovic. 2003. Composition and temperature dependence of terminal and segmental dynamics in polyisoprene/poly(vinylethylene) blends. Macromolecules 36 6142-6151. 

The glass-transition temperature depends on the mobility of the chain segments and can therefore be raised by stiffening the chain (see Section 10.5.3). Thus, a-methyl styrene forms a polymer that, in contrast to poly-(styrene), does not deform at lOC C, because of a glass-transition temperature of 170°C. However, since the thermodynamic ceiling temperature for for the polymerization/depolymerization equilibrium is also simultaneously lowered (see Section 16.3), poly(a-methyl styrene) degrades more easily than poly(styrene), so that it is not so easy to work by injection molding. 

Poly(cyclohexyl methacrylate) PCHMA M = 2x 10 Heterogeneous backbone polymers 359.7 14.8 75.67 374 [99] aj a of local segmental motion from data of local density fluctuation observed by PCS, mechanical relaxation and dielectric relaxation. When referenced to the respective TgS (I.e. plotting log(ar, ) against (T-Tg) the shift factor of PCHMA has a considerably stronger temperature dependence than that of Pn-HMA. 

Measurements of the frequency and temperature dependence of the H T, in poly(dimethyl siloxane) revealed relaxations due to methyl rotation and segmental motions and also an oxygen impurity effect The experimental data could not be fitted using thermally activated Arrhenius behaviour, as was also true of backbone motions in poly(vinyl chloride). " Multiple side-group motions have also been observed in poly (diethyl siloxane) and poly(L-histidine). Backbone motions have been observed in poiy(diethyl siloxane), poly(oxymethylene), poly(ethylene terephthalate), poly(p-phenylene sulphide), aromatic polyamides, and PTFE. A close similarity between the effects of entanglements and radiation cross-linking on the of cis-polyisoprene has been found. ... 

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