Melting molecular mass dependence

Molecular-mass dependence of the melting temperature of polyethylene (CH2 )x... 

Figure 9.20 Molecular mass dependence of the melting temperatures of poly(ethylene oxides) for extended (a) and folded (b) crystal (based on data from References [1, 3]).

Fig. 26. Decay times Tpu) to 1/e of the initial value of the free-induction signals in melts of linear polyethylene at 150 "C as a fimction of molecular mass. The horizontal broken line (a) indicates the instrumental homogeneity limitation determined with a water sample at 30 °C (see Fig. 25). The motional averaging region (b) is characterized by a strong molecular mass dependence equivalent to that of the proper (effective) transverse relaxation time (see Fig. 19d). It is therefore attributed to the combined influence of components B and C. The plateau (c) reached at high molecular masses reflects the unaveraged effect of internal field inhomogeneities corresponding to a full width at half maximum of the resonance line of about 7 ppm. This value can be estimated on the basis of the magnetic susceptibility of polyethylene relative to that of empty voids [152]...

Yield stress values can depend strongly on filler concentration, the size and shape of the particles and the nature of the polymer medium. However, in filled polymer melts yield stress is generally considered to be independent of temperature and polymer molecular mass [1]. The method of determining yield stress from flow curves, for example from dynamic characterization undertaken at low frequency, or extrapolation of shear viscosity measurements to zero shear rate, may lead to differences in the magnitude of yield stress determined [35]. 

Molecular Weight Dependence of Phase Structure. Similar line shape analysis was performed for samples with molecular weight over a very wide range that had been crystallized from the melt. In some samples, an additional crystalline line appears at 34.4 ppm which can be assigned to trans-trans methylene sequences in a monoclinic crystal form. Therefore the spectrum was analyzed in terms of four Lorentzian functions with different peak positions and line widths i.e. for two crystalline and two noncrystalline lines. Reasonable curve fitting was also obtained in these cases. The results are plotted by solid circles on the data of the broad-line H NMR in Fig. 3. The mass fractions of the crystalline, amorphous phases and the crystalline-amorphous interphase are in good accord with those of the broad, narrow, and intermediate components from the broad-line NMR analysis. 

The dependence of on the molecular mass of the polymer has been interpreted as a melting point depression caused by the chain ends, which act as if they were a low molecular weight impurity (solvent). The lower the molecular weight, the larger the proportion of terminal groups and consequently the lower the melting temperature, T. ... 

Carefully performed cryoscopic measurements of solutions of Sg-I-S,j in CS2 yielded a relative molecular mass of 260 corresponding to 8.1 atoms per molecule. This value did not depend significantly on the concentration of the solution nor on the temperature of the sulfur melt (130-350 C) from which the Ss+S solution was prepared [26]. 

The quantity rj/G represents the melt relaxation time to, the time in which shear stress decays to He (34%) of its original value. The relaxation time depends on the molecular mass and the melt temperature, factors which... 

The type of dependences on the composition, on the crystallization temperature, and on the chemical nature and molecular mass of the components observed in kinetic and thermodynamic properties, relative to the isothermal crystallization process, the final overall morphology, and the thermal behaviour, are all to be related to the physical state of the melt, which at is in equilibrium with the developing solid phase. 

Dependence of melting temperatures on relative molecular mass (RMM). At low RMM there is one at higher RMM there is a band of melting temperatures, which is due to the existence of a range of crystal thicknesses in the solid polymer. 

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