Crystalline melting point, molecular

Features of chemical structure that affect the degree of molecular freedom influence both the crystalline melting point and the glass transition temperature. Moreover, such features have roughly similar effects on both properties, so that the empirical rule has been found that for many polymers ... 

Crystalline fructose, 23 485-486 Crystalline glycolic acid, 14 127 Crystalline hybrid compounds, 13 546-548 Crystalline inclusion compounds, 14 184 molecular recognition behavior of, 16 796 preparation of, 14 182 Crystalline melting point, of polymers, 20 399... 

Although polymers exhibit both viscous and elastic responses at all temperatures, the elastic response is particularly strong at temperatures less than 50°C above the glass transition temperature, particularly for polymers well above their critical molecular weight. Polymers are often considered to have dominant viscous rheological responses if they are stressed at temperatures over 100 °C above the glass transition temperature for amorphous polymers or 100°C above the crystalline melting point for semicrystalline resins. 

The prediction of the chemical thermostability is based on the rules on the thermal stability and the reactivity of chemical bonds known for low-molecular-weight compounds. Instead, the physical thermostability depends on the transition points of the macromolecules, i.e., the glass transition temperature Tg in case of amorphous polymers, and additionally the crystalline melting point in case of crystalline polymers. 

The thermomechanical properties of an organic material mainly depend on two factors. Firstly the molecular relaxations (crystalline melting point and glass transitions) which determine the temperature upper limit for applications, and secondly the chemical nature of the backbone which is responsible for the stability in a harsh environment. 

Table 10 also contains values of the unperturbed dimensions of many aliphatic polyesters. Most of these have been evaluated from the extensive results of Batzer and his collaborators (32a, 32b, 32c, 32d, 32c, 33a, 168") which combine intrinsic viscosities with osmotic molecular weights of fractions. Since almost all of these polymers have rather high crystalline melting points, and since the fractionations were generally performed at temperatures well below these melting points, we have somewhat arbitrarily chosen a value of 1.5 for the molecular weight ratio which corresponds to a figure of 1.22 for the correc-... 

Some polymers, such as cellulose, although linear in structure, have such a strong molecular interaction, mostly due to hydrogen bridges and polar groups that they do not soften or melt. Consequently, the transition temperatures as such are less important to this class of polymers. Normally they are highly crystalline, with a crystalline melting point (far) above the decomposition temperature. Their physical behaviour - except for... 

The function Ym (like Yg) has the dimension (K kg moF1). The group increments for this function could be derived from the available literature data on crystalline melting points of polymers, totalling nearly 800. The quantity Ym (like Yg) does not show simple linear additivity due to intra- and inter-molecular interactions between structural groups. The available group contributions and their structural corrections are summarised in Table 6.8. We shall again discuss these data step by step. 

The influence of molecular mass on the crystalline melting point... 

Most crystalline polymers do not exhibit a crystalline melting point but a decomposition point where depolymerization starts (ca. 340 °C for poly-DSP and ca. 420 °C for poly-PDA phenyl ester by DSC). The decomposition point, however, is not strictly definable, because it is greatly affected by the morphology and the molecular weight of the polymer (see Sect. VI. a.). 

In the Phillips process, polyphenylene sulfide (PPS) is obtained from the polymerization mixture in the form of a fine white powder, which, after purification, is designated Ryton V PPS. Characterization of this polymer is complicated by its extreme insolubility in most solvents. At elevated temperatures, however, Ryton V PPS is soluble to a limited extent in some aromatic and chlorinated aromatic solvents and in certain heterocyclic compounds. The inherent viscosity, measured at 206°C in 1-chloronaphthalene, is generally 0.16, indicating only moderate molecular weight. The polymer is highly crystalline, as shown by x-ray diffraction studies (9). The crystalline melting point determined by differential thermal analysis is about 285°C. 

The crystalline melting point and the glass transition temperature of a polymer, in themselves, provide a rough characterization of the polymer properties they also provide reference points for the various regimes within which the quantitative evaluation of properties must be made. How do Tjij and Tg depend on molecular structure ... 

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