Melting-transition temperature transitions

Starch is made thermoplastic at elevated temperatures ia the presence of water as a plasticizer, aHowiag melt processiag alone or ia blends with other thermoplastics (192—194). Good solvents such as water lower the melt-transition temperature of amylose, the crystalline component of starch, so that processiag can be done well below the decomposition—degradation temperature. 

Melt transition temperature, Tm (Section 31.5) The temperature at which crystalline regions of a polymer melt to give an amorphous material. 

Meerwein s reagent, 680 Meisenheimer, Jacob, 573 Meisenheimer complex, 573 Melmac, structure of, 1223 Melt transition temperature (Tm), 1215... 

The melting transition temperature and the heat of fusion of poly(nHAMCL) prepared from various alkanoic acids are collected in Table 5. The glass transition temperatures of poly(nHAMCL)s are usually between -30°C and -20°C. 

The rates of chemical reactions increase with temperature due to the greater proportion of molecules which have energies in excess of the activation energy and this will apply to radiation-induced secondary reactions in polymers. However, solid polymers are also characterized by their glass and melting transition temperatures. Substantial changes in molecular mobility occur across these transitions and the rates of chemical reactions are frequently greatly affected. 

Figure 13.4 Perturbation of the melting transition temperature of a single domain protein as a function of benzyl alcohol content (described as % B.A.). The liquid protein formulation consists of 10 mM Tris, 4% mannitol, and 1% sucrose, pH 7.4. (Permission to use the figure granted by BioPharm.)...

It is interesting that modifying solution conditions by adding different concentrations of ethanol can produce a biphasic effect on melting transition temperatures of lipid-like systems (e.g., acyl chains of hydrocarbons). For example, low concentrations of ethanol reduce the Tm of phosphatidylcholine bilayers, whereas higher concentrations increase the Tm of the same system.122 This effect has been shown to depend upon acyl chain length and can be explained by the... 

Koehler MG, Hopfinger AJ (1989) Molecular modeUing of polymers 5. Inclusion of inter-molecular energetics in estimating glass and crystal-melt transition temperatures. Polymer 30 116-126... 

Fig. 11. Evidence that a membrane-associated immunochemical reaction (complement fixation) depends on the mobility of the target hapten (IX) in the plane of a model membrane. The extent of the immunochemical reaction, complement fixation, is measured by A Absorbance at 413 nm. Temperature is always 32°C, which is above the chainmelting temperature (23°C) of dimyristoylphosphatidylcholine used for the data given in A and below the chain-melting transition temperature (42°C) of dipalmitoylphosphatidyl-choline used for the data in B. Thus A refers to a fluid membrane and B refers to a solid membrane. The numbers by each curve are equal to c, the mole % of spin-label hapten IX in the plane of the lipid membrane. It will be seen that complement fixation, as measured by A Absorbance at 413 nm is far more effective in the fluid membrane than in the solid membrane at low hapten concentrations (i.e., c 0.3 mo e%). In C the lipid membrane host is a 50 50 mole ratio mixture of cholesterol and dipalmitoylphosphatidylcholine. The immunochemical data suggest that this membrane is in a state of intermediate fluidity. Specific affinity-purified IgG molecules were used in these experiments. (For further details, see Ref. 5.)... 

Griffith, J. H., and B. G. RA.nby Dilatometric measurements on poly (4-methyl-l-pentene), glass and melt transition temperatures, crystallization rates and unusual density behavior. J. Polymer. Sci. 44, 369—381 (1960). 

M. G. Koehler and A. J. Hopfinger. Polymer, 30, 116 (1989). Molecular Modelling of Polymers 5. Inclusion of Intermolecular Energetics in Estimating Glass and Crystal-Melt Transition Temperatures. 

Tm, the melt transition temperature, is the temperature at which the crystalline regions of the polymer melt to become amorphous. More ordered polymers have higher values. 

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