Transitions melting

Hoover W G and Ree F H 1967 Use of computer experiments to locate the melting transition and calculate the entropy in the solid phase J. Chem. Phys. 47 4873-8... 

Properties. One of the characteristic properties of the polyphosphazene backbone is high chain dexibility which allows mobility of the chains even at quite low temperatures. Glass-transition temperatures down to —105° C are known with some alkoxy substituents. Symmetrically substituted alkoxy and aryloxy polymers often exhibit melting transitions if the substituents allow packing of the chains, but mixed-substituent polymers are amorphous. Thus the mixed substitution pattern is deUberately used for the synthesis of various phosphazene elastomers. On the other hand, as with many other flexible-chain polymers, glass-transition temperatures above 100°C can be obtained with bulky substituents on the phosphazene backbone. 

Melting transition for poly(dimethylsiloxane) graft segment. 

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. 

The order of melting transitions for the diphenyhnethane bismaleimides is surprising (Table 6) because the 4,4 -MDA-BMI melts lower (155—157°C) than the 3,3 -MDA-BMI. The tetra alkyl-4,4-MDA-BMI also melts around 150°C. The BMI based on the isomeric diphenylindane diamine (24) is very low melting because it is a complex blend of various isomers. 

In some cases there is evidence of multiple solid-solid transitions, either crystal-crystal polymorphism (seen for Cl salts [20]) or, more often, formation of plastic crystal phases - indicated by solid-solid transitions that consume a large fraction of the enthalpy of melting [21], which also results in low-energy melting transitions. The overall enthalpy of the salt can be dispersed into a large number of fluxional modes (vibration and rotation) of the organic cation, rather than into enthalpy of fusion. Thus, energetically, crystallization is often not overly favored. 

The variation of the transition temperatures of these polybibenzoates with the number of methylene units in the spacer is shown in the lower part of Fig. 5. Melting temperatures, Tm, (crystal-isotropic melt transition) are obtained [9] for m > 7 and m = 3 (monotropic behavior), while for the other members, Tm really represents the... 

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... 

Fig. 2. DSC-trace of cyclododecane showing the melting transition at 333.4 K and an additional phase transition at 184.4 K. The sensitivity for the upper curve and the baseline reference was increased ten times. Heating rate 2.5 K/min. (Ref.7))...

Fig. 4. DSC-trace of octamethyltetra-siloxane showing the melting transition at 298 K and a solid state phase transition at 262 K. Heating rate lOK/ min. (Ref. 10))...

Fig. 6. CP-MAS l3C-NMR spectra of polydimethylsiloxane at 75.47 MHz above and below the melting transition. Chemical shifts refer to TMS = 0 ppm and correspond to the scale at the bottom (Ref.10))...

Thermal transitions can be studied by DSC. The crystallization transition is usually sharp with a good baseline. The melting transition is more complex and often not a single transition (Fig. 3.19)48 as it depends on the thermal history of the sample and the structural changes that can take place upon heating. In warming, solid-state transitions can take place in the unit cell, the lamellae can thicken, and secondary crystallization can also take place. The heats of crystallization and... 

We studied the polyamidation in the solid phase process of nylon 4,6, which has a high melting transition (264 - 320 C) and... 

XVIII shows in DSC a melting transition at 38 °C for the PEG segment. The conductivity at room temperature of the complexes of XVIII with LiS03CF3 (5-10 wt%) are between 8x10" and 2x10 S cm"k... 

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