Melting points of polymers

Understanding the factors controlling primary versus secondary insertion of alkenes is critically important to practical applications, because regioerrors (i.e., occasional secondary insertions in a polymer predominantly formed by primary insertions) can adversely affect relative molecular masses, responsivities to hydrogen, and melting points of 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... 

Table 3. Heats of Fusion and Maximum Melting Points of Polymers and Copolymers.

The melting-point-depression method can also be used to estimate melting points of polymers that degrade before they melt. The depressed melting points are simply plotted against the volume fraction vl of solvent in the solution, and extrapolated to the point where Vi equals zero. The method, illustrated in Figure 2.45, has been used for a variety of polymers, particularly for cellulosic materials. 

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. 

RELATIONSHIP BETWEEN GLASS TRANSITION TEMPERATURE AND MELTING POINT OF POLYMERS... 

Figure 1. Melting points of polymers with the monomer unit-iX(CH2)mCCHt A X = NH X = O X = S —m.p. of polyethylene...

A direct determination of the melting point of PVA is difficult because decomposition begins near the melting point. However, it can be determined directly by measurement of the melting point of the polymer in the presence of a diluent. The following equation for the melting point of polymer-diluent is used in this case [77] ... 

How do the pendant groups affect the melting points of polymers ... 

Nucleating agents have usually no influence on melting temperatiue of polymer but they do affect crystallization temperature. There are some cases that influence of nucleating agent on the melting point of polymer is observed (e.g., 0.3 wt% 1,3-2,4-di (p-hydroxyl) benzylidene sorbitol increases melting point by about 3°C). °... 

Fig. 41. Melting points of polymers as a function of methylene groups in the diain / polyter hfhalamidei 2 jpolycarboamids, 3 polyadipamides, 4 poly-terephthaiates. 6 polyetbers, 7 poly(l- ukenes)...

The thermodynamic equilibrium melting point of polymer crystals can be measured by means of DSC and small-angle X-ray diffraction. The following procedure is recommended for the measurement of the equilibrium melting temperature of a polymer crystal,... 

Polymer crystallization and melting are typically first-order phase transitions between the amorphous phase and the crystalline phase. When these two phases are in thermodynamic equilibrium, two phase transitions are thermodynamically reversible under a certain temperature. This temperature is referred to the equilibrium melting point of polymer crystallization. The free energy changes of amorphous phase and crystalline phase under various temperatures are depicted in Fig. 4.1, illustrating the definition of the equilibrium melting point 7. ... 

Fig. 4.1 Schematic free energy curves of amorphous phase and (uystalline phase versus temperature. The temperature at which two curves intersect with each other is defined as the equilibrium melting point of polymers...

The equilibrium melting point of polymers can be calculated by taking into account all the parameters and solving (4.19). 

A//u is the melting enthalpy of polymers per mole of monomers. When the amorphous phase and the crystalline phase become in equiUbiium, their chemical potentials are equal. By combining (4.31) with (4.32) and making them equal to each other, the melting point of polymers in solution is derived as... 

Fig. 5. Melting point of polymers obtained under the same condition as in T.able 1-3 as a function of monomer composition o for SFC, for CPC(AI/Ti =5), + for CPC(A1/Ti=30).

To achieve improved dispersibUity of nanoclay fillers within polymer systems, three familiar methods are commonly used, namely, melt intercalation, solution intercalation, and in situ polymerization. The melt-intercalation method is based on the melting point of polymer matrices and is applied by annealing above the melting point of the polymer (Reddy et al., 2013). This method has been chosen by industrial sectors to produce polymer/clay nanocomposites. However, it is not apphcable to the fabrication of biobased polymer/clay nanocomposites based on thermosetting materials such as epoxy and polyester due to their high viscosities (Wypych and Satyanarayana, 2005 Wang et al., 2014). Therefore, the fabrication of biobased thermosetting polymer/clay nanocomposites is mainly based on solution intercalation or in sim polymerization. 

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