Crystallite Melting Point

Finally, it should be mentioned that polymers can exhibit polymorphism, i.e., they can crystallize in different types of lattices. The different crystal forms generally differ in their physical properties, e.g., crystallite melting point and density. 

Amorphous polymers dissolve much easier than crystalline ones. The latter are often soluble at elevated temperatmes only, i.e., near the crystallite melting point T. ... 

The polyamide-6 (Nylon-6) so obtained has a crystallite melting point around 216 °C. It still contains monomer and low-molecular-weight cyclic oligomers which can be removed by extraction with water or lower alcohols.These oligomers can be separated and identified chromatographically (see Example 4-9). 

In addition to the excellent thermostability, which is due to their high crystallite melting points, poly(arylene ether ketone)s exhibit a very good chemical resistance because of their low solubility. 

An example of a crystalline hard segment is MDI/1,4-BD0 which has a Tin or melt point by DSC. Table 1 shews that MDI/1,4-BD0 hag a small Tg at 110°C, a Tc or crystallization temperature at 182°C and a series of three successive crystallite melting points at 202°C, 220°C, and 236°C the upper temperature being the np of the pure equilibrium crystal. 

The material type that is currently the most important is the isotactic polypropylene obtained by means of stereospecific catalysts according to Ziegler/Natta. It is high crystalline because the regularly formed chains are readily arranged. The softening point is therefore 165 °C (crystallite melting point) as compared to 128 °C for atactic polypropylene. 

Polytetrafluoroethylene (PTFE), density = 2.1-2.2 g/cm, has such a high viscosity above the crystallite melting point (327 °C) that injection moulding is not possible. 

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