0Degree Of Crystallization: It tells that the crystalline and amorphous components inside the polymer.
Crystallization of Polymers: It is the maximum crystallinity that a polymer can achieve at a particulat temperature.
Factors:
Crystallization Tendency: Secondary bonding forces, are responsible for intermolecular bonding in polymers,to maximize the effect of these forces in the process of aggregation of molecules to form a crystalline solid mass, the molecules must come as close together as possible. The tendency for a polymer to crystallize, therefore, depends on the magnitude of the inherent intermolecular bonding forces as well as its structural features.
Stereoregularity: Displayed by monosubstituted vinyl polymers of olefins. these types of polymers can occur in three forms of tacticity: isotactic, syndiotactic, and atactic. Isotactic and syndiotactic polymers possess stereoregular structures. Generally these polymers are rigid, crystallizable, high melting, and relatively insoluble. The flexibility of chain molecules arises from rotation around saturated chain bonds. With a chain of –CH2– units as a basis.
Studies of this type have led to the following general conclusions: • Rapid conformational change due to ease of rotation around single bonds occurs if such groups as (– –CO–O–), (–O–CO–O–), and (–C–N–) are introduced into the main chain.
Polarity: When molecules come together and aggregate into a crystalline solid, a significant cohesion between neighboring chains is possible.
Molecules whose backbone contains –O– units or with polar side groups (–CN, –Cl, –F, or –NO2) exhibit polar bonding. The bonding energies of such dipoles or polarizable units are in the range between hydrogen bonding and van der Waals bonding.
If these groups occur regularly along the chain (isotactic and syndiotactic), the resulting polymers are usually crystalline and have higher melting points than polyethylene.
Tacticity: Polymers of monosubstituted olefins [CH2› CHXl contain a series of asymmetric carbon atoms along the chain. For this type of polymers, in a planar zigzag form, three arrangements are possible, namely:
• Isotactic: All the substituent groups, R, on the vinyl polymer lie above (or below) the plane of the main chain.
• Syndiotactic: Substituent groups lie alternately above and below the plane.
• Atactic: Random sequence of position of substituent occurs along the chain.
