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Why isotactic polymer have high melting point than atactic polymer?
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Ahmed Sayed
Why isotactic polymer have high melting point than atactic polymer?
(R-t-A).
Q: “Why isotactic polymer have high melting point than atactic polymer?”
Polymers are generally consist of crystalline and amorphous phases. It is almost impossible to get fully crystalline polymer (with 100% crystallinity), but it is possible to get fully amorphous polymers. The crystalline structures of polymers mainly depend on the order of macromolecular chains and their arrangements. The difference between isotactic and atactic polymers is the highly ordered structure of the former one. In isotactic polymers, all side groups are oriented in one side of the macromolecular chains; whereas, in atactic polymers, the side groups have no specific orientation and are randomly oriented. In addition to these two sorts of structures, there is syndiotactic structure in which the side groups are alternatively oriented and positioned along the macromolecular chains. Melting phenomenon is restricted to only crystalline phase of polymers, amorphous phase reveal no melting.
Thus, isotactic polymers have higher melting point due to their highly crystalline structures compared with syndiotactic polymers. Atactic polymers have no melting point, as they are completely amorphous, like an extremely high viscosity liquid; as a result of heating and increasing the temperature, their viscosity decreases. Their behaviors transfer from elastic to viscose manner.
For instance, I measured the melting point of an isotactic polypropylene (PP) with a degree of crystallinity of ~ 43.4% as 165.7 deg C using DSC thermal analysis technique (Ref: Processing and characterization of microcellular foamed high-density polythylene/isotactic polypropylene blends), whereas the melting point of a typical syndiotactic PP with a degree of crystallinity of ~ 30% has been reported as 130 deg C (Ref: Polypropylene). As I mentioned above, atactic PP shows no melting behavior, it just becomes softer and eventually flows as a result of heating.
Q: “Why isotactic polymer have high melting point than atactic polymer?”
Polymers are generally consist of crystalline and amorphous phases. It is almost impossible to get fully crystalline polymer (with 100% crystallinity), but it is possible to get fully amorphous polymers. The crystalline structures of polymers mainly depend on the order of macromolecular chains and their arrangements. The difference between isotactic and atactic polymers is the highly ordered structure of the former one. In isotactic polymers, all side groups are oriented in one side of the macromolecular chains; whereas, in atactic polymers, the side groups have no specific orientation and are randomly oriented. In addition to these two sorts of structures, there is syndiotactic structure in which the side groups are alternatively oriented and positioned along the macromolecular chains. Melting phenomenon is restricted to only crystalline phase of polymers, amorphous phase reveal no melting.
Thus, isotactic polymers have higher melting point due to their highly crystalline structures compared with syndiotactic polymers. Atactic polymers have no melting point, as they are completely amorphous, like an extremely high viscosity liquid; as a result of heating and increasing the temperature, their viscosity decreases. Their behaviors transfer from elastic to viscose manner.
For instance, I measured the melting point of an isotactic polypropylene (PP) with a degree of crystallinity of ~ 43.4% as 165.7 deg C using DSC thermal analysis technique (Ref: Processing and characterization of microcellular foamed high-density polythylene/isotactic polypropylene blends), whereas the melting point of a typical syndiotactic PP with a degree of crystallinity of ~ 30% has been reported as 130 deg C (Ref: Polypropylene). As I mentioned above, atactic PP shows no melting behavior, it just becomes softer and eventually flows as a result of heating.
Polymers melt when it becomes possible for their chains to slide past each other. The sliding process is sometimes called reptation, because the chains slide along their length like snakes.
The more difficult it is for the chains to reptate, the more energy is required and hence the higher the melting temperature.
The better packed together the chains are, the more difficult it is for them to reptate.
The more regular the structure of the polymer, the better the chains are able to pack.
Isotactic polymers have all of their side groups on the same side of the backbone chain. This allows their chains to pack together very closely into perfect crystals. Conversely, atactic polymers have randomly distributed side groups. The absence of periodicity makes it impossible to pack the chains into high quality crystals.
Polymers melt when it becomes possible for their chains to slide past each other. The sliding process is sometimes called reptation, because the chains slide along their length like snakes.
The more difficult it is for the chains to reptate, the more energy is required and hence the higher the melting temperature.
The better packed together the chains are, the more difficult it is for them to reptate.
The more regular the structure of the polymer, the better the chains are able to pack.
Isotactic polymers have all of their side groups on the same side of the backbone chain. This allows their chains to pack together very closely into perfect crystals. Conversely, atactic polymers have randomly distributed side groups. The absence of periodicity makes it impossible to pack the chains into high quality crystals.
(R-t-A).
Q: “Why isotactic polymer have high melting point than atactic polymer?”
Polymers are generally consist of crystalline and amorphous phases. It is almost impossible to get fully crystalline polymer (with 100% crystallinity), but it is possible to get fully amorphous polymers. The crystalline structures of polymers mainly depend on the order of macromolecular chains and their arrangements. The difference between isotactic and atactic polymers is the highly ordered structure of the former one. In isotactic polymers, all side groups are oriented in one side of the macromolecular chains; whereas, in atactic polymers, the side groups have no specific orientation and are randomly oriented. In addition to these two sorts of structures, there is syndiotactic structure in which the side groups are alternatively oriented and positioned along the macromolecular chains. Melting phenomenon is restricted to only crystalline phase of polymers, amorphous phase reveal no melting.
Thus, isotactic polymers have higher melting point due to their highly crystalline structures compared with syndiotactic polymers. Atactic polymers have no melting point, as they are completely amorphous, like an extremely high viscosity liquid; as a result of heating and increasing the temperature, their viscosity decreases. Their behaviors transfer from elastic to viscose manner.
For instance, I measured the melting point of an isotactic polypropylene (PP) with a degree of crystallinity of ~ 43.4% as 165.7 deg C using DSC thermal analysis technique (Ref: Processing and characterization of microcellular foamed high-density polythylene/isotactic polypropylene blends), whereas the melting point of a typical syndiotactic PP with a degree of crystallinity of ~ 30% has been reported as 130 deg C (Ref: Polypropylene). As I mentioned above, atactic PP shows no melting behavior, it just becomes softer and eventually flows as a result of heating.
(R-t-A).
Q: “Why isotactic polymer have high melting point than atactic polymer?”
Polymers are generally consist of crystalline and amorphous phases. It is almost impossible to get fully crystalline polymer (with 100% crystallinity), but it is possible to get fully amorphous polymers. The crystalline structures of polymers mainly depend on the order of macromolecular chains and their arrangements. The difference between isotactic and atactic polymers is the highly ordered structure of the former one. In isotactic polymers, all side groups are oriented in one side of the macromolecular chains; whereas, in atactic polymers, the side groups have no specific orientation and are randomly oriented. In addition to these two sorts of structures, there is syndiotactic structure in which the side groups are alternatively oriented and positioned along the macromolecular chains. Melting phenomenon is restricted to only crystalline phase of polymers, amorphous phase reveal no melting.
Thus, isotactic polymers have higher melting point due to their highly crystalline structures compared with syndiotactic polymers. Atactic polymers have no melting point, as they are completely amorphous, like an extremely high viscosity liquid; as a result of heating and increasing the temperature, their viscosity decreases. Their behaviors transfer from elastic to viscose manner.
For instance, I measured the melting point of an isotactic polypropylene (PP) with a degree of crystallinity of ~ 43.4% as 165.7 deg C using DSC thermal analysis technique (Ref: Processing and characterization of microcellular foamed high-density polythylene/isotactic polypropylene blends), whereas the melting point of a typical syndiotactic PP with a degree of crystallinity of ~ 30% has been reported as 130 deg C (Ref: Polypropylene). As I mentioned above, atactic PP shows no melting behavior, it just becomes softer and eventually flows as a result of heating.
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Polymers melt when it becomes possible for their chains to slide past each other. The sliding process is sometimes called reptation, because the chains slide along their length like snakes.
The more difficult it is for the chains to reptate, the more energy is required and hence the higher the melting temperature.
The better packed together the chains are, the more difficult it is for them to reptate.
The more regular the structure of the polymer, the better the chains are able to pack.
Isotactic polymers have all of their side groups on the same side of the backbone chain. This allows their chains to pack together very closely into perfect crystals. Conversely, atactic polymers have randomly distributed side groups. The absence of periodicity makes it impossible to pack the chains into high quality crystals.
Polymers melt when it becomes possible for their chains to slide past each other. The sliding process is sometimes called reptation, because the chains slide along their length like snakes.
The more difficult it is for the chains to reptate, the more energy is required and hence the higher the melting temperature.
The better packed together the chains are, the more difficult it is for them to reptate.
The more regular the structure of the polymer, the better the chains are able to pack.
Isotactic polymers have all of their side groups on the same side of the backbone chain. This allows their chains to pack together very closely into perfect crystals. Conversely, atactic polymers have randomly distributed side groups. The absence of periodicity makes it impossible to pack the chains into high quality crystals.
More
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