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Polystyrene are available in three grades, isotactic, syndiotactic and atactic. Explain why the crystallization process in ps is so slow. Also which grade will crystallize and why?
Accepted Answer
Polystyrene (PS) is a polymer that can exist in three different forms: isotactic, syndiotactic, and atactic. The crystallization process in PS is slow due to the following reasons:
1. Chain Entanglement: PS chains are long and flexible, leading to significant entanglement. This entanglement hinders the movement of chains into ordered crystalline structures.
2. Chain Flexibility: PS chains have some flexibility, allowing them to adopt various conformations. The presence of multiple conformations makes it difficult for chains to align into a regular crystalline lattice.
3. Steric Hindrance: The bulky phenyl groups attached to the PS backbone create steric hindrance, further hindering chain movement and crystallization.
Isotactic PS will crystallize because it has a regular, repeating structure. The tacticity of PS refers to the arrangement of its monomer units. Isotactic PS has all its phenyl groups on the same side of the polymer chain, leading to a more ordered structure and easier crystallization. Syndiotactic PS also has a regular structure but with alternating phenyl groups on opposite sides of the chain, so it can also crystallize. However, atactic PS has a random arrangement of phenyl groups, making it difficult to form ordered structures and hence, it does not crystallize.
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