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Author Question: Why is the cis form of polyisoprene softer than the trans form? What will be an ideal ... (Read 13 times)

Redwolflake15

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on: Aug 19, 2018
Why is the cis form of polyisoprene softer than the trans form?
 
  What will be an ideal response?

Question 2

In some applications, such as grilles for automobiles, engineering plastics such as PET compete with SMC and also with some metals such as zinc, which can be cast or even injection-molded. What would be the three inherent advantages of each of the material types in this kind of application?
 
  What will be an ideal response?

Question 3

What is the mechanism and thermodynamic explanation for why elastomers recover to their original shape after being elastically stretched?
 
  What will be an ideal response?


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Carliemb17

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Reply #1 on: Aug 19, 2018
Answer to Question 1

The cis form will not pack together as easily as the trans form. Hence, there are fewer intermolecular attractions in the cis form and the molecules can slide over each other more easily. This ease of sliding and absence of intermolecular attractions means that the cis form is softer than the trans.

Answer to Question 2

PET: cost, production time, and processability SMC: strength, durability, and equipment costs
Zinc: weatherability, appearance, and marketability

Answer to Question 3

When an elastomer is stretched the molecules become more ordered. This causes a decrease in entropy. Since entropy naturally tends to increase, when the stretching force is removed the natural tendency of entropy to increase supplies the energy for the molecules to return to their more energetically favored, random configuration.


Redwolflake15

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Reply 2 on: Aug 19, 2018
Gracias!

olderstudent

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Reply 3 on: Yesterday
Great answer, keep it coming :)

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