DoITPoMS

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Questions

Quick questions

You should be able to answer these questions without too much difficulty after studying this TLP. If not, then you should go through it again!

  1. Below are pictures of 3 polymers, one each of atactic, syndiotactic and isotactic. Which option has the correct sequence?


    a atactic, syndiotactic, isotactic
    b atactic, isotactic, syndiotactic
    c syndiotactic, atactic, isotactic
    d syndiotactic, isotactic, atactic
    e isotactic, syndiotactic, atactic
    f isotactic, atactic, syndiotactic

  2. Which of the following polymers would be likely to have the highest crystallinity:

    a An atactic polymer with many long side branches
    b An atactic polymer with few short side branches
    c An isotactic polymer with few short side branches
    d An isotactic polymer with many long side branches

Deeper questions

The following questions require some thought and reaching the answer may require you to think beyond the contents of this TLP.

  1. Kuhn length calculations
    a) A polyethylene chain is formed from 3000 ethene monomers. Given that the length of a single carbon-carbon bond is 0.154 nm, calculate the expected end-to-end distance using the random walk model, assuming that each bond is freely jointed.
    b) Given that the Kuhn length of polyethylene is equal to 3.5 C-C bond lengths, calculate an improved estimate of the expected end-to-end distance of the polymer chain.

  2. A polymer sample was found to have the following molecular weight distribution:

    Number of molecules
    Molecular weight / g/mol
    200
    5,000
    300
    10,000
    400
    20,000
    100
    40,000

    Calculate the number average and weight average molecular weights, and the polydispersity index.


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