Multiple choice

Arrange the following polymers in increasing order of their glass transition temperature (Tg)?

  1. Polypropylene
  2. Poly(vinyl chloride)
  3. Polyacrylonitrile

  1. 1 < 2 < 3

  2. 1 < 3 < 2

  3. 2 < 3 <1

  4. 2 < 1 < 3

  5. 3 < 2 < 1
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A Correct answer
Explanation

The presence of strong intermolecular bonds in a polymer chain, i.e., a high value of cohesive energy density, will significantly increase Tg. The steric effects of the pendant groups in given compounds (with side chains CH3, –Cl, and –CN) are similar, but the polarity increases. Consequently, Tg is increased in the order polypropylene ( Tg = –10 °C) < poly(vinyl chloride) (Tg = 87 °C) < polyacrylonitrile (Tg = 103 °C).

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