Questions b. and c. b. Polymer chain with all C and H c. Polymer chain with Cl b

Question

Questions b. and c.

b. Polymer chain with all C and H

c. Polymer chain with Cl bonded to half of the C's

1. The behavior of all polymers exhibits a temperature dependence where, at low temperatures the polymer behaves as a rigid glassy material but above a material specific glass transition temperature or Tg, ehave as a flexible rubbery material At the Tg, the Van Der Waals (VDW) bonds between the chains break down. Thus, stronger bonds will produce a higher Tg. Rank the three polymers below from lowest to highest Tg based on VDW bond strengths. a. Polymer chain with an F bonded to half of the carbons H H b. Polymer chain with all Cand H H H H H H H H H H H C-C-C-C-C-C-C-C-C-C H H H H H H H H H H c. Polymer chain with a Cl bonded to half of the Cs. (substitute Cl for F in polymer

Explanation / Answer

There are several factors that affect the Glass Transition Temperature of Polymers. They can be:-

i) Steric Hindrance (Chain flexibility).

ii) Geometry i.e presence of double bonds, cis-trans configurations etc.

iii) Presence of attractive other forces. (Presence of polar groups)

iv) Crystallinity

v) Plasticization ets..

Now for the above problem,

The chain with all C and H will have the lowest as it has the least steric hindrance and no cross linking polymerization is going on.

Now, for comparison between Polyvinyl Chloride and Polyvinyl Fluoride, the answer should be that PVF must have higher Tg then PVC, as Fluorine is more polar than Chlorine.

But, in PVF there is a degree of Crystallinity. The crystallites may be regarded as physical cross-links that tend to reinforce or stiffen the structure. Viewed this way, it is easy to visualize that Tg will increase with increasing degree of crystallinity.

Henceforth, the final answer order will be (from lower to higher)

a) Polymer chain with all C and H. (Lowest Tg)

b) PVF

c) PVC. (Highest Tg)

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