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Name: Ehsan
Status: student
Grade: 9-12
Country: Turkey
Date: Summer 2011


Question:
What are the factors involved in determining the flexibility in polymers?



Replies:
Ehsan,

As you can imagine, there are several variables that control polymer bulk flexibility.

The polymer chain becomes more flexible with: higher freedom of rotation around main chain bonds - so no double bonds, no bulky side groups that inhibit main-chain bond rotation, no cross-links, etc. Polymer chain motion is enhanced in the presence of a lot of free voluble (in which the bonds can rotate into) - so short side-chains that inhibit chain interaction by literally pushing other chains away, stereoirregularity that inhibits high crystallinity, low polarity functional groups that only interact by London Forces, etc.

The bulk flexibility is increased when there are fewer entanglements between chains, so that the chains are free to reptate - so high molecular weights that tend to entangle is no good, but low molecular weights that tend to crystallize is also not good.

Then there are additives. Small molecules that act as plasticizers increase free volume. Inorganic solids can act as fillers and inhibit motion across the filler space.

There is a lot here, so you may have to study all these different aspects.

Dr. Roberto Ma. Gregorius, Assoc. Prof.


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