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See the following question:

Polymer Crystallinity

I think the answer is A because of the hydrogen bond in the side group, thus the degree of secondary bonding between parallel chain segments is higher. Is my thinking correct?

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  • $\begingroup$ debatable, as glycerol and sugars often do not crystallize. $\endgroup$ – permeakra Jun 29 '14 at 8:21
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    $\begingroup$ That's why the question asks for which one would be crystallized better. Five factors that influence the efficiency of packing polymer chains: 1 - Size of side groups 2 - Extent of chain branching 3 - Tacticity 4 - Complexity of the repeat unit 5 - Degree of secondary bonding between parallel chain segments $\endgroup$ – bauer2010 Jun 29 '14 at 22:06
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Question is, what is "better"? Faster, or higher melting enthalpy, or degree of crystallinity? The methyl group is bulkier and thus hard to get into the right backbone conformation, and the OH group is polar, as you've noted, leading to a melting point of PVA of 230°C (iPP ~175°C).

But then, it all depends on the actual tacticity, which is not specified. The isotactic species have a totally different crystal structure than the syndiotactic, and sample with low tacticity (PVA!) might still have another one. That leads to totally different crystallisation kinetics.

So while a lot speaks for "A", I say there can be no definite answer.

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