Home > Community > Why does the polymer of alkynes have low molecular weight than of alkenes?
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Mark Timko

Why does the polymer of alkynes have low molecular weight than of alkenes?

Chris Hirst  Follow

What I´ll discuss is focused on the Free-Radical Polymerization of these monomers.

Let me guide you through my “chain of reasoning”, and we´ll, finally, get to what you asked!

1)THE OBVIOUS: IT WILL HAVE TO DO WITH THE EXTRA, WEAK, Pi BOND OF THE ALKYNE!

This was the first thought that came to mind. The C=C of the Alkenes is composed of a Sigma (stronger) and a Pi (weaker) bond. The

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David L. Avery  Follow

Claudio’s answer is correct if in your question you mean a comparison of polymers having the same length but one with double bond and one containing double bond.

I’ve another opinion because when you speak about polymer of alkynes you mean a polymer obtained by polymerization of alkynes and you obtain unsaturated polyhydrocarbons (polyalkenes). Polymerization of alkenes produce saturated polymer (polyalkane). Polymerizations of alkenes are very easy to carry out and can produce very high molecular mass. Polymerizations of alkynes are quite complicate and you can not reach molecular mass as high as that obtained with alkenes.

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Daniel Cook  Follow

It depends on the reaction and the catalyst being used. Typically the rate constant k trend follows k(alkynes) > k(alkenes) > k(arenes). Arenes are very stable due to their aromaticity. If you functionalize the arenes with strong electron withdrawing groups, it may become quite reactive.

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Daanish Acadmey  Follow

1-carbon alkenes and alkynes do not exist. Ethene and ethyne do not have isomers. Propyne has a constitutional isomer, commonly called “allene” (1,2-propadiene). Also, cyclopropane is a constitutional isomer of propene and cyclopropene is a constitutional isomer of propyne.

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Dave Young  Follow

Because, ceteris paribus, the number of hydrogen atoms in a chain with the same number of carbon atoms is lower, about one half.

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