# Stronger than Kevlar?

1. Aug 16, 2006

### bomba923

(According to Wikipedia, the strongest hydrogen bonds are O—H...N bonds, occuring between a hydroxyl's hydrogen and a nearby nitrogen atom. That's when I thought of Kevlar...)

Can Mevlar* be stronger than Kevlar? (see the attached images)

(*My slight modification of the Kevlar monomer )

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2. Aug 17, 2006

### geo_alchemist

only experiment can tell you that. there are many factors effecting on this, not only hydrogen bond strength. but also in kevlar, hydrogen bonds are formed between oxygen and hydrogen of benzene ring. this will not happend in your Mevlar* because of steric factor.

3. Aug 17, 2006

### bomba923

? Mevlar* does not introduce any steric hindrance to H-bonding.

If you're referring to this image, simply replace each $$\text{O} \cdots \text{H} - \text{N}$$ with $$\text{O} - \text{H} \cdots \text{N}$$, and move the double bonds from C=O to C=N (to get Mevlar*). No H-bonds involving benzene hydrogens are affected.

Since $$\text{O} - \text{H} \cdots \text{N}$$ type H-bonds are stronger than $$\text{O} \cdots \text{H} - \text{N}$$ type H-bonds, I reason than Melvar* might be a material stronger than Kevlar.

Although only experimentation can determine that (as you said), I don't have any money and a google search of "kevlar isomers" didn't provide anything useful :(

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4. Aug 17, 2006

### geo_alchemist

Ok, but there is a significant difference between Kevlar and Mevlar* 3D models. In Kevlar benzene rings ar almost in the same "flat surface" (sorry about bad English) but not in Mevlar*.
so this is not simple enough to say something without experiment

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5. Aug 17, 2006

### bomba923

Actually, neither Kevlar nor Melvar* is quite as planar as your models show (see my attached 3D images; in fact, Mevlar* appears slightly more planar than Kevlar )

Secondly, the (--NH-C(O)--) in Kevlar and the (--N=C(OH)--) in Mevlar are free to rotate between the benzenes (which can rotate as well). The rotation (energy) barrier to a planar conformation would be overcome via the formation of H-bonds (in either molecule, but especially in Mevlar*)

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6. Aug 17, 2006

### Gokul43201

Staff Emeritus
I don't see what's preventing either of the phenyl groups from rotating (ie., no reason for planarity) in both structures.

7. Aug 20, 2006

### geo_alchemist

this 3D models are created by computer, not me, which calculated that kevlar is more planar ("CambridgeSoft", "chem 3D ultra"). but as I already told, experiment is the best way. ;-)

8. Aug 20, 2006

### 3trQN

Is spaggetti stronger than noodles?