Carbon chemistry - polymerisation

[Stick]

It seems that this area is a bit of a weakness of mine. I really struggle to identify the monomer molecules when provided with a diagram of the polymer. I know it should be simple, and I'm a bit confused as to why I'm not getting it. Any advice?

[Limista]

Trial and error is the only way I think.

Make sure you're really familiar with the structure of 'smaller' hydrocarbons, like propane etc..

Check to see if the polymer has a double bond - then you'll know that a monomer you are looking for is definitely an alkene.

[Stick]

Trial and error is the only way I think.

I never thought of doing that for multiple choice...

How about if it was a short answer question though? Then there would have to be a proper way of deducing the monomers. I get it easily when there's just one type of monomer, but when a copolymer question comes up, I'm essentially bound to get it wrong. :S

[Limista]

Is this short-answer question by any chance the VCAA one (I forgot what year lol)?

Don't think there's a 'proper' way as such. But I'm not sure. Hopefully someone more experienced can help you out instead. 

[Stick]

Is this short-answer question by any chance the VCAA one (I forgot what year lol)?

Nah, I've just been working though my StudyOn and have been getting terrible results with anything related to copolymers (this includes polyesters that are copolymers).

I hope there is a methodical approach to these questions (or at least more methodical than staring at the structure and not deducing anything other than where the linkage is).

[jgoudie]

If it is simply an addition polymer, systematic approach is to add a double bond every second C-C then break the remaining singles.
eg.  C-C-C-C-C-C  -> ...C-C=C-C=C-C... --> C C=C C=C C.  when you have side chains you can see what comes out of it.

With polypeptides, look for your peptide linkage break that up, OH on the left hand side and H₂N on the right.

With polyesters you gotta look for your ester linkage its a little harder as it requires you to think which side the alcohol group will go on, but its not impossible, start by making some polyesters, then work backwards until you see the patterns.

[ealam2]

For polyesters, look at the ester functional group. For example, CH₃CH₂COOCH₂CH₂CH₃

Look at COO. The O side on the right side of the screen would be the alcohol monomer while the CO side on the left side of the screen would be from the carboxylic acid. The above name would be propyl propanoate - propanol + propanoic acid. (include the C from COOH when counting the number of carbons for carboxylic acids. OH is removed from carboxyl group - COOH while H is removed from hydroxy group -OH)

For general condensation polymers: Look at where the functional group is: a polyamide NHCO or ester. Remember that a small molecule is released either  H₂O or HCl. Work out where to put the HCl or H₂O and work out the two monomers.

Hope that helps!

[FlorianK]

Put up some pics. I'll walk you through how I would identify it!

[Will Sparks]

To be honest, I just look at the COO and I split it inbetween the CO and O and from there I work it out.