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Re: study help with chemistry! » Larry Hoover » ace

Posted by Larry Hoover on October 24, 2003, at 5:24:19

In reply to Re: study help with chemistry! » Larry Hoover, posted by ace on October 24, 2003, at 0:18:56

> > > Any chem scholars out there!?
> > >
> > > Can anyone recommend me a good site on polymerization- I have searched the net heaps but am yet to find one!
> >
> > http://mrcemis.ms.nwu.edu/polymer/
> >
> > > Condensation polymers are what I'm focusing on most...
> >
> > Here's a condensation polymerization page:
> >
> > http://mrcemis.ms.nwu.edu/polymer/4-condensation.html
> >
> > By definition, a condensation reaction produces water as a secondary product, so the reactive sites must donate either -OH or +H.

Just for clarity, organic chemistry presumed water was condensed, but hey! chemists don't always talk the same language, even to each other.
>
> > > BTW, in addition (chain-growth) polymerization only one off the pi bonds (of the double bond) is broken...right?
> >
> > Yes, or elsewise there would be no chain formed.
>
> But if we have an 'di-ene' alkene only one of the double bonds is broken in the polymerization? I should have stated my question better!

Polymerization is not always a linear process. A diene could readily cross-link to other chains. You then get a net, instead of spaghetti. Epoxies are an example where that cross-linking process is desired.

The thing with a diene, though, is the symmetry of the monomer comes into play. All pi bonds are reactive, so the resulting polymer can have a diversity of sub-structures within it.

Also, the free-radical process that propogates the polymerization of even a mono-ene (e.g. ethylene, propylene) also permits the abstraction or disproportionation of a proton, allowing a side-chain to graft to the site of abstraction.

This site is a little more advanced than the others. I don't know if you have studied electron push diagrams yet.

http://www.cm.utexas.edu/academic/courses/Fall1997/CH610B/Gilbert/ancillaries/polymers.html

> > > This holds true for EVERY addition polymer?
> >
> > Consider acetylene (triple bond).
> >
> > > Ace.
> >
> > Lar
>
> Also, we can say that every condensation polymer monomer MUST be di-functional?

Yes, *at least* di-funtional. Consider the quintessential example of amino acids forming polypeptides (proteins). They also cross-link, e.g. via sulphur bridges at cysteine residues. Check the amino acid structures for tri-functionals (e.g. polyamines, polycarboxylics, sulhydryls). It's a very important part of enzyme function. It's the mechanism by which a single change in a single DNA base can lead to vastly different enzyme function.

> Man, I prefer stereochemistry to this!

If you can picture enantiomers, in three dimensions, in your brain, then you will be a good chemist. Picturing inversion of a molecule via addition-elimination, the formation of planar intermediates, resonance hybrids, and the like....if you can picture them, you won't ever be confused by them.

The only problem I ever had with stereochemistry was using the CIP rules to develop IUPAC names for complex structures. Thank the Almighty Geek on High for the computer programs that do that for you.

> Thanks for the sites too, Larry.
>
> Ace.

Quick google search.....keyword selection is critical.

My pleasure,
Lar

 

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poster:Larry Hoover thread:272472
URL: http://www.dr-bob.org/babble/social/20031020/msgs/272595.html