Hold on to your goggles, we’re about to do some polymer chemistry!
While I wait for the final edits to come back on the paper I’ve been writing, I have been buttoning up the trusty lab coat to tackle some data for another project. Unfortunately (but par for the research course), science isn’t doing what I want it to.
It’s based on a typical coupling polymerization, like this:
To simplify things, I’ve just got a small molecule with reactive ends A and B. Stick a bunch of them in a pot, stir it up, and you get a polymer chain. Tada! Coupling polymerizations are a good friend of mine, and generally we get along famously.
What I’m really interested in doing is putting some functionality on the “block” of the small molecule, so I can use the resulting polymer chain for even more chemistry later. It actually ends up more like this, where the extra functionality is marked C (for “criminey that’s awesome!” – what, you think I’m beholden to some bourgeois alphabetical labeling?).
That C could be anything to make the final product useful. It could be a chemical group that emits light in the presence of a deadly toxin. It could be a binding site for a protein you want to interact with in a medical application. It can be a miniature Tony Stark who sits around being snarky to all the other non-awesome molecules. Anything. There are thousands of polymers out there with everyone’s pet side group attached to it for doing awesome physics/chemistry/biology.
And that’s the nice thing about coupling reactions. Joining A and B is usually accomplished using a catalyst that’s been finely tuned to be highly efficient. The catalysts work well, and bear more than a passing resemblance to Justice Scalia in that they are extremely selective for joining A-to-B with non of that unnatural horrific A-to-A homocoupling. So generally putting that extra functional group in there doesn’t hurt too much.
Until this unexpectedly happens:
Suddenly that new handy chemical group wants in on the coupling fun! And you end up with a giant gelatinous cross-linked mess in the bottom of your test tube.
The weird thing, and what’s happening for me, is when there’s no clear chemical route for C to start linking in with A and B. It’s definitely happening – there’s really no other way to make grade A chemical goop. So somehow C is getting by the Scalia-like laser vision of the catalyst, and it’s back to the drawing board for me (but not before pinning the data to the wall to maybe check out as a side project for looking into on some rainy day).
Behold the joys of research!