I'm an A-level student studying the F324 unit of OCR GCE Chemistry 'A'.

The exact question is

Explain how condensation polymers may be photodegradable. Equations needed!

I understand:

  • What a condensation polymer is.
  • Photodegradation may be possible by either a) Light-sensitive additives which catalyse a (slow) reaction in the presence of UV OR b) carbonyl bonds (C=O) breaking from the light energy.

What I don't understand:

  • What my teacher wants me to do for option 'a' in terms of equations. I'm inclined to leave that out, as it seems to be well outside the scope of the course.
  • Once the carbonyl bond breaks, what happens then? My best guess is that the oxygen atom receives the electron pair from the bond, then $H^{+}$ ions from 'somewhere' arrive to form water and finish the reaction. If I didn't know better, I'd say you needed a reducing agent for things to photodegrade.

So, what I'd ideally like is an equation (and explanation, if possible) showing what happens after the carbonyl bond breaks from UV.


Having spoken to my Chemistry teacher, the idea is that the UV causes the molecules to split; after the fission, the molecules may rejoin or react with 'other radicals' to break the polymer down, hence degrading it.

E.g. for a polyester:

$R_1COOR_2 \xrightarrow{hv} R_1CO\boldsymbol\cdot + R_2O\boldsymbol\cdot$

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