I did the depolymerization of polymer, so I got the value of Mw and viscosity which decreases with time. To calculate the rate constant of the depolymerization reaction of polymer I need to recalculate the molecular weight into concentration. As the concentration of polymer does not change during the depolymerization of polymer, what value I need to use (instead of concentration) in rate equation?
Thanks!
You cannot assume the number of polymer chains is constant once the zip length exceeds the chain length.
Moles of Monomer = Weight monomer/MW monomer
Moles of Polymer = Weight Polymer/MW polymer
Thanks Peter! It means that in my case the concentrationin in rate equation will be the Moles of Polymer. As I understood, the Weight Polymer - it is the weight which changes with time and the Mw is the intial weight?
Thank you very much!
I'm suspect you are oversimplifying the kinetics. Depolymerisation is a chain reaction with initiation, propagation and termination steps (and probably chain transfer). I think determining the instantaneous moles of monomer and polymer will let you unravel the mystery.
Thanks! Could you please explain in more details what means - determine instantaneous moles of polymer or monomer.?
By instantaneous I mean at each time point where you measured the weight and MW (from viscosity?). If, as I have assumed, this is thermal depolymerisation, the moles of monomer is the weight loss divided by the MW of the monomer and the moles of polymer is the residual weight / MW polymer.
If the depolymerisation is through hydrolysis rather than free radical, this analysis is all wrong.
Thanks! I depolymerizied the polymer and measured the time flow in the viscozimetr. Then,the time flow I recalculated to viscosity and then viscosity to Mw. I just confused what means the weight of polymer and what means the molecular mass in this particular case?
OK, so you are determining the MW of the polymer using viscometry. The weight of polymer is simply the weight of the residue. So the weight of polymer is going to decrease with time, but the molecular weight may stay constant depending on how far each chain de-propagates following scission. The weight of monomer is the weight loss (to vacuum?) and the molecular weight of the monomer is constant (eg. 104.15g/mol for styrene)
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