How to calculate the rate constant of a polymerization process, generalized method? Does any one have a reference for this?
It depends on polymerization mechanism. What kind of polymerization are you interested in?
If you specify the polymer and the type of polymerization, it will be easy to respond.
Jun Ling,
Do you have any reference for calculating the time dependent monomer consumption from HNMR.
from monomer conversion, monomer concentration can be obtained. if your system is first order a plot of ln(Mo/M) vs t should be straight line with a slope equal to k. if your system is second order then a plot of (1/M) vs time is linear that starts from 1/Mo and the slope is the rate constant k
Check the book Chemical Kinetics and Reaction Mechanisms by James Espenson. I have it at work but will be out for the week. If you don't have a satisfactory answer by then I will post again, but the section on polymerization will describe in detail the treatment of initiation, propagation, and termination steps.
For jack
I don't have this book can you please post a link for the e-copy of this book
Thanks
I'll look but it's pretty old and I don't know if one exists. If I find it I will post it.
I'm finally back at work and have been able to look through the section that I was thinking of in the book. It is not specifically on polymerizations, but more generally on chain reactions. It may still be quite helpful to you. If you would like; message me and I will scan that chapter/section and email it to you.
Hello, Jack
Please send me the scan on [email protected], waiting for your email.
You can look at the overall polymerization kinetics or at the time evolution of some chemical bonds. For the last case you can use FTIR, RAMAN, NMR, and in some cases UV-VIS. For radicalar polymerization you may try ESR but usually you may need to deconvolute the signal from the catalyst component (mainly if you are using a transition metal catalyst).
For the overall polymerization rate you need to model the chemical reactions and to see if it is possible to derive it from the evolution of some chemical entities/chemical bonds (measured experimentally). In simple cases, you may confirm it from the mass distribution of the polymer that you obtained.
If you do not have access to expensive analytical equipment, such as FTIR, NMR or ESR, one can measure a rate of polymerization "the old way": by volume change using a mercury capillary column.
To determine the polymerization propagation rate constant kp one generally starts by measuring the rate of polymerization at various monomer concentrations.
In free radical polymerization, without chain transfer, the MW of the polymer is proportional to the kinetic chain length, and thus to the propagation rate. In practice, I have never seen a free radical system without some chain transfer occuring. I am not aware of the determination of kp from the MW distribution, but indeed it may be possible in some specific cases.
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