Bulk polymerization process can be monitored by various techniques, such as FTIR, NIR, dielectric analysis, chromatography, viscometry, ultrasound etc.In the case of copolymerization the reactivity ratios are frequently determined by precipitating the polymer followed by NMR analysis.
I wonder, whether it is possible to get any meaningful data WITHOUT the tedious precipitation process. Let us assume that we take samples at various points of the polymerization process which contain both monomers and polymers. If the NMR signals of the monomers are different (at least in principle) one could determine the monomer composition in the monomer mixture and in the polymer. (I assume that the lines of the polymer would be broader but still measurable in solution). Does anybody know about such attempt?
Wouldn't you be able to use quantitative 1H NMR, by including a standard to your NMR tube? I guess that by adding a diffusion filter in order to get rid of the polymer signals and just keep the monomer ones, you would be able to monitor its disappearence by comparing integrals with the standard. Some papers explain how to get quantitative 1H NMR experiments and explain which pulses show be optimized and how, which standards can be used, and the characteristics that an ideal standard should have if you can come up with one that they do not list.
Hello dear, I think that it is possible depending of system type. For example, You can follow the reaction in the case of insatured monomers, because you can observed in a NMR spectra when the -C=C- bonds are disappearing by the time. In the case of the copolymers, you can take the total conversion of the system, since is difficult know which monomer is reacting in a determined moment.
Dear Edwin, thank you for your note. Yes, I am interested in unsaturated monomers. A similar thing can be done with IR by following the disappearance of the C=C vibration, in some cases it is even possible to distinguish the C=C vibrations belonging to the various monomers, but it does not work quantitatively because of the background corrections. The trends are clear, but it is at best semi-quantitative. In your example you are talking about H-NMR or C13 NMR? How does the lineshape changes when the polymer concentration increases? Do you have experience in such measurements?
Gyorgy,
There was a series of publications, mostly in Org. Lett., about use of no-D 1H-NMR for the reaction monitoring, where the spectra were recorded in the unlocked mode. Take a look, for example, here:
http://pubs.acs.org/doi/abs/10.1021/ol049979%2B?journalCode=orlef7
http://pubs.acs.org/doi/abs/10.1021/bk-2013-1128.ch005
maybe it gives a hint. If the polymerization is homogeneous, I am sure you can monitor it this way, provided the right settings are found.
Wouldn't you be able to use quantitative 1H NMR, by including a standard to your NMR tube? I guess that by adding a diffusion filter in order to get rid of the polymer signals and just keep the monomer ones, you would be able to monitor its disappearence by comparing integrals with the standard. Some papers explain how to get quantitative 1H NMR experiments and explain which pulses show be optimized and how, which standards can be used, and the characteristics that an ideal standard should have if you can come up with one that they do not list.
Dear Gyorgy, if you want to measure the double bond content I suggest Raman in combination with UV-vis curing which have a number of advantages (in situ, RT, glass or fused silica windows, small sample size(thin films), quantitative, no background problems)
https://www.researchgate.net/profile/Michael_Schmitt16
Dear Michael - thank you for the idea. NIR is also applicable although the distinction of the monomers may be complicated. I wonder whether the application of Raman is not complicated by fluoresecence effects (e.g. inhibitor residues etc.)?
With our NIR Laser (--> detection in NIR) only heating is likely problem.
Dear Gyorgy
People have done it. The group of Robin Hutchinson in Queen’s University (Kingston Canada) has just published a paper describing this result. The paper has been published only on-line so far, and it appeared in the last issue of Macromolecular Reaction Engineering journal (Wiley VCH). The title is Modeling the Radical Batch Homopolymerization of Acrylamide in Aqueous Solution by Calista Preusser, Anna Chovancová, Igor Lacík, Robin A. Hutchinson
Dear Enrique, I will try to find the paper, thanks. Meanwhile we also made tests which proved to be successful.
Dear colleagues, with your help I was able to identify further useful references. Thanks.
Time Domain Proton Magnetic Resonance experiments (free induction decay) are quite useful in following polymerization of some monomers (styrenics, acrylics etc). The experiments allow to distinguish quantitatively between fractions with different spin-spin relaxation times (T2). Since T2 in polymer chains (with lower mobility) is significantly lower than that in monomer units, the fraction with low T2 should grow with the polymerization progress (see attached papers).
Dear Michael Thank you for the information, I will read the references.
Dear Dr Schuster
I have read the attached brochures/files. This measurement is based on the measurement of the decay curve alone i.e. on the dependence of T2 (and its subcomponents) on the degree of polymerization. This is a valuable and fast method to monitor the progress of the reaction but e.g. in the case of reaction monitoring it does not provide structural information. Some recently marketed benchtop NMR spectrometers operated at 40-80 MHz tell us more about the chemical structure, therefore they can be used in a wider range of applications. What is your opinion?
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