Polymer & Co.
The NMR analysis was performed to understand the high value of melting temperature obtained by the DSC analysis of nGen flex (between 210 and 225°C which is higher than most copolyesters).
For the preparation part, 30mg of nGen flex was dissolved in 1ml of CDCl3. The analyses were made on unfiltered samples and filtered at 0.2µm and 0.45µm. The only spectrum showed here is the one without filtration because the resulting spectra were exactly the same.
Nuclear Magnetic Resonance spectroscopy is a technique that exploits the property of nuclei to possess a nuclear magnetic moment. Nuclei of atoms are probed so we can obtain information about the environment and the connectivity of these atoms inside a molecule. For electrons, protons and neutrons, the spin quantum number characterizes the angular momentum. The quantum number of total spin (itotal) of a nucleus depends on the number of unpaired protons and neutrons. Only nuclei in which itotal ≠ 0 are observed in NMR. Therefore, Isotopes (1H, 13C, 19F, 29Si and 31P) are a particular interest because they have i=½. For this analysis, the NMR spectroscopy will be limited to 1H. Liquid NMR is the most common technique, in which the sample is dissolved in a solvent.
Results
INTRODUCTION
CONCLUSION
In conclusion, the high melting temperature is still not well understood. The use of additive could explain this value [1], but the content of additive is generally between 0.05 and 5% [2] and thus can be to small to be seen by RMN analysis. To have a better understanding of this material, the use of additional analysis (XPS, mass spectrometry, …) could bring us new information’s and why we get a such high melting temperature.
Bibliography
Bibliography
[1] Patent ”thermoplastic elastomer composition” https://patents.google.com/patent/EP0755974A2
[2] E. Bhoje Gowd thesis “effect of additives and comonomers on crystallization and solid state polymerization of polyesters” January 2015
[3] U.K. Thiele, Dr. Thiele Polyester Technology, Bruchköbel/Germany “polyester additives” http://www.polyester-technology.com/fileadmin/media/literature/70-Thiele_POLYESTER-ADDITIVES-LONGVERSION-2007.pdf
[4] H.J. Reich, university of wisconsin - Madison, https://www.chem.wisc.edu/areas/reich/nmr/
The NMR analysis was performed to understand the high value of melting temperature obtained by the DSC analysis of nGen flex (between 210 and 225°C which is higher than most copolyesters).
For the preparation part, 30mg of nGen flex was dissolved in 1ml of CDCl3. The analyses were made on unfiltered samples and filtered at 0.2µm and 0.45µm. The only spectrum showed here is the one without filtration because the resulting spectra were exactly the same.
The spectrum can be interpreted as follows:
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The peaks between 1 and 2.5 ppm come from aliphatic chains
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The peak at 7.28 ppm comes from the solvent (CDCl3).
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If we look closer between 6.5 and 8 ppm, a very small peak can be seen (not shown on the spectrum here). This latter could be due to aromatic compounds but the intensity is so low that it’s not really significant. Moreover, as this polymer could be dissolved in CDCl3, the presence of aromatics is unexpected.
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The peaks between 3.8 and 4.2 ppm are in the ester zone.. In NMR, the multiplicity of a signal discribes the presence of other H on adjacent carbons. Here we have doublets and triplets, indicating the presence of CH and CH2. The presence of CH was unexpected because this assumes that there are aliphatic carbon cycles or heteroatoms in the polymer. The first hypothesis of aliphatic carbon cycles is not very valid because the effect of aliphatic carbon cycles in a polymer is to decrease the crystallinity and thus to decrease the melting temperature. Therefore, this polymer should not have higher melting temperature than what is expected for polyesters. The second hypothesis of an heteroatom doesn’t seem very plausible either because the presence of an heteroatom should decrease the electron shielding and thus increase the shift. In other words, the peaks here are in the ester zone [4], if there were heteroatoms, the peaks would be more shifted (higher in the ppm scale). Moreover, there is no peak at 3.27 ppm, which is supposed to correspond to CHCl (polyethylene dichloride is known to have a good thermal stability properties and thus is sometimes used to inscrease thermal properties [1]). Moreover, the FTIR analysis didn’t show any CH-Cl bond either (~750cm-1).
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The peak at 3.42ppm could come from polytetrahydrofuran because the theoretical peak of this compound is at 3.5ppm and correspond to the soft part of the polymer.