Polymers 2020 , 12 , 173
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Figure 4. Nuclear magnetic resonance ( 1 H-NMR) spectrum of the polyamine (Polycoat 38 ® ) resin synthesized. Finally, a signal from the NH and the OH protons of the chain would be expected around 8 ppm. However, the signal is not observed due to the presence of the deuterated solvent that causes an exchange of protons with the hydrogens of this groups and decreases the intensity of the signals [25]. The figure also shows the possible structure of the cationic polymer and its corresponding azetidine ring [4]. 3.3. Molecular Weight Determination of the Polycoat 38 ® Resin The molecular weight of the resin was calculated using gel permeation chromatography technique. Retention time of the peak corresponding to the polyamine yield an average molecular weight (Mw) of 3131g / mol and an average number molecular weight (Mn) of 2890 g / mol. Mw was higher since it corresponds to higher molecular weight chains, while Mn is sensitive to low molecular weight chains [22]. On the other hand, these values allowed to elucidate the polydispersity index (PI), which in this case corresponded to 1.08. This value is close to the unit and indicates that the lengths of the chains are practically equal [26]. That will produce a homogeneous distribution on the surface of the yankee, which in turn will generate an optimal contact with the sheet of paper to crepe without the presence of holes caused by spaces between chains of high and low molecular weight [27]. Likewise, the distribution of the cations across the polymer are uniform decreasing the residual epichlorohydrin of the synthetized resin which is an environmental requirement for these processes [28].
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