¹³C‐NMR Study of Anomalous Linkages in Polyurethane

Abstract

Several kinds of model compounds for anomalous linkages in polyurethanes (branching or crosslinking; allophanate and biuret) were prepared. The phenylisocyanate (PHI) based models were identified by IR and NMR. The 13C‐NMR chemical shifts effects due to the anomalous linkages were determined. The 4,4′‐diphenylmethane diisocyanate (MDI) based models were purified incompletely but the characteristic signals of the aromatic carbons were nevertheless found in their spectra. Two types of segmented polyurethane (SPU) were prepared and the anomalous linkages were investigated by 13C‐NMR. The signals due to the allophanate (Al) and the triphenylbiuret (TB) linkages were observed in the spectra of the SPU prepared at high temperature (>80°C) or prepolymer gels yielded by abnormal reaction. A small signal due to a phenyl carbon of biuret (Bi) linkage was observed even in a normally prepared SPU (polyetherurethane‐urea). Employing the phenyl carbon signals was advantageous for the determination of anomalous linkages because of their larger intensities.

Structural, mechanical, and biocompatibility analyses of a novel dental restorative nanocomposite

“…The intensities of signals at 120–121 ppm were halves of the signals at 118–119 ppm, so signals at 120–121 ppm must be due to para carbons (C4). The signals at 118–119 ppm were due to ortho carbon (C2) 20. The aromatic carbons served as characteristic signals of anomalous linkages.…”

Structural investigations of polypropylene glycol (PPG) and isophorone diisocyanate (IPDI)‐based polyurethane prepolymer by 1D and 2D NMR spectroscopy

“…The authors have described the signals of NH protons of anomalous linkages in detail. Koji et al9 have prepared several types of model compounds for anomalous linkages in polyurethane (branching or crosslinking; allophanate and biuret) and analyzed them with 13 C NMR chemical shifts. Yeager et al10 investigated the chemical structure of polyester–urethane with 1 H NMR.…”

Preparation and chemical reactions of rigid cross‐linked poly(vinyl chloride) foams modified by epoxy compounds

“…Because E51 and EOH may react with TDI in the preparation process of c‐PVC foams, to determine the chemical structure of the reaction products, EOH and E51 were mixed with TDI, respectively, and treated in accordance with the process of preparing the prefoam. 13 C‐NMR and 1 H‐NMR spectra were used to investigate the formation of urea, urethane, allophanate, and biuret linkages from the reaction between isocyanate and active hydrogen compounds . Figure (a) shows the 13 C‐NMR spectra of T/E‐b and T/EOH‐b.…”

“…13 C-NMR and 1 H-NMR spectra were used to investigate the formation of urea, urethane, allophanate, and biuret linkages from the reaction between isocyanate and active hydrogen compounds. [28][29][30][31][32] Figure 7(a) shows the 13 C-NMR spectra of T/E-b and T/EOH-b. A very evident carbon signal of methylene attached to epoxy ring at 68.80 ppm (Scheme 2a) in the spectrum of the mixture of TDI and E51 (T/E-b) indicated that there was almost no reaction between TDI and E51.…”