Urethan infrared absorption

The mechanism of chain extension was studied by observing the OH and NH absorptions at 3460 cm-1 and 3340 cm-1 respectively. Since one hydroxy moiety is consumed for each chain extension while one urethane NH is formed, the ratio of OH/NH infrared absorptions will decrease as chain extension occurs. The results of this study are shown in Table I and Figure 1. 

Table II. Infrared Absorption Data on the Cure of (t-Butyl Carbamate) Terminated Urea-Urethane Coating3...

While nearly all previous rate data were obtained by following the rate of disappearance of isocyanate, Kogon [129] followed the rate of formation of urethane, using infrared absorption at 6750 cm The second-order plot of the uncatalysed reaction of 2,4-tolylene diisocyanate was linear to about 60% reaction, and that of 2,6-tolylene diisocyanate to 30% reaction. 

Fig. 28. Polyurethane elastomer formation studied by a combination of saxs and ftir. The chemical reaction forming the polsnirethane can be monitored by following the changes in the infrared absorption bands. In this figure the intensity of the band associated with the hydrogen bonded urethane is coplotted with the saxs invariant. It is clear that the invariant increases before the ftir signal. By applying this method the possibility that structure formation is caused by hydrogen bonding could be excluded and it was shown that the hydrogen bonding is a consequence of the structure formation. A Relative invariant Q ...

Ultraviolet absorptions ofvinylogous lactams were found by MOLCAO calculations and compared with experimental values (663). Infrared spectroscopic studies of vinylogous amides (664) and some fifty vinylogous urethanes (665) allowed configurational and structural assignments. The effect of enamine-imine equilibrium in a series of benzophenone derivatives was established (666) and the effect of structure on enamine basicity studied (667). 

Figure 3. Infrared spectra for Type II urea-urethane/epoxy formulations, respectively, showing decreases in the intensity of the urethane absorption as the1 temperature of the cure reaction is increased from 50-180°C.

In his thorough study of the iV-methyl-pseudostrychnine derivates, Boit (318) investigated the reaction of lithium aluminum hydride on these compounds and showed that both iV-methyl-sec-pseudostrych-nine (CCIV, R=H) and iV -methyl-sec-pseudostrychnidine gave the same product (CCV, R=H), which showed no carbonyl absorption in the infrared but did show a band at 3.Op, due to the hydroxyl group, which could be made to react with phenyl isocyanate to form a crystalline urethan. The same results were produced in the brucine series... 

Dynamic infrared linear polarised spectra of thermoplastic polyester urethane and nylon-6 films were recorded under a varying sinusoidal strain. Dichroic spectra were calculated from the dynamic polarised spectra. The large bipolar bands in the dichroic in-phase spectra, caused by large frequency shifts of the original monopolar absorption bands, were ascribed to hydrogen bonds. 29 refs. 

The applicability of infrared dichroism to the study of PUs has been determined by the availability of at least one weU-characterized absorption band in each type of domain. It has been shown [67, 140, 364] that the soft domains are comprised of prepolymer (polyether or polyester) segments, while the hard domains contain urethane segments. The N-H stretching which is located in the urethane linkage characterizes the orientation of the higher modulus hard domains. For the DBDI polymers, we have shown that it appears at 3 320 cm [67]. Similarly, the asymmetric C-H stretching absorption was determined. It appears at 2 940 cm and was used to describe the orientation of prepolymer segments which comprise the rubbery soft domains. 

A close inspection of the infrared spectra of the polyoxazolidones, synthesised by reaction of BADGE with MDI (see Table 9), revealed that absorptions, probably attributable to terminal groups, altered with the method of precipitation. Where methanol was used the terminal groups were epoxy and urethane, i.e., strong absorptions at 930 and 1665 cm but none at 2250 and 1630 cm S efficient precipitation with water produced a polymer with terminal amine and epoxy groups as evidenced by strong absorptions at 1630 and 930 cm Less efficient precipitation produced polymers of less well defined spectra and these were less soluble in DMF. 

The progress of the reactions was followed spectroscopically with an infrared spectrophotometer. The reaction of PEGME with 1,6-diisocyanatohexane yielded the following absorption bands which are indicative of the urethane linkage and the isocyanate terminal 3300 cm -N-H stretching 1730 cm" C=0 stretching 1530 cm -amide, and 228 cm and the appearance of bands characteristic of urea. 

The IR spectra of pristine TDI and HTPB are compared with that of the reaction product, mainly PBNCO, in Fig. 29. The infrared spectra, after 10min of reaction at 70°C, show a strong absorption band at 1710-1735 cm , corresponding to the stretching of the —C=0 belonging to the (—NH—C(=0—O— ) urethane groups of the formed PBNCO molecules (see Fig. 29c). 

The existence of hybridisation effect in polycyanurate-polyurethane semi-IPNs via chemical interaction between cyanate and urethane groups was confirmed later by the method of multiple attenuated total reflection (ATR) infrared spectroscopy [29]. The ATR infrared spectra for some of the samples studied are given in Figure 14. The disappearance of the 2240-2270 cm" doublet in the spectra of properly prepared samples was accompanied by characteristic spectral changes depending on the polyurethane (PUR) content of the sample. These changes refer especially to appearance and enhancement of the 1560 and 1360 cm" bands of C=N and to absorption of polyurethane at 1700-1740 cm". ... 

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