Photolysis of aromatic diisocyanate‐based polyurethanes in solution

Abstract

Fluorescence analysis has been employed as an analytical technique to elucidate the photolysis mechanism of several aromatic diisocyanate‐based polyurethanes in solution. Based on a comparison with model arylmonocarbamates and arylbiscarbamates, the photo‐Fries rearrangement and cleavage‐type products found for the small‐model arylcarbamates were also identified for the photolyzed polyurethanes in solution. Viscosity and absorbance change results for photolysis of both air and nitrogen‐saturated polyurethane solutions are consistent with a general two‐step mechanism for the photolysis of aromatic diisocyanate‐based polyurethanes.

Durability of Polymer Metal Multilayer: Focus on the Adhesive Chemical Degradation

“…The oxidation of the urethane groups can lead to a strong chromophore structure responsible for the yellowing of PU. From the photo-oxidation mechanism, a possible mechanism of TDI-based PUs thermal degradation was proposed in Scheme 2C (Hoyle and Kim, 1986). The degradation proceeds as a two-step process, giving first the primary aromatic amine products followed by a subsequent reaction to give a quinoid-type compound.…”

Photolysis of bisphenol-based polyurethanes in solution

“…The broadness of the emission peak at 400 -500 nm may be due not only to photo-Fries, but also to quinone-imide type compounds (Scheme 2) and other unknowns. 12 These phenomena might be attributed to the electron-donating nature of isopropylidene, which contributes stability to the transition state of photodegradation and leads to many types of photolytic mechanisms. Our present study, however, deals only with the photo-Fries type mechanism.…”

“…This is due to inhibition of cleavage by oxygen. 12 From this discussion, the photostability of the bisphenol-based polyurethanes in the oxygen atmosphere appears to be as shown in equation (10): For all polymers, we investigated changes in UV absorbance (400 nm) during photolysis and in the presence of nitrogen and oxygen. Figure 10 shows these changes for 0.5 wt % bisphenol Sbased polyurethane in DMF.…”

“…[1][2][3][4][5][6][7] Recently, fluorescence spectroscopy has been used to detect photo-Fries rearrangement products from the photolysis of polymers such as polyurethanes 12 and polycarbonates. [13][14] Hoyle et al 12 reported that photo-Fries products resulting from photolysis of aromatic diisocyanate-based polyurethanes in solution can be identified with this technique. However, most research has dealt mainly with the effect of the structure of aromatic diisocyanates on photolysis of polyurethanes, and the effect of the structure of aromatic diol has not been investigated.…”

Infrared study of the photochemical behaviour of aromatic poly(ether urethanes): effect of various stabilizers

“…The photochemical evolution of the hard segments based on 4,4'methylene bis(phenyl isocyanate) (MDI) involves a dual mechanism. One is the photo-Fries type reaction [3] and the other is an induced oxidation of the central methylene group of MDI [4,5,6]. The latter reaction does not occur in toluene diisocyanate based hard segments due to the absence of methylene groups.…”