Über den aufbau von polyurethan‐kunststoffen. II. Die struktur von polyurethan‐schaumstoffen in abhängigkeit von der temperatur, der zeit und der rezeptur; IR‐spektroskopische nachweisgrenzen für urethan‐ und harnstoffgruppen in polymeren

Abstract

ZUSAMMENFASSUNG:Friihere IR-spektroskopische Untersuchungen an Polyurethan-Schaumstoffen werden auf das Temperaturverhalten der Schaumstoffe, a d Beziehungen zwischen Struktur und Rezeptur sowie auf die zeitliche Reihenfolge der in Frage kommenden Reaktionen ausgedehnt. Bei erhohter Temperatur werden freie Isocyanatgruppen iiber Carbodiimide in deren Polymerisate umgewandelt. Die Biuretgruppen in einem Schaumstoff werden iiber die Spaltung in Harnstoffgruppen und freies Isocyanat abgebaut, letzteres reagiert in situ iiber Carbodiimide ab, Die hderungen des Aufbaus hlngen weitgehend vom Charakter der Polyhydroxylverbhdung ab, nur bei Verwendung von Polyestern erhiilt man mit alkalischen Zusltzen eine Trimerisation der Isocyanatgruppe. Ferner konnte gezeigt werden, daD bei der Schaumstoffherstellung zunlchst Urethan-, dann Harnstoff-und schliel3-lich Biuretgruppen gebildet werden. Ferner wurde unabhlngig die Nachweisgrenze fiir die einzelnen funktionellen Gruppen in niedermolekularen Vergleichsmischungen und an Polymeren bestimmt. SUMMARY:Infra-red spectroscopical examinations previously carried out on polyurethane foams have been extended to the temperature behaviour of the foams, to the relationship between the structure and the recipe as well as to the sequence of the reactions concerned. Free isocyanate groups are converted at elevated temperature via carbodiimides into the polymers thereof. The biuret groups in polyurethane foams are degraded by being split into urea groups and free isocyanate groups, the latter reacting in situ via carbodiimides. The variations in the structure substantially depend upon the nature of the polyhydroxyl compound ; only when using polyester-polyhydroxyl compounds, alkaline additives effect trimerisation of the isocyanate group.It could further be demonstrated that in the production of foams first urethane groups, then urea groups and finally biuret groups are formed.The infra-red detection limit for urea groups and urethane groups in polymers and in mixtures of low molecular weight comparison compounds was independently determined.

Structural investigation of polyurethanes: Infrared spectroscopic investigations of monomeric and polymeric N,N′-diaryl ureas

“…However, a number of discrepancies in the literature redirected our attention to this class of compounds, whose importance in the chemistry of polyurethanes is so great. For instance, Merten et al [1][2][3] found no absorption at 1640 cm-' in the infrared spectrum of a polyurethane foam produced with the aid of water and attributed this to a secondary reaction of the polyurea with isocyanate to form the biuret. An attempt, using model compounds and analogous conditions, to reproduce such a secondary reaction to form the biuret was, however, unsuccessful.…”

Thermal stability of molecularly uniform oligourethanes based on 1,5-naphthalene diisocyanate and 1,4-butanediol

“…The intensity of the carbodiimide band reached its maximum at 280 8C and decreased at higher temperatures because monomeric car- bodiimide (Eq. (4)) converted into polymeric carbodiimide structures 20) . Besides the decrease of the carbodiimide absorption, the carbodiimide polymerization is also recognizable by a broadening of the absorption of the polymeric structures at 1 613 cm -1 which is vaguely seen in the 290 8C curve in Fig.…”

The Effect of Ultraviolet Irradiation On Polyurethane Solution and On Solid Polymer

“…In I R spectra of unexposed polyu rethane ( F igure 1) the absorption bands characteristic of the urethane functional group [ 10,11 ] IR spectra of irradiated solutions ( Figure 1) show the decrease of intensity of absorption bands mentioned above and shift of the carbonyl band from 1700 cm-1 to 1730 cm-l . As the photolysis proceeded the intensity of the bands of the urethane group decreased whereas the band at 1730 crri became at the same time stronger.…”