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

Abstract

Polyurethane prepolymers are widely used in reactive hot melt adhesives and moisture cured coatings. NCO-terminated polyurethane of polypropylene glycol (PPG)-1000 and isophoron diisocyanate (IPDI) with an NCO/OH ratio of 1.2:1 were prepared without any catalyst or solvent. 1D and 2D NMR spectroscopy was used for the structural investigation of the synthesized prepolymer. 1 H NMR spectra and dibutylamine back-titration were used to monitor the reaction of isocyanate groups with the hydroxyl function of PPG and to allow a good description of the evaluation of the urethane groups. The data on percentage conversion were crosschecked with 13 C NMR spectroscopy in the urethane zone for the methanol endcapped prepolymer. The observations show a higher reactivity of the secondary NCO group than of the primary group.

Synthesis and characterization of novel polyurethanes based on 2,6‐bis(4‐hydroxybenzylidene) cyclohexanone hard segments

“…The resonance peaks of the À ÀNHÀ ÀCOOÀ À protons of all of the PUs appeared in the region 9.91-9.94 ppm, except for those of IPDI and HDI-based polymers. In IPDI and HDI-based PUs, À ÀNHÀ ÀCOOÀ À protons are also observed around 5.55-5.75 ppm, which are in conformity with an earlier report, 19 but in the monomer, À ÀOH protons are found around 9.93 ppm.…”

The phase mixing studies on moisture cured polyurethane-ureas during cure

“…As the reaction was carried out for 6 h in the absence of any added catalyst, so the product mixture contains diurethane, monourethane and unreacted diisocyanate. In our earlier paper [24], the structural assignments of different protons and carbons associated with different environment in the liquid state were carried out by 1D and 2D homo and hetero-nuclear nuclear magnetic resonance (NMR) experiments, and have shown that after 6 h of reaction the fractional isocyanate conversion was approximately 10-15% for IPDI based formulation. The % NCO conversion for TDI based system showed 35-40% after 6 h as determined by dibutylamine titration.…”

Synthesis and characterization of novel Schiff base polyurethanes

“…1 Structures of both the diols and PUs were characterized with FTIR and NMR. FTIR spectra indicate the disappearance of bands due to both hydroxyl (at 3390 and 3402 cm 21 ) and isocyanate (at 2268 cm 21 ) groups, but they exhibit several characteristic stretching vibrations due to NÀ ÀH, C¼ ¼O, CH¼ ¼N, and CÀ ÀH moieties. Hydrogen bonding in PUs is of great interest because it is important 18 in determining the phase segregation.…”