Characterization of oligomers from 1,4‐butanediol and toluene diisocyanate

Polyurethane oligomers from 1,4‐butanediol (BD) and toluene diisocyanate (TDI) with a various excess of BD were synthesized. Their molar masses were measured by gel permeation chromatography and the molar mass distribution correlated with the statistic theory. 1H‐, 13C‐, 1H–1H‐COSY–, ATP–, and 15N‐NMR spectra of reaction products were recorded, and from the ratio of proton integrals of characteristic terminal and inner urethane groups, the reactivity ratio of the para and ortho NCO groups in 2,4‐TDI was calculated to be approximately 1.8 at a lower excess of BD. 15N‐NMR spectroscopy was found not to be selective enough to detect small amounts of side reactions.