Degree of branching of highly branched polyurethanes synthesized via the Oligomeric A₂ Plus B₃ methodology

The oligomeric A₂ plus monomeric B₃ synthetic methodology provided highly branched, poly(ether urethane)s based on IMP (B ₃) and isocyanate endcapped polyethers. ¹³C NMR spectroscopic assignments for the branched polyurethanes were verified using model urethane-containing compounds based on TMP and a monofunctional isocyanate (either cyclohexyl or phenyl isocyanate (PI)). Derivatization of hydroxyl endgroups with trifluoroacetic anhydride enhanced the ¹³C NMR resolution in spectra for branched polyurethanes. The ¹³C NMR resonance for the linear unit exhibited a broad shoulder due to quaternary carbons that were attributed to cyclic species in the highly branched polyurethanes. The classical DB calculation revealed the efficiency of the 83 monomer for branching; however, an equation that incorporated the linear contribution of the A₂ oligomer provided a more accurate DB for highly branched polyurethanes.