Degree of branching of highly branched polyurethanes synthesized via the oligomeric A2 plus B3 methodology

The oligomeric A(2) plus monomeric B-3 synthetic methodology provided highly branched, poly(ether urethane)s based on TMP (B-3) and isocyanate endcapped polyethers. C-13 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 C-13 NMR resolution in spectra for branched polyurethanes. The C-13 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 B-3 monomer for branching; however, an equation that incorporated the linear contribution of the A(2) oligomer provided a more accurate DB for highly branched polyurethanes.