Determination of low degrees of long-chain branching in polybutadiene by double-bond hydrogenation followed by 13C NMR and DEPT spectroscopies

Abstract

Long-chain branching (LCB) in polybutadiene (PB) was directly and accurately determined for the first time by combining the hydrogenation of PB with 13C NMR and DEPT spectroscopies. LCB in PB was converted into LCB in polyethylene (PE) by the hydrogenation of PB. No LCB in PE was observed in the 13C NMR spectrum. In contrast, LCB in PE was clearly observed in the 13C DEPT 90° spectrum. The methine carbons in LCB and short-chain branching, which is vinyl branching in PB converted into ethyl branching (EB) in PE, were quantified by 13C NMR and DEPT 90° spectroscopies. The numbers of LCB structures of commercially available PB-A and PB-B were 0.27 and 0.17/1000C, respectively. It was proved that these values were accurate with errors of ca. 10% as determined by analyses of control polymers with various ratios of hexyl branching to EB.