Microstructural Investigation and MolecularWeight Determination of 1, 2-Polybutadiene by Nuclear Magnetic Resonance Spectroscopy

In this research, the microstructural of low molecular weight 1,2-polybutadiene (1,2-PBD) was conducted by 1H and 13C nuclear magnetic resonance spectroscopy (NMR) to determine the isomeric contents of 1,4-cis, 1,4-trans and 1,2-vinyl in 1,2-PBD polymer structures. Number average molecular weight for low molecular weight 1,2-PBD was measured by NMR techniques and the results were compared with gel permeation chromatography. Due to the presence of methyl end group and its comparison with repeating units in 1,2-PBD microstructure, the number average molecular weight was calculated by NMR techniques. For calculation of surface areas, carbon and protons of methyl groups were characterized using distortion enhancement by polarization transfer (DEPT) methods. For proton assignment of methyl end groups in 1H NMR spectral analysis the heteronuclear multiple quantum coherence (HMQC) method was employed. Finally, stereoregularity and tacticity of 1,2-PBD were investigated through pentad and heptad sequences splitting of olefinic methylene and methine carbons pendant groups with various NMR acquisition temperatures from 20 to 50oC. 13C NMR spectra showed that with increasing of NMR acquisition temperature, the number of split peaks of two olefinic carbons increased.