Analysis of Chain Branch of Polyolefins by a New Proton NMR Approach

The crystallinity of polyethylene, which significantly affects the properties of the polymer, is quite sensitive to the concentration of its branches. Thus, it is necessary to estimate branch concentration with reasonable accuracy. Currently, C-13 NMR and gel permeation chromatography Fourier transform infrared spectroscopy are widely-used analysis methods for the analysis of branch concentration. Despite several advantages, these methods sometimes have limitations. For instance, the preparation of samples for C-13-NMR is tedious because high-concentration samples are required and the time for analysis is greater than 12 h. To more efficiently estimate the branch concentration of polyethylene, we developed a new high field H-1 NMR method with an improved peak resolution by employing (1) homonuclear decoupling and (2) 2D heteronuclear correlation. The new method was observed to significantly reduce the experimental time to similar to 30 min; furthermore, sample preparation was relatively simple because the method did not require high-concentration samples.