The potential of branch length discrimination for branches containing six and more carbons via bulk NMR relaxation properties in the melt-state has been explored. A systematic increase in the 13C spin-lattice relaxation time T1 of the terminal branch carbons 1 and 2 was observed when the branch increased from 6 to 16 carbons in length. The measurement of T1 via inversion recovery at high-field showed the most reliable data. The effects of saturation and NOE were addressed by using recycle delays longer than 5×T1 and the use of the saturation recovery was found to be unsatisfactory. All nuclear relaxation times were determined in a highly time efficient manner using a previously developed melt-state MAS NMR method.
