Comprehensive Assignments of1H- and13C-NMR Signals of End-Functional Polyisobutylenes Using Spin-Lattice Relaxation Times and 2D1H-13C Hetcor Spectroscopy

The analysis of 13C spin-lattice relaxation times (T 1′s) provides a direct method for the assignment of 13C-NMR signals of the end groups of polymers. The 13C T 1′s of polyisobutylenes bearing tert-butyl, tert-chloride, exo-olefin, alcohol, aldehyde, and acetal end groups have been determined, and all the signals in their 13C-NMR spectra were assigned according to the gradient of T 1 along the polymer chain with the minimum in the middle. The assignments are in excellent agreement with those established by other techniques, which indicates the reliability of this novel method for the characterization of various end groups in polyisobutylenes. 13C T 1 analysis has also been used to obtain assignments for internal polyisobutylene segments adjacent to aromatic initiator residues. The method provides insight into the interaction of hydroxyl end groups of alcohol-capped PIBs, and allows identification of the low molecular weight impurities in the polymers. Assignments of all the 1H-NMR signals of the above polyisobutylenes were obtained by 2D 1H-13C HETCOR spectroscopy. For some polymers, 1H-NMR signals were also assigned based on their 1H T 1 values and the assignments agree with those generated by HETCOR spectroscopy.