COMPREHENSIVE ASSIGNMENTS OF ~1H- AND ~(13)C-NMR SIGNALS OF END-FUNCTIONAL POLYISOBUTYLENES USING SPIN-LATTICE RELAXATION TIMES AND 2D ~1H-~(13)C HETCOR SPECTROSCOPY

摘要

The analysis of ~(13)C spin-lattice relaxation times (T_1's) provides a direct method for the assignment of ~(13)C-NMR signals of the end groups of polymers. The ~(13)C 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 ~(13)C-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. ~(13)C 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 hy-droxyl 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-~(13)C 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.