2D NMR study on chemical structure of the co-oligomers from carbon dioxide/propylene oxide/diol synthesized by a metal-free catalyst

Co-oligomers of carbon dioxide and propylene oxide with high carbonate content and terminated by hydroxyl groups are practically important polyols to synthesize block copolymers. Despite this, the H-1 and C-13 spectra of such co-oligomers have not been described in detail so far. In this article, a new metal-free synthesis of carbon dioxide/propylene oxide co-oligomers by a triethylborane/organic base (organic base is PPNCl) catalytic system in the presence of diols (1,2-propanediol, 1,4-butanediol) is briefly introduced. The resonances in the H-1 and C-13 NMR spectra of the synthesized products were assigned using 2D NMR spectrometry methods (COSY, TOCSY, selective HMBC, and HSQC). As a result, the signals of different types of chain ends and of propylene oxide units forming ether linkages were found in addition to the peaks of carbonate blocks. Moreover, our study confirmed the occurrence of an efficient chain transfer during the co-oligomerization, which is additionally supported by MALDI TOF mass spectrometry results.