The Structure of Poly(carbonsuboxide) on the Atomic Scale: A Solid‐State NMR Study

Abstract

In this contribution we present a study of the structure of amorphous poly(carbonsuboxide) (C3O2)x by 13C solid-state NMR spectroscopy supported by infrared spectroscopy and chemical analysis. Poly(carbonsuboxide) was obtained by polymerization of carbonsuboxide C3O2, which in turn was synthesized from malonic acid bis(trimethylsilylester). Two different 13C labeling schemes were applied to probe inter- and intramonomeric bonds in the polymer by dipolar solid-state NMR methods and also to allow quantitative 13C MAS NMR spectra. Four types of carbon environments can be distinguished in the NMR spectra. Double-quantum and triple-quantum 2D correlation experiments were used to assign the observed peaks using the through-space and through-bond dipolar coupling. In order to obtain distance constraints for the intermonomeric bonds, double-quantum constant-time experiments were performed. In these experiments an additional filter step was applied to suppress contributions from not directly bonded 13C,13C spin pairs. The 13C NMR intensities, chemical shifts, connectivities and distances gave constraints for both the polymerization mechanism and the short-range order of the polymer. The experimental results were complemented by bond lengths predicted by density functional theory methods for several previously suggested models. Based on the presented evidence we can unambiguously exclude models based on gamma-pyronic units and support models based on alpha-pyronic units. The possibility of planar ladder- and bracelet-like alpha-pyronic structures is discussed.

Distributed Sources in Comets

“…These studies show that if the same kind of polymers is present in comets, a distributed CO 2 source should also be observed, which, to date, is not the case. But laboratory synthesised polymer are extremely unstable as the compound is extremely hygroscopic (Schmedt auf der Günne et al 2005). Exposed to air, it takes up atmospheric water within seconds and undergoes chemical modifications.…”

Sonochemical Disproportionation of Carbon Monoxide in Water: Evidence for Treanor Effect during Multibubble Cavitation

“…The most interesting IR bands, in the range 1212-962 cm À1 , are shown in the inset of Figure 3. According to previously published data [14,15] the bands at 1225-1135 cm…”

“…The FTIR spectrum of (C 3 O 2 ) n under anhydrous conditions shows a band of the ketenyl group, C=C=O, at 2180 cm À1 . [15] However, exposure of the polymer to water results in the disappearance of this band. In our system, the absence of an absorption band at 2180 cm À1 in the FTIR spectrum of CCP also can be explained by hydrolysis of the ketenyl groups.…”

Effective dipolar couplings determined by dipolar dephasing of double-quantum coherences

“…Relaxation effects can often be minimized by using a constant-time setup [33][34][35]. For this purpose the dephasing block is split into two separate periods s 1 and s 2 .…”

“…Hence it is possible to make use of the throughspace dipolar coupling and the through-bond dipolar coupling in a single experiment which resembles the situation in the double-filter DQ constant-time experiment [33]. Compensation for relaxation and experimental imperfections can be achieved following the ideas of DQ constant-time NMR [33][34][35][36].…”