Magic‐angle ¹³C NMR of solid polyphenylacetylenes

Abstract

Some solutions of polyphenylacetylene (PPA) were recently found to display high-resolution 13C NMR spectra.' These were assigned to the crystallizable form of PPA, which was concluded to assume a conformational structure consistent with a cis-cisoid helix. That assignment was based on the similarity of the '3c spectra with those of solutions of 1,3,5-triphenylbenzene. It was suggested that a cis-cisoid helix was also likely to be the characteristic molecular conformation in the solid-state crystal lattice of PPA, but evidence for this conjecture awaited the availability of high-resolution spectra of crystalline PPA. Such spectra have now been obtained.A purified sample of crystalline PPA can be obtained by repetitive exhaustive extraction of amorphous polymer with chloroform.' During most of the extraction process two fluid phases coexist and the polymer being purified goes from a solution phase through a gel phase to a polycrystalline phase.' Washing is continued until the chloroform extract is colorless. A t an initial polymer concentration of 10% by weight and an approximate fivefold dilution in each extraction, approximately 20 such steps are required.

New Substituted Polyacetylenes with Phenyleneethynylene Side Groups [−(C6H4−C⋮C)n−SiiPr3; n = 1, 2]: Synthesis, Characterization, Spectroscopic, and Photoelectric Properties

“…1 H and 13 C NMR Spectra of P1 and P2. NMR spectra of P1 samples are shown in Figures and and the signals' assignment performed by using the APT method and NMR spectra of monomers 16 and various forms of poly(phenylacetylene), PPA, − is summarized in Table for both P1 and P2 samples (for atom numbering, see Scheme ). The disappearance of signals characteristic of terminal triple bonds (3.12 and 3.17 ppm, H1; 78.9 and 79.1 ppm, C1; 83.3 ppm, C2) and preservation of signals of internal triple bonds (at 107 ppm, C7; and at 90−93 ppm, C8, C7‘, and C8‘) demonstrate the high terminal-triple-bond selectivity of polymerizations.…”

“…1 H and 13 C NMR Spectra of P1 and P2. NMR spectra of P1 samples are shown in Figures 2 and 3 and the signals' assignment performed by using the APT method and NMR spectra of monomers 16 and various forms of poly(phenylacetylene), PPA, [34][35][36][37][38][39][40][41][42] is summarized in Table 2 for both P1 and P2 samples (for atom numbering, see Scheme 2). The disappearance of signals characteristic of terminal triple bonds (3.12 and 3.17 According to the resolution of 1 H and 13 C NMR spectra as well as the half-width of the 29 Si NMR signal of pendant groups, the microstructure uniformity of Pn samples decreases in the following sequence: Pn/Rh > Pn/Mo > Pn/WD > Pn/W.…”

Electron spin resonance study of radical formation in cis-poly(phenylacetylene)/ferric acetylacetonate-triethylaluminum (PPA/Fe-Al). 2. Results and interpretation

“…plings were included in the regression analysis of the spectra from samples of the insoluble fraction. An approximation to the line shape of the oxygen-trapped radical was obtained from the spectrum of a heavily oxygen-doped sample; it is a nearly Gaussian line with AHpp = 13 gauss and g = 2.0029. Previous investigations of cis-PPA revealed similar spectra.…”

“…Each batch was separated into a chloroform-soluble and a chloroform-insoluble fraction by a procedure described elsewhere. 13 The latter fraction contained the insoluble crystalline polymer referred to in the Introduction. All samples, from the onset of polymerization through the course of the ESR experiments, were stored in the dark, since light had been shown capable of increasing the spin concentration.14 Samples were stored and treated in air except when in evacuated sample tubes, where they were under 0.2 torr of nitrogen.…”