S. zyxwvutsrqpo E. Evsyukov et al.: Formation of Carbynoid Structures by Chemical Dehydrohalogenation of Poly(Viny1idene Chloride) 837 Formation of Carbynoid Structures by Chemical Dehydrohalogenation of Poly(Viny1idene Chloride). A 13C Solid-state NMR Study zyx S.E. Evsyukov‘)*), S. Paasch, B. Thomas, and R.B. Heimann Technische Universitilt Bergakademie Freiberg, D-09596 Freiberg, Germany zyxw ’) A. N.Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 117813 Moscow, Russia zyx Key Words: Molecular Structure / Polymers / Spectroscopy, Nuclear Magnetic Resonance The products of the interaction of poly(viny1idene chloride) (PVDC) powder with a mixture of alcoholic KOH solution and tetrahydrofuran were studied by solid-state 13C NMR spectroscopy. The reaction was found to be a complex process involving dehydrochlorination as a target reaction and some side reactions, viz., nucleophilic substitution, cross-linking, and secondary transformations of intermediate and final products. The endproducts are “carbynoid-type” polymeric materials containing short carbyne fragments along with various defect links such as alkoxy- and hydroxy groups, carbonyl species, as well as cross-links. The reasons for the concurrent formation of both polyyne and cumulene structures, and the nature of side reactions are discussed. Introduction One of the most fascinating though controversial subjects within the science of elemental carbon is concerned with the existence of a linear (chain-like) carbon allotrope, carbyne. Properties of this carbon form and related materials re- ported to date suggest attractive future applications in mi- croelectronics, optics, microwave and electrical technology, power engineering, and medicine [l]. However, inspite of a large body of publications on carbyne, no rigorous and unambiguous evidence of its existence is available to date. zyxwvut Also, the crystal and molecular structure of carbyne still re- mains the subject of discussions and harsh criticism (see, for example [2]). Chemical dehydrohalogenation of halogen-containing polymers is known to be a convenient and easily accessible method to synthesize conjugated polymers including car- byne-containing materials [3]. Previously, the complete de- hydrohalogenation of poly(viny1idene halides) was claimed to result in the formation of the cumulene-type isomer of carbyne, whereas the triple CGC bonds of the polyyne-type form were supposed to be present in the final dehydrohalo- genation products as defect links caused by structural defects in the original polymers and also as the result of some side reactions [4]. These conclusions were based on Auger electron spectroscopy (AES) and infra-red (IR) spec- troscopy data. It should be noted, however, that experimen- tal AES data were interpreted mostly on the basis of theo- retical calculations, and that the vibrational spectroscopy data are indeed rather controversial zyxwvut [5, 61. Therefore, unambiguous structural characterization of those dehydro- halogenation products is still a pressing problem. The pre- sent paper reports on a study of dehydrohalogenation pro- ducts of poly(vinylidene chloride) by 13C solid-state NMR spectroscopy. The use of NMR spectroscopy provides a *) Author to whom correspondence should be addressed. deeper understanding of the molecular structure of the dehydrohalogenation products of PVDC since individual structural groups can be determined without problems. In particular, the chemical shifts of linear carbynoid fragments occur in a range not occupied, and therefore not influenced by other resonances. Since the lengths of the fragments also control the chemical shift the NMR spectra yield additional information on the conformation of car- byne and carbynoid structures. Experimental Poly(viny1idene chloride) (PVDC) was synthesized by UV-initiated bulk polymerization of vinylidene chloride (1,l -dichloroethylene). Freshly distilled vinylidene chloride (Fluka) was irradiated in a quartz flask with UV-light pro- duced by a high-pressure mercury lamp, at room tempera- ture for 20min while stirring. A finely grained white precipitate formed rapidly within 1 to 2 min. The mixture was stirred for another hour at room temperature, and again irradiated for 20 min and left standing overnight. The precipitate was then filtered off, washed consecutively with hexane and ether, and dried. One gram of PVDC powder thus prepared was dehydro- chlorinated for a given time at room temperature under ni- trogen, with 100 ml of a mixture of saturated (20%) KOH solution in absolute ethanol with tetrahydrofuran (THF) in a 2: 3 volume ratio [4]. The reaction mixture was then poured into water, acidified with diluted HCI, and filtered. The product, a black powder, was washed thoroughly with water, ethanol and acetone, and dried at room temperature over P205 under reduced pressure. 13C NMR spectra were recorded with a Bruker MSL 300 spectrometer at a resonance frequency of 75.47 MHz apply- ing the cross polarization (CP) technique and using the CPCYCL pulse program (Bruker Software). IR spectra were obtained using a Nicolet 510 FT-IR spectro- photometer. The samples were pressed into disks with KBr. Ber. Bunsenges. Phys. Chem. zyxwvutsrqpon 101, 837-841 11997) No. 5 0 VCH Yerlagsgeselkchaft mbH, 0-69451 Weinheim. 1997 000S-9021/97/0505-0837 $ 15.00+.25/0