Synthesis, Characterization, and Membrane Properties of Poly(1-trimethylgermyl-1-propyne) and Its Nanocomposite with TiO 2 Wilfredo Yave, ² Klaus-Viktor Peinemann,* ,² Sergey Shishatskiy, ² Valeriy Khotimskiy,* ,‡ Marina Chirkova, ‡ Samira Matson, ‡ Elena Litvinova, ‡ and Nicolas Lecerf § Institute of Polymer Research, GKSS-Forschungszentrum Geesthacht GmbH, Max-Planck-Str. 1, 21502 Geesthacht, Germany; A.V. TopchieV Institute of Petrochemical Synthesis, Russian Academy of Sciences, Leninsky Prospekt 29, 119991 Moscow, Russia; SINTEF Materials and Chemistry, P.O. Box 124, Blindern, NO-0314 Oslo ReceiVed June 30, 2007; ReVised Manuscript ReceiVed August 31, 2007 ABSTRACT: The relationship between poly(1-trimethylgermyl-1-propyne) (PTMGP) microstructure and gas permeability property is reported. Controlling the synthesis conditions via TaCl 5 and NbCl 5 catalyst systems, tailor-made polyacetylenes in a wide range of cis/trans ratio (trans content from 35 to ∼100%) were obtained. According to the cis and trans ratio in the polymeric chain, a two-phase structure was found characterized by the presence of regions with enhanced level of macrochains ordering and with amorphous regions. The polymer microstructure has been related with free-volume, gas permeability, and polymer resistance toward liquid hydrocarbons. PTMGP membranes with high trans content (80-90%) exhibited higher gas permeability than samples with low trans content. Gas permeability of PTMGP membranes decreased with the density of polymer films, i.e., with the free-volume fraction in polymers with different microstructures. Furthermore, it was demonstrated that gas permeability and resistance toward solvents of the PTMGPs are directly defined by their cis/trans microstructure and supramolecular ordering. PTMGP with well-defined microstructure (trans content between 80 and 90%) can be considered as potential membrane material for gas separation, e.g., separation of higher hydrocarbons from natural gas. PTMGP/TiO 2 nanocomposite membranes were also studied for exploring the gas permeability properties and stability of polyacetylene membranes. Gas transport properties were affected slightly by TiO 2 presence; however, the long-term stability was enhanced. Introduction Exceptional gas transport properties, particularly high selec- tivity (condensable hydrocarbons/permanent gas) of 1,2-disub- stituted poly(acetylenes), have led to considerable interest in their synthesis and detailed investigation on microstructure- property relationships. 1,2 Poly(1-trimethylsilyl-1-propyne) (PTMSP), a silicon-contain- ing polymer belonging to the class of 1,2-disubstituted poly- (acetylenes), exhibits a record level of gas and vapor perme- ability. 3-6 This was attributed to a large free volume of PTMSP (around 28%), where the free-volume voids are big enough to be considered as micropores. The properties of PTMSP have been rationalized with its chemical microstructure, particularly the high stiffness of macrochains 5,7-9 and the presence of a bulky substituent which acts as intersegmental spacer are responsible for the unusual morphology of this polymer. The important feature of PTMSP and some other high- permeable substituted polyacetylenes is their gas and vapor transport properties, which increases with the increase of penetrant molecular size. 4,10-13 Besides, the PTMSP selectivity value for vapor/permanent gas mixture separation is essentially higher than that obtained for pure gas permeation experi- ments. 14,15 The permanent gas permeability of the PTMSP decreases significantly in the presence of vapor, since the vapor condensates in the free volume voids of the polymer and surface diffusion of condensed component becomes dominant. The selectivity of the n-butane/methane mixture separation using the PTMSP membrane is about 30, which is 6 times higher than the pure gas selectivity. 14 This unique property of the PTMSP is attractive for the application in removal of higher hydrocar- bons during natural gas conditioning. However, the presence of higher hydrocarbons in the natural gas streams lead to the degradation of the membrane due to the solubility of PTMSP in liquids hydrocarbons. Thus, from a practical point of view, the study and development of new polyacetylenes with well- defined microstructure and good resistance to high hydrocarbons is important. Our present notions on unusual gas transport behavior of highly permeable glassy polymers are mostly based on data obtained for silicon-containing materials. A detailed investiga- tion of PTMSP synthesis at various conditions and its influence on polymer properties 16 found that gas permeability of PTMSP and its solubility in organic solvents depends on the geometric structure of macromolecules (content of units having cis and trans microstructures) and supramolecular organization (packing of polymer chains). In turn, the geometric structure of macro- molecules depends upon synthesis conditions of the polymer, such as catalytic system, solvent, polymerization temperature, etc. Variation of polymerization conditions allows changing the geometry of polyacetylene macromolecules and hence enable us to tailor polymer properties. Great interest has been noted for the nearest structural analogue of PTMSP, the germanium-containing poly(1-trim- ethylgermyl-1-propyne) (PTMGP). This polymer differs from PTMSP only by the nature of the heteroatom in the side group. The germanium atom has a higher atomic weight and ionic radius than silicon, the Ge-C bond stability is higher than Si-C, 17 and consequently the Ge containing polymer has higher * Corresponding authors. E-mail: klaus-viktor.peinemann@gkss.de; hotimsky@ips.ac.ru. ² GKSS-Forschungszentrum Geesthacht GmbH. ‡ Topchiev Institute of Petrochemical Synthesis. § SINTEF Materials and Chemistry (current address: European Patent Office, Postbus 5818, 2280 HV Rijswijk, The Netherlands). 8991 Macromolecules 2007, 40, 8991-8998 10.1021/ma0714518 CCC: $37.00 © 2007 American Chemical Society Published on Web 11/15/2007