Linear High Molecular Weight Ladder Polymers by Optimized Polycondensation of Tetrahydroxytetramethylspirobisindane and 1,4-Dicyanotetrafluorobenzene † Jingshe Song, ‡ Naiying Du, ‡ Ying Dai, ‡ Gilles P. Robertson, ‡ Michael D. Guiver,* ,‡ Sylvie Thomas, § and Ingo Pinnau § Institute for Chemical Process and EnVironmental Technology, National Research Council of Canada, 1200 Montreal Road, Ottawa, Ontario K1A 0R6, Canada, and Membrane Technology and Research Inc., 1360 Willow Road, Suite 103, Menlo Park, California 94025-1516 ReceiVed May 2, 2008; ReVised Manuscript ReceiVed August 13, 2008 ABSTRACT: A study on the optimization of conditions for polycondensation of 3,3,3′,3′-tetramethyl-1,1′- spirobisindane-5,5′,6,6′-tetrol, TTSBI, with 1,4-dicyanotetrafluorobenzene (DCTB) in dimethylformamide (DMF) at 50-70 °C is reported. A linear PIM-1 polymer (PIM ) polymer with intrinsic microporosity) with high molecular weight was obtained by optimized reaction conditions. Of the solvents tested, DMF was the preferred solvent for this reaction. The optimized molar ratio TTSBI/DCTB/K 2 CO 3 was 1/1/2.04. The mechanism of PIM-1 cross- linking during polymerization was studied, and gel-free, high molecular weight PIM-1 polymer was prepared. The physical properties of anhydrous K 2 CO 3 significantly affected the reaction rate. Flexible tough polymer films were cast from PIM-1 solution in chloroform, and pure permeability data are reported for several gases. 1. Introduction Syntheses of aromatic polyethers are most often based on nucleophilic substitution polycondensation of activated fluoro-, chloro-, or nitroaromatics with sodium or potassium phenox- ides. 1-3 Recently, Budd and co-workers reported 4-8 on the syntheses of high molecular weight linear ladder polymers by irreversible polycondensations of tetraphenols with activated tetrafluoro- or tetrachloroaromatics. The most widely studied example (structure 1 in Scheme 1) of these so-called “polymers with intrinsic microporosity” (PIMs) is based on polyconden- sation of 3,3,3′,3′-tetramethyl-1,1′-spirobisindane-5,5′,6,6′-tetrol (TTSBI) with 1,4-dicyanotetrafluorobenzene (DCTB). These studies were focused on the application of these ladder polymers for gas separation membranes, for adsorption of small molecules, or for heterogeneous catalysts based on an unusually high microporosity due to a high rigidity in combination with a loose chain packing generating a high free volume. However, these papers did not provide detailed information on the monomer purification, synthetic conditions, or reaction mechanism for this kind of ladder polymer. Later the group of Kricheldorf 9 studied the condensation polymerization of the tetraphenoxide of TTSBI with DCTB in four different solvents at 70 °C. They determined that, when the reaction solvent was dimethylformamide (DMF), N-meth- ylpyrrolidone (NMP), and sulfolane, cyclic polymers were formed exclusively as detected by matrix-assisted laser desorp- tion/ionization time-of-flight (MALDI-TOF) mass spectrometry up to masses of around 13 000 Da. When dimethyl sulfoxide (DMSO) was used, linear byproducts were also found. Higher temperatures caused degradation reactions catalyzed by potas- sium carbonate. In contrast with earlier reports by Budd, no linear PIM-1 with high molecular weight and narrow molecular weight distribution was prepared. For the syntheses of normal linear aromatic polyethers, Schwarz et al. observed 10-12 that polycondensations involving silylated diphenols are cleaner and may yield higher conversions and molecular weights than analogous polycondensations em- ploying the phenoxide route. Similar observations were made for cross-linked polyethers prepared from silylated triphenols. 13 Therefore, Schwarz et al. 14 studied polycondensations of sily- lated TTBSI with DCTB under various conditions of solvent temperature, reaction time, and monomer feed ratio. Unfortu- nately, linear ladder polymers with high molecular weight were not obtained. Under optimized reaction conditions, all products detectable by MALDI-TOF mass spectrometry (up to masses around 8000 Da) were shown to be mixtures of cyclic ladder oligomers and polymers. In NMP and DMSO, odd-numbered cycles were formed in addition to the prevailing even-numbered ones. However, in sulfolane, even-numbered cycles were obtained exclusively (detectable up to masses of around 10 000 Da), together with even-numbered linear chains. Temperatures above 100 °C were reported to increase the molecular weights by side reactions, which resulted in reduced solubility and broader molecular weight distribution. * To whom correspondence should be addressed. Phone: (613) 993-9753. Fax: (613) 991-2384. E-mail: Michael.Guiver@nrc-cnrc.gc.ca. † NRCC Publication No. 49183. ‡ National Research Council of Canada. § Membrane Technology and Research Inc. Scheme 1. Synthetic Route to the Linear Ladder Polymer PIM-1 7411 Macromolecules 2008, 41, 7411-7417 10.1021/ma801000u CCC: $40.75  2008 American Chemical Society Published on Web 10/04/2008