Meso- and Microporous High-Performance Polymers Meso- and Microporous High-Performance Polymers Mesoporous Poly(benzimidazole) Mesoporous Poly(benzimidazole) Jens Weber 1,2 , Markus Antonietti 1 and Arne Thomas 1 1) Max Planck Institute of Colloids and Interfaces, Department of Colloid Chemistry, Research Campus Golm, D-14424 Potsdam, Germany 2) present address: Arrhenius Laboratory, Stockholm University, Dept. of Physical, Inorganic & Structural Chemistry, S-106 91 Stockholm, Sweden Microporous Polymers Microporous Polymers Synthesis and Characterization monomers & DMF polycondensation (200°C, 400°C) 4M NH 4 HF 2 etch silica solvent mediated hard-templating of silica spheres (Ludox HS-40): structure of cross-linked Poly(benzimidazole) (PBI) J. Weber, M. Antonietti, A. Thomas, Macromolecules 2007, 40, 1299 porosity analysed by small-angle x-ray scattering (SAXS), N 2 -sorption and TEM: (point collimation) 200 nm 50 nm surface areas tunable from 0 to 200 m 2 g -1 (variation of template content), typical pore size: 10-11 nm, porosities up to 37 vol.-% Proton Conductivity * J. Weber, M. Antonietti, A. Thomas, Macromolecules 2007, 40, 1299 *) in cooperation with K.-D. Kreuer (MPI Solid State Research, Stuttgart, Germany), J. Weber, K.-D. Kreuer, J. Maier, A. Thomas, Adv. Mater. 2008, 20, 2595 exact loading excess loading phosphoric acid loading necessary: ● addition of crystalline H 3 PO 4 ... ● excess loading is necessary because of H 3 PO 4 diffusion into the pore walls (formation of benzimidazolium by protonation) porosity proven by SAXS and Nitrogen sorption no porosity detectable influence of porosity (at fixed acid loading and cross-linking density) influence of flexibility (at fixed acid loading and comparable porosities) amount of cross-linker: proton conductivity enhancement proton conductivity enhancement by nanostructural control by nanostructural control of PBI/H of PBI/H 3 PO PO 4 adducts adducts (all measurements at zero humidity) Proton Conductivity * Proton Conductivity * Nanoreactor - Organocatalysis * *) cooperation: P. Makowski (MPI Golm) & F. Goettmann (CEA Marcoule, France); P. Makowski, J. Weber, A. Thomas, F. Goettmann, Catal. Commun. 2008, 10, 243 Knoevenagel condensation catalyzed by mesoporous PBI: benzimidazole units act as base aldehyde nucleophile (e.g. malononitriles) condensation product ● benzimidazole has to be non-protonated to be active ● nonporous PBI did not show catalytic activity ● less activity for ethylcyanoacetates in comparison to malononitriles (low basicity of PBI) O H CN CN 100 % CN CN O H COOE t CN 95 % COOE t CN O H CN CN 90 % CN CN O H COOE t CN 50 % COOE t CN H O CN CN 95 % CN CN H O COOE t CN 65 % COOE t CN I. Principle and Soluble Microporous Polymers Stiff, contorted polymers from predefined building blocks with 90° kinks cannot pack space-efficiently – ultra high, accessible free volume (micropores) (concept introduced by Budd et al. Chem. Comm. 2004, 230) 9,9'-Spirobifluorene is such a building block: can be modified towards di- or tetrafunctional monomers (dicarboxylic acid and derivatives, diamine, tetrabromo, tetracarboxylic acid, tetraamine...) J. Weber, O. Su, M. Antonietti, A. Thomas, Macromol. Rapid Commun. 2007, 28, 1871 Poly(amide) 1 Poly(amide) 1 M w = 10 kg . mol -1 ,PDI = 1.9; soluble only in DMF, NMP, DMAc... S BET = 0 m 2 g -1 (precipitated from DMF) Poly(amide) 2 Poly(amide) 2 M w = 15 kg . mol -1 ,PDI=2.7; soluble in DMF, NMP, DMAc...and THF! no microporosity if precipitated from DMF, but: S BET = 156 m 2 g -1 (precipitated from THF) Poly(imide) 1 Poly(imide) 1 M w = 15 kg . mol -1 ,PDI=2.7; soluble in DMF, NMP, DMAc...and CHCl 3 ! no microporosity if precipitated from DMAc, but: S BET = 551 m 2 g -1 (from CHCl 3 ) ● strong impact of molecular fine structure (flexibility, interactions, see below) ● processing (choice of solvent) is important! (metastable states?) II. Microporous Networks poly(amide): not microporous (S BET = 50 m 2 g -1 ) poly(imide): microporous (S BET = 982 m 2 g -1 ) ● no influence of synthetic pathway (i.e. onset and course of phase separation) ● need of a structure directing agent (polyimide network from tetra- functional biphenyl monomer did not feature microporosity) N 2 -sorption pressure dependent SAXS structural changes occur! structural changes occur! relaxation might be hindered by secondary interactions (e.g hydrogen bonding for poly(amide) Understanding this phenomenon allows the anticipation of other potentially microporous networks: poly(p-phenylene) type network: microporous + fluorescent (S BET = 450m 2 g -1 , max (emission) = 460 nm) potential hosts for IPNs with charge transport materials However, there are still a lot of open questions: How to characterize “soft”, amorphous microporous materials that undergo structural changes ? (e.g. swelling in liquid nitrogen) Where are the limitations of the concept of intrinsic microporosity? Can we get a better understanding of the acting forces (modeling?) J. Weber, M. Antonietti, A. Thomas, Macromolecules 2008, 41, 2880; J. Weber, A. Thomas, J. Amer. Chem. Soc. 2008, 130, 6334 *strategy already used: Göltner and Weissenberger, Acta Polym. 1998, 49, 704) SiO 2 monoliths (to be stored in solvent to avoid cracks) hybrid material exchange solvent with monomers & initiator, polymerize remove silica (NaOH) (mesoporous) polymer synthesis of mesoporous polymers by two-step nanocasting*: synthesis of hierarchical porous polymers using a replication process: open questions regarding mesoporous polymers: ● pores of ~20 nm are stable in glassy poly(styrene) - what about smaller pores (<10 nm) ? ● stability of pores against solvent and pressure? ● glass transition in weakly cross-linked mesoporous polymers? (compare controversial discussion about T g in thin films, entropic arguments, strain etc...) synthesis of mesoporous, monolithic polymers of varying chemical nature (styrene; various acrylates (MMA, n-Butyl acrylate...) and cross- linking density necessary... and: and: Current Work: Pore Stability in Mesoporous Polymers Current Work: Pore Stability in Mesoporous Polymers † † †) together with Lennart Bergström, Dept. of Physical, Inorganic & structural Chemistry, Arrhenius Laboratory, Stockholm, Sweden macro/mesoporous silica monoliths** fill mesopores with monomers/initiator (capillarity), polymerize & etch silica macro/mesoporous polymer monoliths **prepared by P. Vasiliev: P.O. Vasiliev, Z. Shen, R.P. Hodgkins, L. Bergström, Chem. Mater. 2006, 18, 4933) Acknowledgements: MPI Colloids & Interfaces: Bernd Smarsly, Helmut Schlaad, Regina Rothe, Marlies Gräwert, Ingrid Zenke, Rona Pitschke, Qi Su, Frederic Goettmann, Phillippe Makowski, Pierre Kuhn, Anna Fischer, Michael Bojdys, Chez Briel Kicker Team, ... MPI Solid State Research: K.-D. Kreuer, Annette Fuchs; Philipps-Universität Marburg; Andreas Greiner, Till von Graberg DVB/Styrene silica ● macroscopic shape is maintaned ● mesopore replication needs optimization exemplary picture of a polymer monolith