Meso- and Microporous High-Performance PolymersMeso- and Microporous High-Performance Polymers
Mesoporous Poly(benzimidazole)Mesoporous Poly(benzimidazole)
Jens Weber1,2, Markus Antonietti1 and Arne Thomas1
1) Max Planck Institute of Colloids and Interfaces, Department of Colloid Chemistry, Research Campus Golm, D-14424 Potsdam, Germany2) present address: Arrhenius Laboratory, Stockholm University, Dept. of Physical, Inorganic & Structural Chemistry, S-106 91 Stockholm, Sweden
Microporous PolymersMicroporous PolymersSynthesis and Characterization
monomers & DMF
polycondensation(200°C, 400°C)
4M NH4HF
2
etch silica
solvent mediated hard-templating of silica spheres (Ludox HS-40):
structure of cross-linkedPoly(benzimidazole) (PBI)
J. Weber, M. Antonietti, A. Thomas, Macromolecules 2007, 40, 1299
porosity analysed by small-angle x-ray scattering (SAXS), N2-sorption and TEM:
(point collimation)
200 nm
50 nm
surface areas tunable from 0 to 200 m2g-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
excessloading
phosphoric acid loading necessary:● addition of crystalline H3PO4...● excess loading is necessary because of H3PO4 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 enhancementproton conductivity enhancementby nanostructural controlby nanostructural control
of PBI/Hof PBI/H33POPO
44 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)
condensationproduct
●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
CN100 %
CN
CN
O
H
COOEt
CN95 %
COOEt
CN
O
H
CN
CN90 %
CN
CN
O
H
COOEt
CN50 %
COOEt
CN
H
O
CN
CN95 %
CN
CN
H
O
COOEt
CN65 %
COOEt
CN
I. Principle and Soluble Microporous PolymersStiff, 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) 1Poly(amide) 1Mw= 10 kg.mol-1,PDI = 1.9;
soluble only in DMF, NMP, DMAc...SBET= 0 m2g-1 (precipitated from DMF)
Poly(amide) 2Poly(amide) 2Mw= 15 kg.mol-1,PDI=2.7;
soluble in DMF, NMP, DMAc...and THF!no microporosity if precipitated from DMF, but:
SBET= 156 m2g-1 (precipitated from THF)
Poly(imide) 1Poly(imide) 1Mw= 15 kg.mol-1,PDI=2.7;
soluble in DMF, NMP, DMAc...and CHCl3!no microporosity if precipitated from DMAc,
but: SBET= 551 m2g-1 (from CHCl3)
●strong impact of molecular fine structure (flexibility, interactions, see below)● processing (choice of solvent) is important! (metastable states?)
II. Microporous Networkspoly(amide):not microporous(SBET= 50 m2g-1)
poly(imide): microporous(SBET= 982 m2g-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)
N2-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
(SBET= 450m2g-1, max (emission) = 460 nm)potential hosts for IPNs withcharge 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)
SiO2 monoliths(to be stored in solvent
to avoid cracks)hybrid material
exchange solventwith 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 aboutTg in thin films, entropic arguments, strain etc...)
synthesis of mesoporous, monolithic polymersof varying chemical nature (styrene; various acrylates (MMA, n-Butyl acrylate...) and cross-linking density necessary...
and:and:
Current Work: Pore Stability in Mesoporous PolymersCurrent Work: Pore Stability in Mesoporous Polymers††
†) together with Lennart Bergström, Dept. of Physical, Inorganic & structural Chemistry, Arrhenius Laboratory, Stockholm, Sweden
macro/mesoporoussilica monoliths**
fill mesopores with monomers/initiator
(capillarity),polymerize & etch silica
macro/mesoporouspolymer 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/Styrenesilica
● macroscopic shape is maintaned● mesopore replication needs optimization
exemplary picture ofa polymer monolith