NAMS 2002 Workshop - ICOM 2008

chain packing. To ensure a well phase separated morphology a hard segment
containing uniform tetra-amide units is used.
The soft segment length is varied between 1.000 - 10.000 g/mol, enabling soft
phase concentrations up to 89 wt%. Crystallinity of the uniform hard segment is
high (~ 80%) and the phase separation is very efficient, leading to a pure, flexible
and highly permeable soft phase. Crucial in this case is the fact that PEO
crystallization is absent in all materials at temperatures as low as -5°C.
Pure gas permeabilities are determined using the constant volume, variable
pressure method in a temperature range from -10°C to 50°C at an upstream
pressure of 4 bars. CO2 gas permeabilities at 35°C ranged from 126 Barrer
(1.000 g/mol) to approximately 500 Barrer (10.000 g/mol), while gas selectivity
values are as high as 10 for CO2/H2, 45 for CO2/N2 and 13 for CO2/CH4. These
gas selectivities are comparable with a typical PEO containing block copolymer
like PEBAX® 1074, while permeability is increased with a factor four. At a
temperature of -10°C the CO2 permeability remained high with a value of 235
Barrer for a soft segment length of 10.000 g/mol. At this temperature CO2/H2,
CO2/N2, and CO2/CH4 selectivities reached values of respectively 19, 99 and 31.
Compared to the block copolymer systems described in literature the CO2 gas
permeability is tremendously increased (> 300 Barrer increase) while the
CO2/light gas selectivity is unaffected. The operating window of block copolymers
for CO2 gas separation is thus expanded to the low temperature region which is
interesting for CO2/CH4 as well as CO2/H2 separations.
In the present work we prove that segmented block copolymers are a successful
molecular toolbox to tailor the mass transport properties of polymeric
nanocomposites. A random distribution of 25 mol% PPO within a PEO oligomer
suppresses PEO crystallization in PEO based segmented block copolymers. In
addition, the use of a uniform hard segment results in block copolymers
containing a very pure and flexible soft phase. Combined, their use enhances the
CO2 gas permeability tremendously (up to a fourfold increase) over conventional
PEO based block copolymers without sacrificing selectivity. To our knowledge
these results are the best reported values to date for polyether based block
copolymer systems.