4 research outputs found
Highly Permeable Benzotriptycene-Based Polymer of Intrinsic Microporosity
A novel
polymer of intrinsic microporosity (PIM) was prepared from
a diaminobenzotriptycene monomer using a polymerization reaction based
on Tröger’s base formation. The polymer (PIM-BTrip-TB)
demonstrated an apparent Brunauer, Emmet, and Teller (BET) surface
area of 870 m<sup>2</sup> g<sup>–1</sup>, good solubility in
chloroform, excellent molecular mass, high inherent viscosity and
provided robust thin films for gas permeability measurements. The
polymer is highly permeable (e.g., <i>P</i>H<sub>2</sub> = 9980; <i>P</i>O<sub>2</sub> = 3290 Barrer) with moderate
selectivity (e.g., <i>P</i>H<sub>2</sub>/<i>P</i>N<sub>2</sub> = 11.0; <i>P</i>O<sub>2</sub>/<i>P</i>N<sub>2</sub> = 3.6) so that its data lie over the 2008 Robeson upper
bounds for the H<sub>2</sub>/N<sub>2</sub>, O<sub>2</sub>/N<sub>2</sub>, and H<sub>2</sub>/CH<sub>4</sub> gas pairs and on the upper bound
for CO<sub>2</sub>/CH<sub>4</sub>. On aging, the polymer demonstrates
a drop in permeability, which is typical for ultrapermeable polymers,
but with a significant increase in gas selectivities (e.g., <i>P</i>O<sub>2</sub> = 1170 Barrer; <i>P</i>O<sub>2</sub>/<i>P</i>N<sub>2</sub> = 5.4)
Polymers of Intrinsic Microporosity Containing Tröger Base for CO<sub>2</sub> Capture
Properties of four polymers of intrinsic
microporosity containing
Tröger’s base units were assessed for CO<sub>2</sub> capture experimentally and computationally. Structural properties
included average pore size, pore size distribution, surface area,
and accessible pore volume, whereas thermodynamic properties focused
on density, CO<sub>2</sub> sorption isotherms, and enthalpies of adsorption.
It was found that the shape of the contortion site plays a more important
role than the polymer density when assessing the capacity of the material,
and that the presence of a Tröger base unit only slightly affects
the amount adsorbed at low pressures, but it does not have any significant
influence on the enthalpy of adsorption fingerprint. A comparison
of the materials studied with those reported in the literature allowed
us to propose a set of guidelines for the design of polymers for CO<sub>2</sub> capture applications
Solution-Processable Redox-Active Polymers of Intrinsic Microporosity for Electrochemical Energy Storage
Redox-active organic materials have emerged as promising
alternatives
to conventional inorganic electrode materials in electrochemical devices
for energy storage. However, the deployment of redox-active organic
materials in practical lithium-ion battery devices is hindered by
their undesired solubility in electrolyte solvents, sluggish charge
transfer and mass transport, as well as processing complexity. Here,
we report a new molecular engineering approach to prepare redox-active
polymers of intrinsic microporosity (PIMs) that possess an open network
of subnanometer pores and abundant accessible carbonyl-based redox
sites for fast lithium-ion transport and storage. Redox-active PIMs
can be solution-processed into thin films and polymer–carbon
composites with a homogeneously dispersed microstructure while remaining
insoluble in electrolyte solvents. Solution-processed redox-active
PIM electrodes demonstrate improved cycling performance in lithium-ion
batteries with no apparent capacity decay. Redox-active PIMs with
combined properties of intrinsic microporosity, reversible redox activity,
and solution processability may have broad utility in a variety of
electrochemical devices for energy storage, sensors, and electronic
applications
Molecular Modeling and Gas Permeation Properties of a Polymer of Intrinsic Microporosity Composed of Ethanoanthracene and Tröger’s Base Units
Polymers
of intrinsic microporosity (PIMs) are receiving increasing attention
from the membrane community because of their high gas and vapor permeability.
Recently a novel ethanoanthracene-based PIM synthesized by Tröger’s
base formation (PIM-EA-TB) was reported to have exceptional transport
properties, behaving as a polymer molecular sieve membrane. In the
present work, an extensive investigation of the structural, mechanical,
and transport properties of this polymer, both by experimental analysis
and by molecular simulation, offers deep insight into the behavior
of this polymer and gives an explanation for its remarkable performance
as a membrane material. Transport properties were determined by the
barometric time-lag method, by the volumetric method with gas chromatographic
or mass spectrometric gas analysis, and by gravimetric sorption measurements,
yielding all basic transport parameters, permeability (<i>P</i>), diffusivity (<i>D</i>), and solubility (<i>S</i>). Upon alcohol treatment, PIM-EA-TB exhibited a much stronger permeability
increase than archetypal “benchmark” polymer PIM-1,
with performance above the Robeson upper bound for several gas pairs.
This is in part due to an extremely high gas solubility in PIM-EA-TB,
higher than in PIM-1. The experimental data were supported by extensive
modeling studies of the polymer structure and the spatial arrangement
of its free volume. Modeling confirms that the high gas permeability
must be attributed to the large fractional free volume of the polymer.
The simulated free volume size distribution in PIM-EA-TB is in agreement
with the average experimental free volume elements size determined
by PALS and <sup>129</sup>Xe NMR analysis. The modeled spatial arrangement
of the free volume revealed a slightly lower interconnectivity of
the FV elements in PIM-EA-TB compared to PIM-1. Along with its higher
chain rigidity, determined by analysis of the torsion angles in the
polymer model, this was identified as the main reason for its stronger
size sieving behavior and relatively high permselectivity. A number
of peculiarities in the behavior of PIMs will also be discussed here,
explaining discrepancies between results published in the literature
by different laboratories, the effect of their thermomechanical history,
aging, or conditioning, and the influence of the measurement technique
and of the experimental conditions on the results. This makes this
study of inestimable value for unifying the results of different experimental
techniques and fully understanding the transport properties