Microporous polymers containing tertiary amine functionality for gas separation membrane fabrication

This research reported in this thesis is based on the synthesis of novel polymers of intrinsic microporosity (PIMs) with the aim of fabricating membranes for gas separation applications. PIMs are composed of rigid and awkwardly-shaped monomeric segments which lack the conformational and rotational freedom needed to pack space efficiently. As a result these polymers display high BET surface areas and display excellent gas permeabilities when solution-cast into films which can be used as gas separation membranes. This thesis describes the synthesis of a range of aromatic diamine, tetraamine, dianhydride, and dicarboxylic acid monomers that conform to the PIM design concept, featuring rigid and contorted architectures. These monomers were then used to synthesise five classes of polymer featuring tertiary amine functionality. Structure-property relationships were established between these polymers and BET surface area measurements. Polymers that displayed adequate film forming properties were also evaluated by our collaborators at The Institute of Membrane Technology for their gas transport parameters. Chapter 6 describes the synthesis of a new class of polymer, Tröger's Base PIMs, featuring a novel polymerisation reaction using chemistry first reported 127 years ago. One of these polymers, DMEA.TB, displays a BET surface area of 1028 m2/g which is the highest recorded for any soluble polymer to date. DMEA.TB places gas permeation data for technologically important gas pairs far over the present Robeson upper bound and has unrivalled potential to separate mixtures containing hydrogen. Chapter 7 deals with quaternerisation and subsequent ion exchange of selected Tröger's Base polymers. Chapter 8 discusses the synthesis of three novel polyimides using highly rigid and contorted ethanoanthracene monomers containing methyl groups that restrict rotation around polymer segments. These polymers display only moderate gas permeation characteristics and possess BET surface areas of up to 694 m2/g. Chapter 9 describes the synthesis of a new class of zwitterionic polysquaraines however, these polymers were shown to be non-porous due to strong ionic/hydrogen bonding. Chapter 10 describes the synthesis of polybenzimidazoles using the PIM design concept but it was found that extensive hydrogen bonding reduces free volume, forming non porous solids. Chapter 11 describes the synthesis of novel polypyrrolones with surface areas of up to 284 m2/g however, film formation was not possible with these materials. Chapter 12 features a brief investigation onto the cross-linking of a Tröger's Base membrane using hydrolysed PIM-1 as polyanionic counterion

Fuel cell anode catalyst performance can be stabilized with a molecularly rigid film of polymers of intrinsic microporosity (PIM)

There remains a major materials challenge in maintaining the performance of platinum (Pt) anode catalysts in fuel cells due to corrosion and blocking of active sites.</p

One-step preparation of microporous Pd@cPIM composite catalyst film for triphasic electrocatalysis

Triphasic microporous materials (containing solid, liquid, and gas) are of interest in electrocatalysis. In this exploratory study, a polymer of intrinsic microporosity (PIM-EA-TB) is impregnated with PdCl4 2 − metal precursor and vacuum‑carbonised to give an electrically conductive microporous heterocarbon with embedded Pd nanoparticles of typically 10–30 nm diameter. This microporous composite catalyst is formed (via spin-coating) as “flakes” of typically 100 nm thickness and 1 to 20 μm diameter that are readily re-deposited onto glassy carbon electrode substrates. Due to the triphasic conditions, Pd@cPIM electrocatalytic reactivity is high but only for gases (H2 oxidation or O2 reduction). This selectivity is observed even in the presence of excess formic acid fuel in the aqueous/liquid phase. The potential for application in membrane-less micro-fuel cells is discussed.</p

Catechin or quercetin guests in an intrinsically microporous polyamine (PIM-EA-TB) host: accumulation, reactivity, and release

Microporous polymer materials based on molecularly "stiff"structures provide intrinsic microporosity, typical micropore sizes of 0.5 nm to 1.5 nm, and the ability to bind guest species. The polyamine PIM-EA-TB contains abundant tertiary amine sites to interact via hydrogen bonding to guest species in micropores. Here, quercetin and catechin are demonstrated to bind and accumulate into PIM-EA-TB. Voltammetric data suggest apparent Langmuirian binding constants for catechin of 550 (±50) × 103 M-1 in acidic solution at pH 2 (PIM-EA-TB is protonated) and 130 (±13) × 103 M-1 in neutral solution at pH 6 (PIM-EA-TB is not protonated). The binding capacity is typically 1 : 1 (guest : host polymer repeat unit), but higher loadings are readily achieved by host/guest co-deposition from tetrahydrofuran solution. In the rigid polymer environment, bound ortho-quinol guest species exhibit 2-electron 2-proton redox transformation to the corresponding quinones, but only in a thin mono-layer film close to the electrode surface. Release of guest molecules occurs depending on the level of loading and on the type of guest either spontaneously or with electrochemical stimuli

One-step preparation of microporous Pd@cPIM composite catalyst film for triphasic electrocatalysis

Triphasic microporous materials (containing solid, liquid, and gas) are of interest in electrocatalysis. In this exploratory study, a polymer of intrinsic microporosity (PIM-EA-TB) is impregnated with PdCl42− metal precursor and vacuum‑carbonised to give an electrically conductive microporous heterocarbon with embedded Pd nanoparticles of typically 10–30nm diameter. This microporous composite catalyst is formed (via spin-coating) as “flakes” of typically 100nm thickness and 1 to 20μm diameter that are readily re-deposited onto glassy carbon electrode substrates. Due to the triphasic conditions, Pd@cPIM electrocatalytic reactivity is high but only for gases (H2 oxidation or O2 reduction). This selectivity is observed even in the presence of excess formic acid fuel in the aqueous/liquid phase. The potential for application in membrane-less micro-fuel cells is discussed. Keywords: Gas binding, Triple phase reaction zone, Fuel cell, CO2 reduction, Microporosit

Hydrogen Peroxide Versus Hydrogen Generation at Bipolar Pd/Au Nano-catalysts Grown into an Intrinsically Microporous Polyamine (PIM-EA-TB)

Binding of PdCl42− into the polymer of intrinsic microporosity PIM-EA-TB (on a Nylon mesh substrate) followed by borohydride reduction leads to uncapped Pd(0) nano-catalysts with typically 3.2 ± 0.2 nm diameter embedded within the microporous polymer host structure. Spontaneous reaction of Pd(0) with formic acid and oxygen is shown to result in the competing formation of (i) hydrogen peroxide (at low formic acid concentration in air; with optimum H2O2 yield at 2 mM HCOOH), (ii) water, or (iii) hydrogen (at higher formic acid concentration or under argon). Next, a spontaneous electroless gold deposition process is employed to attach gold (typically 10- to 35-nm diameter) to the nano-palladium in PIM-EA-TB to give an order of magnitude enhanced production of H2O2 with high yields even at higher HCOOH concentration (suppressing hydrogen evolution). Pd and Au work hand-in-hand as bipolar electrocatalysts. A Clark probe method is developed to assess the catalyst efficiency (based on competing oxygen removal and hydrogen production) and a mass spectrometry method is developed to monitor/optimise the rate of production of hydrogen peroxide. Heterogenised Pd/Au@PIM-EA-TB catalysts are effective and allow easy catalyst recovery and reuse for hydrogen peroxide production