Microporous polymers for carbon dioxide capture

The research described in this thesis relates to the development and optimisation of a novel polymerisation reaction and its subsequent use in the generation of novel ‘Polymers of Intrinsic Microporosity’ (PIMs). The polymerisation reaction takes monomers containing two or more aromatic amines and fuses them together by the synthesis of a bridged bicyclic heterocyclic link called Tröger’s base (TB). This link not only strongly holds the polymer chain together, but also provides a site of contortion, which is necessary for a PIM to exhibit microporosity. The first part of this work introduces the background to the research, detailing the reasons behind the development of a new class of PIM and the competitor materials. Following this is detailed the optimisation of the TB forming condensation reaction and the synthesis of a variety of amine functionalised monomers. Also described in this section is the optimisation of a second condensation reaction used for the synthesis of a family of compounds based around a coumaron framework, all of which lack amine functionality. This precedes discussion of X-ray crystal structure analysis of several TB model compounds, amine functionalised monomers and coumaron-based compounds. After this is a description of the development of the novel TB polymerisation reaction, the results of the TB polymerisation of the amine functionalised monomers, characterisation of the successful polymers and the attempted polymerisation of two coumaron-based monomers. The final part of this work reports the experimental procedure for each compound together with full characterisation. In closing, the TB polymerisation reaction has successfully used for the production of highly stable and soluble PIMs exhibiting a wide range of microporosity, with BET surface areas ranging from 0 m2/g to 1035 m2/g. A few of these PIMs have been found to have excellent molecular weight, capable of forming strong membranes, suitable for gas separation, most notably for the purification of oxygen, hydrogen and carbon dioxide from nitrogen. Conversely, the synthesis of coumaron-based PIMs proved unsuccessful, but nevertheless this research should allow the future synthesis of a coumaron-based PIM. The research on TB polymerisation detailed in this thesis has contributed towards an International Patent122 and a paper in Science123so can be deemed to have been successful by that measure

An efficient polymer molecular sieve for membrane gas separations

Microporous polymers of extreme rigidity are required for gas-separation membranes that combine high permeability with selectivity. We report a shape-persistent ladder polymer consisting of benzene rings fused together by inflexible bridged bicyclic units. The polymer’s contorted shape ensures both microporosity—with an internal surface area greater than 1000 square meters per gram—and solubility so that it is readily cast from solution into robust films. These films demonstrate exceptional performance as molecular sieves with high gas permeabilities and good selectivities for smaller gas molecules, such as hydrogen and oxygen, over larger molecules, such as nitrogen and methane. Hence, this polymer has excellent potential for making membranes suitable for large-scale gas separations of commercial and environmental relevance

Polymers of Intrinsic Microporosity Containing Tröger Base for CO₂ Capture

Properties of four polymers of intrinsic microporosity containing Tröger’s base units were assessed for CO₂ 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, CO₂ 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 CO₂ capture applications