No abstract

In this paper, we report the design, synthesis, and characterization of a series of hyper-cross-linked polymers of intrinsic microporosity (PIMs), with high CO 2 uptake and good CO 2 /N 2 and CO 2 /CH 4 selectivity, which makes them competitive for carbon capture and biogas upgrading. The starting hydrocarbon polymers' backbones were functionalized with groups such as −NO 2 , −NH 2 , and −HSO 3 , with the aim of tuning their adsorption selectivity toward CO 2 over nitrogen and methane. This led to a significant improvement in the performance in the potential separation of these gases. All polymers were characterized via Fourier transform infrared (FTIR) spectroscopy and 13 C solid-state NMR to confirm their molecular structures and isothermal gas adsorption to assess their porosity, pore size distribution, and selectivity. The insertion of the functional groups resulted in an overall decrease in the porosity of the starting polymers, which was compensated with an improvement in the final CO 2 uptake and selectivity over the chosen gases. The best uptakes were achieved with the sulfonated polymers, which reached up to 298 mg g −1 (6.77 mmol g −1 ), whereas the best CO 2 /N 2 selectivities were recorded by the aminated polymers, which reached 26.5. Regarding CH 4 , the most interesting selectivities over CO 2 were also obtained with the aminated PIMs, with values up to 8.6. The reason for the improvements was ascribed to a synergetic contribution of porosity, choice of the functional group, and optimal isosteric heat of adsorption of the materials.

Heterogeneous catalysis plays a pivotal role in the preparation of value-added chemicals, and it works more efficiently when combined with porous materials and supports. Because of that, a detailed assessment of porosity and pore size is essential when evaluating the performance of new heterogeneous catalysts. Herein, we report the synthesis and characterization of a series of novel microporous Tröger’s base polymers and copolymers (TB-PIMs) with tunable pore size. The basicity of TB sites is exploited to catalyze the Knoevenagel condensation of benzaldehydes and malononitrile, and the dimension of the pores can be systematically adjusted with an appropriate selection of monomers and comonomers. The tunability of the pore size provides the enhanced accessibility of the catalytic sites for substrates, which leads to a great improvement in conversions, with the best results achieving completion in only 20 min. In addition, it enables the use of large benzaldehydes, which is prevented when using polymers with very small pores, typical of conventional PIMs. The catalytic reaction is more efficient than the corresponding homogeneous counterpart and is ultimately optimized with the addition of a small amount of a solvent, which facilitates the swelling of the pores and leads to a further improvement in the performance and to a better carbon economy. Molecular dynamic modeling of the copolymers’ structures is employed to describe the swellability of flexible chains, helping the understanding of the improved performance and demonstrating the great potential of these novel materials.

No abstract

The climate crisis is the greatest challenge facing this generation, and in order to meet ambitious targets set by global leaders, great advancements in sustainable technologies are needed. This thesis work aimed to develop a new series of polymers of intrinsic microporosity (PIMs) for catalytic applications. PIMs have been of great interest within materials chemistry since their development in the early 2000s, they are purely organic materials that have a lower environmental impact than competing materials and can be synthesised under relatively mild conditions. More specifically, Tröger’s’ base (TB) PIMs are materials that, along with the typical high porosity of PIMs, possess two bridgehead nitrogens that can be used to tune the polarity of the final material. In this work, we have synthesised a series of novel TB-PIMs which can act as basic catalysts because of the basicity of the bridgehead nitrogens. We have demonstrated that by increasing the degree of flexibility in the polymers, we can induce a “swelling” effect that facilitates the accessibility of the catalytic sites and allows the use of larger substrates, thus increasing the catalytic performance. We have also shown that new functionalities can very easily be incorporated into PIM structures, meaning that these materials can be tailor made for specific applications. We have demonstrated that by increasing the number of basic nitrogen sites in a repeated unit, we can further increase the rate of a reaction. Finally, we have shown that post-functionalised PIMs can successfully catalyse a range of environmentally important reactions. For instance, quaternised TB polymers were successfully used to catalyse the cycloaddition of CO2 into epoxides, to form cyclic carbonates that can be employed as sustainable solvents, and sulfonated PIMs have been successful in the transesterification of oils for biodiesel synthesis. We believe that this work lays a foundation for future research into PIM catalysts, as they are a versatile, facile, robust, and efficient catalytic technology.