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Preparation, Characterization and Properties of Polymers Incorporating Spiro-centers
[Thesis]. Manchester, UK: The University of Manchester; 2013.
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Abstract
This research aimed to develop new polymeric materials for use in membrane or adsorption processes for carbon dioxide capture. In particular, it explored the synthesis, characterization and properties of polymers incorporating a spiro-center. A dianhydride containing a spiro-center (An-1), suitable for use in the preparation of polyimides, was synthesized using a previously reported procedure. The spiro-center makes the structure of the resulting polymers (PIM-PIs) similar to polymers of intrinsic microporosity (PIMs), which are known for their high internal surface area and outstanding membrane permeation properties. PIM-polyimides PIM-PI-1 and PIM-PI-5 were successfully synthesized and characterized, and membranes prepared for permeation studies. For PIM-PI-5, gas permeation data were obtained for the first time and were shown to be in reasonable agreement with values predicted by a group contribution method. To produce membranes with even better gas permeation properties, hydroxyl-containing PIM-polyimides were introduced. The presence of a hydroxyl group in the ortho position of the imide linkage made it possible to thermally rearrange the PIM-polyimide to a PIM-polybenzoxazole (PIM-PBO) at 450 oC in an inert atmosphere. PIM-PI-OH-1 with high enough molecular weight to form a freestanding membrane was successfully synthesized using two different synthetic methods: thermal imidization and one-step polycondensation. The PIM-PI-OH-1 polymers prepared by both synthetic methods were compared in terms of gas permeation properties and CO2 uptake capacity, before and after thermal rearrangement. As expected, for polymers prepared by both methods, a significant enhancement was observed in the membranes gas permeation properties upon thermal rearrangement. Ethanol treatment was also performed on the thermally rearranged polymers, which resulted in a large increase in their permeability. The effect of aging was investigated on the ethanol treated PIM-PBO-1 membranes. It was observed that the membranes gradually lose the extra permeability created upon ethanol treatment and return to close to their original permeability value.To increase the concentration of thermally rearrangeable sites in the polymers, a dianhydride (An-2) with a smaller structure and lower molecular weight comparing to the An-1 was synthesized. A copolymer (copolymer-OH(1-2)), was synthesized using An-1 and An-2 (1:1). Gas permeation measurements were performed on the thermally rearranged polymer before and after ethanol treatment. A slight enhancement in the polymer’s selectivity toward CO2/N2 and CO2/CH4 gas pairs was observed, while maintaining the permeability.Having the same aim, PIM-PI-OH-3 was prepared using a smaller and a more rigid diamine, compared to the diamine used in the preparation of PIM-PI-OH-1. Gas permeation studies of the thermally rearranged membrane before and after ethanol treatment showed a significant increase in O2/N2 selectivity, which passed the Robeson 2008 upper bound. In adsorption experiments, CO2 uptake was higher than for PIM-PI-OH-1 and its thermally rearranged product.