NSF Award
9260408
This study is concerned with synthesizing, for gas separations, new polymeric membranes which will have both high permeability and selectivity. The PI focuses on substituted polyacetylene membranes, and notes that of this class PTMSP (poly(trimethylhysilylpropyne): ?(C(CH3) = C(Si(CH3)3)n!) has the highest permeability to most gases of any known polymer. However, its selectivity is very poor; for example its O2/N2 selectivity is only 1.8. The high permeability is due to the stiff backbone, and to the fact that the attached trimethysilyl group is very bulky. Both factors limit efficient packing of the polymer chains, resulting in a large free volume which accounts for the permeability. To improve the selectivity, the PI intends to reduce the free volume size to increase the selectivity at the expense of some permeability. To decrease the free volume, this study will follow two strategies; (a) The first is to develop thermal annealing procedures which result in membranes in which the chains are in a more relaxed state that promotes better packing and a lower free volume. (b) The second strategy is to copolymerize high permeability low selectivity polymers with aryl substituted polyacetylenes that have high selectivity. The idea is that the aryl groups should promote polymer chain cohesion, and that thermally annealed copolymers can be developed with the desired balance of values of permeability and selectivity.
