Date of Award

5-2009

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Chemical Engineering

Advisor

Husson, Scott M.

Committee Member

Hirt , Douglas

Committee Member

Kitchens , Christopher

Committee Member

Luzinov , Igor

Abstract

This dissertation focuses on the fabrication of uniform polymer nanolayers using surface-initiated polymerization. The kinetics of low temperature surface-initiated atom transfer radical polymerization (ATRP) is discussed in detail. The work is then extended to the surface modification of polymeric membranes to tune the physical and chemical properties of the membranes for gas separations. I discuss how atom transfer radical polymerization might be advantageous compared to some of the techniques that have been proposed in the literature for preparing polymeric membranes for CO2 separation.
The first part of this dissertation describes the synthesis of polystyrene (PS) nanolayers by surface-initiated ATRP at low temperatures. Relative to prior work, thick PS brushes were grown from initiator-functionalized layers of poly(glycidyl methacrylate) on silicon, and layer thickness evolution was measured by ellipsometry. Constant growth rates provided indirect evidence that the polymerizations were controlled. A detailed kinetic study was done for surface-initiated ATRP of styrene at 60 °C. An unexpected shift was observed in the reaction order (from first to zero order) with respect to the monomer concentration. A reaction mechanism is proposed for this change in rate order.
The second part of the dissertation focuses on the growth of uniform poly(ionic liquid) (PIL) nanolayers using surface-initiated ATRP. Surface-tethered polymer brushes with variable layer thicknesses were fabricated from silicon substrates and growth kinetics of the nanolayers were characterized.
The methodology that was developed in the silicon substrate work was then extended to modification of commercially available regenerate cellulose membranes for CO2 separation studies. I report a solution to the leaking problem of supported ionic liquid membranes that have been used at the lab scale for CO2 separation and also address the need for high selectivity, high flux membranes for CO2 capture. Using surface-initiated ATRP to graft PIL nanolayers from the surfaces of commercial membrane supports is advantageous because the PIL nanolayer is attached to the membrane surface covalently. Therefore, there is no concern for leakage from the support. Relative to PIL membranes prepared by solvent casting, the composite membranes that I prepared offer an ultrathin selective layer, with uniform coverage ensured by the ATRP process. A nanothin selective layer offers advantages in terms of improving the CO2 flux through the membrane.
Pure-component CO2 and N2 permeabilities were measured for unmodified and modified membranes. Covering the outer surface of the membrane with PGMA seems to improve the membrane integrity during permeation measurements, but has resulted in low permeability membranes, likely due to pore clogging.

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