Experimental
Materials:Poly(tetrafluoroethylene oxide-co-difluoromethylene oxide)α,ω diol (ZDOL, Average M n ca. 3,800 g/mol, 95% Aldrich), 2-Isocyanatoethyl methacrylate (EIM, 99% Aldrich), 2,2-Dimethoxy-2-phenyl acetophenone (DMPA, 99% Aldrich), Dibutyltin diacetate (DBTDA, 99% Aldrich), and 1,1,2-trichlorotrifluoroethane (Freon 113, 99% Aldrich) were used as received.
Preparation of PFPE DMA:In a typical synthesis, ZDOL (5.7227g, 1.5 mmol) was added to a dry 50 mL round bottom flask and purged with argon for 15 minutes. EIM (0.43 mL, 3.0 mmol) was then added via syringe along with Freon 113 (2 mL), and DBTDA (50 µL). The solution was immersed in an oil bath and allowed to stir at 50 o C for 24h. The solution was then passed through a chromatographic column (alumina, Freon 113, 2x5 cm). Evaporation of the solvent yielded a clear, colorless, viscous oil which was further purified by passage through a .22 µm polyethersulfone filter.1 H-NMR (ppm): 2.1, s (3H); 3.7, q (2H); 4.4, t (2H); 4.7, t (2H); 5.3, m (1H); 5.8, s (1H); 6.3, s (1H).
Photocuring of PFPE DMA:In a typical cure, 1 wt% of DMPA (0.05g, 2.0 mmol) was added to PFPE DMA (5g, 1.2 mmol) along with 2 mL Freon 113 until a clear solution was formed. After removal of the solvent, the cloudy viscous oil was passed through a .22 µm polyethersulfone filter to remove any DMPA that did not disperse into the PFPE DMA. The filtered PFPE DMA was then irradiated with a UV source (Electrolite UVcuring chamber model no. 81432-ELC-500, λ = 365nm) while under a nitrogen purge for 10 min. This resulted in a clear, slightly yellow, rubbery material.
Device Fabrication with PFPE DMA:In a typical fabrication, PFPE DMA containing photoinitiator (as described in section 3.) was spin coated to a thickness of 20 µm (800 rpm) onto a Si wafer containing the desired photoresist pattern. This wafer was then placed into the UV curing chamber and irradiated for 6s. Separately, a thick layer
