@article{patil_miles_ko_datta_rao_kiserow_genzer_2018, title={Kinetic Study of Degrafting Poly(methyl methacrylate) Brushes from Flat Substrates by Tetrabutylammonium Fluoride}, volume={51}, ISSN={["1520-5835"]}, DOI={10.1021/acs.macromol.8b01832}, abstractNote={Polymer degrafting is a process in which surface-attached polymer brushes are removed from the substrate by breaking a chemical bond in proximity to the substrate. This paper provides insight into the kinetics of degrafting poly(methyl methacrylate) (PMMA) brushes using tetrabutylammonium fluoride (TBAF) and demonstrates how the process can be modeled using a series of degrafting reactions. The trichlorosilane-based polymerization initiator utilized here to synthesize PMMA grafts by surface-initiated atom transfer radical polymerization anchors to the silica substrate by up to three potential attachment points. During the degrafting sequence this anchoring reduces to two and one chemical bond and finally results in complete liberation of the PMMA macromolecule from the substrate. We investigate the effect of TBAF concentration, the initial grafting density of PMMA grafts on the substrate, and TBAF exposure time on degrafting of PMMA by monitoring the instantaneous areal grafting density of PMMA on the sub...}, number={24}, journal={MACROMOLECULES}, author={Patil, Rohan and Miles, Jason and Ko, Yeongun and Datta, Preeta and Rao, Balaji M. and Kiserow, Douglas and Genzer, Jan}, year={2018}, month={Dec}, pages={10237–10245} }
 @article{li_lin_ko_kiserow_genzer_2018, title={Visualization of Mechanochemically-Assisted Degrafting of Surface-Tethered Poly(Acrylic Acid) Brushes}, volume={7}, ISSN={["2161-1653"]}, DOI={10.1021/acsmacrolett.8b00241}, abstractNote={We report visualization of mechanochemically assisted degrafting of surface-tethered poly(acrylic acid) (PAA) brushes in a basic aqueous buffer at nanometer to micrometer length scale by monitoring changes in local etching of silicon substrates. PAA brushes were prepared by surface-initiated atom transfer radical polymerization and incubated in 0.1 M ethanolamine buffer (pH 9.0) with 0.5 M NaCl. Morphological changes of the underlying substrates were monitored by scanning electron microscopy and atomic force microscopy. The appearance of regular-shaped pits indicated etching of the substrate, and both their number and size grew with increasing incubation time. We compared the etching behaviors for PAA, poly(methyl methacrylate) (PMMA), and poly(poly(ethylene glycol) methacrylate) (PPEGMA) brushes grafted on silicon substrates. After incubation for 7 days, the substrate of PMMA brush remained intact. In PAA brush systems, we detected the formation of a few large pits whose size grew in time. Many pits showed up on the substrate of PPEGMA brush but with substantially smaller size compared to PAA. Our findings suggest that hydrophobicity and stability of the grafted polymers play an important role in the morphological changes of the underlying silicon substrates under given incubation conditions.}, number={6}, journal={ACS MACRO LETTERS}, author={Li, Yuanchao and Lin, Yiliang and Ko, Yeongun and Kiserow, Douglas and Genzer, Jan}, year={2018}, month={Jun}, pages={609–613} }
 @article{li_ko_lin_kiserow_genzer_2017, title={Enhanced Stability of Surface-Tethered Diblock Copolymer Brushes with a Neutral Polymer Block and a Weak Polyelectrolyte Block: Effects of Molecular Weight and Hydrophobicity of the Neutral Block}, volume={50}, ISSN={["1520-5835"]}, DOI={10.1021/acs.macromol.7b01825}, abstractNote={We study the stability of diblock copolymer brushes featuring a bottom neutral block, poly(methyl methacrylate) (PMMA) or poly(poly(ethylene glycol) methacrylate) (PPEGMA), and a top poly(acrylic acid) (PAA) block on flat silicon substrate. The polymer brushes are prepared by surface-initiated atom transfer radical polymerization (SI-ATRP). We use a combinatorial design featuring a molecular weight gradient in the bottom neutral block to investigate systematically the effect of the molecular weight of that block on the stability of the copolymer brush. We measure variations in dry thickness of the diblock copolymer brush by ellipsometry after different incubation times in aqueous buffer (pH = 9.0) as a function of thickness of the neutral block, indicating degrafting of the mechanically activated copolymer chains via hydrolysis of ester groups in the initiator and/or Si–O bonds that attach the polymer to the substrate. The stability of the diblock copolymer brushes is higher than that of PAA homopolymer b...}, number={21}, journal={MACROMOLECULES}, author={Li, Yuanchao and Ko, Yeongun and Lin, Yiliang and Kiserow, Douglas and Genzer, Jan}, year={2017}, month={Nov}, pages={8580–8587} }
 @article{patil_kiserow_genzer_2015, title={Creating surface patterns of polymer brushes by degrafting via tetrabutyl ammonium fluoride}, volume={5}, ISSN={["2046-2069"]}, DOI={10.1039/c5ra17000a}, abstractNote={We demonstrate the use of tetrabutyl ammonium fluoride (TBAF) for creating spatial patterns of poly(methyl methacrylate) (PMMA) brushes on a flat silica support by degrafting PMMA grafted chains from selected regions on the substrate.}, number={105}, journal={RSC ADVANCES}, author={Patil, Rohan and Kiserow, Douglas and Genzer, Jan}, year={2015}, pages={86120–86125} }
 @article{patil_turgman-cohen_srogl_kiserow_genzer_2015, title={Direct Measurement of Molecular Weight and Grafting Density by Controlled and Quantitative Degrafting of Surface-Anchored Poly(methyl methacrylate)}, volume={4}, ISSN={["2161-1653"]}, DOI={10.1021/mz5007188}, abstractNote={We report on quantitative determination of the molecular weight distribution (MWD) and grafting density (σP) of polymer assemblies grown by controlled radical polymerization from flat substrates as a function of polymerization time and the ratio between the inhibitor and catalyst species. Specifically, we grow poly(methyl methacrylate) (PMMA) brushes on flat silica-based surfaces by surface-initiated atom transfer radical polymerization (SI-ATRP), cleave the PMMA grafts quantitatively using tetrabutyl ammonium fluoride (TBAF), and analyze their MWD by size exclusion chromatography equipped with a high-sensitivity differential refractive index detector. The polymer growth and degrafting processes are followed by ellipsometry, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry. The σP is independent of polymerization time and increases with increasing SI-ATRP inhibitor/catalyst ratio. Specifically, σP increases from 0.48 ± 0.06 to 0.58 ± 0.06 chains/nm2 as the inhibitor/catalyst molar ratio increases from 0 to 0.015, respectively, providing evidence that high inhibitor/catalyst ratio offers better control of the SI-ATRP reaction, by lowering number of terminations, and leading to denser PMMA brush assemblies.}, number={2}, journal={ACS MACRO LETTERS}, author={Patil, Rohan R. and Turgman-Cohen, Salomon and Srogl, Jiri and Kiserow, Douglas and Genzer, Jan}, year={2015}, month={Feb}, pages={251–254} }
 @article{patil_turgman-cohen_srogl_kiserow_genzer_2015, title={On-Demand Degrafting and the Study of Molecular Weight and Grafting Density of Poly(methyl methacrylate) Brushes on Flat Silica Substrates}, volume={31}, ISSN={["0743-7463"]}, DOI={10.1021/la5044766}, abstractNote={We report on degrafting of surface-anchored poly(methyl methacrylate) (PMMA) brushes from flat silica-based substrates using tetrabutylammonium fluoride (TBAF) and determining their molecular weight distribution (MWD) using size exclusion chromatography (SEC). The grafted PMMA layer was synthesized using surface-initiated atom transfer radical polymerization (SI-ATRP) of MMA for polymerization times ranging from 6 to 24 h. X-ray photoelectron spectroscopy, ellipsometry, and time-of-flight secondary ion mass spectrometry were employed in tandem to characterize the degrafting process. The SEC eluograms were fit to various polymer distributions, namely Zimm-Schulz, ATRP in continuous stirred tank reactor, Wesslau, Schulz-Flory, and Smith et al. The ATRP model gives the best fit to the experimental data. The dry PMMA brush thickness and the number-average molecular weight (obtained from the MWD) suggest that the grafting density of the PMMA grafts is independent of polymerization time, indicating well-controlled/living growth of MMA. The observed polydispersity index (PDI) was higher than that generally observed in bulk grown polymers under similar conditions, indicating an effect due to chain confinement and crowding. We detect small but noticeable dependence of the polymer brush grafting density on the inhibitor/catalyst ratio. Higher inhibitor/catalyst ratio offers better control with lower early terminations, which results in a small increase in the apparent grafting density of the chains.}, number={8}, journal={LANGMUIR}, author={Patil, Rohan R. and Turgman-Cohen, Salomon and Srogl, Jiri and Kiserow, Douglas and Genzer, Jan}, year={2015}, month={Mar}, pages={2372–2381} }
 @article{cain_roberts_kiserow_carbonell_2011, title={Modeling the thermodynamic and transport properties of decahydronaphthalene/propane mixtures: Phase equilibria, density, and viscosity}, volume={305}, ISSN={["0378-3812"]}, DOI={10.1016/j.fluid.2011.02.009}, abstractNote={Abstract The density and viscosity of propane mixed with 66/34 trans/cis -decahydronaphthalene were measured over a wide range of temperatures (323–423 K), pressures (2.5–208 bar), and compositions (0–65 mol% propane). For conditions giving two phases, the composition of the dense phase was measured in addition to the density and viscosity. The modified Sanchez-Lacombe Equation of State (MSLEOS) was used with a single linearly temperature-dependent pseudo-binary interaction parameter to correlate the phase compositions and densities. The compositions and densities of the mixtures were captured well with absolute average deviations between the model and the data of 5.3% and 2.3%, respectively. The mixture viscosities were computed from a free volume model (FVM) by using a single constant binary interaction parameter. Density predictions from the MSLEOS were used as input mixture density values required for the FVM. The FVM was found to correlate well with the mixture viscosity data with an absolute average deviation between the model and the data of 5.7%.}, number={1}, journal={FLUID PHASE EQUILIBRIA}, author={Cain, Nathaniel and Roberts, George and Kiserow, Douglas and Carbonell, Ruben}, year={2011}, month={Jun}, pages={25–33} }
 @article{cain_haywood_roberts_kiserow_carbonell_2011, title={Polystyrene/Decahydronaphthalene/Propane Phase Equilibria and Polymer Conformation Properties from Intrinsic Viscosities}, volume={49}, ISSN={["0887-6266"]}, DOI={10.1002/polb.22282}, abstractNote={Abstract}, number={15}, journal={JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS}, author={Cain, Nathaniel and Haywood, Alexander and Roberts, George and Kiserow, Douglas and Carbonell, Ruben}, year={2011}, month={Aug}, pages={1093–1100} }
 @article{dong_turgman-cohen_roberts_kiserow_2010, title={Effect of Polymer Size on Heterogeneous Catalytic Polystyrene Hydrogenation}, volume={49}, ISSN={["0888-5885"]}, DOI={10.1021/ie1011905}, abstractNote={The effect of polymer coil size on the rate of polystyrene (PS) hydrogenation was studied in a slurry reactor with mixtures of decahydronaphthalene (DHN) and carbon dioxide (CO2) as the solvent for the polymer. The PS coil size was changed by varying the polymer molecular weight from 9300 g/mol to 357 000 g/mol and by varying the CO2 concentration. Using a 5% Pd/5% Ru/SiO2 catalyst, the rate of aromatic ring hydrogenation at 150 °C was found to be strongly dependent on the size of a polymer coil relative to the average pore diameter of the catalyst. Significant pore diffusion limitations, as indicated by values of the Weisz modulus, were observed with increasing polymer molecular weight. Increasing the concentration of CO2 resulted in increased reaction rates, with an improvement of nearly 2 orders of magnitude at the highest PS molecular weight.}, number={22}, journal={INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH}, author={Dong, Laura Beth and Turgman-Cohen, Salomon and Roberts, George W. and Kiserow, Douglas J.}, year={2010}, month={Nov}, pages={11280–11286} }
 @article{dong_mcvicker_kiserow_roberts_2010, title={Hydrogenation of polystyrene in CO2-expanded liquids: The effect of catalyst composition on deactivation}, volume={384}, number={1-2}, journal={Applied Catalysis. A, General}, author={Dong, L. B. and McVicker, G. B. and Kiserow, D. J. and Roberts, G. W.}, year={2010}, pages={45–50} }
 @article{kim_dong_kiserow_roberts_2009, title={Complex Effects of the Sweep Fluid on Solid-State Polymerization: Poly(bisphenol A carbonate) in Supercritical Carbon Dioxide}, volume={42}, ISSN={["1520-5835"]}, DOI={10.1021/ma802193q}, abstractNote={The effects of the sweep fluid on solid-state polymerization (SSP) of poly(bisphenol A carbonate) (BPA-PC) were investigated. Prepolymers with two different number-average molecular weights, PCP6C (Mn = 3800 g/mol) and PCP9C (Mn = 2400 g/mol), were synthesized using melt transesterification. Solid-state polymerization of these prepolymers was carried out at temperatures in the range of 150−190 °C with supercritical carbon dioxide (scCO2) and N2 as the sweep fluids. It was found that scCO2 at 207 bar could either increase or decrease the rate of SSP relative to the rate in atmospheric N2, depending on the prepolymer molecular weight. At 190 °C, the molecular weights of the polymers synthesized from the higher-molecular-weight prepolymer (PCP6C) were higher with scCO2 as the sweep fluid compared to those of the polymers synthesized with N2. In contrast, at the same temperature of 190 °C, the molecular weights of the polymers synthesized from the lower-molecular-weight prepolymer (PCP9C) were lower with scCO...}, number={7}, journal={MACROMOLECULES}, author={Kim, Jaehoon and Dong, Laura Beth and Kiserow, Douglas J. and Roberts, George W.}, year={2009}, month={Apr}, pages={2472–2479} }
 @article{dong_carbonell_roberts_kiserow_2009, title={Determination of polystyrene-carbon dioxide-decahydronaphthalene solution properties by high pressure dynamic light scattering}, volume={50}, ISSN={["1873-2291"]}, DOI={10.1016/j.polymer.2009.09.069}, abstractNote={The diffusion coefficients of polystyrene (PS) in decahydronaphthalene (DHN) and in solutions of carbon dioxide (CO2) and DHN were measured for dilute PS solutions over a range of temperatures and CO2–DHN ratios using high pressure dynamic light scattering. Infinite dilution diffusion coefficients (D0) of PS and dynamic second virial coefficients (kD) were determined for essentially monodisperse 308 kDa PS. At a system pressure of 20.7 MPa, PS diffusion coefficients increased by a factor of 2.5, and the activation energy of diffusion decreased by approximately 16% when DHN was “expanded” with 44 mol% CO2. However, the hydrodynamic radius of PS at a given temperature was not particularly sensitive to the CO2 concentration. Solvent quality, as measured by kD, decreased at higher CO2 concentrations. The addition of CO2 to polymer solutions may offer a way to “tune” the properties of the solution to facilitate the heterogeneous catalytic hydrogenation of polymers.}, number={24}, journal={POLYMER}, author={Dong, Laura Beth and Carbonell, Ruben G. and Roberts, George W. and Kiserow, Douglas J.}, year={2009}, month={Nov}, pages={5728–5732} }
 @article{kim_kelly_lamb_roberts_kiserow_2008, title={Characterization of palladium (Pd) on alumina catalysts prepared using liquid carbon dioxide}, volume={112}, ISSN={["1932-7447"]}, DOI={10.1021/jp711495n}, abstractNote={Palladium (II) hexafluoroacetylacetonate (Pd(hfac)2) dissolved in liquid carbon dioxide (L-CO2) was used to deposit Pd nanoparticles onto low-surface-area α-alumina (13 m2/g) and high-surface-area γ-alumina (207 m2/g). These nanoparticles were prepared by contacting Pd(hfac)2 dissolved in L-CO2 with the alumina at 6.9 MPa and 28.5 °C and then slowly venting gaseous CO2 until L-CO2 was completely evaporated. After depressurization to remove the CO2 and unabsorbed Pd(hfac)2, the impregnated Pd(hfac)2 was reduced in hydrogen at a relatively low temperature of 75 °C. The adsorption isotherm of Pd(hfac)2 on γ-alumina suggests a weak interaction between the organometallic compound and the support. The average Pd particle size on the low-surface-area α-alumina, measured by scanning electron microscopy, increased from 13.1 ± 3.5 to 59.9 ± 11.3 nm, and the metal dispersion, measured by pulsed CO chemisorption, decreased from 11 to 3%, as the Pd loading on the alumina was increased from 0.15 to 1.54 wt %. With the ...}, number={28}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Kim, Jaehoon and Kelly, M. Jason and Lamb, H. Henry and Roberts, George W. and Kiserow, Douglas J.}, year={2008}, month={Jul}, pages={10446–10452} }
 @article{kim_gracz_roberts_kiserow_2008, title={Spectroscopic analysis of poly(bisphenol A carbonate) using high resolution C-13 and H-1 NMR}, volume={49}, ISSN={["0032-3861"]}, DOI={10.1016/j.polymer.2007.11.046}, abstractNote={Quantitative structural and end-group analysis of poly(bisphenol A carbonate) (BPA-PC) was carried out and number average molecular weights (Mn) were determined using 125.76 MHz 13C and 500.13 MHz 1H nuclear magnetic resonance (NMR) spectroscopy. BPA-PC with a wide range of end-group ratios (0.26–2.83) and number average molecular weights (1500–9000 g/mol) was synthesized using melt transesterification by changing the initial monomer (bisphenol A and diphenyl carbonate) ratios and reaction conditions. Results of the NMR analysis for the melt-polymerized samples were compared with those of a commercial BPA-PC with a Mn of 16,000 g/mol. It was demonstrated that NMR spectroscopy is a very selective and accurate method not only for quantification of both phenolic and phenyl chain end-groups but also in the structural analysis of main chain groups. Extremely small concentrations of end-groups (∼0.02 per repeating unit) were analyzed. In addition, NMR spectroscopy was found to be an excellent tool for detecting residual monomer and the presence of the reaction byproduct (phenol). The molecular weights that were determined using NMR end-group quantification agreed well with the molecular weights measured by gel-permeation chromatography (GPC).}, number={2}, journal={POLYMER}, author={Kim, Jaehoon and Gracz, Hanna S. and Roberts, George W. and Kiserow, Douglas J.}, year={2008}, month={Jan}, pages={394–404} }
 @article{whittier_xu_zanten_kiserow_roberts_2006, title={Viscosity of polystyrene solutions expanded with carbon dioxide}, volume={99}, ISSN={["1097-4628"]}, DOI={10.1002/app.22483}, abstractNote={Abstract}, number={2}, journal={JOURNAL OF APPLIED POLYMER SCIENCE}, author={Whittier, RE and Xu, DW and Zanten, JH and Kiserow, DJ and Roberts, GW}, year={2006}, month={Jan}, pages={540–549} }
 @article{xu_carbonell_kiserow_roberts_2005, title={Hydrogenation of polystyrene in CO2-expanded solvents: Catalyst poisoning}, volume={44}, ISSN={["0888-5885"]}, DOI={10.1021/ie040243q}, abstractNote={Organic solvents expanded with supercritical carbon dioxide can be excellent media for hydrogenation reactions. However, catalyst poisoning by CO formed via the reverse water-gas-shift reaction occurs during many hydrogenations in the presence of CO2. In this research, the hydrogenation of polystyrene in CO2-expanded decahydronaphthalene was studied in a batch reactor using two hydrogenation catalysts, 5%Pd/BaSO4 and 65%Ni/Al2O3/SiO2. The 5%Pd/BaSO4 catalyst deactivated at 150 °C and CO2 pressures of 250−2250 psig (1.8−15.6 MPa). Approximately 50 ppm CO was present in the CO2-rich light phase after about 10 h at 150 °C, 750 psig H2 pressure, and 2250 psig CO2 pressure. A model that incorporates CO poisoning was developed to describe deactivation of the Pd/BaSO4 catalyst. The 65%Ni/Al2O3/SiO2 catalyst was more active for ring hydrogenation than 5%Pd/BaSO4, and very little CO was formed in the presence of CO2. The Ni catalyst deactivated in the presence of CO2 at 180 °C, possibly due to H2O formed in a meth...}, number={16}, journal={INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH}, author={Xu, DW and Carbonell, RG and Kiserow, DJ and Roberts, GW}, year={2005}, month={Aug}, pages={6164–6170} }
 @article{kiserow_shi_roberts_gross_desimone_2005, title={Solid-state polymerization of poly(bisphenol A carbonate) facilitated by supercritical carbon dioxide}, volume={898}, ISBN={["0-8412-3887-1"]}, ISSN={["0097-6156"]}, DOI={10.1021/bk-2005-0898.ch007}, abstractNote={During the solid state polymerization (SSP) of poly(bisphenol A carbonate), both the forward reaction rate constant and the phenol diffusion coefficient inside the polymer particle were significantly higher when SSP was carried out in supercritical carbon dioxide (scCO 2 ) compared to in atmospheric N 2 . These enhancements depended on the reaction conditions, and can be understood in terms of the CO 2 concentrations in the polymer. Polymer with a M w as high as 78100 has been synthesized by SSP with scCO 2 as the sweep fluid.}, journal={ADVANCES IN POLYCARBONATES}, author={Kiserow, DJ and Shi, CM and Roberts, GW and Gross, SM and DeSimone, JM}, year={2005}, pages={86–94} }
 @misc{roberts_xu_kiserow_carbonell, title={Hydrogenation of polymers in the presence of supercritical carbon dioxide}, volume={7,408,009}, number={2007 Apr. 11}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Roberts, G. W. and Xu, D. and Kiserow, D. J. and Carbonell, R. G.} }