@article{ahmed_abdelaziz_roberts_2016, title={Preparation of Al2O3/AlF3-supported ruthenium catalysts for the hydrogenolysis of biodiesel-derived crude glycerol}, volume={55}, number={19}, journal={Industrial & Engineering Chemistry Research}, author={Ahmed, T. S. and Abdelaziz, O. Y. and Roberts, G. W.}, year={2016}, pages={5536–5544} }
 @article{ahmed_desimone_roberts_2010, title={Continuous precipitation polymerization of vinylidene fluoride in supercritical carbon dioxide: A model for understanding the molecular-weight distribution}, volume={65}, ISSN={["1873-4405"]}, DOI={10.1016/j.ces.2009.08.039}, abstractNote={Abstract Poly(vinylidene fluoride) (PVDF) that is synthesized by precipitation polymerization in supercritical carbon dioxide (scCO2) has a bimodal molecular weight distribution (MWD) and a very broad polydispersity index (PDI) under certain reaction conditions. Different models have been formulated to account for this behavior. This paper presents a homogenous model for a continuous stirred-tank reactor (CSTR) that includes the change of the termination reaction from kinetic control to diffusion control as the chain length of the polymeric radicals increases, and accounts for the change in the termination rate constant with macroradical chain length in the diffusion-controlled region. The model also includes the chain transfer to polymer reaction. Comparison of the model output with experimental data demonstrates that changes of the MWD, including the development of a bimodal distribution, with such reaction conditions as monomer concentration and average residence time are successfully predicted. In addition, the model can capture the occurrence of gelation, which appears to be responsible for a region of inoperability that was observed in the polymerization experiments. The success of this homogeneous model is consistent with recent research demonstrating that the CO2-rich phase is the main locus of polymerization for the precipitation polymerization of vinylidene fluoride and vinylidene fluoride/hexafluoropropylene mixtures in scCO2, at the conditions that have been studied to date.}, number={2}, journal={CHEMICAL ENGINEERING SCIENCE}, author={Ahmed, Tamer S. and DeSimone, Joseph M. and Roberts, George W.}, year={2010}, month={Jan}, pages={651–659} }
 @article{kim_kim_kim_ahmed_dong_roberts_oh_2010, title={The effect of prepolymer crystallinity on solid-state polymerization of poly(bisphenol A carbonate)}, volume={51}, number={12}, journal={Polymer}, author={Kim, J. and Kim, Y. J. and Kim, J. D. and Ahmed, T. S. and Dong, L. B. and Roberts, G. W. and Oh, S. G.}, year={2010}, pages={2520–2526} }
 @article{ahmed_desimone_roberts_2009, title={Kinetics of the Homopolymerization of Vinylidene Fluoride and Its Copolymerization with Hexafluoropropylene in Supercritical Carbon Dioxide: The Locus of Polymerization}, volume={42}, ISSN={0024-9297 1520-5835}, url={http://dx.doi.org/10.1021/ma801911j}, DOI={10.1021/ma801911j}, abstractNote={In previous studies, the continuous polymerization of vinylidene fluoride (VF2) and mixtures of VF2 with hexafluoropropylene (HFP) was carried out in supercritical carbon dioxide (scCO2) using a continuous stirred-tank reactor (CSTR). Most of the polymerizations were heterogeneous; i.e., polymer particles precipitated during the reaction. However, some were homogeneous, especially at higher HFP concentrations. In this study, the data from the earlier experiments have been tested against three kinetic models to determine the primary locus of the heterogeneous polymerizations. The first model, the “solution polymerization” model, is based on the assumption that all of the polymerization reactions take place in the continuous, CO2-rich phase, with no reaction in the polymer phase. In the second model, the “surface polymerization” model, chain initiation occurs in the continuous phase, while chain propagation and termination occur in a thin zone on the surface of the polymer particles. The third model, the “i...}, number={1}, journal={Macromolecules}, publisher={American Chemical Society (ACS)}, author={Ahmed, Tamer S. and DeSimone, Joseph M. and Roberts, George W.}, year={2009}, month={Jan}, pages={148–155} }
 @article{ahmed_desimone_roberts_2008, title={Continuous copolymerization of vinylidene fluoride with hexafluoropropylene in Supercritical carbon dioxide: High-hexafluoropropylene-content amorphous copolymers}, volume={41}, ISSN={["0024-9297"]}, DOI={10.1021/ma702526u}, abstractNote={Copolymerization of vinylidene fluoride (VF2) and hexafluoropropylene (HFP) was carried out in supercritical carbon dioxide using a continuous stirred tank reactor. Three different HFP/VF2 molar feed ratios were studied, 59:41, 66:34, and 73:27, giving rise to amorphous copolymers containing about 23, 26, and 30 mol % HFP, respectively. The experiments were carried out at 40 °C with pressures in the range of 207–400 bar using perfluorobutyryl peroxide as the free radical initiator. Depending on the copolymer composition, the molecular weight, and the reaction pressure, either a homogeneous (solution) or a heterogeneous (precipitation) polymerization was observed. The effects of feed monomer concentration and reaction pressure were explored at otherwise constant conditions. The rate of polymerization (Rp) and the number-average molecular weight (Mn) increased linearly with the total monomer concentration, independent of the mode of polymerization, i.e., homogeneous or heterogeneous. Both Rp and Mn increase...}, number={9}, journal={MACROMOLECULES}, author={Ahmed, Tamer S. and DeSimone, Joseph M. and Roberts, George W.}, year={2008}, month={May}, pages={3086–3097} }
 @article{ahmed_desimone_roberts_2007, title={Continuous copolymerization of vinylidene fluoride with hexafluoropropylene in Supercritical carbon dioxide: Low hexafluoropropylene content semicrystalline copolymers}, volume={40}, ISSN={["0024-9297"]}, DOI={10.1021/ma0713613}, abstractNote={The copolymerization of vinylidene fluoride with hexafluoropropylene (HFP) was carried out in supercritical carbon dioxide by precipitation polymerization using a continuous stirred tank reactor. Copolymers with ca. 10 mol % HFP were synthesized at 40 °C and pressures in the range of 207−400 bar using perfluorobutyryl peroxide as the free radical initiator. The effects of feed monomer concentration and reaction pressure were both explored at otherwise constant conditions. The rate of polymerization (Rp) and the number-average molecular weight (Mn) increased linearly with the total monomer concentration up to about 6 M, the highest concentration investigated. The Rp and the Mn were strongly influenced by the reaction pressure. An 80% increase in both Rp and Mn was observed when the reaction pressure rose from 207 to 400 bar. The molecular weight distributions of the synthesized copolymer showed a long tail that increased to become a broad shoulder with increasing total monomer concentration. This tail incr...}, number={26}, journal={MACROMOLECULES}, author={Ahmed, Tamer S. and DeSimone, Joseph M. and Roberts, George W.}, year={2007}, month={Dec}, pages={9322–9331} }