No description available.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1992. / Vita. Abstract. Includes bibliographical references (leaves 120-126). Also available via the Internet.

The synthesis of propylene oxide by electrolysis of dilute sodium bromide solution with propylene gas was investigated in an electrochemical bipolar reactor consisting of six parallel fixed beds of graphite particles separated by polypropylene felt diaphragms. One reactor was operated in single pass and recycle mode with two phase co-current flow of propylene and sodium bromide solution through the beds of graphite particles. The maximum pressure in the system was 2.22 atmospheres absolute. The effects of superficial current density* (413 - 2687 A/m²), electrolyte (sodium bromide solution) concentration (0.2 M and 0.5 M), electrolyte flow rate (100 and 300 cm³ /min), propylene gas flow rate (100/1000/1500/2000 cm³/min at STP), reactor outlet temperature (30° and 60°C), bed thickness (six beds - 8.57/4.29/3.07 cm) and different carbon types (Union Carbide and Ultra Carbon) on the space time yield and selectivity for propylene oxide were measured. Depending on the condition for single pass runs, the space-time yield for propylene oxide was between 5.5 kg/hr m³ and 97.2 kg/hr m³, and the selectivity was between 54.5% and 87.3%. The current efficiency and the specific energy consumption varied from 14.0 to 58.2 percent and 5.7 to 59.9 Kwh/kg of propylene oxide. The space-time yield for propylene oxide increased with decreasing bed thickness. For the recycle mode the space-time yield decreases with time. The highest space time yield obtained after one hour of operation was 127.8 kg/hr m³ with a selectivity of 95.9%. The current efficiency for hydrogen, oxygen and dibromopropane was also determined. *Superficial current density = applied current/electrode area. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

Industry has found practical application of most inexpensive bulk homopolymers . As new polymers were developed, new uses were found. However, it has become apparent that few new and potentially useful polymers will be synthesized, save for polymers with specialty application, because the range of possibilities has already largely been explored. Since the demand for new and improved properties remains, new techniques for achieving them must be developed.

Thesis (M.Eng.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / Injection pressures available on commercial injection molding machines have increased from 10,000 to 20,000 psi with 40,000 psi in prospect. The pressure during solidification should strongly influence the crystallinity, and hence mechanical properties, of those regular polymers which can crystallize when cooled from the melt. In this study, samples of isotactic polypropylene were solidified under pressures up to 40,000 psi. In addition to tensile properties, the resultant density, microstructure and DTA structure were examined. From all measurements, it was concluded that the degree of crystallinity decreased with increasing solidification pressure. Spherulites formed under higher pressure were smaller in size and less branched than those formed at low pressure. Yield and tensile strengths were reduced as the solidi fication pressure was increased, the reduction being about 10% when solidi fication occurred at 40,000 psi. At first glance, these findings appear to predict strength differences within a particular molded part depending on the molding pressure used. It is concluded, however, that the strength variation would be less in a commercial part. The loss of pressure in the cavity as a result of freezing off at the in-gate should lead to a reduction in cavity pressure early in the solidification process, a lower mean pressure during freezing, and a relatively higher degree of crystallinity. / 2031-01-01

No description available.

A family of C2-symmetric catalysts was designed and synthesized with the intent to polymerize propylene. The catalyst was designed to be C2-symmetric for the specific goal that the catalyst would have two identical sites for the propagation of the polymer and therefore eliminate some of the stereoerrors that occur in the propagation of the polymer chain. This catalyst would also operate under simple enantiomorphic site control and therefore the insertion of the monomer would be governed by the ligand surrounding the active site. The ligands were synthesized with increasing degrees of steric bulk with the intention to determine if a catalyst system could generate elastomeric polypropylene. Enantiomorphic site control polypropylene utilizes statistical methods to determine the Si and Re content of a given polymer chain as a function of the variable E. Polypropylene samples generated by the catalyst family were analyzed using high temperature pentad analysis of the methyl region to calculate the E value. The goal was to observe E to be equal to 0.78 provided that the number molecular weight of the polymer was 100,000. The catalyst systems generated polymers with values higher and lower than the desired 0.78, indicating too high or too low enantioselectivity of the catalyst systems respectively at Tp = 0°C.

A family of C2-symmetric catalysts was designed and synthesized with the intent to polymerize propylene. The catalyst was designed to be C2-symmetric for the specific goal that the catalyst would have two identical sites for the propagation of the polymer and therefore eliminate some of the stereoerrors that occur in the propagation of the polymer chain. This catalyst would also operate under simple enantiomorphic site control and therefore the insertion of the monomer would be governed by the ligand surrounding the active site. The ligands were synthesized with increasing degrees of steric bulk with the intention to determine if a catalyst system could generate elastomeric polypropylene. Enantiomorphic site control polypropylene utilizes statistical methods to determine the Si and Re content of a given polymer chain as a function of the variable E. Polypropylene samples generated by the catalyst family were analyzed using high temperature pentad analysis of the methyl region to calculate the E value. The goal was to observe E to be equal to 0.78 provided that the number molecular weight of the polymer was 100,000. The catalyst systems generated polymers with values higher and lower than the desired 0.78, indicating too high or too low enantioselectivity of the catalyst systems respectively at Tp = 0°C.

Thesis (M. Phil.)--University of Hong Kong, 1989.

No description available.