Zugl.: Aachen, Techn. Hochsch., Diss., 2005.

Studies concerning two different copolymerization processes are detailed in this dissertation: propylene oxide/CO2 coupling to afford poly(propylene carbonate) and Nbutylaziridine/ CO coupling to afford poly-??-butylalanoid. The copolymerization of propylene oxide and CO2 to form the industrially useful poly(propylene carbonate) has been investigated employing chromium(salen)N3 complexes as catalysts. Unfortunately the reaction could not be studied in real time via in situ infrared spectroscopy, thereby obtaining detailed kinetic data, because of the copolymer-limited solubility in most solvents. Studies employing batch reactor runs concentrating on varying the cocatalyst, the equivalents of cocatalysts, and the steric and electronic structure of the catalyst through modification of the salen ligand were undertaken. It was discovered that the optimal catalyst for copolymer selectivity vs. the monomeric propylene carbonate was one that contained a salen ligand with an electron withdrawing phenylene backbone and electron donating tert-butyl groups in the phenolate rings. This catalyst was used to investigate the effect of altering the nature of the cocatalyst and its concentration. The coupling of carbon monoxide and aziridines has been shown to be selective for comonomer-alternating enchainment in the presence of PhCH2C(O)Co(CO)4 to afford poly-??-peptoids. The mechanistic aspects of the reaction of CO and Nbutylaziridine by means of in situ infrared spectroscopy employing CH3C(O)Co(CO)3L (L = PPh3 and P(o-tolyl)3) as precatalysts was investigated. It was found the PPh3 precatalyst exists in solution under catalytic conditions as an equilibrium mixture of CH3C(O)Co(CO)3PPh3 and CH3C(O)Co(CO)4, and affords both poly-??-butylalanoid and the corresponding lactam as a side-product. By way of contrast, the P(o-tolyl)3 precatalyst which possesses the sterically bulky and labile phosphine ligand, affords only the acyl cobalt tetracarbonyl species in solution during catalysis with the selective production of the copolymer. Kinetic studies conducted with CH3C(O)Co(CO)3P(otolyl) 3 showed the coupling reaction to have a first order dependence on catalyst, a first order dependence on N-butylaziridine, and only a slight dependence on the concentration of CO over the pressure range 17-69 bar. The working mechanistic model for the copolymerization reaction involves first aziridine insertion into the cobalt-acyl bond, rate determining ring opening by the cobaltate species, followed by the migratory CO insertion.

Heidelberg, Univ., Diss., 2002. / Computerdatei im Fernzugriff.

Heidelberg, Univ., Diss., 2002. / Computerdatei im Fernzugriff.

Heidelberg, Universiẗat, Diss., 2002.

Current thermoplastic processing techniques involve high capital costs for moulds and significant use of energy to melt or soften the materials. Single-step process cold forming techniques, such as stretch forming, could be cost effective methods for manufacturing large parts with shallow cross-sections from plastic sheet. The present work is a preliminary investigation of a cold forming technique for polycarbonate. The objective of this work is to characterize the bulk deformation behaviour of polycarbonate using tensile tests and dome stretch forming tests. Two different molecular weight polycarbonate sheets with 1.6 mm thickness were studied: (i) one with Mw = 42,000 g/mol and (ii) the other with Mw = 52,000 g/mol. For the latter, 3.2 mm sheets were also studied. Tensile tests conducted at three different cross-head speeds, i.e., 2, 20 and 200 mm/min showed very similar elastic and plastic deformation properties for the two molecular weights. Correspondingly, the activation volumes at yield were almost identical. There was also negligible difference in the thermophysical properties between the two materials as found by differential scanning calorimetry. Dome stretch forming tests were conducted on a metal forming machine. Specimens of varying width were tested to give different strain states ranging from deep drawing to biaxial. The limiting dome height or the maximum level of stretch forming iv increases with specimen width. This is due to biaxial deformation which increases the maximum strain. Forming limit diagrams (FLDs) were also constructed from the local strains measured from printed fine circle grid patterns on the polycarbonate sheet surfaces. The FLDs showed common general characteristics with metals except for a few key differences. An area of very few data points was found to lie between the “safe zone” and the “necked zone”. This void was referred to as the “unstable neck formation zone”. It exists because of the large local increases in strain associated with the unstable nature of polymer neck formation. Much more study is required before polycarbonate can be cold formed at strains below the unstable neck deformation. However, the materials and techniques used in this work have demonstrated that the process can be viable for forming shallow large parts from relatively thin thermoplastic sheet a as long as the local biaxial strains are less than 20%.

Current thermoplastic processing techniques involve high capital costs for moulds and significant use of energy to melt or soften the materials. Single-step process cold forming techniques, such as stretch forming, could be cost effective methods for manufacturing large parts with shallow cross-sections from plastic sheet. The present work is a preliminary investigation of a cold forming technique for polycarbonate. The objective of this work is to characterize the bulk deformation behaviour of polycarbonate using tensile tests and dome stretch forming tests. Two different molecular weight polycarbonate sheets with 1.6 mm thickness were studied: (i) one with Mw = 42,000 g/mol and (ii) the other with Mw = 52,000 g/mol. For the latter, 3.2 mm sheets were also studied. Tensile tests conducted at three different cross-head speeds, i.e., 2, 20 and 200 mm/min showed very similar elastic and plastic deformation properties for the two molecular weights. Correspondingly, the activation volumes at yield were almost identical. There was also negligible difference in the thermophysical properties between the two materials as found by differential scanning calorimetry. Dome stretch forming tests were conducted on a metal forming machine. Specimens of varying width were tested to give different strain states ranging from deep drawing to biaxial. The limiting dome height or the maximum level of stretch forming iv increases with specimen width. This is due to biaxial deformation which increases the maximum strain. Forming limit diagrams (FLDs) were also constructed from the local strains measured from printed fine circle grid patterns on the polycarbonate sheet surfaces. The FLDs showed common general characteristics with metals except for a few key differences. An area of very few data points was found to lie between the “safe zone” and the “necked zone”. This void was referred to as the “unstable neck formation zone”. It exists because of the large local increases in strain associated with the unstable nature of polymer neck formation. Much more study is required before polycarbonate can be cold formed at strains below the unstable neck deformation. However, the materials and techniques used in this work have demonstrated that the process can be viable for forming shallow large parts from relatively thin thermoplastic sheet a as long as the local biaxial strains are less than 20%.

The purpose of this research was to deposit the protective diamond-like carbon (DLC) films on polycarbonate substrates for optical applications. In this study, by using the PECVD method is the better way to deposit DLC film on polycarbonate substrates since the whole process were performed at low temperature to avoiding any degradation of the adhesion of DLC film on polycarbonate substrates occurred at high temperature. In order to further increase the adhesion between the polycarbonate substrates and the DLC film, we deposited the SiO2 layer as an interlayer, and select HMDSO as precursor because it contain Si and O atoms. It is because that SiOx films that can be deposited from HMDSO/oxyzen feeds are relatively hard and against mechanical damages due to forming the glass-link structure. In addition, SiOx films are fully transparent in the UV range and decrease the difference of TCE ( thermal expansion coefficient) of PC and coating films. In experiments, it is preceded being focus on the analysis of Raman spectrum for the films grown at various CH4 gas fluxes, substrates bias voltages, Si-doping concentrations and the distance of electrode separation. The dependence of the intensity ratio of D-band and G-band ( ID/IG ) on the surface roughness, hardness and mechanical properties were investigated, and the adhesion of coating layer depends on the thickness of intermediate layer were studied under various substrate bias voltage. At least, the properties of diamond-like carbon (DLC) film coatings on phase-change recording media were characterized by Raman spectroscopy, atomic force microscope (AFM), UV-visible spectrometer and disc testers. The dependence of mechanical, optical and structural properties of DLC films included the characteristics of surface roughness, hardness, transmittance and electrical signals of discs on serveral DLC film thicknesses were investigated. Our experimental results indicate that DLC films provide a suitable coating to protect PC substrate and make it no difference for data stored on phase-change optical discs.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2009. / Title from title screen (site viewed February 25, 2010). PDF text: 201 p. : col. ill. ; 4 Mb. UMI publication number: AAT 3386550. Includes bibliographical references. Also available in microfilm and microfiche formats.

Erlangen, Nürnberg, Univ., Diss., 2002. / Computerdatei im Fernzugriff.