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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

The emulsion polymerization of alkylbutadienes.

Aikin, Archibald McKinlay. January 1949 (has links)
The polymerization of alkylbutadienes has a long history, dating from Grenville William's experiments with isoprene, obtained from the destructive distillation of natural rubber (l). However no large scale production of polymers of butadienes was attempted until World War I, when the Germans manufactured over 2300 tons of polydimethylbutadiene. Until then the natural sources of rubber yielded adequate supplies for world needs. Some research was continued in the field of synthetic rubber andby 1939 the Germans, and later the Western Allies, were able to produce large quantities of synthetic elastomers (the name given to high polymers that possess rubber-like properties). A copolymer of butadiene and styrene, called Buna-S or GR-S, wasconsidered to be the best general purpose synthetic elastomer and this copolymer is produced on a large scale on this continent. Much research has been done on this material but the pure polymers, such as polybutadiene and polyisoprene, have not been investigated as thoroughly since they have failed to show promising properties. As copolymers have the extra variable of compositional heterogeneity, it is thought that the study of pure polymers may lead to an easier and better understanding of the problems involved in obtaining elastomers of the desired properties.[...]

Rod-climbing in molten polymers

Vu, Thi Khanh Phuong January 1976 (has links)
No description available.

The morphology of fibrillar polyolefin crystals.

Wikjord, Alfred George. January 1968 (has links)
No description available.

The negative thermal expasion along the chain direction for polymer crystals.

January 1980 (has links)
by Wong Sai-peng. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1980. / Includes bibliographical references (leaves 144-145).

The interaction between polyelectrolytes and surfaces

Kong, Chung Yin 01 January 2001 (has links)
The interactions between surfaces and polymer chains are at the heart of many polymer problems, such as flow in confined geometries, development of new nano-lithography methods, understanding of the structure of block copolymer grains, polyelectrolyte adsorption, and modeling polymer brushes. The latter two systems will be the focus of this dissertation. The physical properties of each system are studied using statistical mechanics, and results from computer simulations are presented. The first topic of this thesis is the study of adsorption of a polyelectrolyte chain in an electrolyte solution to a uniformly charged surface. By using off-lattice Monte Carlo simulations, the conditions of adsorption of a uniformly charged polyelectrolyte onto oppositely charged planar and spherical surfaces have been investigated. These conditions are functions of the strength of the electrostatic interaction, Debye screening length, chain length, charge density and curvature of the surface. The adsorption can be tuned by using anyone of these parameters. The chain's conformation, adsorption energy and thickness of the adsorbed polymer are obtained under different adsorption conditions. We find the Monte Carlo simulation data to be in good agreement with the theoretical prediction derived previously by using the assumptions of ground state dominance and separability. The second topic is on the adsorption transition of a uniformly charged polyelectrolyte onto heterogeneously charged planar surfaces investigated with Monte Carlo simulations. Each of these surfaces contains both positive and negative charges. In addition to the usual case of adsorption of a polyelectrolyte to a surface with net charge opposite to that of the polymer, we show that a polyelectrolyte can adsorb onto a surface with net surface charge density similar to that of the polyelectrolyte. This adsorption is due to the spatial inhomogeneity of the surface charges which creates attractive regions with charge density different from the overall charge density of the surface. The spatial inhomogeneity of the surface charges also leads to differences in the conformation of the adsorbed polyelectrolyte. The critical conditions of strength and range of electrostatic interactions and chain length necessary for adsorption of a polyelectrolyte to a heterogeneously charged surface are determined. The last topic deals with applying self-consistent field theory (SCFT) to polyelectrolyte brushes grafted onto uncharged curved surfaces with no added salt. The goal of this study is to test the validity of the Debye-Hückel approximation for the electrostatic interaction in polyelectrolyte brushes. Our results show that the Debye-Hückel approximation is a good approximation for a weakly charged polymer brush grafted on a surface with small radius. The geometry of the system also plays an important role in the validity of the Debye-Hückel approximation. The approximation gives better results in spherical geometry then cylindrical.

Chain scission in turbulent flow of dilute polymer solutions

Price, Brian Gray 01 January 2002 (has links)
Flows with strong extensional components are capable of unraveling and breaking dissolved polymer chains, yielding a distribution of chain fragments that continually alters the molecular weight distribution, MWD, of a given sample over time of exposure to the flow. The evolution of the MWD is described in terms of scission rates and probabilities along the polymer backbone that a scission event will occur. These scission event probability distributions, p(f), where f is the fractional position along the backbone, depend on the flow condition, and quantitative characterization of the breadth of p(f) by the standard deviation relative to chain length, R, reveals information about the configuration of the chain at the time of scission. In this thesis, we have developed a generalized scission kinetics formulation that does not make unsupported assumptions regarding p( f), and applied this formulation to the analysis of MWDs, measured by quantitative gel electrophoresis, and arising from degradation of NaPSS in both turbulent Taylor-Couette and sonication flows. For the first time, we have reported R for turbulent flow-induced degradation and found that essentially random scission best describes the degradation process, with R = 9.5 for a single Gaussian description. Including the possibility of scission of a folded chain as a dual Gaussian description we found similarly that Rsingle = 9.5 and Rfolded = 0.09, with 70% of the chains breaking via the folded pathway, but with negligible improvement in the error in fit. We contrasted this result with our result for scission in sonication flow. With the single Gaussian description, we found a best fit R = 0.28, and with the dual Gaussian description, we found best fit parameters of Rsingle = 0.17 and R folded = 0.09, with the folded chain breaking more than twice as frequently. The latter fit was reduced 30% in error from the single Gaussian fit. In developing our understanding of the technique of quantitative gel electrophoresis, we have developed fundamental models of the diffusion-mediated, post-electrophoresic staining process. The single and dual binding models accurately predict the edge-like appearance of the diffusing dye front which is not predicted by the Crank model37 of probe diffusion in a binding medium.


ALLEGREZZA, ANTHONY E. 01 January 1972 (has links)
Abstract not available


WU, CHESTER CHERNG-CHIOU 01 January 1971 (has links)
Abstract not available


GO, SANTOS W 01 January 1972 (has links)
Abstract not available


SU, TIEN-KUEI 01 January 1975 (has links)
Abstract not available

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