The behaviour of some homopolymers around their melting points
The behaviour of some homopolymers around their melting points
Structural changes occuring in well annealed samples of isotactic polypropylene as the temperature is raised to just below the melting point were studied by infrared spectroscopy. A transition was observed well below the melting point, at around 130oC, involving the helical molecular coils found in crystalline isotactic polypropylene. The transition was then investigated using Raman spectroscopy, differential scanning calorimetry, 13C nuclear magnetic resonance, the degree of linear expansion with temperature and, to a lesser extent x-ray spectroscopy to determine the nature of the transition. It was concluded that this transition involved a gain in molecular freedom associated with a loss of helical material in the crystalline regions of the sample. There was no evidence of appreciable melting or oxidation in the samples studied. As an extension to this work the infrared spectrum of isotactic polypropylene below room temperature was also studied. A transition similar in nature to that at 130oC was found, corresponding to the glass transition temperature. This was also detected in the low temperature study of atactic polypropylene. Two other polymers were also investigated by infrared spectroscopy: poly(4-methylpent-1-ene) and isotactic polystyrene. The glass transition temperature was seen in both instances, but no definite example of a transition similar to that seen for isotactic polypropylene was observed. A method of obtaining the infrared spectrum of a flowing polymer melt was developed using a reflectance technique. This method was employed to study changes in the spectra of high-density polyethylene and polypropylene at different shear rates using both polarised and unpolarised spectra. Surprisingly little evidence was found for the development of the order which would be expected to explain the amount of die swell obtained. (D82534)
University of Southampton
1988
Hanna, Lesley Anne
(1988)
The behaviour of some homopolymers around their melting points.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Structural changes occuring in well annealed samples of isotactic polypropylene as the temperature is raised to just below the melting point were studied by infrared spectroscopy. A transition was observed well below the melting point, at around 130oC, involving the helical molecular coils found in crystalline isotactic polypropylene. The transition was then investigated using Raman spectroscopy, differential scanning calorimetry, 13C nuclear magnetic resonance, the degree of linear expansion with temperature and, to a lesser extent x-ray spectroscopy to determine the nature of the transition. It was concluded that this transition involved a gain in molecular freedom associated with a loss of helical material in the crystalline regions of the sample. There was no evidence of appreciable melting or oxidation in the samples studied. As an extension to this work the infrared spectrum of isotactic polypropylene below room temperature was also studied. A transition similar in nature to that at 130oC was found, corresponding to the glass transition temperature. This was also detected in the low temperature study of atactic polypropylene. Two other polymers were also investigated by infrared spectroscopy: poly(4-methylpent-1-ene) and isotactic polystyrene. The glass transition temperature was seen in both instances, but no definite example of a transition similar to that seen for isotactic polypropylene was observed. A method of obtaining the infrared spectrum of a flowing polymer melt was developed using a reflectance technique. This method was employed to study changes in the spectra of high-density polyethylene and polypropylene at different shear rates using both polarised and unpolarised spectra. Surprisingly little evidence was found for the development of the order which would be expected to explain the amount of die swell obtained. (D82534)
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Published date: 1988
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Local EPrints ID: 461861
URI: http://eprints.soton.ac.uk/id/eprint/461861
PURE UUID: 560d2aee-ae0f-4315-9cd2-0f421e991fc1
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Date deposited: 04 Jul 2022 18:57
Last modified: 04 Jul 2022 18:57
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Author:
Lesley Anne Hanna
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