ISSN:
1435-1536
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Description / Table of Contents:
Summary The restriction of molecular mobility of unsaturated polyester resins during the curing process is investigated by NMR measurements. By combining pulse and wide-line methods it is possible to study the whole curing process from the liquid resin to the cured material. Three kinds of protons can be distinguished: very mobile, less mobile and immobile ones, corresponding essentially to the unpolymerized styrene, the free polyester molecules and the already cured and glasslike regions, respectively. Both spin spin relaxation times of the liquid resins depend only on the viscosity of the solutions, but not on the structure of the resins. During the curing process a decrease of the larger relaxation time from approximately 0.3 to 2 · 10− 5 s and an increase of the rigid proton fraction is found. With the materials having a glass transition temperature above room temperature, still 7 to 18 percent of the protons are mobile after a curing at room temperature. By curing at increased temperature the mobile fraction drops to 3 to 7 percent. At the same time the mechanical strength of the sample increases. With the materials having a glass transition temperature below room temperature, however, the mobile fraction is much larger and there is no change with thermal treatment observed. The size of the mobile regions can be estimated from the fitting of the relaxation time and the mobile fractions at a fixed time of the curing. From light scattering and NMR measurements a new model for the structure of the cured materials is obtained. The model explains several properties of the cured material which cannot be explained by the model of an infinite network of the polyester molecules being connected by styrene bridges.
Notes:
Zusammenfassung Die Einschränkung der Molekularbeweglichkeit während der Härtung ungesättigter Polyesterharze wird durch NMR-Messungen verfolgt. Durch Kombination von Impuls- und Breitlinienmethode läßt sich der gesamte Härtungsablauf vom flüssigen Harz bis zum Formstoff untersuchen. Dabei werden drei Arten von Protonen unterschieden: stark bewegliche, die vornehmlich dem nicht einpolymerisierten Styrol zuzuschreiben sind, schwächer bewegliche, die im wesentlichen den unvernetzten Polyestermolekülen entsprechen und unbewegliche, die den bereits vernetzten und glasartig erstarrten Bereichen angehören.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01638100
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