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1

Digitale Medien

Differential thermal analysis of polyethylene under high pressureThis paper was presented in part at the 1966 IUPAC meeting in Tokyo and Kyoto. (1969)

Davidson, Theodore ; Wunderlich, Bernhard

New York : Wiley-Blackwell

Journal of Polymer Science Part A-2: Polymer Physics 7 (1969), S. 377-388

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ISSN: 0449-2978

Schlagwort(e): Physics ; Polymer and Materials Science

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie , Physik

Notizen: The design of a differential thermal analysis apparatus for use at elevated pressure is described. Experiments on melting and crystallization of folded-chain crystals of polyethylene and poly(ethylene-butene-1) copolymer, and melting of extended-chain polyethylene crystals have been conducted at pressures up to 4200 bars. The precision in transition temperature measurement was ±1°C. The Clausius-Clapeyron equation predicts the melting point increase with pressure at atmospheric pressure to be 32.0°C/kb. The melting point depression due to copolymerization remained constant over the complete pressure range analyzed on the poly(ethylene-butene-1) used in this study. Crystallization of polyethylene is retarded at elevated pressures, and a 50% larger degree of supercooling is necessary at 5000 bars to give a crystallization rate equal to that observed at atmospheric pressure. The difference in melting point between folded-chain and extended-chain polyethylene increases from 8.4°C at 1 bar to 25.6°C at 3000 bars.

Zusätzliches Material: 3 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/pol.1969.160070209

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2

Digitale Medien

Extended-chain crystals. II. Crystallization of polyethylene under elevated pressureThis paper was presented in part at the IUPAC Macromolecular Symposium, Toronto 1968. (1969)

Davidson, Theodore ; Wunderlich, Bernhard

New York : Wiley-Blackwell

Journal of Polymer Science Part A-2: Polymer Physics 7 (1969), S. 2051-2059

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ISSN: 0449-2978

Schlagwort(e): Physics ; Polymer and Materials Science

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie , Physik

Notizen: A report on crystallization of polyethylene at elevated pressures to an extended-chain morphology is presented. The crystals have been characterized by electron microscopy and density determination. Pressure, supercooling (temperature), and crystallization time have been varied to find the best conditions for production of perfect crystals. At 10-30°C supercooling completely crystallized polyethylene was obtained between 4.5 and 7 kb crystallization pressure in 1-8 hr. Analysis of fracture surfaces of samples crystallized for different lengths of time shows an increase in size and number of crystal lamellae and an improvement of extended chain crystals in the early stages of crystallization. A further improvement of the less well crystallized material between the lamellae occurs after 15 min of crystallization time.

Zusätzliches Material: 5 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/pol.1969.160071207

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3

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Extended-chain crystals. I. General crystallization conditions and review of pressure crystallization of polyethylene (1969)

Wunderlich, Bernhard ; Davidson, Theodore

New York : Wiley-Blackwell

Journal of Polymer Science Part A-2: Polymer Physics 7 (1969), S. 2043-2050

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ISSN: 0449-2978

Schlagwort(e): Physics ; Polymer and Materials Science

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie , Physik

Notizen: This is the first paper of a series of reports concerning extended-chain crystals of flexible, linear high polymers. The general conditions for crystal growth are discussed. Polymer crystallization is described as a two-step process: nucleation of each crystallizing molecule to a folded-chain conformation, followed by an increase in fold length in a solid-state reorganization step. This reorganization step is enhanced in the case of polyethylene by crystallization at high temperature under elevated pressure. Mechanical deformation during crystallization is also able to produce extended-chain crystals. The most promising method, however, is crystallization during polymerization. Previous work on crystallization of polyethylene under elevated pressure is critically reviewed.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/pol.1969.160071206

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4

Digitale Medien

Kinetics of the 20°C phase transformation in polytetrafluoroethylene (1972)

Natarajan, Raj T. ; Davidson, Theodore

New York : Wiley-Blackwell

Journal of Polymer Science: Polymer Physics Edition 10 (1972), S. 2209-2222

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ISSN: 0098-1273

Schlagwort(e): Physics ; Polymer and Materials Science

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie , Physik

Notizen: The rate at which PTFE transforms from the triclinic to the hexagonal phase has been measured under isothermal conditions. Samples in a series of decreasing density and crystallinity show increased isothermal rates of transformation. Observed kinetic data are interpreted on the basis of a modified Avrami-Johnson-Mehl treatment. A model for the transformation in which planes of helix-hand reversal propagate through the lattice is shown to fit the experimental results. The transformation rate is observed to be proportional to the total (001) surface area in the polytetrafluoroethylene specimens, suggesting that nucleation of the transformation takes place at grain boundaries.

Zusätzliches Material: 9 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/pol.1972.180101108

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5

Digitale Medien

Microstructure of particle-form polyethylene (1970)

Davidson, Theodore

New York : Wiley-Blackwell

Journal of Polymer Science Part B: Polymer Letters 8 (1970), S. 855-859

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ISSN: 0449-2986

Schlagwort(e): Chemistry ; Polymer and Materials Science

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie

Zusätzliches Material: 4 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/pol.1970.110081204

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