Abstract The thermo‐oxidative stability of high‐density polyethylene (HDPE) prepared by silica supported Ziegler‐Natta, bis(triphenylsilyl)chromate and bis(cyclopentadienyl)‐chromium(II) catalyst systems was examined by chemiluminescence (CL) techniques and thermogravimetric (TG) analysis. In particular, the technique of dynamic CL in nitrogen allows the concentration of polymer hydroperoxides and the relative stability of these to be simultaneously determined. Polymer hydroperoxides in Ziegler‐Natta catalyzed HDPE are relatively stable because titanium and aluminum residues are poor pro‐oxidants compared with chromium residues. HDPE produced by bis(cyclopentadienyl)chromium(II) has a low intrinsic thermo‐oxidative stability due to the chromium‐catalyzed conversion of polymer hydroperoxides into degradation products during thermal aging. Concentrations of residual chromium as low as 1 ppm can profoundly affect the oxidative stability of the polymer and exert a much greater influence than either the extent of branching or the degree of unsaturation. The appearance of the silica catalyst support before and after gas‐phase polymerization was studied by scanning electron microscopy. During polymerization the silica support shatters and the resulting submicron fragments are dispersed throughout the polymer particles. On exposure of the nascent polymer to the atmosphere, bis(cyclopentadienyl)chromium(II) is converted to a trivalent chromium species which remains associated with the silica substrate. The presence of trivalent chromium in the poisoned chromium catalyst was confirmed by UV/visible spectrophotometry and the nature of the Cr(III) species was investigated by diffuse reflectance Fourier transform infrared (FTIR) spectroscopy. The high surface area of the catalyst residue renders it a powerful pro‐oxidant despite its low concentration. © 1992 John Wiley & Sons, Inc.

High-density polyethylene

Thermal Stability

10.1002/pola.1992.080300910

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Citations (20)

The morphology of polyethylenes produced by alumina-supported zirconium tetrabenzyl

Polymer (1983)

Ahmet Akar N. C. Billingham Paul Calvert

Morphology

10.1016/0032-3861(83)90209-4

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Citations (15)

Designing polymer additives to minimise loss

Makromolekulare Chemie Macromolecular Symposia (1989)

N. C. Billingham

Abstract The solubility of additives in polymers is shown to determine the state of the additive in a processed sample and the mechanisms by which it may be lost. The loss of additives is described in terms of a model which considers the effects of solubility, diffusion rate and volatility, and it is shown that the rate and mechanism of loss depends upon these quantities and upon the sample geometry. The effects of additive structure on loss mechanism and rate are discussed and the implications for additive design are reviewed.

10.1002/masy.19890270110

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Citations (12)

Sixth post‐doctoral course on degradation and stabilization of polymeric materials

Macromolecular Rapid Communications (1996)

N. C. Billingham

Degradation

Course (navigation)

10.1002/marc.1996.030170111

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Citations (0)

FT-IR studies on thermal degradation of electrically conducting polymers