Molecular weight distribution in polyethylene obtained by the action of the catalyst α-TiCl3Al(C2H5)3

SynopsisThe molecular weight distribution (MWD) of bulk ultrahigh molecular weight polyethylene (UHMWPE) was determined by an increasing temperature sequential extraction technique. Using decahydronapthalene (decalin) as the solvent, 5 g samples of UHMWPE were fractionated stepwise from room temperature to 190°C in 10Co increments. Results via high temperature capillary viscometry show that intrinsic viscosity ( [ q ] ) ranges from 12.0 to 37.0 dL/g or that the viscosity average molecular weight ( a o , r a n g e s from approximately 1.6 to 7.4 X lo6. When the integral distribution is plotted against M, on logarithmic probability graph paper, a straight line (i.e., a Wesslau distribution) results. Although the present methodology is tedious, many previous problems which have led to degradation are overcome by this technique.

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Molecular weight distribution of a bulk ultra‐high molecular weight polyethylene product—impax 5M+ UHMW–NAT

Kusy

Whitley

1986

J. Biomed. Mater. Res.

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A bulk ultra‐high molecular weight polyethylene product, IMPAX 5M+ UHMW–NAT, was fractionated using an increasing‐temperature sequential‐extraction technique. In the presence of an inert atmosphere and an antioxidant, 5 g of material were methodically dissolved in decahydronaphthalene over the temperature range, 80–191°C. Initially, intrinsic viscosities were measure in decalin at 135°C by single point capillary viscometry. From this data the viscosity average molecular weights were estimated using a logarithmic expression. Results showed that the intrinsic viscosities (molecular weights) increased linearly with extraction temperature over a range from 10 to 40 dL/g (1 to 8 × 106) and that the molecular weight distribution was log normal. Mass balances both before and after extraction indicated that less than 0.3% of the material had a molecular weight less than 106 and that less than 0.1% of the material was gel. Zero shear viscometry of bulk fractionated polymer and powdered whole polymers confirmed that capillary viscometry increasingly under‐estimates the true intrinsic viscosities as the polymer chain lengths (molecular shear forces) increase. Indeed, the actual molecular weights ranged from about 2–14 × 106. Knowledge of the molecular weight distribution of bulk products and the presence of either volatiles or crosslinked networks is critical for the continued design and development of superior wearing and fatigueresistant implants.

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Molecular weight distribution in polyethylene obtained by the action of the catalyst α-TiCl3Al(C2H5)3

Cited by 5 publications

References 8 publications

Fractionation of Polymers

Fractionation of Polymers

Use of a sequential extraction technique to determine the MWD of bulk UHMWPE

Molecular weight distribution of a bulk ultra‐high molecular weight polyethylene product—impax 5M+ UHMW–NAT

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