Polymerisation Residues

Further information on the various types of non-polymeric components that can occur in polymers is discussed in the next section. 

Low pressure polyethylene might contain minute traces of oxygen or nitrogen or sulfur chain transfer catalyst residues. These are usually labile and can be ignored from the foodstuff contamination point of view. Polymers such as polyethylene, polypropylene and polystyrene manufactured by a catalysed low pressure route will however, usually contain appreciable catalyst residues usually appearing in the form of aluminium, chromium, magnesium and titanium, also possibly lithium and sodium. As the example quoted in Table 3.1 indicates these impurities can occur in the polymer at levels approaching 100 ppm. 

Suspension or emulsion processes for the polymerisation of styrene or vinyl chloride can impart to the polymer significant amoimts (up to 0.05%) of proton donating processing chemicals such as potassium and ammonium persulfate or benzyl and lauryl peroxide and their decomposition products, (potassium sulfate, ammonium carbonate, urea and benzoic or lauric acid, respectively), and these are of significance in relation to safety in use for food. 

Catalysts and accelerators used in the manufacture of thermosets include peroxides, organic nitrogen compounds and copper and cobalt salts of naphthenic and other organic acids. 

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The presence of impurities or polymerisation residues, some of which may be combined with the polymer. 

Cupery, M. E. et al., J. Amer. Chem. Soc., 1934, 56, 1167 During isolation of the title product from polymerised l,5-hexadiene-3-yne, high vacuum distillation must be carried only to a limited extent to prevent sudden explosive decomposition of the more highly polymerised residue. 

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