There are three types of olefinic groups present in sufficient concentrations to warrant consideration, one or more of which can normally be found in any polyethylene (4). The three types are: trans-vinylene, R - CH = CH - R′, sometimes referred to as transinternal unsaturation; vinylidene or pendent methylene, RR′C = CH₂; and vinyl unsaturation, R - CH = CH₂, also referred to as terminal unsaturation.

The type and quantity of these groups can influence the chemical and physical properties of the resin. Information concerning their presence may also be used to characterize or identify unknown resins or blends of resins.

Vinylidene unsaturation represents the major portion of the unsaturation present in most low-density polyethylenes.

Infrared spectroscopy can be used for the determination of unsaturation in polyethylene (1, 3, 5). The values determined by infrared agree with those determined by IC1 uptake (5).

1.1 This test method is applicable to all types of polyethylenes, those ethylene plastics consisting of ethylene and -olefin copolymers longer than propylene, and blends of the above in any ratio.

1.2 The values stated in SI units are to be regarded as the standard.

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Specific hazards statements are given in Section 8.

Note 1—There is no similar or equivalent ISO standard.