Determination of End Groups in Thermoplastic Addition Polymers by Oligomer Separation and Characterization

Low-molecular-weight fractions have been isolated from polystyrene, poly(vinyl chloride) and high-density polyethylene (HDPE) by fractionation methods. These fractions were subjected to high-performance gel permeation chromatography (HPGPC) to separate individual oligomer species. Repeated injection of fractions and collection of the individual oligomers allowed characterization by nuclear magnetic resonance spectroscopy and mass spectroscopy. Structures for end groups in these oligomers have been deduced, and shown to be consistent with polymerization mechanisms for the formation of each addition polymer. An example of an HPGPC procedure is provided for quantifying the concentration of an oligomer in HDPE by a standard addition method.