TABLE OF CONTENTS In this chapter the instrumentation used for the determination of volatile materials present in polymers is discussed. These include:
Monomers, e.g., styrene, acrylonitrile, vinyl chloride.
Volatile dimers, trimers of monomers, i.e., oligomers.
Residual polymerisation solvents, e.g., aliphatic hydrocarbons in low-pressure polyethylene.
Unreacted impurities from the original monomer, e.g., ethylbenzene in polstyrene (PS).
Methods for the determination of volatiles in polymers are based principally on direct gas chromatography (GC) of solutions or extracts of the polymer, high-performance liquid chromatography (HPLC), polarography of solutions or extracts of the polymer, headspace analysis, headspace gas chromatography mass spectrometry (MS), and purge and trap analysis. These various techniques are discussed in the following sections.
The sample is introduced to the column in an ideal state, i.e., uncontaminated by septum bleed or previous sample components, without modification due to distillation effects in the needle, and quantitatively, i.e., without hold-up or adsorption prior to the column. The instrument parameters that influence the chromatographic separation are precisely controlled. Sample components do not escape detection, i.e., highly sensitive and reproducible detection and subsequent data processing are essential.
There are two types of separation column used in GC: capillary and packed. Packed columns are still used extensively, especially in routine analysis. They are essential when sample components have high partition coefficients and/or high concentrations. Capillary columns provide a high number of theoretical plates, hence a very high resolution, but they cannot be used in all applications because there are not many types of chemically bonded capillary...
