Qualitative and quantitative analysis of styrene and its various oligomers by liquid chromatography

Two polystyrenes (crystal PS 1 and choc PS 2) were tested to determine the composition of low-molecular-mass products. The RP-HPLC method shows clearly, in both polystyrenes, two oligomeric entities: higher-molecular-mass (n>5) and lower-molecular-mass (n<5). The ratio between fractions exhibits respectively the same value (1/4) in PS 1 and PS 2. However it is logical that the total oligomeric fraction in PS 1 was larger than in PS 2. In addition, the styrene level in polystyrene crystal determined by RP-HPLC coupled with gel permeation chromatography (GPC) was 2500 mg/kg. This technique exhibits a satisfactory recovery (79+/-5%). Styrene could not be determined in polystyrene choc. Automation of combined GPC-RP-HPLC, in the future, will permit quantification of the lower styrene levels in commercial packaging polystyrene.