The significance of sample preparation of historical and contemporary poly(vinyl chloride) objects to investigate the distribution and changes of molar mass by SEC-MALS-dRI

Abstract

The distribution of molar mass of historical and contemporary poly(vinyl chloride) objects was determined using size exclusion chromatography with multi-angle light scattering detection. The weight average molar mass was determined for a collection of 57 samples, ranging from 75 to 186 kg/mol with a median of 102 kg/mol. Rigid PVC objects were found to have a significantly lower weight average molar mass (Mw = 81 kg/mol) than plasticized ones (Mw = 102 kg/mol). Thin objects also exhibited significantly lower Mw than bulky objects. A substantial presence of aggregates was noted and characterized as an ‘aggregate ratio’ for the entire collection. Heating a solution of poly(vinyl chloride) in THF at 55 °C for 5 h proved successful in the dissociation of the aggregates and allowed for an accurate determination of molar mass. The uncertainty of the Mw determination was statistically evaluated and used to study the effects of accelerated degradation on Mw. No statistically significant changes in Mw were observed in samples artificially aged at 50 °C to 80 °C for up to 15 weeks, indicating that Mw does not decrease during degradation of a PVC heritage object and that accelerated degradation does not lead to polymer crosslinking.