Determination of Polymer Type and Comonomer Content in Polyethylenes by Pyrolysis−Photoionization Mass Spectrometry

Rapid microanalysis of a wide variety of polyolefins was performed using pyrolysis−photoionization mass spectrometry (py-PI-MS). Solid samples (∼10 μg) were pyrolyzed on a heated probe in the source region of a time-of-flight mass spectrometer. Pyrolysates were “softly” ionized using coherent vacuum ultraviolet radiation (118 nm). The resulting mass spectra were clearly different for low-density polyethylene, high-density polyethylene, and several ethylene/α-olefin copolymers. A combination of principal component analysis and linear discriminant analysis was used to classify polyolefin samples directly from their photoionization mass spectra. The compositions of ethylene−butene and ethylene−octene copolymers were predicted using partial least-squares analyses. The values obtained using py-PI-MS were in good agreement with the measured 13C NMR values. Samples of ethylene−octene containing 30 wt % carbon black and ethylene−butene containing 20 wt % silica were correctly classified and compositionally analyzed using py-PI-MS. Samples containing these additives are typically not amenable to study by solution-state 13C NMR or IR.