Abstract
Direct analysis in real time (DART) was coupled with a thermal desorption/pyrolysis (TDPy) device for the analysis of fluoropolymers. The product ions were analyzed using a Fourier transform cyclotron resonance mass spectrometer (FT-ICR MS). Two different polyvinylidene fluoride (PVDF) samples were studied individually and in a 50/50 mixture. This study demonstrates the capability of TDPy DART FT-ICR MS to provide information on PVDF polymers, including the determination of end-groups and the detection of comonomers.
The temperature program used enabled the desorption of the smallest oligomers (Mn ≈ 600 Da) below 400 °C, allowing for the identification of the end-groups, which ensured the differentiation of the PVDF. At temperatures above 400 °C, Cw Hx Fy- ions were predominantly formed as a result of the thermal cleavage of the PVDF backbone.
Specific pyrolysis products observed for one PVDF sample suggested the presence of 4.6 mol% hexafluoropropylene (HFP), as determined by NMR measurements. The molar percentage of HFP was also determined by a new approach using TDPy DART MS. The analysis of a 50/50 PVDF blend revealed species from both polymers during the thermo-desorption and pyrolysis events, confirming the ability of the proposed methodology to determine the mol% of the HFP comonomer. This represents the first TDPy DART FT-ICR MS study of fluoropolymers. Applicable to non-soluble or poorly soluble polymers, the proposed methodology enables the identification of end-groups, suggests the possibility of distinguishing fluoropolymers, and identifies blend composition. Additionally, the molar percentage of comonomers can be defined for poly(VDF-co-HFP) copolymers.