Perfluoropolyether characterization by nuclear magnetic resonance spectroscopy and gel permeation chromatography

Perfluoropolyethers (PFPEs) are vital lubricants in the aerospace and magnetic recording industry, and they have potential applications in micro-electromechanical and optoelectronic devices. Precise control of their physical properties requires analytical tools, such as nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC) to characterize, chain composition end groups, and molecular weight distribution. The 19F chemical shifts for Z-, D- and K-type perfluoropolyethers, and six different end groups are compiled into tables within. Application of NMR spectra to derive the number average molecular weight and chain composition is illustrated. A GPC system was developed to measure the perfluoropolyether Zdol molecular weight distributions. Significant variation in the Zdol refractive index with molecular weight was observed in the differential refractometer during GPC. The index variation compared favorably with that calculated from the molar refraction of subunits and end groups. Oligomer peaks found in the low molecular weight tail of the molecular weight distribution are well described by a statistical model. Both the NMR spectroscopy and GPC were simultaneously employed to follow the evolution of the molecular weight distribution during Zdol evaporation.