MECHANICAL SCISSION OF PERFLUOROPOLYETHERS

Mechanical scission of two typical perfluoropolyethers was investigated: Y, a copolymer of -CF(CF3)CF2O-, -CF2O-, and -CF(CF3)O-, and Z, a copolymer of - (CF2)nO-, with n = 1, 2, 3, 4. Undiluted polymers were subjected to prolonged shearing in a media mill with ZrO2 particles. A chemical extraction of the polar ZrO2 particles was carried out to collect adsorbed polar scission products. Mechanochemical scission products from both the Y and Z fluorocarbon polymers were identified by F-19-NMR. A significant amount of CF3CO2- was present after the milling and the primary functional groups formed at scissioned chain ends were -CO2-. A hydrodynamic expression was derived and the maximum extension rate was estimated to be in the range of 5 X 10(6) s-1. Initial degrees of polymerization were between 20 and 200, well below levels for which flow-induced scission is expected to occur. Final degrees of polymerization were less than 10, and the scission was noncentral and nonrandom in both polymers. (C) 1993 John Wiley & Sons, Inc.