A process to polymerize one or more monomer(s) to form a polymer, comprising contacting one or more monomer(s) in a polymerization medium comprising one or more Lewis acid(s), a weakly coordinating anion, and a diluent comprising one or more non-aryl hydrofluorocarbon(s) (HFC); wherein the one or more Lewis acid(s) is not a compound represented by formula MX3, where M is a group 13 metal and X is