Esterification of 4-methyloctanoic acid with polyethylene glycol at different a(w)

Novozym 435(R) (immobilized Candida antarctica lipase B) was used to esterify 4-methyloctanoic acid with polyethylene glycols (PEGs) of different molecular weights (PEG-600, PEG-3000 and PEG-20000) at different water activities. A system composed of 4-methyloctanoic acid and PEG-600 was monophasic, except at a high water activity. Even at a water activity of 0.8, PEG was still converted to its mono- or diester, which proves the unique character of PEG. The PEG-esters accumulated in the apolar phase.