Abstract Static vapour pressures are reported for the barium β-diketonate polyether adducts Ba(hfac)2· (tetraglyme) and Ba(hfac)2· (18-crown-6), which are important as precursors in chemical vapour deposition (hfac = 1,1,1,5,5,5-hexafluoropentane-2,4-dionato, (CF3COCHCOCCF3)−, tetraglyme = 2,5,8,11,14-pentaoxapentadecane, CH3O (CH2CH2O)4CH3, 18-crown-6 = 1,4,7,10,13,16-hexaoxacyclooctadecane,c-(CH2CH2O)6). The thermal behaviour of the compounds was also investigated by d.s.c., elemental analysis, and visual observations. Under moderately fast heating, Ba(hfac)2· (tetraglyme) melts without significant decomposition at the temperatureT≈ 428 K. However, the compound may melt during prolonged heating at considerably lower temperatures because of the formation of trace impurities. The molar enthalpy of fusion was measured as (34.8 ± 0.5) kJ·mol−1. Vapour pressures for molten Ba(hfac)2· (tetraglyme) in the temperature range 401 K to 447 K were fitted to the equation: 1g (p/Pa) = 13.69 − 5318 (T/K)−1, consistent with a value of (101.8 ± 1.2) kJ·mol−1for the average molar enthalpy of vaporisation. Ba(hfac)2· (18-crown-6) samples melted with decomposition only atT> ≈ 533 K. This compound undergoes a solid-state phase transition, study of which is complicated by slow kinetics. Conversion of the low-temperature form to the high-temperature form was demonstrated at temperatures as low as 423 K, and is accompanied by a molar enthalpy change of (16.7 ± 0.3) kJ·mol−1. Vapour pressures for solid Ba(hfac)2· (18-crown-6) in the temperature range 412 K to 468 K were fitted to the equation: 1g (p/Pa) = 12.82 − 5480 (T/K)−1, consistent with a value of (104.9 ± 1.3) kJ·mol−1for the average molar enthalpy of sublimation.