The development of a new thermoregulated polyethylene glycol (PEG) biphasic system composed of PEG-400/1,4-dioxane/n-heptane is reported in this paper. By applying this system in the hydroformylation of 1-dodecene catalyzed by Rh complexes modified with phosphite ligand containing PEG chains, TMPGP (P[O(CH2CH2O)(n)CH3](3), n = 8), the conversion of 1-dodecene and the yield of aldehydes reached up to 96% and 94%, respectively. The catalyst, after being recycled twenty-three times, showed no appreciable loss of catalyst activity. The average Rh loss was 0.65% each run. (c) 2006 Elsevier B.V. All rights reserved.