A series of novel phosphite ligands tri-(methoxyl polyethylene glycol)-phosphite (TMPGP) (1a-1d) have been synthesized and used in the rhodium-catalyzed hydroformylation of p-isobutylstyrene (IBS) in thermoregulated polyethylene glycol (PEG) biphase system. Under the conditions of P=5.0 MPa (H-2:CO=1:1), P/Rh=13(molar ratio), reaction time=2 h and temperature=120 degrees C, the conversion of IBS was 100% and the yield of aldehyde was 96%. The catalyst could be easily separated from the product by phase separation and reused for nine times without evident loss of activity. (c) 2006 Elsevier B.V. All rights reserved.