The phase behavior in water of hydroxypropylcellulose (HPC) and HPC partially esterified with methacryloyl chloride (HPCM) has been studied by measuring the variation of solution turbidity in the temperature range -5 to 46 degrees C. The resulting phase diagram is compared to previous results on HPC/water system and a qualitative agreement is observed. The HPCM phase diagram shifts towards lower values of temperature and polymer concentration; which may be mainly explained by the presence of hydrophobic residues introduced along the HPC chain. The progressive loss of the structure of water molecules around these groups as temperature or concentration increase reduces the area of the isotropic region with respect to that of the anisotropic phase. (C) 2000 Elsevier Science Ltd. All rights reserved.