Abstract: The synthesis of hydroxypropyl cellulose (HPC) and hydroxypropyl cellulose acetate(HPCA) has been carrled out.The suitable conditions for HPC synthesis wcre: 40℃ and 2 hours or more.The hydroxypropyl content of HPC increased linearly with the increase of the concentration of propylene oxide in the reaction system.With the hydroxypropyl contentbeing increased, the time needed for acetylation and hydrolysis could be shortened Additionof glycerin-n-propanol mixture or phosphoric acid as additives and evaporation for 30 to 60 seconds appeared favorable to preparation of reverse osmosis membranes by casting technique.The membranes obtained bave 95～98% of NaCl rejection and 1.0～2.1 mL/cm²·h of waterflux under the operation pressure of 20kg/cm².The highest working temperature of HPCA membrane is about 10℃ higher than that of CA membrane.

Key words: hydroxypropyl cellulose acetate, synthesis, reverse osmosis membrane, desalination