Reverse osmosis membranes of carboxylated poly(phenylene oxide) (c-PPO) were prepared with its Na salt form. C-PPO was synthesized by organometallic reaction. The degree of carboxylation of synthesized c-PPO was controlled by [BuLi]/[PPO] ratio, and found to be in the range of 4-63 mol %.
The presence of COOH pendant groups in c-PPO was verified by FT-IR spectrum showing the characteristic carbonyl stretch of hydrogen bonded carbonyls at $1720 cm^{-1}$. It was also verified by $^1H$ NMR spectrum.
The glass transition temperature of c-PPO increased slightly with increasing degree of carboxylation. C-PPO showed no significant degradation up to 230℃, but the thermal stability of c-PPO was not so good as that of unmodified PPO.
It was found that the hydrophilicity and reverse osmosis performance of c-PPO were governed by the concentration of COONa. In the case of dense membranes, solute rejection of 75-96 5 was obtained with membranes of c-PPO having 25-35 mol 5 COONa. Dense membrane prepared with Na salt of c-PPO was stable to 100 ppm chlorine for 10 days.
Thin film composite membranes were prepared by spin-coating the Na salt of c-PPO onto porous polysulfone substrates. Permeation properties were influenced by the preparation conditions. The composite membrane which had been coated with 3 wt 5 methanol solution of Na salt of 28 mol 5 c-PPO had the skin layer thickness of 0.5-0.7㎛ and showed solute rejection of 94 5 and permeate flux of 9 $gallon/ft^2$ day.
Phase inversion membranes of c-PPO were made with varying the preparation conditions, and their properties were investigated. Increasing DMF content in the casting solution caused decrease in the solute rejection and increase in the permeate flux. Porosity of the membrane increased greatly with the presence of non-solvent such as ethanol and/or inorganic salt such as $MgCl_2$ in the casting solution.
Annealed membrane showed higher solute rejection than non-annealed membrane, but low permeate flux. Great increase in the solute rejection was observed when the annealing temperature was between 200℃ and 220℃, which was around glass transition temperature of c-PPO.
