DISSOLUTION RATES OF COPOLYMERS BASED ON 4-HYDROXYSTYRENE AND STYRENE

Copolymers were synthesized by free-radical polymerization using 4-acetoxystyrene and styrene in various ratios. These polymers then were hydrolyzed to the corresponding 4-hydroxystyrene (phenol) copolymers. The dissolution rates of the copolymers (using laser interferometry) decreased with a decrease in hydroxyl group content in aqueous developers (sodium hydroxide, potassium hydroxide, and a tetramethylammonium hydrolride based commercial developer). While an increase in pH value enhances the dissolution, an increase in cation size of these hydroxides at constant pH decreases the dissolution rate. The polymers become essentially insoluble in aqueous developers when the content of the monomer containing the hydroxyl group is less than 70 mole%. The dissolution rate of P(4HS/S) in organic solvents, methyl isobutyl ketone (MIBK), isopropyl alcohol (IPA), and their mixtures, increases as the styrene content increases. However,in IPA, dissolution rate goes through a maximum and then drops down with styrene content greater than 50 mole%. In mixtures of these two solvents, the polymer dissolves faster than it does in either pure solvent.