Composition control of copolyester was examined by using hydrodynarnically induced phase separation, during solution polymerization, of p-acetoxybenzoic acid and m-acetoxybenzoic acid (m-ABA). Polymerizations were carried out in liquid paraffin at 1.0% of concentration under shear flow. The polymers were obtained as precipitates formed via phase separation of oligomers and the subsequent polymerization in the precipitates. When the feed ratio of m-ABA (χf) was 20 mol %, the molar ratio of m-oxybenzoyl moiety in the precipitated polymers (χp) was 5.3, 3.1, and 2.3 mol % at a shear rate (γ) of 0, 147, and 489 s-1, respectively. The values of χp were much lower than those of χf, and shear flow lowered the value of xp
thus, controlling shear flow influenced both the reaction rate of the monomers and the miscibility of the oligomers. It especially enhanced the difference on the miscibihty between homo-oligomers and co-oligomers. This change in the miscibility by shear flow brought about the more rapid precipitation of homo-oligomers than co-oligomers, leading to the selective formation of poly(p-oxybenzoyl). © 2008 American Chemical Society.