Effect of Ligand andn-Butyl Acrylate on Cobalt-Mediated Radical Polymerization of Vinyl Acetate

The electron-withdrawing effect of the ligand in the cobalt complex was studied in cobalt-mediated radical polymerization of vinyl acetate (VOAc) initiated by 2,2‘-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70). The polymerization of VOAc with V-70 and a series of bis(acetylacetonate)cobalt derivatives, Co(R 1 COCH COR 2 ) 2 (R 1 = R 2 = CH 3 ( 1 ), R 1 = CF 3, R 2 = CH 3 ( 2 ), R 1 = R 2 = CF 3 ( 3 )), was conducted under the same conditions. Complexes 1 and 2 successfully mediated the radical polymerization of VOAc, resulting in poly(VOAc) with predetermined M n and low polydispersity. In contrast, complex 3 did not control the radical polymerization of VOAc, resulting in poly(VOAc) with higher molecular weight and higher polydispersity. While complex 1 was not able to control the radical polymerization of n -butyl acrylate ( n BA), the copolymerization of n BA with various amounts of VOAc (9%, 23%, and 50%) in the presence of V-70 and 1 showed that M n and M w / M n of copolymers decreased with increasing VOAc ratio. This indicated that the extent of control in the copolymerization improved with increasing molar ratio of VOAc. The VOAc content of poly( n BA- co -VOAc) copolymers was determined by 1 H NMR spectroscopy when 50% VOAc was initially added to the copolymerization system. The VOAc content increased with conversion, indicating a gradient sequence distribution in the copolymer. Furthermore, the block copolymer composed of a poly( n BA- grad -VOAc) segment and a poly(VOAc) block was successfully synthesized when the copolymerization was performed under the VOAc-rich condition (77%) in the initial feed.