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

Abstract

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(RCOCHCOR)2 (R1 = R2 = CH3 (1), R1 = CF3, R2 = CH3 (2), R1 = R2 = CF3 (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 (nBA), the copolymerization of nBA 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(nBA-co-VOAc) copolymers was determined by 1H 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(nBA-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.

Radical Polymerization of Vinyl Acetate with Bis(tetramethylheptadionato)cobalt(II): Coexistence of Three Different Mechanisms

“…The fluorinated analogues [Co-A C H T U N G T R E N N U N G (acac-F 3 )] (2; acac-F 3 = 1,1,1-trifluoropenta-2,4-dionato) and [CoA C H T U N G T R E N N U N G (acac-F 6 ) 2 ] (3; acac-F 6 = 1,1,1,5,5,5-hexafluoropenta-2,4-dionato) were investigated by Matyjaszewski et al for VAc and related monomers. [23,24] Whereas compound 2 exerts a level of control comparable to that of 1, compound 3 yields higher molecular weights and higher polydispersities.…”

Mechanistic Insights into the Cobalt‐Mediated Radical Polymerization (CMRP) of Vinyl Acetate with Cobalt(III) Adducts as Initiators

“…[28] This technique, known as cobalt-mediated radical polymerization (CMRP), allows poly(vinyl acetate) (PVAc) and poly(vinyl alcohol) (PVOH, merely upon hydrolysis) to be synthesized with a predetermined molecular weight, and to be constitutive components of block copolymers, which are very difficult to obtain by other techniques. [29][30][31][32] Well-defined statistical copolymers [33,34] could also be prepared and fullerene was successfully grafted by PVAc and PVOH. [35] Until recently, CMRP was explained by a reversible termination mechanism based on the homolytic cleavage of the terminal CoÀC bond.…”

Organometallic mediated radical polymerization of vinyl acetate with Fe(acac)2

“…All these results are consistent with a controlled polymerization, although the controllability is far from ideal when compared with that of reported for Co systems. 32,33,[35][36][37][38][39][40][41] When carried out under more diluted conditions (50% v/v in toluene, see Table 1, entries 6-8), the polymerization was expectedly much slower, reaching only a 34% conversion in 312 h. The molecular weights were once again higher than the theoretical ones, but now by a much smaller factor relative to the bulk experiment, indicating improved efficiency of the Fe(acac) 2 trapping agent. Hence, a greater fraction of the iron centers appear to play a role in the moderation of chain growth in the more dilute solution.…”