The simultaneous control of the tacticity and molecular weight of poly(vinyl acetate) during the radical polymerization of vinyl acetate (VAc) is reported for the first time. A series of fluoroalcohols [(CF3)3COH, (CF3)2CHOH, PhC(CF3)2OH, m-C6H4{C(CF3)2OH}2] were employed as solvents for the iodine transfer radical polymerization of VAc, in which the molecular weight of the resultant polymer was determined by the monomer-to-transfer agent ratio and its tacticity was controlled by the solvent. Among the fluoroalcohols, the use of fluorodiol, m-C6H4{C(CF3)2OH}2, not only led to a higher syndiotacticity (r ∼ 60%) but also improved the molecular weight control, resulting in narrow molecular weight distributions (MWD) (M w/M n ∼ 1.20) in the presence of CH2I(CO2Et) and an azo-initiator [2,2‘-azobis(4-methoxy-2,4-dimethylvaleronitrile)] at 20 °C. High molecular weight polymers (M n > 7 × 104) with a relatively narrow MWD (M w/M n < 1.6) were obtained with the same system. The content of the head-to-head linkages was obviously lower in the fluoroalcohols (∼0.8%) than in the bulk (∼1.2%). Thus, the fluoroalcohols not only led to a higher syndiotacticity but also improved the molecular weight control and the regiospecificity by suppressing the head-to-head propagation.

The highly active, versatile, and photoresponsive controlled/living radical polymerizations were developed using Mn 2 (CO) 10 coupled with an alkyl iodide initiator (R-I) under weak visible light. The photoinduced polymerization of vinyl acetate (VAc) proceeded very fast even at 40 °C with a catalytic amount of Mn 2 (CO) 10 (0.025 mol % of VAc or 5.0 mol % of R-I) and completed within a few hours to give the polymers with controlled molecular weights up to 10 5 . The controlled polymerization was photoresponsive; that is, the polymerization proceeded only during the lighting period while maintaining the controlled molecular weights for the entire period. This system was also effective in controlled radical polymerizations of conjugated monomers such as styrene and methyl acrylate in conjunction with an appropriate alkyl iodide initiator. The contributions of the metal-catalyzed and the degenerative iodine transfer processes were also examined by analyzing the model reactions.

A highly active manganese complex [Mn2(CO)10] efficiently induced the controlled/living radical copolymerizations of a conjugated polar vinyl monomer, methyl acrylate (MA), and an unconjugated nonpolar olefin, 1-hexene (1-Hex), in the presence of ethyl 2-iodoisobutyrate (EMA−I) as an initiator under weak visible light at 40 °C to give the copolymers with controlled molecular weights. The further use of protic fluoroalcohols as solvents enhanced the copolymerization without losing the molecular weight control to result in a high 1-Hex content up to 50 mol %, for which the predominant alternating sequences were confirmed by the 13C NMR analysis of the copolymers. The kinetic analysis of the copolymerizations revealed an increase in the reactivity of the MA-radical to the 1-Hex monomer in the fluoroalcohol [1/r MA = 0.49 in (CF3)2CHOH vs 0.081 in toluene], which can be attributed to the 1:1 hydrogen-bonding interaction between the MA unit and the fluoroalcohol as suggested by the 13C NMR analysis of the MA−fluoroalcohol mixtures [K assn = 2.21 L/mol for (CF3)2CHOH]. Thus, a combination of a highly active Mn2(CO)10 catalyst and a protic fluoroalcohol solvent is effective for the alternating controlled/living radical copolymerization of acrylic monomers and α-olefins.

The controlled/living radical polymerization of vinyl acetate (VAc) and its copolymerization with methyl acrylate (MA) were investigated in bulk or fluoroalcohols using manganese complex [Mn 2 (CO) 10 ] in conjunction with an alkyl iodide (RAI) as an initiator under weak visible light. The manganese complex induced the controlled/living radical polymerization of VAc even in the fluoroalcohols without any loss of activity. The RAI/Mn 2 (CO) 10 system was also effective for the copolymerization of MA and VAc, in which MA was consumed faster than VAc, and then the remaining VAc was continuously and quantitatively consumed after the complete consumption of MA. The 1 H and 13 C NMR analyses revealed that the obtained products are block copolymers consisting of gradient MA/VAc segments, in which the VAc content gradually increases, and homopoly(VAc). The use of fluoroalcohols as solvents increased the copolymerization rate, controllability of the molecular weights, and copolymerizability of VAc. The saponification of the VAc units in poly(MA-grad-VAc)block-poly(VAc) resulted in the corresponding poly(MA-co-c-lactone)-block-poly(vinyl alcohol) due to the intramolecular cyclization between the hydroxyl and neighboring carboxyl groups in the gradient segments.

A dinuclear manganese complex [Mn 2 (CO) 10 ] induced the controlled/living radical polymerization of various conjugated and unconjugated vinyl monomers including vinyl acetate, methyl acrylate, and styrene in conjunction with dithiocarbonyl compounds [R-SC(S)Z] under weak visible light at 40 C. The obtained polymers had controlled molecular weights, narrow molecular weight distributions, and well-defined chain-end groups originating from R-SC(S)Z, as indicated by SEC, 1 H NMR, and MALDI-TOF-MS analyses. The polymerization most probably proceeds via the reversible activation of the C-SC(S)Z bond by Á Mn(CO) 5 via the metal-catalyzed process and/or by the carbon-centered radical species via the additionfragmentation chain transfer (RAFT) process.KEY WORDS: Vinyl Acetate / Acrylate / Styrene / Living Radical Polymerization / RAFT Polymerization / Manganese Complex / Various aspects of the controlled/living radical polymerization have been significantly developed in this decade, including a variety of initiating systems, controllable monomers, polymer structures, fusion with other substances, and applications to functional materials. Among the numerous initiating systems, there are now three representatives in terms of wide applicability and good controllability; i.e., the nitroxide-mediated radical polymerization (NMP), 1,2 metal-catalyzed living radical polymerization or atom transfer radical polymerization (ATRP), [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] and reversible addition-fragmentation chain transfer (RAFT) 18 polymerization or macromolecular design via interchange of xanthate (MADIX). 19 Although the components and the mechanisms are different, they are all based on the reversible transient activation of the dormant covalent species into the growing radical species. However, each system has its own characteristics or features due to the differences, which suggests that the choice of initiating systems is important depending on the monomers, conditions, purposes, etc.The metal-catalyzed living radical polymerization or ATRP is one of the best methods in terms of the well-defined architecture of the polymers from a variety of conjugated monomers, such as methacrylates, acrylates, acrylamides, acrylonitrile, and styrenes. This polymerization is generally initiated by the carbon radical generated from the alkyl halide upon the activation of the carbon-halogen bond by the transition metal catalyst, and then proceeds via the metalcatalyzed reversible activation of the carbon-halogen terminal into the growing radical species. One growing polymer chain end is thus generated from one carbon-halogen bond, which can permit the well-defined polymer synthesis. Although various transition metals, such as ruthenium, 3 20 The choice of the metal complexes including metals and ligands as well as the halides is important for the precise control of the polymerizations depending on the monomers.In contrast, the RAFT/MADIX system with the dithiocarbonyl compounds [R-SC(S)Z] is one of the most widely applica...