Iodine Transfer Radical Polymerization of Vinyl Acetate in Fluoroalcohols for Simultaneous Control of Molecular Weight, Stereospecificity, and Regiospecificity

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 [(CF 3 ) 3 COH, (CF 3 ) 2 CHOH, PhC(CF 3 ) 2 OH, m -C 6 H 4 {C(CF 3 ) 2 OH} 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- C 6 H 4 {C(CF 3 ) 2 OH} 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 CH 2 I(CO 2 Et) and an azo-initiator [2,2‘-azobis(4-methoxy-2,4-dimethylvaleronitrile)] at 20 °C. High molecular weight polymers ( M n > 7 × 10 4 ) 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.