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

Abstract

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.

Mn2(CO)10-Induced RAFT Polymerization of Vinyl Acetate, Methyl Acrylate, and Styrene

“…A similar result was observed in the iodine transfer radical polymerization of VAc. 33,43,[49][50][51] The number-average molecular weights [M n (NMR)] calculated from the -(h=2) and !-end signals (j=2) to the mainchain VAc units (b) was 4100 and 4500, respectively, which were more or less lower than that by SEC [M n ðSECÞ ¼ 5000] based on the polystyrene calibration. The number-average endfunctionality (F n ) obtained from the M n (NMR) and M n (SEC) [F n = M n (SEC)/M n (NMR, -or !-end)] was close to unity for both the -and !-terminals: F n ðÞ ¼ 1:22 and F n ð!Þ ¼ 1:10.…”

RAFT Polymerization of Vinyl Esters: Synthesis and Applications

“…This can be achieved by playing on either steric hindrance or polar effects by using bulky [13][14][15] or polar [14,16] substituents. Use of specific solvents [17,18]-particularly fluoroalcohols [16,[19][20][21][22]-or addition of Lewis acids [23] constitute other options to induce higher syndiotacticities [19]. For these reasons, vinyl esters represent a large palette of monomers for creating materials with tuneable properties such as T g , T m , solubility (i.e., in scCO 2 ), alkaline resistance and tacticity.…”

Stereospecific living radical polymerization for simultaneous control of molecular weight and tacticity

“…17 On the other hand, the stereospecific radical polymerization of this monomer was achieved in bulky fluoroalcohols, such as (CF 3 ) 3 COH, to give the syndiotactic poly(VAc) and poly (vinyl alcohol) with a high melting temperature (T m ). 23 Thus, we investigated the iodine-transfer radical polymerization of VAc in various fluoroalcohols [(CF 3 ) 3 46 The polymers obtained in m-C 6 H 4 {C(CF 3 ) 2 OH} 2 showed an especially very narrow MWD (M w /M n $ 1.2) in comparison to that from the bulk iodine-transfer radical polymerization (M w /M n $ 1.5) as well as a high racemo content (r ¼ 59%) similar to that obtained without the iodide compound in the fluoroalcohol (Fig. 5).…”