The Mechanism and Thermodynamic Studies of CMRP: Different Control Mechanisms Demonstrated by Co^II(TMP), Co^II(salen*), and Co^II(acac)₂ Mediated Polymerization, and the Correlation of Reduction Potential, Equilibrium Constant, and Control Mechanism

Abstract

The mechanism study of cobalt mediated radical polymerization (CMRP) is performed with CoII(TMP), CoII(salen*), and CoII(acac)2 at 60 °C to demonstrate that the control of vinyl acetate radical polymerization is achieved via a degenerative transfer pathway when CoII(TMP) and CoII(salen*) are used but via a reversible termination process with equilibrium constant (Keq) equal to 1.4 × 106 m−1 when CoII(acac)2 is the mediator. Given by the measured Keq in CMRP with varied cobalt complexes and the reduction potential (E1/2) of the corresponding cobalt complexes, a linear correlation between log(Keq), and E1/2 is found and can be used to estimate the Keq of other CMRP systems. With the enriched database of Keq values, the control mechanisms of CMRP are quantitatively defined by CoII/CoIII equilibrium constant. The connection of reduction potential, equilibrium constant, and control mechanism would contribute to the in‐depth understanding of CMRP process.

Oxygen‐Triggered Switchable Polymerization for the One‐Pot Synthesis of CO2‐Based Block Copolymers from Monomer Mixtures

“…An [AIBN]/[Co II ] ratio of 7:1 could well balance the efficiency and polymerization control (see Figures S1 and S2 in the Supporting Information). The kinetic plots for the OMRP displayed good linearity and an initiation period of 310 min, which is typical for this system . Also, repeat experiments showed excellent reproducibility.…”

“…Thek inetic plots for the OMRP displayed good linearity and an initiation period of 310 min, which is typical for this system. [20] Also,r epeat experiments showed excellent reproducibility.E lectrospray ionization (ESI) mass analysis of low-molecular-weight (Salen)Co III ÀPVAc (M n = 2.1 kDa, = 1.05) was performed in methanol, wherein two main series of signals were observed in accordance with [CN(CH 3 ) 2 C(VAc) n ]Na + and [CN(CH 3 ) 2 C(VAc) n ]H + ,r espectively ( Figure 1a). This result suggests that the cyanoisopropyl radical generated from AIBN [CC(CH 3 ) 2 CN] predominantly adds to VA ca nd generates (Salen)Co III À(VAc) n ÀC(CH 3 ) 2 CN dormant species (Figure 2).…”

Oxygen‐Triggered Switchable Polymerization for the One‐Pot Synthesis of CO2‐Based Block Copolymers from Monomer Mixtures

“…The first step of the polymer synthesis consisted of the OMRP of VAc mediated by (Salen)Co II , with initiation by AIBN at 60 °C in bulk, following the protocol of Peng and co‐workers . The only difference consisted of running the polymerization in an autoclave rather than in regular glassware to facilitate the one‐pot switch to the ROCOP step, which requires operation under CO 2 pressure.…”

Highly effective organometallic‐mediated radical polymerization of vinyl acetate using alumina‐supported Co(acac)2 catalyst: A case study of adsorption and polymerization

“…In this regard, organometallic‐mediated radical polymerization (OMRP) techniques and more particularly cobalt‐mediated radical polymerization (CMRP) can be successfully applied to the control polymerization of vinyl acetate using cobalt complexes as the controlling agent. Depending on the reaction conditions, CMRP process follows a reversible termination pathway or a degenerate chain transfer pathway, which, in simplified form is shown in Scheme . In suggested mechanisms, the role of the cobalt center includes the reversible formation of Co–carbon covalent bond .…”

“…Another challenge involved in PVAc synthesis through CMPR method using Co(acac) 2 catalyst is about the long induction time at the beginning of the polymerization . Therefore, several attempts have been recently made to reduce the induction time and accelerate the polymerization.…”