“Living”/controlled free radical polymerization of MMA in the presence of cobalt(II) 2‐ethylhexanoate: A switch from RAFT to ATRP mechanism

Abstract

A metal complex, cobalt(II) 2‐ethylhexanoate (CEH), was added to the system of thermal‐initiated reversible addition‐fragmentation chain transfer (RAFT) polymerization of methyl methacrylate (MMA) with 2‐cyanoprop‐2‐yl 1‐dithionaphthalate (CPDN) as the RAFT agent at 115 °C. The polymerization rate was remarkably enhanced in the presence of CEH in comparison with that in the absence of CEH, and the increase of the CPDN concentration also accelerated the rate of polymerization. The polymerization in the concurrence of CPDN and CEH demonstrated the characters of “living”/controlled free radical polymerization: the number‐average molecular weights (Mn) increasing linearly with monomer conversion, narrow molecular weight distributions (Mw/Mn) and obtained PMMA end‐capped with the CPDN moieties. Meanwhile, CEH can also accelerate the rate of RAFT polymerization of MMA using the PMMA as macro‐RAFT agent instead of CPDN. Similar polymerization profiles were obtained when copper (I) bromide (CuBr)/N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine was used instead of CEH. Extensive experiments in the presence of butyl methacrylate, bis(cyclopentadienyl) cobalt(II) and cumyl dithionaphthalenoate were also conducted; similar results as those of MMA/CPDN/CEH system were obtained. A transition of the polymerization mechanism, from RAFT process without CEH addition to atom transfer radical polymerization in the presence of CEH, was possibly responsible for polymerization profiles. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5722–5730, 2007

Raft polymerization of MMA in the presence of ferrocene: A new way to realize the rate enhancement

“…Such a significant effect of Fe(Cp) 2 on the polymerization rate was out of our original expectation. If it was true that the CPDN acted as the ATRP initiator, Fe(Cp) 2 , which was a non‐ATRP catalyst, should not accelerate the polymerization according to the mechanism shift31 or the concurrent mechanism 34. Figure 2 indicates the dependence of the number‐average molecular weight ( M n,GPC ) and the polydispersion index (PDI = M w / M n ) on the monomer conversion at different concentrations of Fe(Cp) 2 .…”

“…Recently, our group reported the thermal initiation of RAFT polymerization of methyl methacrylate (MMA) and styrene29, 30, 46 with a relatively low rate of polymerization. We further reported an enhanced RAFT polymerization system, in which an ATRP catalyst, CuBr/PMDETA or cobalt(Π) 2‐ethyl hexanoate (CEH)31–33 was added to a common RAFT polymerization using thermal initiation method 31. It was discovered that after the addition of the metal salt, the polymerization rate was remarkably enhanced and the polymerization behavior was different from the RAFT process 31.…”

“…We further reported an enhanced RAFT polymerization system, in which an ATRP catalyst, CuBr/PMDETA or cobalt(Π) 2‐ethyl hexanoate (CEH)31–33 was added to a common RAFT polymerization using thermal initiation method 31. It was discovered that after the addition of the metal salt, the polymerization rate was remarkably enhanced and the polymerization behavior was different from the RAFT process 31. Based on the results, the polymerization mechanism possibly evolved from the RAFT into an ATRP process, in which CuBr/PMDETA (or CEH) acted as a catalyst and the RAFT agent (CPDN) functioned as an ATRP pseudohalogen initiator.…”

“…Based on the mechanism‐shift31 or concurrent mechanism,34 it has been commonly accepted that the common RAFT agent could serve as a pseudohalogen initiator in the presence of ATRP catalyst. In other words, it could be assumed that the polymerization rate and polymerization behavior would not change if a non‐ATRP catalyst was added into the RAFT system.…”

Mechanism study and molecular design in controlled/“living” radical polymerization

“…When a metal complex, cobalt (II) 2-ethylhexanoate (CEH), was added to the system of RAFT polymerization of MMA system, the polymerization rate was enhanced remarkably as indicated in Figure 14 [86]. The polymerization showed controlled characteristics with narrow molecular weight distribution.…”