Homolytically weak metal-carbon bonds make robust controlled radical polymerizations systems for “less-activated monomers”

Abstract

This article is an account of work, mostly carried out in the authors' laboratory, on the use of organometallic compounds with homolytically fragile metal-carbon bonds as dormant species in the controlled radical polymerization of a variety of monomers in what is now universally called "organometallic-mediated radical polymerization" (OMRP). The article retraces a brief history of OMRP, shows how it can potentially intervene in every radical polymerization process based on atom transfer (ATRP), which is a more popular controlling method where the metal plays a catalytic role, and how it can be in competition with another catalyzed process involving chain transfer to monomer (CCT). It highlights the challenges of controlled radical polymerization in the area of the "less activated monomers" (LAMs) and particularly the problem of the monomer addition errors, demonstrating how ligand engineering and coordination chemistry constitute additional handles, not available to other moderating species, providing acceptable ad hoc solutions. It details how OMRP could achieve unsurpassed levels of control for two specific monomers: vinyl acetate (VAc) and vinylidene fluoride (VDF). Finally, it lays the principles for the development of efficient chain transfer catalysts for less activated monomers.

Aromatic Xanthates and Dithiocarbamates for the Polymerization of Ethylene through Reversible Addition–Fragmentation Chain Transfer (RAFT)

“…We decreased the concentration of CTAcompared to our previous work on 4 and 5,inwhich we used [CTA]/[AIBN] = 10:1 and 50 mg of AIBN. [13] All aromatic xanthates (6, 7)a nd dithiocarbamates (8)(9)(10)(11)(12) resulted in retardation, and acceptable polymerization rates could only be attained by reducing their concentrations. Figure 1a shows the ethylene conversion versus polymerization time for the respective xanthate systems in comparison to aconventional polymerization system with no CTA.…”

“…[7] Furthermore,p ropagating polyethylenyl radicals (PEC)a re very reactive.G enerating this reactive species through homolytic bond cleavage is difficult, which rules out RDRP techniques based on reversible termination (for example,n itroxide-mediated polymerization [8] or atomtransfer radical polymerization [9,10] ). [11,12] We recently showed the first successful reversible additionfragmentation chain-transfer (RAFT) polymerization of ethylene using alkyl xanthates [13] and organotellurium-mediated radical polymerization (TERP) of ethylene [14] under rather mild (for ethylene) polymerization conditions (200 bar, 70 8 8C). [11,12] We recently showed the first successful reversible additionfragmentation chain-transfer (RAFT) polymerization of ethylene using alkyl xanthates [13] and organotellurium-mediated radical polymerization (TERP) of ethylene [14] under rather mild (for ethylene) polymerization conditions (200 bar, 70 8 8C).…”

Cobalt(II) phenoxy‐imine complexes in radical polymerization of vinyl acetate: The interplay of catalytic chain transfer and controlled/living radical polymerization

“…In addition to catalytic CCTP, cobalt complexes have also shown a remarkable capability to achieve the controlled/living radical polymerization (C/LRP) of both conjugated vinyl monomers and unconjugated vinyl monomers . Cobalt(II) porphyrin complex, Co II (TMP) [Scheme (c)], was first reported to mediate the controlled/living radical polymerization (C/LRP) of methyl acrylate (MA) by Wayland et al Another milestone was attributed to Jérôme et al who used cobalt(II) acetylacetonate [Co II (acac) 2 , Scheme (d)] to control the VAc polymerization .…”

“…11,12 Recently, Engelis et al used the cobaloxime to unconjugated vinyl monomers. [16][17][18][19][20][21][22][23] Cobalt(II) porphyrin complex, Co II (TMP) [Scheme 1(c)], was first reported to mediate the controlled/living radical polymerization (C/LRP) of methyl acrylate (MA) by Wayland et al 24 Another milestone was attributed to Jérôme et al who used cobalt(II) acetylacetonate [Co II (acac) 2 , Scheme 1(d)] to control the VAc polymerization. 25 Afterward, several cobalt complexes were then applied to mediate controlled/living radical polymerization.…”

Fluoroalkyl Pentacarbonylmanganese(I) Complexes as Initiators for the Radical (co)Polymerization of Fluoromonomers

“…polymerization (RDRP) of VDF has been possible via iodine transfer polymerization (ITP) [3,[9][10][11][12][13] and, more recently, by reversible addition−fragmentation chain-transfer (RAFT) polymerization [14,15] and by organometallic-mediated radical polymerization (OMRP) [16,17]. Specifically, OMRP is based on the reversible trapping of the growing radical chain by a transition metal complex to generate an organometallic dormant species [18][19][20][21]. ITP and RAFT led to a loss of control once the inverted monomer additions led to the full conversion of the dormant species to the tail isomer, respectively PVDF T -I and PVDF T -xanthate, which are less easily reactivated than the corresponding PVDF H -I and PVDF H -xanthate species.…”