How the interplay of different control mechanisms affects the initiator efficiency factor in controlled radical polymerization: An investigation using organometallic MoIII-based catalysts

Abstract

Compound CpMoI 2 (iPr 2 dad) (iPr 2 dad = iPrN@CHACH@NiPr), obtained by halide exchange from CpMoCl 2 (iPr 2 dad) and NaI, has been isolated and characterized by EPR spectroscopy, cyclic voltammetry, and X-ray crystallography. Its action as a catalyst in atom transfer radical polymerization (ATRP) and as a spin trap in organometallic radical polymerization (OMRP) of styrene and methyl acrylate (MA) monomers has been investigated and compared with that of the dichloro analogue. Compound CpMoCl 2 (iPr 2 dad) catalyzes the ATRP of styrene and MA with low efficiency factors f (as low as 0.37 for MA and ethyl 2-chloropropionate as initiator), while it irreversibly traps the corresponding growing radical chains under OMRP conditions. On the other hand, compound CpMoI 2 (iPr 2 dad) has a greater ATRP catalytic activity than the dichloro analogue and yields f = 1 for MA and ethyl 2-iodopropionate as initiator. Under OMRP conditions, it does not irreversibly trap the growing radical chains. This comparison serves to illustrate the general principle that low initiator efficiency factors, sometimes observed in ATRP, may result from the interplay of the ATRP and OMRP mechanisms, when the latter ones involves an irreversible radical trapping process.

ATRP/OMRP/CCT Interplay in Styrene Polymerization Mediated by Iron(II) Complexes: A DFT Study of the α‐Diimine System

“…This phenomenon is called catalytic chain transfer (CCT; Scheme ). Interplay of these three reaction pathways was demonstrated for a Mo system13–15 and other metal complexes, including osmium,16–17 chromium,18–20 vanadium,21, 22 and iron [23] have subsequently revealed an ATRP/OMRP interplay.…”

Controlled radical polymerization of vinyl acetate mediated by a vanadium complex

“…Organometallic mediated radical polymerization (OMRP) is based upon the lability of metalcarbon bonds under thermal or photolytic treatment, where the reversible formation of an organometallic dormant chain is in equilibrium with a lower oxidationstate metal complex and a polymeric radical. The OMRP process has been most thoroughly studied for cobalt-mediated radical polymerization, [3] and has also been implicated in molybdenum [4] and iron systems, [5] including significant study into the interplay between ATRP and OMRP in these systems. [6] For these CRP processes, vinyl acetate has proven to be a particularly challenging monomer to control [7] due to an imbalance between metal-halogen and carbon-halogen bond strengths in ATRP and strong metalcarbon bonds in OMRP.…”

Copper(I/II) and cobalt(II) coordination chemistry of relevance to controlled radical polymerization processes

“…Our group investigates the intimate details of coordination chemistry related to transition metal mediated CRP. We have developed a family of compounds capable of simultaneous control by ATRP and OMRP [9][10][11], rationalized the effect of certain Lewis acid promoters [12,13] and explained reason for the observation of low initiator efficiencies under certain conditions [14]. The possible interplay of various one-electron processes in CRP has been recently outlined in a review [2].…”