Cuso₄ -amine redox-initiated radical polymerization of methyl methacrylate mediated by a CuCl₂ complex: Homogeneous reverse ATRP

Abstract

Kinetic results of CuSO4/2,2'‐bipyridine(bPy)‐amine redox initiated radical polymerization of methyl methacrylate (MMA) at 70 to 90 °C in dimethylsulfoxide suggest that such initiation is characteristic of a slow rate and a low initiator efficiency, but tertiary amines exhibit a relatively higher rate. UV‐Vis spectroscopy confirms the alpha‐amino functionality of PMMA chains. CuCl2/bPy successfully mediates the redox‐initiated radical polymerization of MMA with aliphatic tertiary amines in a fashion of slow‐initiated reverse atom transfer radical polymerization (ATRP), i.e. both the initiator efficiency of aliphatic tertiary amines and the average molecular weight of PMMA increase gradually, while the molecular weight distribution remains narrow but become broader with the conversions. As the PMMA chains contain alpha amino and omega C‐Cl moieties, UV‐induced benzophenone‐initiated radical polymerization and CuICl/bPy‐catalyzed ATRP initiated from PMMA lead to block copolymers from terminal functionalities. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 2562‐2578

Ultra-High Molecular Weight Alpha-Amino Poly(Methyl Methacrylate) with HighTgthrough Emulsion Polymerization by Using Transition Metal Cation-Tertiary Amine Pairs as a Mono-Centered Initiator

“…Various oxidizing agents, such as transition metal cations in super‐normal (such as Cu 3+ in highly alkaline media) or high oxidation state (such as Cu 2+ in alkaline media and Ce 4+ in acidic media, respectively), peroxides, and diarylketone under ultraviolet (UV) irradiation, are able to oxidize low molecular weight tertiary amines to aminoalkyl radicals to initiate polymerization of electron‐deficient monomers such as (meth)acrylates, (meth)acrylamides, acrylonitrile . When used as a reducing agent, tertiary amines are oxidized by peroxides to carbon‐centered primary aminoalkyl radicals alpha adjacent to nitrogen (C alpha radicals) via a sequential electron‐transfer followed by proton‐transfer (ET–PT) process, and peroxides generate acyoyl or alkyoyl radicals, i.e., they undergo a dual‐centered radical initiation process .…”

Cu I -catalyzed aerobic oxidation of tertiary amines as chain initiation for radical polymerization of methyl methacrylate. Syndiotactic-rich alpha-amino PMMA via mono-centered initiation

“…The PMMA collected from 4 h to 12 h exhibited a M n,GPC of about 2.46 × 10 4 -2.82 × 10 4 g mol −1 and a PDI of 1.55-2.07. Thus, the CuCl 2 /bPy-based initiation efficiency, defined as the number of propagating PMMA chains generated per CuCl 2 /bPy molecule [17], gradually increased from 0.20 (4 h) to 0.50 (12 h) at 90 • C in air-saturated DMSO. Clearly, on the one hand, CuX 2 /bPy-TEA pairs formed radicals as the active species to initiate polymerization of MMA, in diametric contrast to the postulation that no active radicals results from CuX 2 /L-tertiary amine redox processes in AGET or ARGET ATRP using tertiary amines as the reducing agent to generate in-situ Cu I /L complexes [21], different from ATRP using aerobic oxidation of alcohols catalyzed by Cu I /L or Fe II /L complexes to aldehydes and ketones in a non-radical Scheme 4.…”

“…oxidizing TEA to primary radicals and then deactivate PMMA • radicals to dormant species, as sketched in Scheme 4. Cu II /bPy-TEA is rather slow (rate constant ≈ 1.7 L mol −1 h −1 at 90 • C in DMSO) [17], and deactivation of carbon-centered PMMA· propagating radicals by Cu II /bPy complexes with a X − ligand, i.e. (Cu II -X − )/bPy complexes, is quantitative (rate constant ≈10 5 -10 7 L mol −1 s −1 at 25 • C) [23].…”

“…So-obtained PMMA chains were anticipated to contain an alpha amino moiety per propagating radical as the residue of amine substrates, which could be used as a macro-sensitizer in UV-induced diarylketon-initiated radical polymerization [14].UV-induced BPinitiated radical polymerization of MA was performed to verify the as-proposed initiation mechanism, as illustrated in Scheme 2 (bottom part) [17]. Fig.…”

“…Recently, we have reported Cu II /L-amine (L: redox-inert ligand, such as bPy) mono-centered redox-initiated radical polymerization of MMA in dimethylsulfoxide (DMSO), as shown in Scheme 2 (top part) [17]. Although it generated only aminoalkyl radicals and led to 100% homogeneous alpha-amino functional PMMA, such Cu II /Lamine redox-initiation was characteristic of a low efficiency as the initiation efficiency of Cu II /L complexes was less than 30% after a 3-h reaction at 70 • C, i.e.…”