Organometallic‐Mediated Radical Polymerization: Developing Well‐Defined Complexes for Reversible Transition Metal‐Alkyl Bond Homolysis

Smith, Kevin M.; McNeil, W. Stephen; Abd‐El‐Aziz, Alaa S.

doi:10.1002/macp.200900581

Cited by 52 publications

(17 citation statements)

References 83 publications

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“…This equilibrium is by itself capable of moderating a controlled chain growth in what is now universally known as organometallic-mediated radical polymerization (OMRP, Scheme 1). [9][10][11][12] However, the active chain R n C and the reduced complex L/Mt x may also engage in hydrogen-atom transfer from a b-CÀH bond to the metal, to yield a dead macromolecule with an unsaturated chain end (P n ) and a hydride complex (L/Mt x+1 ÀH), which can initiate a new chain upon hydrogen-atom transfer to a monomer. This phenomenon is called catalytic chain transfer (CCT; Scheme 1).…”

Section: Introductionmentioning

confidence: 99%

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

Poli

Shaver

2014

Chemistry A European J

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A DFT study of various model systems has addressed the interference of catalytic chain transfer (CCT) as a function of the R(2) substituent in the atom-transfer radical polymerization (ATRP) of styrene catalyzed by [FeCl2 (R(1) N=C(R(2))C(R(2))=NR(1))] complexes. All model systems used R(1) =CH3 in place of the experimental Cy and tBu substituents and 1-phenylethyl in place of the polystyrene (PS) chain. A mechanistic investigation of 1) ATRP activation, 2) radical trapping in organometallic-mediated radical polymerization (OMRP), and 3) pathways to the hydride CCT intermediate was conducted with a simplified system with R(2)=H. This study suggests that CCT could occur by direct hydrogen-atom transfer without any activation barrier. Further analysis of more realistic models with R(2)=p-C6 H4 F or p-C6 H4 NMe2 suggests that the electronic effect of the aryl para substituents significantly alters the ATRP activation barrier. Conversely, the hydrogen-atom-transfer barrier is essentially unaffected. Thus, the greater ATRP catalytic activity of the p-NMe2 system makes the background CCT process less significant. The DFT study also compares the [FeCl2 (R(1) N=C(R(2))=C(R(2))=NR(1))] systems with a diaminobis(phenolato) derivative for which the CCT process shows even greater accessibility but has less incidence because of faster ATRP chain growth and interplay with a more efficient OMRP trapping. The difference between the two systems is attributed to destabilization of the Fe(II) catalyst by the geometric constraints of the tetradentate diaminobis(phenolato) ligand.

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Section: Introductionmentioning

confidence: 99%

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

Poli

Shaver

2014

Chemistry A European J

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“…Organometallic‐mediated radical polymerization (OMRP) is an emergent controlled radical polymerization technique based on the reversible formation of a covalent bond between the growing polymer chains and an organometallic complex 1, 2. In particular, cobalt complexes3 have received the most interest as OMRP mediators and led to the so‐called cobalt‐mediated radical polymerization (CMRP) 4.…”

Section: Introductionmentioning

confidence: 99%

Characteristics of patients who refuse do‐not‐resuscitate orders upon admission to an acute palliative care unit in a comprehensive cancer center

Parsons

Cruz

Zhukovsky

et al. 2010

Cancer

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BACKGROUND: Refusal of appropriately indicated do-not-resuscitate (DNR) orders may cause harm and distress for patients, families, and the medical team. We conducted a retrospective study to determine the frequency and predictors of refusals of DNR in advanced cancer patients admitted to an acute palliative care unit. METHODS: A total of 2538 consecutive admissions were reviewed. Demographic and clinical characteristics from 200 consecutive patients with DNR orders and 100 consecutive patients who refused DNR were collected, and differences between the groups were determined by multivariate regression and recursive partitioning analysis. RESULTS: Of 2538 admissions, 2530 (99%) were appropriate for DNR discussion. Of the 2530 admissions, 2374 were unique patients, and 100 (4%) of 2374 refused DNR. Refusers had median (interquartile range, IQR) pain of 7 (4-9) versus 5 (3-8, P ¼ .0005), nausea of 2 (0-7) versus 1 (0-4, P ¼ .05), and dyspnea of 1 (0-5) versus 4 (0-7, P ¼ .002) as compared with DNR nonrefusers, respectively. Patients with hematological malignancies and advance directives had a lower DNR refusal risk (odds ratio [OR], 0.38; P ¼ .02, and OR, 0.36; P < .0001, respectively). Multivariate regression analysis revealed that patients with moderate-severe pain (OR, 3.19; P ¼ .002) and with no advance directives (OR, 2.94; P .001) had higher DNR refusal risk. There were more inpatient deaths among DNR nonrefusers (87 of 200 vs 1 of 100, P < .0001). Median (IQR) time from discharge to death was 18 (8-35) days for those with DNR orders and 85 (25-206) days for DNR refusers (P .0001). CONCLUSIONS: DNR refusal in patients admitted to the acute palliative care unit is low, more frequent in patients with more pain and nausea and no advance directives, and associated with longer survival. This study demonstrates possible predictors of complicated DNR discussions. Cancer 2010;116:3061-70.

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“…(2), Scheme 1) [51] or a degenerative transfer (DT) one (Eq. (3), Scheme 1) [53,54]. The latter is observed when the amount of radicals exceeds the amount of cobalt complex.…”

Section: Introductionmentioning

confidence: 98%

In situ bidentate to tetradentate ligand exchange reaction in cobalt-mediated radical polymerization

Kermagoret

Jérôme

Detrembleur

et al. 2015

European Polymer Journal

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a b s t r a c tOrganometallic-mediated radical polymerization (OMRP) has seen a significant growth in the last years notably due to the development of new metal complexes, especially cobalt derivatives. Despite of this, none of the reported complexes offers optimal control for monomers with very different reactivity, which somewhat limits the synthesis of copolymers. In order to expand the scope of cobalt-mediated radical polymerization (CMRP), we investigated an in situ ligand exchange reaction for modulating the properties of the cobalt complex at the polymer chain-end and adjusting the CACo bond strength involved in the control process. With the aim of improving the synthesis of poly(vinyl acetate)-b-poly (n-butyl acrylate) copolymers, bidentate acetylacetonate ligands, which impart high level of control to the polymerization of vinyl acetate (VAc), were replaced in situ at the PVAcAcobalt chain-end by tetradentate Salen type ligands that are more suited to acrylates.

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Organometallic‐Mediated Radical Polymerization: Developing Well‐Defined Complexes for Reversible Transition Metal‐Alkyl Bond Homolysis

Cited by 52 publications

References 83 publications

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

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

Characteristics of patients who refuse do‐not‐resuscitate orders upon admission to an acute palliative care unit in a comprehensive cancer center

In situ bidentate to tetradentate ligand exchange reaction in cobalt-mediated radical polymerization

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