An official website of the United States government
ABSTRACT Electrochemically mediated atom transfer radical polymerizations (ATRPs) provide well‐defined polymers with designed dispersity as well as under external temporal and spatial control. In this study, 1‐cyano‐1‐methylethyl diethyldithiocarbamate, typically used as chain‐transfer agent (CTA) in reversible addition–fragmentation chain transfer (RAFT) polymerization, was electrochemically activated by the ATRP catalyst CuI/2,2′‐bipyridine (bpy) to control the polymerization of methyl methacrylate. Mechanistic study showed that this polymerization was mainly controlled by the ATRP equilibrium. The effect of applied potential, catalyst counterion, catalyst concentration, and targeted degree of polymerization were investigated. The chain‐end functionality was preserved as demonstrated by chain extension of poly(methyl methacrylate) withn‐butyl methacrylate and styrene. This electrochemical ATRP procedure confirms that RAFT CTAs can be activated by an electrochemical stimulus. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem.2019,57, 376–381
more »
« less
ATRP of N ‐Hydroxyethyl Acrylamide in the Presence of Lewis Acids: Control of Tacticity, Molecular Weight, and Architecture
Abstract Good control of tacticity, molecular weight, and architecture is attained via atom transfer radical polymerization (ATRP) ofN‐hydroxyethyl acrylamide (HEAA), in a one‐pot process in the presence of Y(OTf)3. The effect of temperature, ratio of [Y(OTf)3]/[HEAA], and ATRP procedure on the tacticity and degree of control over the polymerization is investigated in detail. Under optimal conditions, using photo ATRP and 15% Y(OTf)3,the content of meso dyads (m) can be increased from 42% to 80% in a homopolymer with a dispersityD = 1.22. Well‐defined stereoblock copolymers, atactic‐b‐isotactic poly(HEAA), withD = 1.27, are obtained by adding Y(OTf)3at a specific conversion, initially started without Y(OTf)3.
more »
« less
- Award ID(s):
- 1707490
- PAR ID:
- 10083435
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Macromolecular Rapid Communications
- Volume:
- 40
- Issue:
- 10
- ISSN:
- 1022-1336
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract We introduce the heterocumulene ligand [(Ad)NCC(tBu)]−(Ad=1‐adamantyl (C10H15),tBu=tert‐butyl, (C4H9)), which can adopt two forms, the azaalleneyl and ynamide. This ligand platform can undergo a reversible chelotropic shift using Brønsted acid‐base chemistry, which promotes an unprecedented spin‐state change of the [VIII] ion. These unique scaffolds are prepared via addition of 1‐adamantyl isonitrile (C≡NAd) across the alkylidyne in complexes [(BDI)V≡CtBu(OTf)] (A) (BDI−=ArNC(CH3)CHC(CH3)NAr), Ar=2,6‐iPr2C6H3) and [(dBDI)V≡CtBu(OEt2)] (B) (dBDI2−=ArNC(CH3)CHC(CH2)NAr). ComplexAreacts with C≡NAd, to generate the high‐spin [VIII] complex with a κ1‐N‐ynamide ligand, [(BDI)V{κ1‐N‐(Ad)NCC(tBu)}(OTf)] (1). Conversely,Breacts with C≡NAd to generate a low‐spin [VIII] diamagnetic complex having a chelated κ2‐C,N‐azaalleneyl ligand, [(dBDI)V{κ2‐N,C‐(Ad)NCC(tBu)}] (2). Theoretical studies have been applied to better understand the mechanism of formation of2and the electronic reconfiguration upon structural rearrangement by the alteration of ligand denticity between1and2.more » « less
-
Abstract Photolyses oftrans‐Fe(CO)3(P((CH2)n)3P) (n=10 (a), 12 (b), 14 (c), 16 (d), 18 (e)) in the presence of PMe3provide the first economical and scalable route to macrobicyclic dibridgehead diphosphines P((CH2)n)3P (1). These are isolated as mixtures ofin,in/out,outisomers that equilibrate with degeneratein,out/out,inisomers at 150 °C via pyramidal inversion at phosphorus. For the entire series, VT31P NMR data establish or boundKeq, rates, and activation parameters for a variety of phenomena, many of which involve homeomorphic isomerizations, topological processes by which certain molecules can turn themselves inside out (e. g.,in,in⇌out,out). This provides the first detailed mapping of such trends in homologous series of aliphatic bicyclic compounds XE((CH2)n)3EX with any type of bridgehead. Isomeric diborane adducts1 a,d ⋅ 2BH3are also characterized. Crystal structures ofout,out‐1 aandin,in‐1 a ⋅ 2BH3aid isomer assignments and reveal unusual cage conformations.more » « less
-
Abstract Reactions of (O=)PH(OCH2CH3)2and BrMg(CH2)mCH=CH2(4.9–3.2 equiv;m=4 (a), 5 (b), 6 (c)) give the dialkylphosphine oxides (O=)PH[(CH2)mCH=CH2]2(2 a–c; 77–81 % after workup), which are treated with NaH and then α,ω‐dibromides Br(CH2)nBr (0.49–0.32 equiv;n=8 (a′), 10 (b′), 12 (c′), 14 (d′)) to yield the bis(trialkylphosphine oxides) [H2C=CH(CH2)m]2P(=O)(CH2)n(O=)P[(CH2)mCH=CH2]2(3 ab′,3 bc′,3 cd′,3 ca′; 79–84 %). Reactions of3 bc′and3 ca′with Grubbs’ first‐generation catalyst and then H2/PtO2afford the dibridgehead diphosphine dioxides(4 bc′,4 ca′; 14–19 %,n′=2m+2);31P NMR spectra show two stereoisomeric species (ca. 70:30). Crystal structures of two isomers of the latter are obtained,out,out‐4 ca′and a conformer ofin,out‐4 ca′that features crossed chains, such that the (O=)P vectors appearout,out. Whereas4 bc′resists crystallization, a byproduct derived from an alternative metathesis mode, (CH2)12P(=O)(CH2)12(O=)P(CH2)12, as well as3 ab′and3 bc′, are structurally characterized. The efficiencies of other routes to dibridgehead diphosphorus compounds are compared.more » « less
-
Abstract Reaction of [CuH(PPh3)]6with 1 equiv. of Tl(OTf) results in formation of [Cu6TlH6(PPh3)6][OTf] ([1]OTf]), which can be isolated in good yields. Variable‐temperature1H NMR spectroscopy, in combination with density functional theory (DFT) calculations, confirms the presence of a rare Tl−H orbital interaction. According to DFT, the1H chemical shift of the Tl‐adjacent hydride ligands of[1]+includes 7.7 ppm of deshielding due to spin‐orbit effects from the heavy Tl atom. This study provides valuable new insights into a rare class of metal hydrides, given that[1][OTf]is only the third isolable species reported to contain a Tl−H interaction.more » « less
