An iron‐mediated reverse ATRP of methyl methacrylate (MMA) is successfully carried out in water in the absence of any dispersants, using a water‐soluble 2,2′‐azobis(2‐methylpropionamidine) dihydrochloride (V‐50) as the initiator and the stabilizer, and using an oil‐soluble N,N‐butyldithiocarbamate ferrum (Fe(S2CN(C4H9)2)3) as the catalyst without adding any additional ligands. Micron‐sized PMMA particles with UV light‐sensitive ‐S2CN(C4H9)2 end group are obtained, and monomer droplet nucleation and suspension polymerization mechanism are proposed. Polymerization results demonstrated typical “living”/controlled characteristics of ATRP: first‐order polymerization kinetics, linear increase of molecular weights with monomer conversion and narrow molecular weight distributions for the resultant PMMA particles. NMR spectroscopy and chain‐extension experiments under UV light irradiation confirm the attachment and livingness of UV light‐sensitive ‐S2CN(C4H9)2 group in the chain end.
A novel photo‐induced homogeneous atom transfer radical polymerization (ATRP) system is constructed using an organic copper salt (Cu(SC(S)N(C2H5)2)2) as a photo‐induced catalyst at 30 °C. Herein, N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine (PMDETA) is used as a ligand, ethyl 2‐bromophenylacetate (EBPA) as an ATRP initiator, and (2,4,6‐trimethylbenzoyl) diphenylphosphine oxide (TPO) as a photo‐induced radical initiator to establish an ICAR (initiators for continuous activator regeneration) ATRP using methyl methacrylate (MMA) as a modal monomer. The effect of the concentration of the organic copper on the polymerization is investigated in detail. It is found that well‐controlled polymerization can be obtained even with the amount of (Cu(SC(S)N(C2H5)2)2 decreasing to a 1.56 ppm level, with the molecular weight of the resultant polymers increasing linearly with monomer conversion while maintaining a narrow molecular weight distribution (/ < 1.3).
ATRP of 2‐(N,N‐dimethylamino)ethyl acrylate (DMAEA) was investigated using CuBr or CuCl with different multidentate ligands. The catalyst was found active for DMAEA polymerization when ligated with tris[2‐(N,N‐dimethylamino)ethyl]amine. Good control over molecular weight was achieved, but quaternization of the terminal monomeric/polymeric tertiary amine by the C Br group of polyDMAEA caused chain termination. Using a chloride‐based system helped to suppress chain termination. Amphiphilic poly(methyl acrylate)‐block‐polyDMAEA was synthesized using polyMA as a macroinitiator.
Molecular weights and polydispersities of polyDMAEA versus DMAEA conversion for different catalyst systems. 相似文献
A one‐pot procedure for the synthesis of hyperbranched polyethylenes tethered with ATRP initiating sites by chain walking ethylene copolymerization with an acrylate‐type ATRP inimer, 2‐(2‐bromoisobutyryloxy) ethyl acrylate (BIEA) is reported. Because of its ability to incorporate acrylate‐type comonomers and tolerance toward the α‐bromoester group, the chain walking Pd‐diimine catalyst, [(ArNC(Me) (Me)CNAr)Pd(CH3)(NCMe)]SbF6 (Ar = 2,6‐(iPr)2C6H3), allowed the successful synthesis of a series of hyperbranched copolymers tethered with 2‐bromoisobutyryl groups at different densities. These copolymers may serve as polyfunctional macroinitiators for the ATRP of functional monomers to further synthesize core‐shell structured functionalized copolymers with a hyperbranched polyethylene core grafted with side chains of the functional monomers.
A DFT study of various model systems has addressed the interference of catalytic chain transfer (CCT) as a function of the R2 substituent in the atom‐transfer radical polymerization (ATRP) of styrene catalyzed by [FeCl2(R1N?C(R2)?C(R2)?NR1)] complexes. All model systems used R1=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 R2=H. This study suggests that CCT could occur by direct hydrogen‐atom transfer without any activation barrier. Further analysis of more realistic models with R2=p‐C6H4F or p‐C6H4NMe2 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(R1N?C(R2)?C(R2)?NR1)] 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 FeII catalyst by the geometric constraints of the tetradentate diaminobis(phenolato) ligand. 相似文献
How to simply and efficiently separate and recycle catalyst has still been a constraint for the wide application of atom transfer radical polymerization (ATRP), especially for the polymerization systems with hydrophilic monomers because the polar functional groups may coordinate with transition metal salts, resulting in abundant catalyst residual in the resultant water‐soluble polymers. In order to overcome this problem, a latent‐biphasic system is developed, which can be successfully used for ATRP catalyst separation and recycling in situ for various kinds of hydrophilic monomers for the first time, such as poly(ethylene glycol) monomethyl ether methacrylate (PEGMA), 2‐hydroxyethyl methacrylate (HEMA), 2‐(dimethylamino)ethyl methacrylate (DMAEMA), N,N‐dimethyl acrylamide (DMA), and N‐isopropylacrylamide (NIPAM). Herein, random copolymer of octadecyl acrylate (OA), MA‐Ln (2‐(bis(pyridin‐2‐ylmethyl)amino)ethyl acrylate), and POA‐ran‐P(MA‐Ln) is designed as the macroligand, and heptane/ethanol is selected as the biphasic solvent. Copper(II) bromide (CuBr2) is employed as the catalyst, PEG‐bound 2‐bromo‐2‐methylpropanoate (PEG350‐Br) as the water‐soluble ATRP initiator and 2,2′‐azobis(isobutyronitrile) (AIBN) as the azo‐initiator to establish an ICAR (initiators for continuous activator regeneration) ATRP system. Importantly, well‐defined water‐soluble polymers are obtained even though the recyclable catalyst is used for sixth times.
Summary: Controlled polymerization of N‐isopropylacrylamide (NIPAAM) was achieved by atom transfer radical polymerization (ATRP) using ethyl 2‐chloropropionate (ECP) as initiator and CuCl/tris(2‐dimethylaminoethyl)amine (Me6TREN) as a catalytic system. The polymerization was carried out in DMF:water 50:50 (v/v) mixed solvent at 20 °C. The first order kinetic plot was linear up to 92% conversion. Controlled molecular weights up to 2.2 × 104 and low polydispersities (1.19) were obtained. The living character of the polymerization was also demonstrated by self‐blocking experiments. Block copolymers with N,N‐dimethylacrylamide (DMAAM) and 3‐sulfopropyl methacrylate (SPMA) were successfully prepared.
Molecular weights and polydispersities of polyNIPAAM versus NIPAAM conversion for two different degrees of polymerization. 相似文献
It is well known that the recently developed photoinduced metal‐free atom transfer radical polymerization (ATRP) has been considered as a promising methodology to completely eliminate transition metal residue in polymers. However, a serious problem needs to be improved, namely, large amount of organic photocatalysts should be used to keep the controllability over molecular weights and molecular weight distributions. In this work, a novel photocatalyst 1,2,3,5‐tetrakis(carbazol‐9‐yl)‐4,6‐dicyanobenzene (4CzIPN) with strong excited state reduction potential is successfully used to mediate a metal‐free ATRP of methyl methacrylate just with parts per million (ppm) level usage under irradiation of blue light emitting diode at room temperature, using ethyl α‐bromophenyl‐acetate as a typical initiator with high initiator efficiency. The polymerization kinetic study, multiple controlled “on–off” light switching cycle regulation, and chain extension experiment confirm the “living”/controlled features of this promising photoinduced metal‐free ATRP system with good molecular weight control in the presence of ppm level photocatalyst 4CzIPN.
A series of rare‐earth‐metal–hydrocarbyl complexes bearing N‐type functionalized cyclopentadienyl (Cp) and fluorenyl (Flu) ligands were facilely synthesized. Treatment of [Y(CH2SiMe3)3(thf)2] with equimolar amount of the electron‐donating aminophenyl‐Cp ligand C5Me4H‐C6H4‐o‐NMe2 afforded the corresponding binuclear monoalkyl complex [({C5Me4‐C6H4‐o‐NMe(μ‐CH2)}Y{CH2SiMe3})2] ( 1 a ) via alkyl abstraction and C? H activation of the NMe2 group. The lutetium bis(allyl) complex [(C5Me4‐C6H4‐o‐NMe2)Lu(η3‐C3H5)2] ( 2 b ), which contained an electron‐donating aminophenyl‐Cp ligand, was isolated from the sequential metathesis reactions of LuCl3 with (C5Me4‐C6H4‐o‐NMe2)Li (1 equiv) and C3H5MgCl (2 equiv). Following a similar procedure, the yttrium‐ and scandium–bis(allyl) complexes, [(C5Me4‐C5H4N)Ln(η3‐C3H5)2] (Ln=Y ( 3 a ), Sc ( 3 b )), which also contained electron‐withdrawing pyridyl‐Cp ligands, were also obtained selectively. Deprotonation of the bulky pyridyl‐Flu ligand (C13H9‐C5H4N) by [Ln(CH2SiMe3)3(thf)2] generated the rare‐earth‐metal–dialkyl complexes, [(η3‐C13H8‐C5H4N)Ln(CH2SiMe3)2(thf)] (Ln=Y ( 4 a ), Sc ( 4 b ), Lu ( 4 c )), in which an unusual asymmetric η3‐allyl bonding mode of Flu moiety was observed. Switching to the bidentate yttrium–trisalkyl complex [Y(CH2C6H4‐o‐NMe2)3], the same reaction conditions afforded the corresponding yttrium bis(aminobenzyl) complex [(η3‐C13H8‐C5H4N)Y(CH2C6H4‐o‐NMe2)2] ( 5 ). Complexes 1 – 5 were fully characterized by 1H and 13C NMR and X‐ray spectroscopy, and by elemental analysis. In the presence of both [Ph3C][B(C6F5)4] and AliBu3, the electron‐donating aminophenyl‐Cp‐based complexes 1 and 2 did not show any activity towards styrene polymerization. In striking contrast, upon activation with [Ph3C][B(C6F5)4] only, the electron‐withdrawing pyridyl‐Cp‐based complexes 3 , in particular scandium complex 3 b , exhibited outstanding activitiy to give perfectly syndiotactic (rrrr >99 %) polystyrene, whereas their bulky pyridyl‐Flu analogues ( 4 and 5 ) in combination with [Ph3C][B(C6F5)4] and AliBu3 displayed much‐lower activity to afford syndiotactic‐enriched polystyrene. 相似文献
Polymersomes that encapsulate a hydrophilic polymer are prepared by conducting biocatalytic atom transfer radical polymerization (ATRP) in these hollow nanostructures. To this end, ATRPase horseradish peroxidase (HRP) is encapsulated into vesicles self‐assembled from poly(dimethylsiloxane)‐block‐poly(2‐methyl‐2‐oxazoline) (PDMS‐b‐PMOXA) diblock copolymers. The vesicles are turned into nanoreactors by UV‐induced permeabilization with a hydroxyalkyl phenone and used to polymerize poly(ethylene glycol) methyl ether acrylate (PEGA) by enzyme‐catalyzed ATRP. As the membrane of the polymersomes is only permeable for the reagents of ATRP but not for macromolecules, the polymerization occurs inside of the vesicles and fills the polymersomes with poly(PEGA), as evidenced by 1H NMR. Dynamic and static light scattering show that the vesicles transform from hollow spheres to filled spheres during polymerization. Transmission electron microscopy (TEM) and cryo‐TEM imaging reveal that the polymersomes are stable under the reaction conditions. The polymer‐filled nanoreactors mimic the membrane and cytosol of cells and can be useful tools to study enzymatic behavior in crowded macromolecular environments.
Summary: The communication provides a novel and alternative route to generate chemically tethered binary polymer‐brush pattern through two‐step surface‐initiated atomic‐transfer radical polymerization (SI‐ATRP). Polymer brush‐1 was prepared by SI‐ATRP, passivated by a reaction with NaN3, and etched with UV irradiation through a transmission electron microscopy grid to create exposed sites for the subsequently attached initiator on which polymer brush‐2 was grown.
Schematic representation of the resultant binary polymer brush patterns. 相似文献
The reaction between K(1‐C5H9C9H6) and anhydrous LnCl3 (Ln=Sm, Yb) in the molar ratio of 2:1 in THF with subsequent treatment by Na‐K alloy afforded (1‐C5H9C9H6)2Ln‐(THF)n(Ln=Sm, n=1; Ln=Yb, n=2), while the reaction of Sml2 with K(1‐C5H9C9H6) in the molar ratio of 1:2 in THF gave the anionic complex K(1‐C5H9C9H6)3Sm(THF)3. The X‐ray structure of (1‐C5H9C9H6)2Yb(THF)2 showed that central metal Yb is coordinated by two cyclopentadienyl rings of 1‐cyclopentylindenyls and two oxygen atoms from two tetrahydrofuran molecules to form pseudo‐tetrahedral coordinate geometry. All these complexes are active for the polymerization of acrylonitrile. 相似文献