Synthesis of starlike PtBA‐g‐PEO amphiphilic graft copolymer via highly efficient Cu‐catalyzed SET‐NRC reaction at ambient temperature

Two new amphiphilic star graft copolymers bearing hydrophobic poly(tert‐butyl acrylate) backbone and hydrophilic poly(ethylene oxide) (PEO) side chains with different molecular weights were synthesized by sequential reversible addition fragmentation chain transfer (RAFT) polymerization and single electron transfer‐nitroxide radical coupling (SET‐NRC) reaction under mild conditions. RAFT homopolymerization of tert‐butyl 2‐((2‐bromopropanoyloxy)methyl)acrylate was mediated by a four‐armed chain transfer agent in a controlled way to afford a well‐defined starlike backbone with a narrow molecular weight distribution (M_w/M_n = 1.26). The target poly(tert‐butyl acrylate)‐g‐PEO (PtBA‐g‐PEO) star graft copolymers were synthesized by SET‐NRC reaction between Br‐containing PtBA‐based starlike backbone and PEO end functionalized with 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) group using copper/N,N,N′,N′,N″‐pentamethyldiethylenetriamine as catalytic system at ambient temperature via grafting‐onto strategy. The critical micelle concentration values of the obtained amphiphilic star graft copolymers in aqueous media and brine were determined by fluorescence probe technique using pyrene as probe. Diverse micellar morphologies were formed by varying the content of hydrophilic PEO segment as well as the initial concentration of stock solution. In addition, poly(acrylic acid)‐g‐PEO double hydrophilic star graft copolymers were obtained by selective acidic hydrolysis of hydrophobic PtBA starlike backbone without affecting PEO side chains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

ATNRC and SET‐NRC synthesis of PtBA‐g‐PEO well‐defined amphiphilic graft copolymers

A series of new well‐defined amphiphilic graft copolymers containing hydrophobic poly(tert‐butyl acrylate) backbone and hydrophilic poly(ethylene oxide) side chains were reported. Reversible addition‐fragmentation chain transfer homopolymerization of tert‐butyl 2‐((2‐bromopropanoyloxy)methyl)acrylate was first performed to afford a well‐defined backbone with a narrow molecular weight distribution (M_w/M_n = 1.07). The target poly(tert‐butyl acrylate)‐g‐poly(ethylene oxide) (PtBA‐g‐PEO) graft copolymers with low polydispersities (M_w/M_n = 1.18–1.26) were then synthesized by atom transfer nitroxide radical coupling or single electron transfer‐nitroxide radical coupling reaction using CuBr(Cu)/PMDETA as catalytic system. Fluorescence probe technique was employed to determine the critical micelle concentrations (cmc) of the obtained amphiphilic graft copolymers in aqueous media. Furthermore, PAA‐g‐PEO graft copolymers were obtained by selective acidic hydrolysis of hydrophobic PtBA backbone while PEO side chains kept inert. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Heteroarm H‐shaped terpolymers through the combination of the Diels–Alder reaction and controlled/living radical polymerization techniques

Heteroarm H‐shaped terpolymers (PS)(PtBA)–PEO–(PtBA)(PS) and (PS)(PtBA)–PPO–(PtBA)(PS) [where PS is polystyrene, PtBA is poly(tert‐butyl acrylate), PEO is poly(ethylene oxide), and PPO is poly(propylene oxide)], containing PEO or PPO as a backbone and PS and PtBA as side arms, were prepared via the combination of the Diels–Alder reaction and atom transfer radical and nitroxide‐mediated radical polymerization routes. Commercially available PEO or PPO containing bismaleimide end groups was reacted with a compound having an anthracene functionality, succinic acid anthracen‐9‐yl methyl ester 3‐(2‐bromo‐2‐methylpropionyloxy)‐2‐methyl‐2‐[2‐phenyl‐2‐(2,2,6,6‐tetramethylpiperidin‐1‐yloxy)ethoxycarbonyl]propyl ester, with a Diels–Alder reaction strategy. The obtained macroinitiator with tertiary bromide and 2,2,6,6‐tetramethylpiperidin‐1‐oxy functional end groups was used subsequently in the atom transfer radical polymerization of tert‐butyl acrylate and in the nitroxide‐mediated free‐radical polymerization of styrene to produce heteroarm H‐shaped terpolymers with moderately low molecular weight distributions (<1.31). The polymers were characterized with ¹H NMR, ultraviolet, gel permeation chromatography, and differential scanning calorimetry. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3947–3957, 2006     

Synthesis of double hydrophilic poly(ethylene oxide)‐b‐poly(2‐hydroxyethyl acrylate) by single‐electron transfer–living radical polymerization

In this study, the polymerization of (2‐hydroxyethyl) acrylate (HEA), in polar media, using Cu(0)‐mediated radical polymerization also called single‐electron transfer–living radical polymerization (SET‐LRP) is reported. The kinetics aspects of both the homopolymerization and the copolymerization from a poly(ethylene oxide) (PEO) macroinitiator were analyzed by ¹H NMR. The effects of both the ligand and the solvent were studied. The polymerization was shown to reach very high monomer conversions and to proceed in a well‐controlled fashion in the presence of tris[2‐(dimethylamino)ethyl]amine Me6‐TREN and N, N,N′, N″, N″‐pentamethyldiethylenetriamine (PMDETA) in dimethylsulfoxide (DMSO). SET‐LRP of HEA was also led in water, and it was shown to be faster than in DMSO. In pure water, Me₆‐TREN allowed a better control over the molar masses and polydispersity indices than PMDETA and TREN. Double hydrophilic PEO‐b‐PHEA block copolymers, exhibiting various PHEA block lengths up to 100 HEA units, were synthesized, in the same manner, from a bromide‐terminated PEO macroinitiator. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

On the Reactivity of NHCtBuAuCl towards Rb6Cs6Si17: The First Gold-Silicon Cluster [(NHCtBuAu)6(η2-Si4)]Cl2·7NH3 and an Imide Capped Gold Triangle (NHCtBuAu)3NHCl

Crystals of the two new compounds (NHC^tBuAu)₃NHCl and [(NHC^tBuAu)₆(η²-Si₄)]Cl₂ · 7NH₃ could be isolated from the reaction of Rb₆Cs₆Si₁₇ with NHC^tBuAuCl in the presence of [2.2.2]-cryptand in liquid ammonia. Both compounds were characterized by single-crystal X-ray diffraction and crystallize trigonally without any alkali metals or chelating ligands. Additionally, the crystal of [(NHC^tBuAu)₆(η²-Si₄)]Cl₂ · 7NH₃ was further interpreted by means of ELF and NBO calculations. In the case of (NHC^tBuAu)₃NHCl, NMR experiments provided an exceptional insight into the reaction processes in solution and allowed for the detection of sequential precursors. In the class of capped gold triangles (NHC^tBuAu)₃NHCl impresses with its unique characteristics of being capped by an imide and bound to N-heterocyclic carbenes as ligands instead of the ubiquitously employed phosphines. The gold capped silicon tetrahedron [(NHC^tBuAu)₆(η²-Si₄)]Cl₂ · 7NH₃ represents the first known silicide-gold compound, as well as the first known functionalized Zintl anion, crystallized with a cationic central moiety.     

Synthesis and characterization of macroinitiator‐amino terminated PEG and poly(γ‐benzyl‐L‐glutamate)‐PEO‐poly(γ‐benzyl‐L‐glutamate) triblock copolymer

Macroinitiator‐amino terminated poly(ethylene glycol) (PEG) (NH₂‐PEO‐NH₂) was prepared by converting both terminal hydroxyl groups of PEG to more reactive primary amino groups. The synthetic route involved reactions of chloridize, phthalimide and finally hydrazinolysis. Furthermore, poly(γ‐benzyl‐L ‐glutamate)‐poly(ethylene oxide)‐poly(γ‐benzyl‐L ‐glutamate) (PBLG‐PEO‐PBLG) triblock copolymer was synthesized by polymerization of γ‐benzyl‐L ‐glutamate N‐carboxyanhydride (Bz‐L‐GluNCA) using NH₂‐PEO‐NH₂ as macroinitiator. The resultant NH₂‐PEO‐NH₂ and triblock copolymer were characterized by FT‐IR, ¹H‐NMR and gel permeation chromatography (GPC) techniques. The results demonstrated that the degree of amination of the NH₂‐PEO‐NH₂ could be up to 1.95. The molecular weight of the PBLG‐PEO‐PBLG triblock copolymer could be adjusted easily by controlling the molar ratio of Bz‐L ‐Glu NCA to the macroinitiator NH₂‐PEO‐NH₂. Copyright © 2004 John Wiley & Sons, Ltd.     

Encapsulation and release by star‐shaped block copolymers as unimolecular nanocontainers

A five‐arm star‐shaped poly(ethylene oxide) (PEO) with terminal bromide groups was used as a macroinitiator for the atom transfer radical polymerization of tert‐butyl acrylate (tBA), resulting in five‐arm star‐shaped poly(ethylene oxide)‐block‐poly(tert‐butyl acrylate) block copolymers. The polymerization proceeded in a controlled way using a copper(I)bromide/pentamethyl diethylenetriamine catalytic system in acetonitrile as solvent. The hydrolysis of the tBA blocks of the amphiphilic star‐shaped PEO‐b‐PtBA block copolymer resulted in dihydrophilic star structures. The encapsulation of the star‐block copolymers and their release properties in acid environment have been followed by UV‐spectroscopy and color changes, using the dye methyl orange as a hydrophilic guest molecule. Characterization of the structures has been done by ¹H NMR, size exclusion chromatography, MALDI‐TOF, and differential scanning calorimetry. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 650–660, 2008     

N‐Heterocyclic Carbenes and Imidazole‐2‐thiones as Ligands for the Gold(I)‐Catalysed Hydroamination of Phenylacetylene

Gold(I) complexes of 1‐[1‐(2,6‐dimethylphenylimino)alkyl]‐3‐(mesityl)imidazol‐2‐ylidene (C^Imine_R), 1,3‐dimesitylimidazol‐2‐ylidene (IMes) and of the corresponding thione derivatives (S^Imine_R and IMesS) were prepared and structurally characterised. The solid‐state structure of the C^Imine_R and S^Imine_R gold(I) complexes showed monodentate coordination of the ligand and a dangling imine group that could bind reversibly to the metal centre to stabilise otherwise unstable catalytic intermediates. Interestingly, reaction of C^Imine_tBu with [AuCl(SMe₂)] led to the formation of [(C^Imine_tBu)AuCl], which rearranges upon crystallisation into the unusual complex cation [(C^Imine_tBu)₂Au]⁺, with AuCl₂^? as the counterion. The activity of the gold complexes in the hydroamination of phenylacetylene with substituted anilines was tested and compared to control catalyst systems. The best catalytic performance was obtained with [(C^Imine_tBu)AuCl], with the exclusive formation of the Markovnikov addition product in excellent yield (>95 %) regardless of the substituents on aniline.     

Amphiphilic copolymers with poly(meth)acrylic acid chains “grafted from” caprolactone 2‐(methacryloyloxy)ethyl ester‐based backbone

Well‐defined amphiphilic graft copolymers containing hydrophilic poly((meth)acrylic acid) (PMAA) or poly(acrylic acid) (PAA) side chains with gradient and statistical distributions were synthesized. For this purpose, the hydroxy‐functionalized copolymers with various gradient degrees, in which 2‐(6‐hydroxyhexanoyloxy)ethyl (meth)acrylate units (caprolactone 2‐[methacryloyloxy]ethyl ester, CLMA) formed strong gradient with tert‐butyl acrylate (tBA), slight gradient copolymers with tert‐butyl (meth)acrylate (tBMA), and statistical copolymers with methyl (meth)acrylate (MMA) were modified to bromoester multifunctional macroinitiators, P(tBMA‐grad‐BrCLMA), P(BrCLMA‐grad‐tBA), and P(BrCLMA‐co‐MMA). In the next step, they were applied in controlled radical polymerization of tBMA and tBA yielding graft copolymers with various lengths of side chains as well as graft densities. Further, the tert‐butyl groups in copolymers were successfully removed via acidolysis in the presence of trifluoracetic acid, which caused transformation of the hydrophobic graft copolymers into amphiphilic ones with ability of self‐assembly for the future biomedical applications. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis,characterization, and bulk properties of amphiphilic copolymers containing fluorinated methacrylates from sequential copper‐mediated radical polymerization

The partly fluorinated monomers, 2,2,2‐trifluoroethyl methacrylate (3FM), 2,2,3,3,4,4,5,5‐octafluoropentyl methacrylate (8FM), and 1,1,2,2‐tetrahydroperfluorodecyl methacrylate (17FM) have been used in the preparation of block copolymers with methyl methacrylate (MMA), 2‐methoxyethyl acrylate (MEA), and poly(ethylene glycol) methyl ether methacrylate (PEGMA) by Atom Transfer Radical Polymerization. A kinetic study of the 3FM homopolymerization initiated with ethyl bromoisobutyrate and Cu(I)Br/N‐(n‐propyl)‐2‐pyridylmethanimine reveals a living/controlled polymerization in the range 80–110 °C, with apparent rate constants of 1.6 · 10⁻⁴ s⁻¹ to 2.9 · 10⁻⁴ s⁻¹. Various 3FM containing block copolymers with MMA are prepared by sequential monomer addition or from a PMMA macroinitiator in all cases with controlled characteristics. Block copolymers of 3FM and PEGMA resulted in block copolymers with PDI < 1.22, whereas block copolymers from 3FM and MEA have less controlled characteristics. The block copolymers based on MMA with 8FM and 17 FM have PDI's < 1.30. The glass transition temperatures of the block copolymers are dominated by the majority monomer, as the sequential monomer addition results in too short pure blocks to induce observable microphase separation. The thermal stability of the fluorinated poly((meth)acrylate)s in inert atmosphere is less than that of corresponding nonfluorinated poly((meth)acrylate)s. The presence of fluorinated blocks significantly increases the advancing water contact angle of thin films compared to films of the nonfluorinated poly((meth)acrylate)s. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 8097–8111, 2008     

One‐pot preparation of 3‐miktoarm star terpolymers via click [3 + 2] reaction

The preparation of 3‐miktoarm star terpolymers using nitroxide mediated radical polymerization (NMP), ring opening polymerization (ROP), and click reaction [3 + 2] are carried out by applying two types of one‐pot technique. In the first one‐pot technique, NMP of styrene (St), ROP of ε‐caprolactone (ε‐CL), and [3 + 2] click reaction (between azide end‐functionalized poly(ethylene glycol) (PEG‐N₃)/or azide end‐functionalized poly(methyl methacrylate) (PMMA‐N₃) and alkyne) are carried out in the presence of 2‐(hydroxymethyl)‐2‐methyl‐3‐oxo‐3‐(2‐phenyl‐2‐(2,2,6,6‐tetramethylpiperidin‐1‐yloxy)ethoxy) propyl pent‐4‐ynoate, 2 , as an initiator for 48 h at 125 °C (one‐pot/one‐step). As a second technique, NMP of St and ROP of ε‐CL were conducted using 2 as an initiator for 20 h at 125 °C, and subsequently PEG‐N₃ or azide end‐functionalized poly(tert‐butyl acrylate (PtBA‐N₃) was added to the polymerization mixture, followed by a click reaction [3 + 2] for 24 h at room temperature (one‐pot/two‐step). The 3‐miktoarm star terpolymers, PEG‐poly(ε‐caprolactone)(PCL)‐PS, PtBA‐PCL‐PS and PMMA‐PCL‐PS, were recovered by a simple precipitation in methanol without further purification. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3588–3598, 2007     

Reversible addition–fragmentation chain transfer synthesis of amidine‐based,CO2‐responsive homo and AB diblock (Co)polymers comprised of histamine and their gas‐triggered self‐assembly in water

Well‐defined homopolymers of pentafluorophenyl acrylate (PFPA) and AB diblock copolymers of N,N‐dimethylacrylamide (DMA) and poly(ethylene glycol) methyl ether acrylate (PEGA) with PFPA were prepared by reversible addition–fragmentation chain transfer (RAFT) radical polymerization. Three PFPA homopolymers of different molecular weights were reacted with the commercially available amidine and guanidine species histamine (HIS) dihydrochloride and L ‐arginine methyl ester (ARG) dihydrochloride in the presence of S‐methyl methanethiosulfonate to yield, quantitatively, the corresponding amidine and guanidine‐based acrylamido homopolymers. Both the HIS and ARG homopolymers are known to reversibly bind CO₂ with, in the case of the former, CO₂ fixation being accompanied with a switch from a hydrophobic to hydrophilic state. The RAFT synthesis of PFPA‐DMA and PEGA‐PFPA diblock copolymers yielded well‐defined materials with a range of molar compositions. These precursor materials were converted to the corresponding HIS and ARG block copolymers whose structure was confirmed using ¹H NMR spectroscopy. Employing a combination of dynamic light scattering and transmission electron microscopy, we demonstrate that the DMA‐HIS and PEGA‐HIS diblock copolymers are able to undergo reversible and cyclable self‐directed assembly in aqueous media using CO₂ and N₂ as the triggers between fully hydrophilic and amphiphilic (assembled) states. For example, in the case of the 54:46 DMA‐HIS diblock, aggregates with hydrodynamic diameters of about 40.0 nm are readily formed from the molecularly dissolved state. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Convenient synthesis of thermo‐responsive PtBA‐g‐PPEGMEMA well‐defined amphiphilic graft copolymer without polymeric functional group transformation

A series of well‐defined amphiphilic graft copolymers bearing hydrophobic poly(tert‐butyl acrylate) backbone and hydrophilic poly[poly(ethylene glycol) methyl ether methacrylate)] (PPEGMEMA) side chains were synthesized by sequential reversible addition fragmentation chain transfer (RAFT) polymerization and single‐electron‐transfer living radical polymerization (SET‐LRP) without any polymeric functional group transformation. A new Br‐containing acrylate monomer, tert‐butyl 2‐((2‐bromoisobutanoyloxy)methyl)acrylate (tBBIBMA), was first prepared, which can be homopolymerized by RAFT to give a well‐defined PtBBIBMA homopolymer with a narrow molecular weight distribution (M_w/M_n = 1.15). This homopolymer with pendant Br initiation group in every repeating unit initiated SET‐LRP of PEGMEMA at 45 °C using CuBr/dHbpy as catalytic system to afford well‐defined PtBBIBMA‐g‐PPEGMEMA graft copolymers via the grafting‐from strategy. The self‐assembly behavior of the obtained graft copolymers in aqueous media was investigated by fluorescence spectroscopy and TEM. These copolymers were found to be stimuli‐responsive to both temperature and ions. Finally, poly(acrylic acid)‐g‐PPEGMEMA double hydrophilic graft copolymers were obtained by selective acidic hydrolysis of hydrophobic PtBA backbone while PPEGMEMA side chains kept inert. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of ABCD 4‐miktoarm star polymers by combination of RAFT,ROP, and “Click Chemistry”

The ABCD 4‐miktoarm star polymers based on polystyrene (PS), poly(ε‐caprolactone) (PCL), poly(methyl acrylate) (PMA), and poly(ethylene oxide) (PEO) were synthesized and characterized successfully. Using the mechanism transformation strategy, PS with three different functional groups (i.e., hydroxyl, alkyne, and trithiocarbonate), PS‐HEPPA‐SC(S)SC₁₂H₂₅, was synthesized by the reaction of the trithiocarbonate‐terminated PS with 2‐hydroxyethyl‐3‐(4‐(prop‐2‐ynyloxy)phenyl) acrylate (HEPPA) in tetrahydrofuran (THF) solution. Subsequently, the ring‐opening polymerization (ROP) of ε‐caprolactone (CL) was carried out in the presence of stannous(II) 2‐ethylhexanoate and PS‐HEPPA‐SC(S)SC₁₂H₂₅, and then the PS‐HEPPA(PCL)‐SC(S)SC₁₂H₂₅ obtained was used in reversible addition‐fragmentation chain transfer (RAFT) polymerization of methyl acrylate (MA) to produce the ABC 3‐miktoarm star polymer, S(PS)(PCL)(PMA) carrying an alkyne group. The ABCD 4‐miktoarm star polymer, S(PS)(PCL)(PMA)(PEO) was successfully prepared by click reaction of the alkyne group on the HEPPA unit with azide‐terminated PEO (PEO‐N₃). The target polymer and intermediates were characterized by NMR, FTIR, GPC, and DSC. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6641–6653, 2008     

Cyclodimerization versus Polymerization of Methyl Methacrylate Induced by N‐Heterocyclic Carbenes: A Combined Experimental and Theoretical Study

The activation behavior of two N‐heterocyclic carbenes (NHCs), namely, 1,3‐bis(isopropyl)imidazol‐2‐ylidene(NHCiPr) and 1,3‐bis(tert‐butyl) imidazol‐2‐ylidene (NHCtBu), as organic nucleophiles in the reaction with methyl methacrylate (MMA) is described. NHCtBu allows the polymerization of MMA in DMF at room temperature and in toluene at 50 °C, whereas NHCiPr reacts with two molecules of MMA, forming an unprecedented imidazolium–enolate cyclodimer (NHCiPr/MMA=1:2). It is proposed that the reaction mechanism occurs by initial 1,4‐nucleophilic addition of NHCiPr to MMA, generating a zwitterionic enolate 2 , followed by addition of 2 to a second MMA molecule, forming a linear imidazolium–enolate 3 (NHCiPr/MMA=1:2). Proton transfer, generating intermediate 5 , followed by cyclization and release of methanol yielded the aforementioned zwitterionic cyclodimer 1:2 adduct 7 , the molecular structure of which has been established by NMR spectroscopy, X‐ray diffraction, and mass spectrometry. This unexpected difference between NHCtBu and NHCiPr in the reaction with MMA (polymerization and cyclodimerization, respectively) can be rationalized by using DFT calculations. In particular, the nature of the NHC strongly influences the cyclodimerization pathway, the cyclization of 5 and the release of methanol are the discriminating step and limiting step, respectively. In the case of NHCtBu, both steps are strongly disfavoured compared with that of NHCiPr (energetic difference of around 14 and 9 kcal mol^?1, respectively), preventing the cyclization mechanism from a kinetic viewpoint. Moreover, addition of a third molecule of MMA in the polymerization pathway results in a lower activation barrier than that of the limiting step in the cyclodimerization pathway (difference of around 14 kcal mol^?1), in agreement with the formation of polymethyl methacrylate (PMMA) by using NHCtBu as nucleophile.     

1,3‐Dipolar Cycloaddition of Diazo Compounds to Electron‐Deficient Alkenes: Kinetics and Mechanism of Formation of Dimethyl‐4,5‐dihydro‐1H‐pyrazol‐3,5‐dicarboxylate

1,3‐Dipolar cycloaddition of methyl diazoacetate to methyl acrylate was investigated by kinetic ¹Н NMR spectroscopy. It was established that the mechanism of the process includes parallel formation of trans‐ and cis‐dimethyl‐4,5‐dihydro‐3H‐pyrazol‐3,5‐dicarboxylates as a result of [3 + 2]‐cycloaddition of methyl diazoacetate to methyl acrylate; the corresponding rate constants were denoted k_1t and k_1c. The reaction rate of the isomerization of 3Н‐pyrazolines to 4,5‐dihydro‐1H‐pyrazol‐3,5‐dicarboxylate (3Н → 1Н‐pyrazoline rearrangement) was found to be sensitive to both the methyl acrylate (k_2t, k_2c) and 1Н‐pyrazoline concentrations (k_3t, k_3c). Kinetic analysis showed that the proposed scheme is valid for various reagent concentrations. The numerical solution of the system of differential equations corresponded to the reaction scheme and was used to determine the complete set of reaction rate constants (k (× 10⁵ M^–1·s^–1), 298 K; solvent, benzene‐d₆): k_1t = 2.3 ± 0.3, k_1c = 1.6 ± 0.2, k_2t = 1.1 ± 0.3, k_2c = 1.8 ± 0.5, k_3t = 1.2 ± 0.4, k_3c = 2.2 ± 0.7.     

Preparation of H‐shaped ABCAB terpolymers by atom transfer radical coupling

H‐shaped ABCAB terpolymers composed of polystyrene (PS) (A), poly(ethylene oxide) (PEO) (B), and poly(tert‐butyl acrylate) (PtBA) (C) were prepared by atom transfer radical coupling reaction using ABC star terpolymers as precursors, CuBr and N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) as catalysts, and nanosize copper as the reducing agent. The synthesis of 3‐miktoarm star terpolymer PS‐PEO‐(PtBA‐Br) involved following steps: (1) the preparation of PS with an active and an ethoxyethyl‐ptotected hydroxyl group at the same end; (2) the preparation of diblock copolymer PS‐b‐PEO with ethoxyethyl‐protected group at the junction point through the ring‐opening polymerization (ROP) of EO; (3) after de‐protection of ethoxyethyl group and further modification of hydroxyl group, tBA was polymerized by atom transfer radical polymerization using PS‐b‐PEO with 2‐bromoisobutyryl functional group as macroinitiator. The H‐shaped terpolymer could be successfully formed by atom transfer radical coupling reaction in the presence of small quantity of styrene, CuBr/PMDETA, and Cu at 90 °C. The copolymers were characterized by SEC, ¹H NMR, and FTIR in detail. The optimized coupling temperature is 90 °C. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 59–68, 2009     

Oxygen‐Triggered Switchable Polymerization for the One‐Pot Synthesis of CO2‐Based Block Copolymers from Monomer Mixtures

Switchable polymerization provides the opportunity to regulate polymer sequence and structure in a one‐pot process from mixtures of monomers. Herein we report the use of O₂ as an external stimulus to switch the polymerization mechanism from the radical polymerization of vinyl monomers mediated by (Salen)Co^III?R [Salen=N,N′‐bis(3,5‐di‐tert‐butylsalicylidene)‐1,2‐cyclohexanediamine; R=alkyl] to the ring‐opening copolymerization (ROCOP) of CO₂/epoxides. Critical to this process is unprecedented monooxygen insertion into the Co?C bond, as rationalized by DFT calculations, leading to the formation of (Salen)Co^III?O?R as an active species to initiate ROCOP. Diblock poly(vinyl acetate)‐b‐polycarbonate could be obtained by ROCOP of CO₂/epoxides with preactivation of (Salen)Co end‐capped poly(vinyl acetate). Furthermore, a poly(vinyl acetate)‐b‐poly(methyl acrylate)‐b‐polycarbonate triblock copolymer was successfully synthesized by a (Salen)cobalt‐mediated sequential polymerization with an O₂‐triggered switch in a one‐pot process.     

H‐shaped (ABCDE type) quintopolymer via click reaction [3 + 2] strategy

H‐shaped quintopolymer containing different five blocks: poly(ε‐caprolactone) (PCL), polystyrene (PS), poly(ethylene glycol) (PEG), and poly(methyl methacrylate) (PMMA) as side chains and poly(tert‐butyl acrylate) (PtBA) as a main chain was simply prepared from a click reaction between azide end‐functionalized PCL‐PS‐PtBA 3‐miktoarm star terpolymer and PEG–PMMA‐block copolymer with alkyne at the junction point, using Cu(I)/N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) as a catalyst in DMF at room temperature for 20 h. The H‐shaped quintopolymer was obtained with a number–average molecular weight (M_n) around 32,000 and low polydispersity index (M_w/M_n) 1.20 as determined by GPC analysis in THF using PS standards. The click reaction efficiency was calculated to have 60% from ¹H NMR spectroscopy. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4459–4468, 2008     

Synthese,spektroskopische Charakterisierung und Molekülstrukturen ausgewählter Lewis‐Basen‐Addukte der Alkalimetall‐tri(tert‐butyl)silylphosphanide

Synthesis, Spectroscopic Characterization, and Molecular Structures of Selected Lewis‐Base Adducts of the Alkali Metal Tri(tert‐butyl)silylphosphanides The metalation of tri(tert‐butyl)silylphosphane with butyllithium and the bis(trimethylsilyl)amides of sodium, potassium, and rubidium yields quantitatively the corresponding alkali metal tri(tert‐butyl)silylphosphanides, which crystallize after addition of appropriate Lewis‐bases as dimeric (DME)LiP(H)SitBu₃ ( 1 ), chain‐like (DME)NaP(H)SitBu₃ ( 2 ), monomeric ([18]Krone‐6)KP(H)SitBu₃ ( 3 ), and dimeric (TMEDA)_1.5RbP(H)SitBu₃ ( 4 ). The reaction of H₂PSitBu₃ with cesium bis(trimethylsilyl)amide at room temperature gives monocyclic and tetrameric cesium tri(tert‐butyl)silylphosphanide ( 5 ) with two additional coordinated CsN(SiMe₃)₂ molecules. At 80 °C this complex reacts with excess of phosphane to the tetrameric toluene adduct (η⁶‐Toluol)CsP(H)SitBu₃ ( 6 ) which contains a central Cs₄P₄‐heterocubane fragment. The constitution of these compounds was verified by X‐ray structure determinations.