High‐throughput experimentation in atom transfer radical polymerization: A general approach toward a directed design and understanding of optimal catalytic systems

High‐throughput experimentation (HTE) was successfully applied in atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) for the rapid screening and optimization of different reaction conditions. A library of 108 different reactions was designed for this purpose, which used four different initiators [ethyl 2‐bromoisobutyrate, methyl 2‐bromopropionate, (1‐bromoethyl)benzene, and p‐toluenesulfonyl chloride], five metal salts (CuBr, CuCl, CuSCN, FeBr₂, and FeCl₂), and nine ligands (2,2′‐bipyridine and its derivatives). The optimal reaction conditions for Cu(I) halide, CuSCN, and Fe(II) halide‐mediated ATRP systems with 2,2′‐bipyridine and its 4,4′‐dialkyl‐substituted derivatives as ligands were determined. Cu(I)‐mediated systems were better controlled than Fe(II)‐mediated ones under the examined conditions. A bipyridine‐type ligand with a critical length of the substituted alkyl group (i.e., 4,4′‐dihexyl 2,2′‐bipyridine) exhibited the best performance in Cu(I)‐mediated systems, and p‐toluenesulfonyl chloride and ethyl 2‐bromoisobutyrate could effectively initiate Cu(I)‐mediated ATRP of MMA, resulting in polymers with low polydispersities in most cases. Besides, Cu(I) halide‐mediated ATRP with 4,5′‐dimethyl 2,2′‐bipyridine as the ligand and p‐toluenesulfonyl chloride as the initiator proved to be better controlled than those with 4,4′‐dimethyl 2,2′‐bipyridine as the ligand, and polymers with much lower polydispersities were obtained in the former cases. This successful HTE example opens up a way to significantly accelerate the development of new catalytic systems for ATRP and to improve the understanding of structure–property relationships of the reaction systems. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1876–1885, 2004     

Synthesis and characterization of multifunctional polymers via atom transfer radical polymerization of N‐(ω′‐alkylcarbazolyl) methacrylates initiated by Ru(II) polypyridyl chromophores

A series of poly(N‐(ω′‐alkylcarbazoly) methacrylates) tris(bipyridine) Ru‐centered bifunctional polymers with good filming, thermal, and solubility properties were synthesized and characterized. Atom transfer radical polymerization (ATRP) of N‐(ω′‐alkylcarbazoly) methacrylates in solution was used, where Ru complexes with one and three initiating sites acted as metalloinitiators with NiBr₂(PPh₃)₂ as a catalyst. ATRP reaction conditions with respect to polymer molecular weights and polydispersity indices (PDI) of the target bifunctional polymers were examined. Electronic absorption and emission spectra of the resultant functional polymers provided evidence of chromophore presence within a single polymeric chain. The thermal properties of all polymers were also investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), and these analyses have indicated that these polymers possess higher thermal stabilities than poly(methyl methacrylate) (PMMA) obtained via free radical polymerization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6057–6072, 2005     

Synthesis of polypropylene graft copolymers by the combination of a polypropylene copolymer containing pendant vinylbenzene groups and atom transfer radical polymerization

This article discusses a facile and inexpensive reaction process for preparing polypropylene‐based graft copolymers containing an isotactic polypropylene (i‐PP) main chain and several functional polymer side chains. The chemistry involves an i‐PP polymer precursor containing several pendant vinylbenzene groups, which is prepared through the Ziegler–Natta copolymerization of propylene and 1,4‐divinylbenzene mediated by an isospecific MgCl₂‐supported TiCl₄ catalyst. The selective monoenchainment of 1,4‐divinylbenzene comonomers results in pendant vinylbenzene groups quantitatively transformed into benzyl halides by hydrochlorination. In the presence of CuCl/pentamethyldiethylenetriamine, the in situ formed, multifunctional, polymeric atom transfer radical polymerization initiators carry out graft‐from polymerization through controlled radical polymerization. Some i‐PP‐based graft copolymers, including poly(propylene‐g‐methyl methacrylate) and poly(propylene‐g‐styrene), have been prepared with controlled compositions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 429–437, 2005     

Molybdenum tetracarbonyl complexes with linear chain polyether‐containing Schiff base ligands and their reactivity in the polymerization of methyl methacrylate

Mo(CO)₆ was reacted with the Schiff base ligand obtained by condensation reaction of 2‐acetyl‐ or benzoylpyridine with poly(propylene glycol)bis(2‐aminopropyl ether) to obtain polymeric, dinuclear metal tetracarbonyl compounds. The long‐chain Schiff base complexes are highly soluble even in non‐polar solvents such as petroleum ether, diethyl ether and n‐hexane. These complexes, as free‐radical initiators, afforded methyl methacrylate polymerization in chlorinated solvents. Copyright © 2005 John Wiley & Sons, Ltd.     

Polymeric ruthenium bipyridine complexes: New potential materials for polymer solar cells

Methyl methacrylate‐containing bipyridine monomers were synthesized with a hydoxy‐functionalized bipyridine. The 4′‐methyl group of the 2,2′‐bipyridine was used to introduce hydoxy‐functionalized alkyl spacers of two different lengths. Two, different synthetic routes were applied for the preparation of the hydoxy‐functionalized bipyridine via a bromo‐(C₇ spacer) or a silylated‐(C₃ spacer) intermediate. A copolymer of poly(methyl methacrylate) with bipyridine units in the side chains was prepared by free‐radical copolymerization and characterized with ¹H NMR, ultraviolet–visible, and IR spectroscopy as well as gel permeation chromatography. The bipyridine units of the copolymer were reacted with ruthenium bipyridine precursors. The resulting graft copolymers displayed promising photophysical and electrochemical properties, opening interesting perspectives for applications in the field of solar‐cell devices. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 374–385, 2004     

Heteroarm H‐shaped terpolymers through click reaction

Heteroarm H‐shaped terpolymers, (polystyrene)(poly(methyl methacrylate))‐ poly(tert‐butyl acrylate)‐(polystyrene)(poly(methyl methacrylate)), (PS)(PMMA)‐PtBA‐(PMMA)(PS), and, (PS)(PMMA)‐poly(ethylene glycol)(PEG)‐(PMMA)(PS), through click reaction strategy between PS‐PMMA copolymer (as side chains) with an alkyne functional group at the junction point and diazide end‐functionalized PtBA or PEG (as a main chain). PS‐PMMA with alkyne functional group was prepared by sequential living radical polymerizations such as the nitroxide mediated (NMP) and the metal mediated‐living radical polymerization (ATRP) routes. The obtained H‐shaped polymers were characterized by using ¹H‐NMR, GPC, DSC, and AFM measurements. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1055–1065, 2007     

Cu(0)/2,6‐bis(imino)pyridines catalyzed single‐electron transfer‐living radical polymerization of methyl methacrylate initiated with poly(vinylidene fluoride‐co‐chlorotrifluoroethylene)

A series of 2,6‐bis(imino)pyridines, as common ligands for late transition metal catalyst in ethylene coordination polymerization, were successfully employed in single‐electron transfer‐living radical polymerization (SET‐LRP) of methyl methacrylate (MMA) by using poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) (P(VDF‐co‐CTFE)) as macroinitiator with low concentration of copper catalyst under relative mild‐reaction conditions. Well‐controlled polymerization features were observed under varied reaction conditions including reaction temperature, catalyst concentration, as well as monomer amount in feed. The typical side reactions including the chain‐transfer reaction and dehydrochlorination reaction happened on P(VDF‐co‐CTFE) in atom‐transfer radical polymerization process were avoided in current system. The relationship between the catalytic activity and the chemical structure of 2,6‐bis(imino)pyridine ligands was investigated by comparing both the electrochemical properties of Cu(II)/2,6‐bis(imino)pyridine and the kinetic results of SET‐LRP of MMA catalyzed with different ligands. The substitute groups onto N‐binding sites with proper steric bulk and electron donating are desirable for both high‐propagation reaction rate and C? Cl bonds activation capability on P(VDF‐co‐CTFE). The catalytic activity of Cu(0)/2,6‐bis(imino)pyridines is comparable with Cu(0)/2,2′‐bipyridine under the consistent reaction conditions. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4378–4388     

Mixed iridium(III) and ruthenium(II) polypyridyl complexes containing poly(ε‐caprolactone)‐bipyridine macroligands

A hydroxy‐functionalized bipyridine ligand was polymerized with ε‐caprolactone utilizing the controlled ring‐opening polymerization of ε‐caprolactone in the presence of stannous octoate. The resulting poly(ε‐caprolactone)‐containing bipyridine was characterized by ¹H NMR and IR spectroscopy, and gel permeation chromatography, as well as matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry, revealing the successful incorporation of the bipyridine ligand into the polymer chain. Coordination to iridium(III) and ruthenium(II) precursor complexes yielded two macroligand complexes, which were characterized by NMR, gel permeation chromatography, matrix‐assisted laser desorption/ionization time‐of‐flight MS, cyclic voltammetry, and differential scanning calorimetry. In addition, both photophysical and electrochemical properties of the metal‐containing polymers proved the formation of a trisruthenium(II) and a trisiridium(III) polypyridyl species, respectively. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4153–4160, 2004     

Uni‐molecular nanoparticles of poly(2‐oxazoline) showing tunable thermoresponsive behaviors

Herein, cylindrical molecular bottlebrushes grafted with poly(2‐oxazoline) (POx) as a shaped tunable uni‐molecular nanoparticle were synthesized via the grafting‐onto approach. First, poly(glycidyl methacrylate) (PGMA) backbones with azide pendant units were prepared via reversible addition fragmentation transfer (RAFT) polymerization followed by post‐modification. The degree of polymerization (DP) of the backbones was tuned in a range from 20 to 800. Alkynyl‐terminated POx side chains were synthesized by living cationic ring opening polymerization (LCROP) of 2‐ethyl‐2‐oxazoline (EtOx) and 2‐methyl‐2‐oxazoline (MeOx), respectively. The DP of side chains was varied between 20 and 100. Then, the copper‐catalyzed azide‐alkynyl cycloaddition (CuAAC) click chemistry was conducted with a feed ratio of [alkynyl]:[azide] = 1.2:1 to yield a series of brushes. Depending on the DP of side chains, the grafting density ranged between 47 and 85%. The resulting brushlike nanoparticles exhibited shapes of sphere, rod and worm. Aqueous solutions of PEtOx brushes demonstrated a thermoresponsive behavior as a function of the length of backbones and side chains. Surprisingly, it was found that the lower critical solution temperature of PEtOx brushes increased with a length increase of backbones. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 174–183     

Effect of ligand on the synthesis of star polymers by resorcinarene‐based ATRP initiators

The effect of the steric hindrance on the initiating properties of two multifunctional resorcinarene‐based initiators in atom transfer radical polymerization (ATRP) was studied by using Cu(I)‐complexes of three multidentate amine ligands in the polymerization of tert‐butyl acrylate and methyl methacrylate. These ligands are less sterically hindered and have higher activities in the catalysis of ATRP of (meth)acrylates than 2,2′‐bipyridine. The polymerizations were faster and more controlled than with the 2,2′‐bipyridyl catalyst, but the tendency for bimolecular coupling increased. Even though the initiator was octafunctional, the resulting star polymers had only four arms. This indicates that the steric hindrance arising from the conformations of the initiators determines the structure of the polymer, but the ligand noticeably affects the controllability of the polymerization © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3349–3358, 2005     

Catalytic effect of dimethyl sulfoxide in the Cu(0)/tris(2‐dimethylaminoethyl)amine‐catalyzed living radical polymerization of methyl methacrylate at 0–90 °C initiated with CH3CHClI as a model compound for α,ω‐di(iodo)poly(vinyl chloride) chain ends

A variety of conditions, including catalysts [CuCl, CuI, Cu₂O, and Cu(0)], ligands [2,2′‐bipyridine (bpy), tris(2‐dimethylaminoethyl)amine (Me₆‐TREN), polyethyleneimine, and hexamethyl triethylenetetramine], initiators [CH₃CHClI, CH₂I₂, CHI₃, and F(CF₂)₈I], solvents [diphenyl ether, toluene, tetrahydrofuran, dimethyl sulfoxide (DMSO), dimethylformamide, ethylene carbonate, dimethylacetamide, and cyclohexanone], and temperatures [90, 25, and 0 °C] were studied to assess previous methods for poly(methyl methacrylate)‐b‐poly(vinyl chloride)‐b‐poly(methyl methacrylate) (PMMA‐b‐PVC‐b‐PMMA) synthesis by the living radical block copolymerization of methyl methacrylate (MMA) initiated with α,ω‐di(iodo)poly(vinyl chloride). CH₃CHClI was used as a model for α,ω‐di(iodo)poly(vinyl chloride) employed as a macroinitiator in the living radical block copolymerization of MMA. Two groups of methods evolved. The first involved CuCl/bpy or Me₆‐TREN at 90 °C, whereas the second involved Cu(0)/Me₆‐TREN in DMSO at 25 or 0 °C. Related ligands were used in both methods. The highest initiator efficiency and rate of polymerization were obtained with Cu(0)/Me₆‐TREN in DMSO at 25 °C. This demonstrated that the ultrafast block copolymerization reported previously is the most efficient with respect to the rate of polymerization and precision of the PMMA‐b‐PVC‐b‐PMMA architecture. Moreover, Cu(0)/Me₆‐TREN‐catalyzed polymerization exhibits an external first order of reaction in DMSO, and so this solvent has a catalytic effect in this living radical polymerization (LRP). This polymerization can be performed between 90 and 0 °C and provides access to controlled poly(methyl methacrylate) tacticity by LRP and block copolymerization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1935–1947, 2005     

Cationic polymerization of isobutyl vinyl ether initiated with transition‐metal ate complexes

The cationic polymerization of isobutyl vinyl ether was examined with transition‐metal ate complexes with trityl cation as initiators. The initiators were generated by the reaction of triphenylmethyl chloride [trityl chloride (TrCl)] with ate complexes of Nb, Mo, and W with lithium cation, which were obtained in situ by the reaction of the transition‐metal halides with anionic reagents (organolithium or lithium amide). When the polymerization was initiated with a mixture of TrCl and Li⁺[NbH₅(NnBuPh)]^?, the resulting poly(isobutyl vinyl ether)s had narrow molecular weight distributions (weight‐average molecular weight/number‐average molecular weight = 1.13–1.20). Although the polymerization was supposed to be initiated by the electrophilic attack of the trityl cation, matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry analysis of the resulting poly(isobutyl vinyl ether)s revealed the presence of H at the α‐chain end. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2636–2641, 2006     

Side‐chain terpyridine polymers through atom transfer radical polymerization and their ruthenium complexes

Polymers containing side‐chain terpyridine ligands of well‐defined architectures and controllable molecular weights and molecular weight distributions are reported. These polymers were synthesized by the atom transfer radical polymerization (ATRP) of a newly synthesized terpyridine monomer with three functional initiators. The obtained polymers were characterized with ¹H NMR and gel permeation chromatography techniques. The efficiency of the ATRP technique and the overall control of the molecular characteristics of the polymers were demonstrated by a kinetic study of the polymerization reaction. Subsequently, the ruthenium(III)/ruthenium(II) complexation chemistry was employed for the attachment of bis(dodecyloxy)‐functionalized terpyridine moieties onto each side 2,2′:6′,2″‐terpyridine unit of the main polymeric backbone. Thus, the grafting approach was successfully combined with the metal–ligand coordination chemistry for the preparation of highly soluble polymeric complexes. The resulting complexes were fully characterized by means of ¹H NMR, gel permeation chromatography, and ultraviolet–visible spectroscopy. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4838–4848, 2005     

Side‐chain functionalized polymers containing bipyridine coordination sites: Polymerization and metal‐coordination studies

Monomers containing (trisbipyridine) ruthenium(II), (bisbipyridine) palladium(II), and heteroleptic ruthenium complexes were synthesized and polymerized via ruthenium‐catalyzed ring‐opening metathesis polymerization in nonpolar solvents. The solubility of the resulting polyelectrolytes in nonpolar solutions could be tuned by alkyl functionalization of the ligands around the metal centers. These polymers are the first polynorbornenes containing a 2,2′‐bipyridine‐based metal complex at each repeating unit and might be used in numerous applications, including luminescent and electroluminescent materials. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2973–2984, 2004     

Tailor‐made poly(ethyl acrylate) by atom transfer radical polymerization

Atom transfer radical polymerization (ATRP) of ethyl acrylate (EA) was carried out using different initiators, CuBr or CuCl as catalyst in combination with different ligands e.g., 2,2′‐bipyridine (bpy) and N,N,N′,N″N″‐pentamethyl diethylenetriamine (PMDETA). Use of PMDETA as ligand resulted in faster polymerization rate (95% conversion in 15 min) than those using bipyridine (～58% conversion in 10.5 h). This is due to the lower reduction potential of copper‐amine than that of copper‐bpy complex, resulting in higher rates of activation of dormant halides. Use of ethylene carbonate as solvent lead to faster polymerization rate and better control in polymerization when compared with p‐xylene as solvent. The reaction temperature had a positive effect on polymerization rate and the optimum reaction temperature was found to be 90 °C. An apparent enthalpy of activation of ～85 kJ/mol was determined for the ATRP of ethyl acrylate, corresponding to an enthalpy of equilibrium of ～64 kJ/mol. By judicious choice of the reaction parameters it was possible to tailor the end group of the final polymer. MALDI‐TOF‐MS analysis and the chain extension experiment of poly(ethyl acrylate) (PEA) prepared using bpy as ligand showed the presence of ? Br as the end group. On the contrary, when PMDETA was used as the ligand, the mass spectra analysis showed hydrogen terminated polymer as the major species towards the end of polymerization. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1661–1669, 2007     

Star polymers by ATRP of styrene and acrylates employing multifunctional initiators

Multifunctional initiators for atom transfer radical polymerization (ATRP) are prepared by converting ditrimethylolpropane with four hydroxyl groups, dipentaerythritol with six hydroxyl groups, and poly(3‐ethyl‐3‐hydroxymethyl‐oxetane) with ～11 hydroxyl groups to the corresponding 2‐bromoisobutyrates or 2‐bromopropionates as obtained by reaction with acid bromides. Star polystyrene (PS) is produced by using these macroinitiators and neat styrene in a controlled manner by ATRP at 110 °C, employing the catalytic system CuBr and bipyridine. M_n up to 51,000 associated with narrow molecular weight distributions (PDI < 1.1) are obtained with conversions up to 32%. Hydrolysis of the star‐PS leads to linear chains having the expected M_n values. The star‐PS polymers based on dipentaerythritol degrade thermally in nitrogen in a two‐step process in which the first low‐temperature step involves scission of the ester linkages and the second step corresponds to the normal PS degradation. Star poly(methyl acrylates) with various cores are likewise prepared in a controlled manner by ATRP of methyl acrylate in bulk and in solution at 60–80 °C with the 1,1,4,7,7‐pentamethyldiethylene triamine ligand. Under these conditions, higher conversions were possible still maintaining low PDI signaling controlled star growth. Multiarm stars of poly(n‐butyl acrylate) and poly(n‐hexyl acrylate) with controlled characteristics have also been prepared. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3748–3759, 2005     

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     

Thermoresponsive Poly(2‐oxazine)s

The monomers 2‐methyl‐2‐oxazine (MeOZI), 2‐ethyl‐2‐oxazine (EtOZI), and 2‐n‐propyl‐2‐oxazine (nPropOZI) were synthesized and polymerized via the living cationic ring‐opening polymerization (CROP) under microwave‐assisted conditions. pEtOZI and pnPropOZI were found to be thermoresponsive, exhibiting LCST behavior in water and their cloud point temperatures (T_CP) are lower than for poly(2‐oxazoline)s with similar side chains. However, comparison of poly(2‐oxazine) and poly(2‐oxazoline)s isomers reveals that poly(2‐oxazine)s are more water soluble, indicating that the side chain has a stronger impact on polymer solubility than the main chain. In conclusion, variations of both the side chains and the main chains of the poly(cyclic imino ether)s resulted in a series of distinct homopolymers with tunable T_CP.     

Comparative studies on miscibility and phase behavior of linear and star poly(2‐methyl‐2‐oxazoline) blends with poly(vinylidene fluoride)

The comparative studies on the miscibility and phase behavior between the blends of linear and star‐shaped poly(2‐methyl‐2‐oxazoline) with poly(vinylidene fluoride) (PVDF) were carried out in this work. The linear poly(2‐methyl‐2‐oxazoline) was synthesized by the ring opening polymerization of 2‐methyl‐2‐oxazoline in the presence of methyl p‐toluenesulfonate (MeOTs) whereas the star‐shaped poly(2‐methyl‐2‐oxazoline) was synthesized with octa(3‐iodopropyl) polyhedral oligomeric silsesquioxane [(IC₃H₆)₈Si₈O₁₂, OipPOSS] as an octafunctional initiator. The polymers with different topological structures were characterized by means of Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. It is found that the star‐shaped poly(2‐methyl‐2‐oxazoline) was miscible with poly(vinylidene fluoride) (PVDF), which was evidenced by single glass‐transition temperature behavior and the equilibrium melting‐point depression. Nonetheless, the blends of linear poly(2‐methyl‐2‐oxazoline) with PVDF were phase‐separated. The difference in miscibility was ascribed to the topological effect of PMOx macromolecules on the miscibility. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 942–952, 2006