Effect of the synthetic method and support porosity on the structure and performance of silica‐supported CuBr/pyridylmethanimine atom transfer radical polymerization catalysts. I. Catalyst preparation and characterization

Silica‐supported CuBr/pyridylmethanimine (PMI) complexes that facilitate the atom transfer radical polymerization of methyl methacrylate have been prepared and characterized. Four different synthetic routes, including multistep‐grafting (M1), two‐step‐grafting (M2), one‐pot (M3), and preassembled‐complex (M4) methods, have been evaluated on three different silica supports (mesoporous SBA15 with 48‐ and 100‐Å pores and nonporous Cab‐O‐Sil EH5). The resulting solids have been characterized by a battery of techniques, including thermogravimetric analysis/differential scanning calorimetry, FT‐Raman spectroscopy, ¹³C and ²⁹Si magic‐angle‐spinning and cross‐polarity/magic‐angle‐spinning spectroscopy, low‐temperature nitrogen physisorption, and elemental analysis. The combination of elemental analysis and spectroscopic results has indicated that a variety of different surface species likely exist for most catalysts, including copper species that are both monocoordinated and biscoordinated by PMI ligands, and PMI‐free copper bromide species interacting with the silica surface. M4 appears to give a material that has the smallest amount of the uncomplexed ligand (by FT‐Raman spectroscopy) and is, therefore, the most homogeneous. After M4, the metallation efficiency decreases in the order M2 ≥ M3 > M1, with M1 giving a material with a highly heterogeneous surface composition. The ligand loading on all the catalysts has been determined to be approximately 1 mmol/g of SiO₂, with Cab‐O‐Sil‐supported materials giving much higher ligand densities because of its lower surface area. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1367–1383, 2004     

One‐pot synthesis of block copolymers by ring‐opening polymerization and ultraviolet light‐induced ATRP at ambient temperature

We successfully synthesized poly(l ‐lactide)‐b‐poly (methyl methacrylate) diblock copolymers at ambient temperature by combining ultraviolet light‐induced copper‐catalyzed ATRP and organo‐catalyzed ring‐opening polymerization (ROP) in one‐pot. The polymerization processes were carried out by three routes: one‐pot simultaneous ATRP and ROP, one‐pot sequential ATRP followed by ROP, and one‐pot sequential ROP followed by ATRP. The structure of the block copolymers is confirmed by nuclear magnetic resonance and gel permeation chromatography, which suggests that the polymerization method is facile and attractive for preparing block copolymers. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 699–704     

Atom transfer radical polymerization of methyl methacrylate via reversibly supported catalysts on silica gel via self‐assembly

A reversible catalyst immobilization system via self‐assembly of hydrogen bonding between thymine anchored on silica gel support and 2,6‐diaminopyridine functionalized with a catalyst (copper bromide‐N,N,N′,N′‐tetraethyldiethylenetriamine (TEDETA) complex) was developed for the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA). At elevated temperatures, the hydrogen bonding disassociated and released the catalyst as free small molecules for catalysis, which effectively mediated a living polymerization of MMA, producing PMMA with controlled molecular weight and narrow molecular weight distribution (<1.3). At room temperature, the catalyst assembled on the silica gel support by hydrogen bonding, and thus could be recovered and reused for a second run of ATRP. The recovered catalyst still mediated a living polymerization of MMA with reduced activity (54–64%), but had much improved control of the polymerization. The resulting PMMA had molecular weights very close to theoretical vales. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 22–30, 2004     

Ring‐opening polymerization of ε‐caprolactone and L‐lactide from silica nanoparticles surface

Coating of silica nanoparticles by biocompatible and biodegradable polymers of ε‐caprolactone and L ‐lactide was performed in situ by ring‐opening polymerization of the cyclic monomers with aluminum, yttrium, and tin alkoxides as catalysts. Hydroxyl groups were introduced on the silica surface by grafting of a prehydrolyzed 3‐glycidoxypropyl trimethoxysilane to initiate a catalytic polymerization in the presence of metal alkoxides. In this manner, free polymer chains were formed to grafted ones, and the graft density was controlled by the nature of the metal and the alcohol‐to‐metal ratio. The grafting reaction was extensively characterized by spectroscopic techniques and quantified. Nanocomposites containing up to 96% of polymer were obtained by this technique. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1976–1984, 2004     

One‐Pot synthesis of functional poly(methacrylate) by ATRP and 1,8‐Diazacyclo‐[5,4,0]undec‐7‐ene catalyzed transesterification

A facile one‐pot 1,8‐diazacyclo‐[5,4,0]undec‐7‐ene (DBU) catalyzed transesterification/atom transfer radical polymerization (ATRP) strategy has been successfully developed through the combination of copper/DBU‐catalyzed ATRP and DBU‐catalyzed transesterification reactions. Well‐defined poly(methacrylate)s with various side ester groups have been synthesized by ATRP and transesterification of acyl donor 2,2,2‐trifluoethyl methacrylate with various alcohols, such as benzyl alcohol, n‐butanol, iso‐propyl alcohol, methanol, triethylene glycol monomethyl ether, propargyl alcohol, and 6‐azido‐1‐hexanol by the one‐pot process. Kinetic studies indicate that the ATRP process proceeded in a controllable manner without the interference of the transesterification reactions. Expansion of the binary system to a higher level ternary system has been successfully achieved by the combination of copper(I)‐catalyzed azide–alkyne cycloaddition, transesterification, and ATRP reactions. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2998–3003     

Atom transfer radical polymerization of n‐butyl acrylate from silica nanoparticles

This article reports the synthesis of atom transfer radical polymerization (ATRP) of active initiators from well‐defined silica nanoparticles and the use of these ATRP initiators in the grafting of poly(n‐butyl acrylate) from the silica particle surface. ATRP does not require difficult synthetic conditions, and the process can be carried out in standard solvents in which the nanoparticles are suspended. This “grafting from” method ensures the covalent binding of all polymer chains to the nanoparticles because polymerization is initiated from moieties previously bound to the surface. Model reactions were first carried out to account for possible polymerization in diluted conditions as it was required to ensure the suspension stability. The use of n‐butyl acrylate as the monomer permits one to obtain nanocomposites with a hard core and a soft shell where film formation is facilitated. Characterization of the polymer‐grafted silica was done from NMR and Fourier transform infrared spectroscopies, dynamic light scattering, and DSC. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4294–4301, 2001     

Graft copolymerization of butyl acrylate and 2‐ethyl hexyl acrylate from labile chlorines of poly(vinyl chloride) by atom transfer radical polymerization

Trace amounts of labile chlorines present in poly(vinyl chloride) (PVC) were found to act as initiation sites for the preparation of graft copolymers of PVC by copper‐mediated atom transfer radical polymerization (ATRP). High grafting yields were attained during the graft copolymerizations of n‐butyl acrylate (161.8%) and 2‐ethyl hexyl acrylate (51.2%) in 7.5 h. In both cases, the grafting proceeded with first‐order kinetics with respect to the monomer concentrations, this being typical for ATRP. Gel permeation chromatography traces of the resulting products did not exhibit additional peaks attributable to the formation of free homopolymers. The presented procedure offers an efficient means of preparing self‐plasticized PVC structures. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3457–3462, 2003     

Synthesis of well‐defined polymer brushes on the surface of zinc antimonate nanoparticles through surface‐initiated atom transfer radical polymerization

Zinc antimonate nanoparticles consisting of antimony and zinc oxide were surface modified in a methanol solvent medium using triethoxysilane‐based atom transfer radical polymerization (ATRP) initiating group (i.e.,) 6‐(2‐bromo‐2‐methyl) propionyloxy hexyl triethoxysilane. Successful grafting of ATRP initiator on the surface of nanoparticles was confirmed by thermogravimetric analysis that shows a significant weight loss at around 250–410 °C. Grafting of ATRP initiator onto the surface was further corroborated using Fourier transform Infrared spectroscopy (FT‐IR) and X‐ray photoelectron spectroscopy (XPS). The surface‐initiated ATRP of methyl methacrylate (MMA) mediated by a copper complex was carried out with the initiator‐fixed zinc antimonate nanoparticles in the presence of a sacrificial (free) initiator. The polymerization was preceded in a living manner in all examined cases; producing nanoparticles coated with well defined poly(methyl methacrylate) (PMMA) brushes with molecular weight in the range of 35–48K. Furthermore, PMMA‐grafted zinc antimonate nanoparticles were characterized using Thermogravimetric analysis (TGA) that exhibit significant weight loss in the temperature range of 300–410 °C confirming the formation of polymer brushes on the surface with the graft density as high as 0.26–0.27 chains/nm². The improvement in the dispersibility of PMMA‐grafted zinc antimonate nanoparticles was verified using ultraviolet‐visible spectroscopy and transmission electron microscopy. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

A new tetradentate ligand for atom transfer radical polymerization

The properties of a ligand, including molecular structure and substituents, strongly affect the catalyst activity and control of the polymerization in atom transfer radical polymerization (ATRP). A new tetradentate ligand, N,N′‐bis(pyridin‐2‐ylmethyl‐3‐hexoxo‐3‐oxopropyl)ethane‐1,2‐diamine (BPED) was synthesized and examined as the ligand of copper halide for ATRP of styrene (St), methyl acrylate (MA), and methyl methacrylate (MMA), and compared with other analogous linear tetrdendate ligands. The BPED ligand was found to significantly promote the activation reaction: the CuBr/BPED complex reacted with the initiators so fast that a large amount of Cu(II)Br₂/BPED was produced and thus the polymerizations were slow for all the monomers. The reaction of CuCl/BPED with the initiator was also fast, but by reducing the catalyst concentration or adding CuCl₂, the activation reaction could be slowed to establish the equilibrium of ATRP for a well‐controlled living polymerization of MA. CuCl/BPED was found very active for the polymerization of MA. For example, 10 mol% of the catalyst relatively to the initiator was sufficient to mediate a living polymerization of MA. The CuCl/BPED, however, could not catalyze a living polymerization of MMA because the resulting CuCl₂/BPED could not deactivate the growing radicals. The effects of the ligand structures on the catalysis of ATRP are also discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3553–3562, 2004     

Effects of molecular mass and surface treatment on adsorbed poly(methyl methacrylate) on silica

The behavior of relatively monodisperse adsorbed poly(methyl methacrylate) (PMMA) samples, from 19 to 587 kDa on silica, was studied using modulated differential scanning calorimetry and FTIR. On untreated Cab? O? Sil silica, the glass transition temperatures (T_gs) were higher (by around 30 °C), and the transitions were significantly broader (by a factor of 5–6) than those for the corresponding bulk samples. While the T_gs for the bulk polymers showed the expected dependence on molecular mass, the polymers on untreated silica showed little dependence, i.e., at the same adsorbed amounts, the glass transitions were very similar. The FTIR spectra of the adsorbed PMMA (on untreated silica) showed the presence of at least two resonances, one for the bound (hydrogen bonded to surface silanols) and another for free carbonyls. Fitting of the spectra allowed the estimation of the bound fractions of carbonyls that were dependent on the adsorbed amount, but not molecular mass. On Cab? O? Sil treated with hexamethyldisilizane (HMDS), the adsorbed PMMA exhibited glass transition behavior with little molecular‐mass dependence; the T_gs for the different PMMA samples were very similar to those of the high‐molecular mass bulk polymer, but with additional broadening of about a factor of 2. FTIR spectra for the PMMA samples on the treated silica did not show significant amounts of any of the hydrogen‐bonded carbonyl groups. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 649–658, 2008     

Click chemistry in materials synthesis. 1. Adhesive polymers from copper‐catalyzed azide‐alkyne cycloaddition

The copper(I)‐catalyzed cycloaddition reaction between azides and alkynes has been employed to make metal‐adhesive materials. Copper and brass surfaces supply the necessary catalytic Cu ions, and thus the polymerization process occurs selectively on these metals in the absence of added catalysts. Alternatively, copper compounds can be added to monomer mixtures and then introduced to reducing metal surfaces such as zinc to initiate polymerization. The resulting materials were found to possess comparable or superior adhesive strength to standard commercial glues, and structure‐activity correlations have identified several important properties of the monomers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4392–4403, 2004     

Synthesis of proton‐conducting membranes by the utilization of preirradiation grafting and atom transfer radical polymerization techniques

The atom transfer radical polymerization (ATRP) of styrene onto poly(vinylidene fluoride)‐graft‐poly(vinylbenzyl chloride) (PVDF‐g‐PVBC) membranes was investigated. Novel membranes were designed for fuel‐cell applications. The benzyl chloride groups in the PVDF‐g‐PVBC membranes functioned as initiators, and a Cu‐based catalytic system with the general formula Cu(n)X_n/ligand [where X is Cl or Br and the ligand is 2,2′‐bipyridyl (bpy)] was employed for the ATRP. In addition, 10 vol % dimethylformamide was added for increased solubility of the catalyst complex in styrene. The system was homogeneous, except for the membrane, when the initiator/copper halide/ligand/monomer molar ratio was 1/1/3/500. As anticipated, the fastest polymerization rate of styrene was observed with the copper bromide/bpy‐based catalyst system. The reaction rate was strongly temperature‐dependent within the studied temperature interval of 100–130 °C. The degree of grafting increased linearly with time, thereby indicating first‐order kinetics, regardless of the polymerization temperature. Furthermore, 120 °C was the maximum polymerization temperature that could be used in practice because the membrane structure was destroyed at higher temperatures. The degree of styrene grafting reached 400% after 3 h at 120 °C. Such a high degree of grafting could not be reached with conventional uncontrolled radiation‐induced grafting methods because of termination reactions. On the basis of an Arrhenius plot, the activation energy for the homogeneous ATRP of styrene was 217 kJ/mol. The prepared membranes became proton‐conducting after sulfonation of the polystyrene grafts. The highest conductivity measured for the prepared membranes was 70 mS/cm, which is comparable to the values normally measured for commercial Nafion membranes. The scanning electron microscopy/energy‐dispersive X‐ray results showed that the membranes had to be grafted through the matrix with both PVBC and polystyrene to become proton‐conducting after sulfonation. In addition, PVDF‐g‐[PVBC‐g‐(styrene‐block‐tert‐butyl acrylate)] membranes were also synthesized by ATRP. © 2002 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 591–600, 2002; DOI 10.1002/pola.10146     

Novel superhydrophobic silica/poly(siloxane‐fluoroacrylate) hybrid nanoparticles prepared via two‐step surface‐initiated ATRP: Synthesis,characterization, and wettability

Poly(siloxane‐fluoroacrylate)‐grafted silica hybrid nanoparticles were prepared by surface‐initiated atom transfer radical polymerization (SI‐ATRP). The silica nanoparticles with α‐bromo‐ester initiator group for copper‐mediated ATRP were prepared by the self‐assembled monolayers of (3‐aminopropyl)triethoxysilane and 2‐bromoisobutyrate bromide. Well‐defined diblock copolymer brushes consisting of poly(methacryloxypropyltrimethoxysilane) and poly(2,2,3,3,4,4,4‐heptafluorobutyl methacrylate) blocks were obtained by using initial homopolymer brushes as the macroinitiators for the SI‐ATRP of the second monomer. Chemical compositions and structures of the nanoparticles were characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, and gel permeation chromatography. Surface properties and morphology of the nanoparticles were investigated with X‐ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, and water contact angle measurement. It is revealed that the surfaces of the nanocomposites are rough at the microscale and nanoscale. The formation reason of the superhydrophobic surfaces was also discussed in this work. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Surface modification of polystyrene latex particles via atom transfer radical polymerization

The atom transfer radical polymerization (ATRP) technique using the copper halide/ N,N′,N′,N″,N″‐pentamethyldiethylenetriamine complex was applied to the graft polymerization of methyl methacrylate and methyl acrylate on the uniform polystyrene (PS) seed particles and formed novel core‐shell particles. The core was submicron crosslinked PS particles that were prepared via emulsifier‐free emulsion polymerization. The crosslinked PS particles obtained were transferred into the organic phase (tetrahydrofuran), and surface modification using the chloromethylation method was performed. Then, the modified seed PS particles were used to initiate ATRP to prepare a controlled poly(methyl methacrylate) (PMMA) and poly(methyl acrylate) (PMA) shell. The final core‐shell particles were characterized using Fourier transform infrared spectroscopy, nuclear magnetic resonance, scanning electron microscopy, thermogravimetric analysis, and elementary analysis. The grafting polymerization was conducted successfully on the surface of modified crosslinked PS particles, and the shell thickness and weight ratio (PMMA and PMA) of the particles were calculated. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 892–900, 2002; DOI 10.1002/pola.10160     

Iron halide mediated atom transfer radical polymerization of methyl methacrylate with N‐alkyl‐2‐pyridylmethanimine as the ligand

The controlled atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) catalyzed by iron halide/N‐(n‐hexyl)‐2‐pyridylmethanimine (NHPMI) is described. The ethyl 2‐bromoisobutyrate (EBIB)‐initiated ATRP with [MMA]₀/[EBIB]₀/[iron halide]₀/[NHPMI]₀ = 150/1/1/2 was better controlled in 2‐butanone than in p‐xylene at 90 °C. Initially added iron(III) halide improved the controllability of the reactions in terms of molecular weight control. The p‐toluenesulfonyl chloride (TsC1)‐initiated ATRP were uncontrolled with [MMA]₀/[TsC1]₀/[iron halide]₀/[NHPMI]₀ = 150/1/1/2 in 2‐butanone at 90 °C. In contrast to the EBIB‐initiated system, the initially added iron(III) halide greatly decreased the controllability of the TsC1‐initiated ATRP. The ration of iron halide to NHPMI significantly influenced the controllability of both EBIB and TsC1‐initiated ATRP systems. The ATRP with [MMA]₀/[initiator]₀/[iron halide]₀/[NHPMI]₀ = 150/1//1/2 provided polymers with PDIs ≥ 1.57, whereas those with [iron halide]₀/[NHPMI]₀ = 1 resulted in polymers with PDIs as low as 1.35. Moreover, polymers with PDIs of approximately 1.25 were obtained after their precipitation from acidified methanol. The high functionality of the halide end group in the obtained polymer was confirmed by both ¹H NMR and a chain‐extenstion reaction. Cyclic voltammetry was utilized to explain the differing catalytic behaviors of the in situ‐formed complexes by iron halide and NHPMI with different molar ratios. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4882–4894, 2004     

Photoinitiated atom transfer radical polymerization: Current status and future perspectives

In macromolecular and material science, atom transfer radical polymerization (ATRP) has intensely influenced the research strategies facilitating fabrication of a wide range of polymers with well‐defined structures and functions and their conjugation with biomolecules. Recently, the required copper (I) catalyst for ATRP process is generated by photoinduced redox reactions involving the in situ reduction of Cu(II) to Cu(I). Photochemically initiated reactions provide several distinct advantages, including temporal and spatial controls, rapid and energy efficient activation. The process is based on photoredox reactions of copper catalysts under various radiation sources with or without various photoinitiators. This Highlight focuses on the historical development, mechanistic aspects, limitations, and opportunities of photoinitiated ATRP along with selected examples. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2878–2888     

A Chaperonin as Protein Nanoreactor for Atom‐Transfer Radical Polymerization

The group II chaperonin thermosome (THS) from the archaea Thermoplasma acidophilum is reported as nanoreactor for atom‐transfer radical polymerization (ATRP). A copper catalyst was entrapped into the THS to confine the polymerization into this protein cage. THS possesses pores that are wide enough to release polymers into solution. The nanoreactor favorably influenced the polymerization of N‐isopropyl acrylamide and poly(ethylene glycol)methylether acrylate. Narrowly dispersed polymers with polydispersity indices (PDIs) down to 1.06 were obtained in the protein nanoreactor, while control reactions with a globular protein–catalyst conjugate only yielded polymers with PDIs above 1.84.     

Very rapid copper‐mediated atom transfer radical polymerization of benzyl methacrylate at ambient temperature

The ability to do very rapid bulk atom transfer radical polymerization (ATRP) of benzyl methacrylate using a CuX/PMDETA complex at room temperature was demonstrated in this study. The experimental conditions required to synthesize low‐ and high‐molecular‐weight poly(benzyl methacrylate) with low polydispersity are reported here. The controlled/living nature of the polymerization was demonstrated through kinetic studies, and chain‐extension studies. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1053–1057, 2004     

Novel superhydrophobic silica/poly(siloxane‐fluoroacrylate) hybrid nanoparticles prepared via surface‐initiated ATRP and their surface properties: The effects of polymerization conditions

A series of superhydrophobic poly(methacryloxypropyltrimethoxysilane, MPTS‐b‐2,‐2,3,3,4,4,4‐heptafluorobutyl methacrylate, HFBMA)‐grafted silica hybrid nanoparticles (SiO₂/PMPTS‐b‐PHFBMA) were prepared by two‐step surface‐initiated atom transfer radical polymerization (SI‐ATRP). Under the adopted polymerization conditions in our previous work, the superhydrophobic property was found to depend on the SI‐ATRP conditions of HFBMA. As a series of work, in this present study, the effects of polymerization conditions, such as the initiator concentration, the molar ratio of monomer and initiator, and the polymerization temperature on the SI‐ATRP kinetics and the interrelation between the kinetics and the surface properties of the nanoparticles were investigated. The results showed that the SI‐ATRP of HFBMA was well controlled. The results also showed that both the surface microphase separation and roughness of the hybrid nanoparticles could be strengthened with the increase of the molecular weight of polymer‐grafted silica hybrid nanoparticles. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Surface modification of thermally expandable microspheres by grafting poly(glycidyl methacrylate) using ARGET ATRP

This study demonstrates the surface modification of thermally expandable core/shell microspheres by grafting glycidyl methacrylate (GMA) using activators regenerated by electron transfer (ARGET) ATRP. To retain the expansion properties it was essential to minimize the shear forces, use solvents compatible with the microspheres and keep the reaction times short (three hours or less). Using microspheres with hydroxyl groups on the surface, it was found that after converting these to α-bromo esters, GMA could be grafted by ARGET ATRP using only 50 ppm of copper catalyst in toluene at 30 °C. Decent control of the polymerization was achieved with PMDETA as ligand reaching PDIs of 1.4 for the solution polymerization of GMA. When microspheres were present, the polymerization was less controlled with higher PDIs. The epoxide groups of the grafted microspheres were hydrolyzed by HCl in THF providing a hydrophilic surface of the microsphere. The expansion property of the microspheres was studied after each reaction step by thermal mechanical analysis, and it was found that the expansion capacity was well preserved with only limited negative effect on the microspheres.