Designing functional aromatic multisulfonyl chloride initiators for complex organic synthesis by living radical polymerization

The similarities and differences between sulfonyl chloride and alkyl halide initiators for metal‐catalyzed living radical polymerizations are discussed. The differences in the rates of formation, reactivities, and reactions of primary radicals derived from sulfonyl halides and alkyl halides demonstrated the design principles for monosulfonyl and multisulfonyl chlorides that provided quantitative initiation and higher rates of initiation than of propagation. Multifunctional initiators with two, three, four, six, and eight sulfonyl chloride groups that produced perfect star polymers in 95% conversions were designed and synthesized on the basis of these principles. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4776–4791, 2000     

Living radical polymerization of diisopropyl fumarate to obtain block copolymers containing rigid poly(substituted methylene) and flexible polyacrylate segments

Living radical polymerizations of diisopropyl fumarate (DiPF) are carried out to synthesize poly(diisopropyl fumarate) (PDiPF) as a rigid poly(substituted methylene) and its block copolymers combined with a flexible polyacrylate segment. Reversible addition‐fragmentation chain transfer (RAFT) polymerization is suitable to obtain a high‐molecular‐weight PDiPF with well‐controlled molecular weight, molecular weight distribution, and chain‐end structures, while organotellurium‐mediated living radical polymerization (TERP) and reversible chain transfer catalyzed polymerization (RTCP) give PDiPF with controlled chain structures under limited polymerization conditions. In contrast, controlled polymerization for the production of high‐molecular‐weight and well‐defined PDiPF is not achieved by atom transfer radical polymerization (ATRP) and nitroxide‐mediated radical polymerization (NMP). The block copolymers consisting of rigid poly(substituted methylene) and flexible polyacrylate segments are synthesized by the RAFT polymerization. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2136–2147     

Novel catalyst system of MCl2/FeCl3·6H2O/PPh3 (M = Ni,Co, or Mn) for the atom transfer radical polymerization of methyl methacrylate

MCl₂ (M = Ni, Co, Sn, or Mn) and PPh₃ together acted as a catalyst for the radical polymerization of methyl methacrylate (MMA) in the presence of ethyl 2‐bromoisobutyrate as an initiator. The four systems all led to conventional radical polymerizations, which yielded polymers with a weight‐average molecular weight/number‐average molecular weight (M_w/M_n) ratio greater than 2.0 and became well controlled when a certain amount of FeCl₃·6H₂O was added. The polymerizations of MMA catalyzed by these four FeCl₃‐modified catalyst systems provided well‐defined polymers with low polydispersities (M_w/M_n < 1.28). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2625–2631, 2005     

Seleno‐containing poly(vinyl acetate) prepared by diselenocarbonates‐mediated controlled free radical polymerizations

The living free radical polymerizations of vinyl acetate (VAc) were successfully achieved in the presence of a novel organic selenium compound (diselenocarbonates), with 2,2′‐azobisisobutyronitrile (AIBN) as the initiator. The living characteristics of the VAc polymerization were confirmed by the linear first‐order kinetic plots and linear increase of molecular weights (M_n) of the polymers with monomer conversions, while keeping the relatively low molecular weight distributions. In addition, the end of the polymers contains selenium element which may be useful in biotechnological and biomedical applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3159–3165     

Synthesis of linear and starlike polymers from poly(propylene glycol) methacrylate using controlled radical polymerization

The copper‐catalyzed atom transfer radical polymerization (ATRP) of poly(propylene glycol) methacrylate (PPGM) in solution to produce linear and starlike polymers is reported, using methylethyl ketone as the solvent and a temperature of 80 °C. The ATRP system used was efficient for polymerization of the functionalized monomer without protecting hydroxyl end groups of monomer. The polymerizations were consistent with “living” or controlled processes, as revealed by the linear evolution of molecular weight with conversion. Increasing the [M]₀:[I]₀ ratio resulted in increasing molecular weights, whereas the polydispersity indices remained low (M_w/M_n < 1.4) even at high conversion. Decreasing the [CuBr]₀:[I]₀ ratio resulted in lower conversions, slightly larger polydispersities, and decreased molecular weights, likely resulting from a lower initiation efficiency. Polymers were characterized by ¹H and ¹³C NMR; molecular weights of polymers with low degrees of polymerization were estimated by end‐group analysis from ¹³C NMR spectra obtained using distortionless enhancement by polarization transfer and the gated decoupling techniques. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 334–343, 2002     

Iniferter concept and living radical polymerization

Iniferters are initiators that induce radical polymerization that proceeds via initiation, propagation, primary radical termination, and transfer to initiator. Because bimolecular termination and other transfer reactions are negligible, these polymerizations are performed by the insertion of the monomer molecules into the iniferter bond, leading to polymers with two iniferter fragments at the chain ends. The use of well‐designed iniferters would give polymers or oligomers bearing controlled end groups. If the end groups of the polymers obtained by a suitable iniferter serve further as a polymeric iniferter, these polymerizations proceed by a living radical polymerization mechanism in a homogeneous system. In these cases, the iniferters (C S bond) are considered a dormant species of the initiating and propagating radicals. In this article, I describe the history, ideas, and some characteristics of iniferters and living radical polymerization with some iniferters that contain dithiocarbamate groups as photoiniferters and several compounds as thermal iniferters. From the viewpoint of controlled polymer synthesis, iniferters can be classified into several types: thermal or photoiniferters; monomeric, polymeric, or gel iniferters; monofunctional, difunctional, trifunctional, or polyfunctional iniferters; monomer or macromonomer iniferters; and so forth. These lead to the synthesis of various monofunctional, telechelic, block, graft, star, and crosslinked polymers. The relations between this work and other recent studies are discussed. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2121–2136, 2000     

Polarons radical polymerization

Polystyrene has been typically prepared with radical polymerization by benzoyl peroxide (BPO) or azobisisobutyronitrile (AIBN). In this report, polymerization of styrene was carried out by radical cations of polyaniline (PANI). Polarons of conducting polymers are consisting of radical cations. The polarons bear electrical conduction as a charge carrier. We employ the polarons as an initiator for radical polymerization. Polymerization of styrene and acrylonitrile by the polarons was conducted to explore new possibility of conducting polymers. Fourier‐transfer infrared absorption (FTIR) spectroscopy measurements for the resultant polymers obtained with polarons of polyaniline indicates that the polystyrene thus synthesized grows from polyaniline. The qualitative solubility, average molecular weight, and thermal stability are comparable to that of polystyrene obtained by the common method with BPO. Radical polymerization by polarons may provide a new avenue for radical polymerizations through application of conducting polymer. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 805–811     

Immortal polymerization: The outset,development, and application

The story of the outset of the concept of immortal polymerization is presented. Immortal polymerization is the polymerization that gives polymers with a narrow molecular distribution, even in the presence of a chain transfer reaction, because of its reversibility, which leads to the revival of the polymers once dead, that is, the immortal nature of the polymers. As a result, immortal polymerization can afford polymers with a controlled molecular weight, the number of polymer molecules being more than that of the initiator. The compound that plays a leading role is metalloporphyrin, in which the metal‐axial ligand bond has an unusually high reactivity. Immortal polymerization can be carried out in the ring‐opening polymerizations of epoxides, episulfides, and lactones by the selection of an appropriate metalloporphyrin as the initiator and a protic compound as the chain transfer agent. Immortal polymerization is an effective method for synthesizing end‐functional polymers and oligomers with narrow molecular weight distributions. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2861–2871, 2000     

Atom transfer radical polymerization of n‐butyl methacrylate in an aqueous dispersed system: A miniemulsion approach

Ultrasonication was applied in combination with a hydrophobe for the copper‐mediated atom transfer radical polymerization of n‐butyl methacrylate in an aqueous dispersed system. A controlled polymerization was successfully achieved, as demonstrated by a linear correlation between the molecular weights and the monomer conversion. The polydispersities of the polymers were small (weight‐average molecular weight/number‐average molecular weight < 1.5). The influence of several factors, including ultrasonication, the amount of the surfactant, and the nature of the initiator, on the polymerization kinetics, molecular weight, and particle size was studied. The polymerization rate and molecular weights were independent of the number of particles and only depended on the atom transfer equilibrium. The final particle size, however, was a function of all the parameters. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4724–4734, 2000     

Controlled synthesis of functionalized polymers by transition‐metal‐mediated living radical polymerization

This paper discusses recent progress in transition‐metal‐catalyzed living radical polymerizations, partly focusing on the search of metal complex catalysts that play a critical role in controlling polymer molecular weights, then‐distributions, and architectures. Following a brief overview of the design of initiating systems (initiators and metal catalysts), half‐metallocene‐type complex catalysts are presented that induce living radical polymerizations of methacrylates, acrylates, and styrene to give markedly narrow molecular weight distributions and controlled molecular weights. Some of these halfmetallocenes also work in water where suspension living radical polymerization is feasible.     

Application of ketenes to well‐defined polyester synthesis. II. Synthesis of reactive polyester by living anionic polymerization of (4‐halophenyl)ethylketene

Novel ketenes, (4‐chlorophenyl)ethylketene and (4‐bromophenyl)ethylketene, were synthesized by dehydrochlorination of 2‐(4‐halophenyl)butanoyl chlorides, and their anionic polymerizations by lithium (4‐methoxyphenoxide) in tetrahydrofuran at ?20 °C were carried out to afford the corresponding polyesters with narrow molecular weight distributions (weight‐average molecular weight/number‐average molecular weight < 1.3) quantitatively. Polymerizations with various feed ratios afforded the corresponding polyesters with predictable molecular weights and narrow molecular weight distributions. Kinetic studies of the polymerizations at ?78 °C revealed that the polymerization rates were apparently larger than that of ethylphenylketene, which is considered to be responsible for the enhanced electrophilicities of the monomers via the introduction of electron‐negative halogen atoms. Monomer conversion agreed with the first‐order kinetic equation. These results strongly support the living mechanism of this polymerization. The obtained polyesters were modified by a palladium‐catalyzed coupling reaction of the side‐chain 4‐halophenyl group with 4‐methoxyphenylboronic acid, demonstrating their potential as reactive polymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2093–2102, 2001     

Arenesulfonyl bromides: The second universal class of functional initiators for the metal‐catalyzed living radical polymerization of methacrylates,acrylates, and styrenes

The metal‐catalyzed living radical polymerization of methyl methacrylate, n‐butyl acrylate, and styrene, initiated with p‐toluenesulfonyl bromide and phenoxybenzene‐4,4′‐disulfonyl bromide and catalyzed with CuBr/2,2′‐bipyridine (bpy) and various self‐regulated Cu‐based catalytic systems such as Cu₂O/bpy, Cu₂S/bpy, Cu₂Se/bpy, and Cu₂Te/bpy, is reported. Similarities and differences between the arenesulfonyl chloride and arenesulfonyl bromide initiators are discussed. The arenesulfonyl bromide initiators require reduced reaction times to produce polymers in high conversions under milder reaction conditions than the corresponding arenesulfonyl chloride initiators. At the same time, they exhibit 100% initiator efficiency and generate polymers with narrow molecular weight distributions and functional chain ends. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 319–330, 2005     

Sulfonic acids as water‐soluble initiators for cationic polymerization in aqueous media with Yb(OTf)3

Aqueous sulfonic acids (HOSO₂R; R = CH₃, Ph‐p‐CH₃, and Ph‐p‐NO₂), coupled with a water‐tolerant Lewis acid, ytterbium triflate [Yb(OTf)₃; OTf =  OSO₂CF₃], initiate the cationic suspension polymerization of p‐methoxystyrene (pMOS) in heterogeneous aqueous media. They induce controlled polymerization of pMOS at 30 °C, and the molecular weights of the polymers (weight‐average molecular weight/number‐average molecular weight ∼ 1.7) increase with conversion. These suspension polymerizations are initiated by the entry of sulfonic acid from the aqueous phase into the organic phase and proceed via reversible activation of the sulfonyl terminus by the Lewis acid. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2728–2733, 2000     

Simultaneous control of the stereospecificity and molecular weight in the ruthenium‐catalyzed living radical polymerization of methyl and 2‐hydroxyethyl methacrylates and sequential synthesis of stereoblock polymers

The stereospecific living radical polymerizations of methyl methacrylate (MMA) and 2‐hydroxyethyl methacrylate (HEMA) were achieved with a combination of ruthenium‐catalyzed living radical and solvent‐mediated stereospecific radical polymerizations. Among a series of ruthenium complexes [RuCl₂(PPh₃)₃, Ru(Ind)Cl(PPh₃)₂, and RuCp*Cl(PPh₃)₂], Cp*–ruthenium afforded poly(methyl methacrylate) with highly controlled molecular weights [weight‐average molecular weight/number‐average molecular weight (M_w/M_n) = 1.08] and high syndiotacticity (r = 88%) in a fluoroalcohol such as (CF₃)₂C(Ph)OH at 0 °C. On the other hand, a hydroxy‐functionalized monomer, HEMA, was polymerized with RuCp*Cl(PPh₃)₂ in N,N‐dimethylformamide and N,N‐dimethylacetamide (DMA) to give syndiotactic polymers (r = 87–88%) with controlled molecular weights (M_w/M_n = 1.12–1.16). This was the first example of the syndiospecific living radical polymerization of HEMA. A fluoroalcohol [(CF₃)₂C(Ph)OH], which induced the syndiospecific radical polymerization of MMA, reduced the syndiospecificity in the HEMA polymerization to result in more or less atactic polymers (mm/mr/rr = 7.2/40.9/51.9%) with controlled molecular weights in the presence of RuCp*Cl(PPh₃)₂ at 80 °C. A successive living radical polymerization of HEMA in two solvents, first DMA followed by (CF₃)₂C(Ph)OH, resulted in stereoblock poly(2‐hydroxyethyl methacrylate) with syndiotactic–atactic segments. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3609–3615, 2006     

Acrylonitrile‐containing polymers via a combination of metal‐catalyzed living radical and nitroxide‐mediated free‐radical polymerization routes

2‐Phenyl‐2‐[(2,2,6,6‐tetramethylpiperidino)oxy] ethyl 2‐bromopropanoate was successfully used as an initiator in consecutive living radical polymerization routes, such as metal‐catalyzed living radical polymerization and nitroxide‐mediated free‐radical polymerization, to produce various types of acrylonitrile‐containing polymers, such as styrene–acrylonitrile, polystyrene‐b‐styrene–acrylonitrile, polystyrene‐b‐poly(n‐butyl acrylate)‐b‐polyacrylonitrile, and polystyrene‐b‐polyacrylonitrile. The kinetic data were obtained for the metal‐catalyzed living radical polymerization of styrene–acrylonitrile. All the obtained polymers were characterized with ¹H NMR, gel permeation chromatography, and differential scanning calorimetry. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3374–3381, 2006     

New stage in living cationic polymerization: An array of effective Lewis acid catalysts and fast living polymerization in seconds

Our recent extensive research on Lewis acid catalysts with a weak base for the cationic polymerization of vinyl ethers led to unprecedented living reaction systems: fast living polymerization within 1–3 s; a wide choice of metal halides containing Al, Sn, Fe, Ti, Zr, Hf, Zn, Ga, In, Si, Ge, and Bi; and heterogeneously catalyzed living polymerization with Fe₂O₃. The use of added bases for the stabilization of the propagating carbocation and the appropriate selection of Lewis acid catalysts were crucial to the success of such new types of living polymerizations. In addition, the base‐stabilized living polymerization allowed the quantitative synthesis of star‐shaped polymers with a narrow molecular weight distribution via polymer‐linking reactions and the precision synthesis and self‐assembly of stimuli‐responsive block copolymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1801–1813, 2007.     

Universal xanthate‐mediated controlled free radical polymerizations of the “less activated” vinyl monomers

The living free radical polymerizations of three “less activated” monomers (LAMs), vinyl acetate, N‐vinylcarbazole, and N‐vinylpyrrolidone, were successfully achieved in the presence of a disulfide, isopropylxanthic disulfide (DIP), using 2,2′‐azoisobutyronitrile (AIBN) as the initiator. The living behaviors of polymerizations of LAMs are evidenced by first‐order kinetic plots and linear increase of molecular weights (M_ns) of the polymers with monomer conversions, while keeping the relatively low molecular weight distributions, respectively. The effects of reaction temperatures and molar ratios of components on the polymerization were also investigated in detail. The polymerization proceeded with macromolecular design via interchange of xanthate process, where xanthate formed in situ from reaction of AIBN and DIP. The architectures of the polymers obtained were characterized by GPC, ¹H NMR, UV–vis, and MALDI‐TOF‐MS spectra, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Iron‐mediated atom transfer radical polymerization of styrene with tris(3,6‐dioxaheptyl) amine as a ligand

The atom transfer radical bulk polymerization of styrene with FeX₂ (X = Br or Cl)/tris(3,6‐dioxaheptyl) amine as the catalyst system was successfully implemented at 110 °C. The number‐average molecular weight of the polymers with a narrow molecular weight distribution (weight‐average molecular weight/number‐average molecular weight = 1.2–1.5) increased linearly with the monomer conversion and matched the predicted molecular weight. The polymerization rate, initiation efficiency, and molecular weight distribution were influenced by the selection of the initiator and iron halide. The high functionality of the halide end group in the obtained polymers was confirmed by both ¹H NMR and a chain‐extension reaction. Because of its water solubility, the iron complexes could be removed easily from the reaction mixture through the washing of the polymerization mixture with water. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 483–489, 2006     

SET‐RAFT of MMA mediated by ascorbic acid‐activated copper oxide

In this work, cupric oxide (CuO) or cuprous oxide (Cu₂O) was used as the catalyst for the single electron transfer‐reversible addition‐fragmentation chain transfer (SET‐RAFT) polymerization of methyl methacrylate in the presence of ascorbic acid at 25 °C. 2‐Cyanoprop‐2‐yl‐1‐dithionaphthalate (CPDN) was used as the RAFT agent. The polymerization occurred smoothly after an induction period arising from the slow activation of CuO (or Cu₂O) and the “initialization” process in RAFT polymerization. The polymerizations conveyed features of “living”/controlled radical polymerizations: linear evolution of number‐average molecular weight with monomer conversion, narrow molecular weight distribution, and high retention of chain end fidelity. From the polymerization profile, it was deduced that the polymerization proceeded via a conjunct mechanism of single electron transfer‐living radical polymerization (SET‐LRP) and RAFT polymerization, wherein CPDN acting as the initiator for SET‐LRP and chain transfer agent for RAFT polymerization. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Single electron transfer‐living radical polymerization of methyl methacrylate in fluoroalcohol: Dual control over molecular weight and tacticity

The Cu(0)‐mediated single electron transfer‐living radical polymerization (SET‐LRP) of methyl methacrylate (MMA) using ethyl 2‐bromoisobutyrate (EBiB) as an initiator with Cu(0)/N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine as a catalyst system in 1,1,1,3,3,3‐hexafluoro‐2‐propanol (HFIP) was studied. The polymerization showed some living features: the measured number‐average molecular weight (M_n,GPC) increased with monomer conversion and produced polymers with relatively low polydispersities. The increase of HFIP concentration improved the controllability over the polymerization with increased initiation efficiency and lowered polydispersity values. ¹H NMR, MALDI‐TOF‐MS spectra, and chain extension reaction confirmed that the resultant polymer was end‐capped by EBiB species, and the polymer can be reactivated for chain extension. In contrast, in the cases of dimethyl sulfoxide or N,N‐dimethylformamide as reaction solvent, the polymerizations were uncontrolled. The different effects of the solvents on the polymerization indicated that the mechanism of SET‐LRP differed from that of atom transfer radical polymerization. Moreover, HFIP also facilitated the polymerization with control over stereoregularity of the polymers. Higher concentration of HFIP and lower reaction temperature produced higher syndiotactic ratio. The syndiotactic ratio can be reached to about 0.77 at 1/1.5 (v/v) of MMA/HFIP at ?18 °C. In conclusion, using HFIP as SET‐LRP solvent, the dual control over the molecular weight and tacticity of PMMA was realized. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6316–6327, 2009