Azobenzene‐based initiator for atom transfer radical polymerization of methyl methacrylate

2‐Bromopropionic acid 2‐(4‐phenylazophenyl)ethyl ester, 2‐bromopropionic acid 6‐(4‐phenylazophenoxy)hexyl ester (BPA₆), 2‐bromopropionic acid‐(4‐phenylazoanilide), and 2‐bromopropionic acid 4‐[4‐(2‐bromopropionyloxy)phenylazo]phenyl ester (BPPE) were used as initiators with monofunctional or difunctional azobenzene for the heterogeneous atom transfer radical polymerization of methyl methacrylate with a copper(I) chloride/N,N,N′,N″,N″‐pentamethyldiethylenetriamine catalytic system. The rates of polymerizations exhibited first‐order kinetics with respect to the monomer, and a linear increase in the number‐average molecular weight with increasing monomer conversion was observed for these initiation systems. The polydispersity indices of the polymer were relatively low (1.15–1.44) up to high conversions in all cases. The fastest rate of polymerization and the highest initiation efficiency were achieved with BPA₆, and this could be explained by the longer distance between the halogen and azobenzene groups and the better solubility of the BPA₆ initiator. The redshifting of the UV absorptions of the polymers only occurred for the BPPE‐initiated system. The intensity of the UV absorptions of the polymers were weaker than those of the corresponding initiators in chloroform and decreased with the increasing molecular weights of the polymers in all cases. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2358–2367, 2005     

Synthesis and characterization of poly(methyl methacrylate)‐block‐poly(methylphenylsilane)‐ block‐poly(methyl methacrylate) by atom transfer radical polymerization

ABA block copolymers of methyl methacrylate and methylphenylsilane were synthesized with a methodology based on atom transfer radical polymerization (ATRP). The reaction of samples of α,ω‐dihalopoly(methylphenylsilane) with 2‐hydroxyethyl‐2‐methyl‐2‐bromoproprionate gave suitable macroinitiators for the ATRP of methyl methacrylate. The latter procedure was carried out at 95 °C in a xylene solution with CuBr and 2,2‐bipyridine as the initiating system. The rate of the polymerization was first‐order with respect to monomer conversion. The block copolymers were characterized with ¹H NMR and ¹³C NMR spectroscopy and size exclusion chromatography, and differential scanning calorimetry was used to obtain preliminary evidence of phase separation in the copolymer products. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 30–40, 2003     

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     

Preparation of anthracene-labelled poly(methyl methacrylate) via atom transfer radical polymerization

Anthracene-labelled poly(methyl methacrylate) (PMMA) was prepared via atom transfer radical polymerization (ATRP) where 9,10-bis(chloromethyl)anthracene and CuCl/2,2′-bipyridine were used as the initiator and catalyst, respectively. Both the linear increase of the number average molecular mass with conversion and the narrow polydispersity in the resulting polymers suggest that the polymerization proceeds in a “living” fashion and the anthracene molecule is incorporated into the middle of the polymer backbone. The initiation efficiency was low, ca. 13%, presumably due to some side reactions which compete with the initiation reaction.     

Living radical graft polymerization of methyl methacrylate to polyethylene film with typical and reverse atom transfer radical polymerization

Nickel‐mediated atom transfer radical polymerization (ATRP) and iron‐mediated reverse ATRP were applied to the living radical graft polymerization of methyl methacrylate onto solid high‐density polyethylene (HDPE) films modified with 2,2,2‐tribromoethanol and benzophenone, respectively. The number‐average molecular weight (M_n) of the free poly(methyl methacrylate) (PMMA) produced simultaneously during grafting grew with the monomer conversion. The weight‐average molecular weight/number‐average molecular weight ratio (M_w/M_n) was small (<1.4), indicating a controlled polymerization. The grafting ratio showed a linear relation with M_n of the free PMMA for both reaction systems. With the same characteristics assumed for both free and graft PMMA, the grafting was controlled, and the increase in grafting ratio was ascribed to the growing chain length of the graft PMMA. In fact, M_n and M_w/M_n of the grafted PMMA chains cleaved from the polyethylene substrate were only slightly larger than those of the free PMMA chains, and this was confirmed in the system of nickel‐mediated ATRP. An appropriate period of UV preirradiation controlled the amount of initiation groups introduced to the HDPE film modified with benzophenone. The grafting ratio increased linearly with the preirradiation time. The graft polymerizations for both reaction systems proceeded in a controlled fashion. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3350–3359, 2002     

Synthesis of poly(4‐vinylpyridine) by reverse atom transfer radical polymerization

Controlled radical polymerization of 4‐vinylpyridine (4VP) was achieved in a 50 vol % 1‐methyl‐2‐pyrrolidone/water solvent mixture using a 2,2′‐azobis(2,4‐dimethylpentanitrile) initiator and a CuCl₂/2,2′‐bipyridine catalyst–ligand complex, for an initial monomer concentration of [M]₀ = 2.32–3.24 M and a temperature range of 70–80 °C. Radical polymerization control was achieved at catalyst to initiator molar ratios in the range of 1.3:1 to 1.6:1. First‐order kinetics of the rate of polymerization (with respect to the monomer), linear increase of the number–average degree of polymerization with monomer conversion, and a polydispersity index in the range of 1.29–1.35 were indicative of controlled radical polymerization. The highest number–average degree of polymerization of 247 (number–average molecular weight = 26,000 g/mol) was achieved at a temperature of 70 °C, [M]₀ = 3.24 M and a catalyst to initiator molar ratio of 1.6:1. Over the temperature range studied (70–80 °C), the initiator efficiency increased from 50 to 64% whereas the apparent polymerization rate constant increased by about 60%. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5748–5758, 2007     

甲基丙烯酸甲酯的反向原-子转移自由基聚合反应研究

在较低的温度(60℃)和较低的AIBN/CuCl~2/配位剂摩尔比(1:2:4)条件下,用乙腈为溶剂,实现了甲基丙烯酸甲酯(MMA)的反向原子转移自由基聚合(RATRP)。联二吡啶(bpy)为配位剂时,所合成的聚甲基丙烯酸甲酯(PMMA)的分子量分布可低至1.08。用1,10-菲咯啉(phen)代替bpy,MMA的聚合反应速率加快,但其分子量分布稍宽(1.40左右),并进一步研究了bpy和phen作为混合配位剂时对MMA反向ATRP聚合的影响。用RATRP反应所得的带有卤素端基的PMMA作为苯乙烯ATRP的大分子引发剂,成功地合成了具有预期结构的苯乙烯与甲基丙烯酸甲酯嵌段共聚物,大分子引发剂的引发效率接近于1,说明在RATRP过程中由自由基引发剂引发MMA进行一般自由基聚合反应的可能性甚微。     

Self-initiated atom transfer radical polymerization of methyl methacrylate in cyclohexanone

The self-initiated atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) in cyclohexanone (CHO) in the presence of CuCl₂/N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) is reported. The linear semilogarithmic plot of ln([M]₀/[M]) vs time, the linear increase of number-average molecular weight (M_n) with conversion, and rather narrow molecular weight distributions (MWDs) have been observed, which are in agreement of the characteristics of living/controlled polymerization. The NMR spectrum revealed the existence of terminal chlorine. The chain extension further proved the living characteristic. The polymerization can only be successful using CHO as the solvent, and is well controlled at the temperature as low as 50 °C. The effects of ligand, solvent, temperature and monomer to catalyst ratio are all discussed.     

Supported nickel bromide catalyst for atom transfer radical polymerization (ATRP) of methyl methacrylate

A new supported catalytic system, i.e. nickel bromide catalyst ligated by triphenylphosphine (TPP) ligands immobilized onto crosslinked polystyrene resins (PS-TPP) is reported. Per se, this catalyst does not allow any control over the polymerization of methyl methacrylate (MMA) initiated by ethyl 2-bromoisobutyrate but, in the presence of a given amount of purposely added free TPP, it promotes controlled ATRP of MMA. Indeed colorless PMMA chains of low polydispersity indices are readily recovered, the molecular weight of which linearly increases with monomer conversion and agrees with the expected values. Recycling of the supported catalyst is evidenced and does not prevent the polymerization from being controlled.     

Reverse atom transfer radical polymerization of methyl methacrylate in room‐temperature ionic liquids

The reverse atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) was successfully carried out in 1‐butyl‐3‐methylimidazolium hexafluorophosphate with 2,2′‐azobisisobutyronitrile/CuCl₂/bipyridine as the initiating system, which had been reported as not able to promote a controlled process of MMA in bulk. The living nature of the polymerization was confirmed by kinetic studies, end‐group analysis, chain extension, and block copolymerization results. The polydispersity of the polymer obtained was quite narrow, with a weight‐average molecular weight/number‐average molecular weight ratio of less than 1.2. In comparison with other reverse ATRPs in bulk or conventional solvents, a much smaller amount of the catalyst was used. After a relatively easy removal of the polymer and residue monomer, the ionic liquid and catalytic system could be reused without further treatment. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 143–151, 2003     

Reverse atom transfer radical polymerization of methyl methacrylate initiated by p‐chlorobenzenediazonium tetrafluoroborate

The controlled polymerization of methyl methacrylate (MMA) in bulk was initiated with p‐chlorobenzenediazonium tetrafluoroborate ( 1 ) and Cu(II) or Cu(I)/Cu(II)/N,N,N′,N″,N″‐pentamethyldietylene triamine (PMDETA) complex system at various temperatures (20, 60, and 90 °C). The proposed polymerization mechanism is based on the Meerwein‐type arylation reaction followed by a reverse atom transfer radical polymerization. In this mechanism, aryl radicals formed by the reaction with 1 and Cu(I) and/or PMDETA initiated the polymerization of MMA. The polymerization is controlled up to a molecular weight of 46,000 at 90 °C. Chain extension was carried out to confirm the controlled manner of the polymerization system. In all polymerization systems, the polydispersity index and initiator efficiency ranged from 1.10–1.57 to 0.10–0.21, respectively. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2019–2025, 2003     

A neutral Ni(II) acetylide-mediated radical polymerization of methyl methacrylate using the atom transfer radical polymerization method

A neutral nickel σ-acetylide complex [Ni(CCPh)₂(PBu₃)₂] (NBP) is used for possible atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) in conjunction with an organic halide as an initiator [R-X: CCl₄, CH₃Cl, BrCCl₃, C₂H₅Br, and C₅H₉Br] in toluene at 80 °C. Among these initiating systems, BrCCl₃/NBP gave the best controlled radical polymerization of MMA and produced polymer with relatively narrow molecular weight distribution (M_w/M_n≈1.3). The ATRP of MMA is preliminarily identified by the following facts: (1) the present MMA polymerization initiated by BrCCl₃/NBP is completely hindered by the addition of TEMPO; (2) the conversion shows a typical linear variation with time in semilogarithmic coordinates; (3) the measured number-average molecular weights of polymer show a linear increase with conversion and agree closely with the theoretical values; (4) the resulting polymer chain contains a dormant carbon-halogen terminal.     

Synthesis of poly(methyl methacrylate)‐b‐polystyrene containing a crown ether unit at the junction point via combination of atom transfer radical polymerization and nitroxide mediated radical polymerization routes

Poly(methyl methacrylate)‐b‐polystyrene (PMMA‐b‐PS) containing a benzo‐15‐crown‐5 unit at the junction point was prepared by combining atom transfer radical polymerization and nitroxide‐mediated radical polymerization. For this purpose, 6,7,9,10,12,13,15,16‐octahydro‐5,8,11,14,17‐pentaoxa‐benzocyclopentadecene‐2‐carboxylic acid 3‐(2‐bromo‐2‐methyl‐propionyloxy)‐2‐methyl‐2‐[2‐phenyl‐2‐(2,2,6,6‐tetramethyl‐piperidin‐1‐yloxy)‐ethoxycarbonyl]‐propyl ester ( 3 ) was synthesized and used as an initiator in atom transfer radical polymerization of methyl methacrylate in the presence of CuCl and pentamethyldiethylenetriamine at 60°C. A linear behavior was observed in both plots of ln([M]₀/[M]) versus time and M_n,_GPC versus conversion indicating that the polymerization proceeded in a controlled/living manner. Thus obtained PMMA precursor was used as a macroinitiator in nitroxide‐mediated radical polymerization of styrene (St) at 125°C to give well‐defined PMMA‐b‐PS with crown ether per chain. Kinetic data were also obtained for copolymerization. Moreover, potassium picrate (K⁺ picrate) complexation of 3 and PMMA‐b‐PS copolymer was studied. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3242–3249, 2006     

Emulsion atom transfer radical block copolymerization of 2‐ethylhexyl methacrylate and methyl methacrylate

The emulsion atom transfer radical block copolymerization of 2‐ethylhexyl methacrylate (EHMA) and methyl methacrylate (MMA) was carried out with the bifunctional initiator 1,4‐butylene glycol di(2‐bromoisobutyrate). The system was mediated by copper bromide/4,4′‐dinonyl‐2,2′‐bipyridyl and stabilized by polyoxyethylene sorbitan monooleate. The effects of the initiator concentration and temperature profile on the polymerization kinetics and latex stability were systematically examined. Both EHMA homopolymerization and successive copolymerization with MMA proceeded in a living manner and gave good control over the polymer molecular weights. The polymer molecular weights increased linearly with the monomer conversion with polydispersities lower than 1.2. A low‐temperature prepolymerization step was found to be helpful in stabilizing the latex systems, whereas further polymerization at an elevated temperature ensured high conversion rates. The EHMA polymers were effective as macroinitiators for initiating the block polymerization of MMA. Triblock poly(methyl methacrylate–2‐ethylhexyl methacrylate–methyl methacrylate) samples with various block lengths were synthesized. The MMA and EHMA reactivity ratios determined by a nonlinear least‐square method were ～0.903 and ～0.930, respectively, at 70 °C. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1914–1925, 2006     

In situ Cu(0)‐mediated single electron transfer living radical polymerization of methyl methacrylate using nickel powder

Single electron transfer living radical polymerization of methyl methacrylate catalyzed by the in situ prepared Cu(0) at ambient temperature was first examined using various metallic powders, including Zn(0), Ni(0), Mg(0), and Fe(0). Importantly, the polymerization initiated with Ni(0)/EBiB/CuBr₂/PMDETA system exhibited optimal living/controlled nature and generated polymers with polydispersity index as low as 1.04 for 75.27% conversion and controlled molecular weights close to theoretical ones. A wide of range of Cu(II) salts were also investigated as catalyst sources instead of CuBr₂. The recycling of Ni(0) was very convenient due to its magnetic property, which enables its extensive application. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

New ligands for atom‐transfer radical polymerization

A new type of ligands based on organic acids, such as acetic acid, iminodiacetic acid, succinic acid and isophthalic acid, has been successfully employed in the iron‐mediated atom‐transfer radical polymerization (ATRP) of vinyl monomers, such as styrene (St) and methyl methacrylate (MMA). The systems containing different organic acids can react at 250°C to 1300°C in “living”/controlled radical polymerizations giving polymers with relatively narrow molecular weight distributions (M_w/M_n = 1.2–1.5). ¹H NMR spectroscopy has been used to study the structure of the resulting polymers. Block copolymers were synthesized to confirm the ìlivingî nature of the system. The measured molecular weights are close to the calculated values for the polymerization of MMA and are somewhat lower than the theoretical ones for styrene.     

Supported atom transfer radical polymerization of methyl methacrylate mediated by CuBr–tetraethyldiethylenetriamine grafted onto silica gel

Silica‐gel particles grafted with tetraethyldiethylenetriamine were synthesized as support for CuBr for the heterogeneous atom transfer radical polymerization of methyl methacrylate (MMA). The immobilized CuBr mediated a living polymerization of MMA, demonstrated by an increase in molecular weight with conversion and low polydispersity. An excessive amount of catalyst (typically, CuBr/initiator = 1.5) was required to achieve a living process because of the limited mobility of the supported catalyst. The silica‐gel concentration had a strong effect on the polymerization. The recycled catalyst still mediated a living process but showed a reduced catalytic activity due to the presence of Cu(II). After being regenerated by a reaction with Cu(0), the catalyst regained its activity. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1051–1059, 2001