Synthesis, characterization and fluorescence adjustment of well-defined polymethacrylates with pendant π-conjugated benzothiazole via atom transfer radical polymerization (ATRP)

Two compounds containing the benzothiazole moiety, 4-(2-benzothiazole-2-yl-vinyl)-phenyl methacrylate (BVMA) and 2-bromo-2-methyl-propionic acid 4-(2-benzothiazole-2-yl-vinyl)-phenyl ester (BPBVE) were synthesized. Atom transfer radical polymerization (ATRP) of BVMA was conducted at 60 °C using BPBVE and CuBr/2,2′-bipyridine (BPY) as initiator and catalyst, respectively. Chain extension with 4-methacryloxy-hexyloxy-4′-nitrostilbene (MHNS) was conducted using PBVMA as the macroinitiator. The homopolymer PBVMA in DMF solution emitted blue fluorescence, and the copolymer PBVMA-b-PMHNS emitted orange fluorescence at about 610 nm due to the intramolecular energy transfer. ATRP of BVMA was also conducted using 2-bromo-2-methyl-propionic acid 4-nitrostilbene-hexyloxy ester (BPNHE) as an initiator. The obtained polymer was characterized via ¹H NMR and the fluorescence intensity was found to change with increasing number average molecular weight (M_n). The polymer with M_n = 15900 emitted white fluorescence in DMF solution.     

Fabrication of hybrid nanocomposites with polystyrene and multiwalled carbon nanotubes with well-defined polystyrene via multiple atom transfer radical polymerization

The PS-grafted multiwalled carbon nanotubes (MWNTs) were produced by the bromo-ended PS (PS-Br) and pristine MWNTs in 1,2-dichlorobenzene at 110 °C for 72 h via atom transfer radical polymerization (ATRP). Bromo-ended PS (PS-Br) used as an initiator for the functionalization of MWNTs was synthesized with styrene by ATRP conditions using CuBr and N,N,N′,N′,N″-pentamethyldiethylenetriamine as catalyst. The PS-grafted MWNTs were fully characterized by ¹H-NMR, FT-IR, DSC, TGA, and SEM. The PS-grafted MWNTs were found to be highly soluble in a variety of organic solvents. The PS was chemically attached to the surfaces of MWNTs via ATRP approach, and the grafting amount of PS was 40–90%. From TGA and DSC measurements, the PS-grafted MWNTs were decomposed at lower temperature compared to that of PS-Br, and the functionalization of MWNTs increased the glass-transition temperature (T_g) of the grafted PS. The PS/PS-grafted MWNTs nanocomposites were prepared with PS and PS-grafted MWNTs by solution mixing in dimethylformamide (DMF). The resulting nanocomposites were found to be the homogeneous dispersion of PS-grafted MWNTs in PS matrix via aromatic (π–π) interactions between PS and PS-grafted MWNTs as determined by SEM and TEM.     

AlCl3 promoting living-radical polymerization of MMA based on sec-butyl chlorine in n-butanol

The effect of metal halide AlCl₃ as additive on the living-radical polymerization of methyl methacrylate (MMA) in n-butanol at 80 °C was investigated. The initiator was sec-butyl chlorine (SBC), which was used as a model initiator containing secondary R-Cl bond and the catalyst was FeCl₂/(PPh₃)₄. The polymerization reaction of MMA, using SBC/FeCl₂ (PPh₃)₄ as initiating system, was very slow or even did not take place without AlCl₃. The addition of AlCl₃ accelerated the polymerization to some great extent and the polymers obtained have almost controlled molecular weights and narrow molecular weight distribution. These experimental results were different from those of the literatures, in which metal chlorides would slow down the polymerization rate of MMA for ATRP reactions.     

Emulsion atom transfer radical polymerization of 2-ethylhexyl methacrylate

The emulsion atom transfer radical polymerization (ATRP) of 2-ethylhexyl methacrylate (EHMA) was carried out with ethyl 2-bromoisobutyrate (EBiB) as an initiator and copper bromide (CuBr)/4,4′-dinonyl-2,2′-bipyridyl (dNbpy) as a catalyst system. The effects of surfactant type and concentration, temperature, monomer/initiator ratio, and CuBr₂ addition on the system livingness, polymer molecular weight control, and latex stability were examined in detail. It was found that the polymerization systems with Tween 80 and Brij 98 as surfactants at 30 °C gave the best latex stability. The polymer samples prepared under these conditions had narrow molecular weight distributions (M_w/M_n=1.1-1.2) and linear relationships of number-average molecular weight versus monomer conversion.     

Synthesis and characterization of perfluorocyclobutyl aryl ether-based amphiphilic diblock copolymer

Perfluorocyclobutyl aryl ether-based amphiphilic diblock copolymer containing hydrophilic poly(ethylene glycol) segment was synthesized by atom transfer radical polymerization (ATRP). Perfluorocyclobutyl-containing methacrylate-based monomer, 4-(4′-p-tolyloxyperfluorocyclobutoxy)benzyl methacrylate, was prepared firstly, which can be polymerized by ATRP in a controlled way to obtain well-defined homopolymers with narrow molecular weight distributions (M_w/M_n ≤ 1.30). The molecular weights increased linearly with the conversions of monomer and the apparent polymerization rate exhibited first-order relation with respect to the concentration of monomer. ATRP of 4-(4′-p-tolyloxyperfluorocyclobutoxy)benzyl methacrylate was initiated by PEG-based macroinitiators with different molecular weights to obtain amphiphilic diblock copolymers with narrow molecular weight distributions (M_w/M_n < 1.35) and the number of perfluorocyclobutyl linkage can be tuned by the feed ratio and the conversion of the fluorine-containing methacrylate monomer. The critical micelle concentrations of these amphiphilic diblock copolymers in water and brine were determined by fluorescence probe technique. The morphologies of the micelles were found to be spheres by TEM.     

Controllable synthesis of poly(N-vinylpyrrolidone) and its block copolymers by atom transfer radical polymerization

At room temperature atom transfer radical polymerization (ATRP) of N-vinylpyrrolidone (NVP) was carried out using 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetra-azacyclo-tetradecane (Me₆Cyclam) as ligand in 1,4-dioxane/isopropanol mixture. Methyl 2-chloropropionate (MCP) and copper(I) chloride were used as initiator and catalyst, respectively. The polymerization of NVP via ATRP could be mediated by the addition of CuCl₂. The resultant poly(N-vinylpyrrolidone) (PNVP) has high conversion of up to 65% in 3 h, a controlled molecular weight close to the theoretical values and narrow molecular weight distribution between 1.2 and 1.3. The living nature of the ATRP for NVP was confirmed by the experiments of PNVP chain extension. With PNVP-Cl as macroinitiator and N-methacryloyl-N′-(α-naphthyl)thiourea (MANTU) as a hydrophobic monomer, novel fluorescent amphiphilic copolymers poly(N-vinylpyrrolidone)-b-poly(N-methacryloyl-N′-(α-naphthyl)thiourea) (PNVP-b-PMANTU) were synthesized by ATRP. PNVP-b-PMANTU copolymers were characterized by ¹H NMR, GPC-MALLS and fluorescence measurements. The results revealed that PNVP-b-PMANTU presented a blocky architecture.     

Stereospecific preparation of polyacrylamide with low polydispersity by ATRP in the presence of Lewis acid

The stereospecific atom transfer radical polymerizations of acrylamide were achieved in the presence of the Lewis acid Y(OTf)₃ or AlCl₃ as stereospecific catalyst using chloroacetic acid/CuCl/N,N,N′,N′-tetramethyl-ethylenediamine (TMEDA) as initiating system. The addition of Lewis acid Y(OTf)₃ in the ATRP of acrylamide led to an increased polymerization rate and an improved tacticity of polyacrylamide (m ∼ 71%) at the expense of controllability of the molecular weight distribution. In the case of AlCl₃, the polymerizations were committed to afford the resultant polyacrylamide with lower polydispersity index ranging from 1.03 to 1.42 and well-controlled tacticity with meso content ranging from 57 to 76% depending on the different reaction conditions used. Lower temperature or higher concentration of the feeding Lewis acid helped to obtain the polyacrylamide with increased tacticity which revealed a decreased glass transition temperature (T_g).     

Synthesis by self-condensing AGET ATRP and solution properties of arborescent poly(sodium 2-acrylamido-2-methyl-N-propane sulfonate)

Randomly branched (arborescent) poly(sodium 2-acrylamido-2-methyl-N-propanesulfonates) (NaPAMPS) were synthesized via self-condensing vinyl polymerization using activators generated by electron transfer atom transfer radical polymerization (AGET ATRP). The controlled self-condensing AGET ATRP of NaAMPS was realized in the presence of 2-(2-bromopropionyloxy)ethyl acrylate (BPEA) as a branching monomer (inimer) in water/pyridine (35-50% of Py) mixed solvents. The content of BPEA in the reaction feed was varied from 10 to 30 wt% allowing the synthesis of NaPAMPS with different degree of branching. SEC determined molecular weight of the prepared NaPAMPS was M_w = 94 000-120 000 g/mol, and the accompanying polydispersity index PDI ranged from 1.84 to 2.47. The definite evidence of highly branched structure of NaPAMPS was provided by the dependence of radius of gyration R_g on weight-average molecular weight M_w with characteristic slope a = 0.38-0.42, and by small-angle X-ray scattering (SAXS) analysis. Molecular parameters, conformation and dynamics of the branched NaPAMPS in dilute salt-free solutions and in the presence of a salt were elucidated by static and dynamic light scattering and SAXS.     

Synthesis of cross-linked poly(4-vinylpyridine) and its copolymer microgels using supercritical carbon dioxide: Application in the adsorption of copper(II)

Compared with conventional precipitation polymerization method, cross-linked poly(4-vinylpyridine) (P4VP) and its microgels copolymerized with α-methacrylic acid (MAA) were synthesized through a new route of stabilizer-free polymerization in supercritical fluids. The yellow, dry, fine powders were directly obtained from precipitation polymerization of 4-vinylpyridine in supercritical carbon dioxide (scCO₂) at pressures ranging from 70.0 to 230 bar, using N,N′-methylenebisacrylamide as cross-linker. The effects of the reaction pressure, cross-linker ratio, initiator concentration, and reaction time were investigated. The capacity of this microgel for adsorption of copper(II) was also studied. At higher cross-linker concentrations, a high yield of the cross-linked P4VP microgel was generated in scCO₂, and its particle size was less than 300 nm. Polymerization of cross-linked P4VP in scCO₂ was extremely sensitive to the density of the continuous phase. The adsorption followed the Langmuir isotherm. The adsorption capacities of cross-linked P(4VP-co-MAA) and cross-linked P4VP were 47.2 and 26.9 mg g⁻¹, respectively.     

PTPFCBBMA-b-PEG-b-PTPFCBBMA amphiphilic triblock copolymer: Synthesis and self-assembly behavior

We present the synthesis and self-assembly behavior of a new semi-fluorinated amphiphilic triblock copolymer. A series of perfluorocyclobutyl aryl ether-based amphiphilic ABA triblock copolymer containing hydrophilic poly(ethylene glycol) segment as the middle block were synthesized by atom transfer radical polymerization (ATRP). ATRP of 4-(4′-p-tolyloxyperfluorocyclobutoxy)benzyl methacrylate was initiated by PEG-based bifunctional macroinitiators with different molecular weights to obtain the desired copolymers with narrow molecular weight distributions (M_w/M_n ≤ 1.30) and the number of perfluorocyclobutyl linkage can be tuned by the feed ratio and the conversion of the fluorine-containing methacrylic monomer. The critical micelle concentrations of these amphiphilic ABA triblock copolymers in aqueous media were determined by fluorescence probe technique. They could aggregate to form spherical and cylindrical micelles visualized by TEM with varying the content of hydrophobic segment.     

原子转移自由基聚合的研究新进展——AGET ATRP

原子转移自由基聚合(ATRP)是目前高分子化学领域的研究重点之一,AGET ATRP又是在传统ATRP基础上衍生出的一种摒弃ATRP一些缺点的新型活性/可控聚合方法。重点介绍了AGET ATRP反应的机理、引发体系、催化体系、还原剂、反应介质及反应条件,以及对AGET ATRP技术的前景与展望。     

Fe(III)-catalyzed AGET ATRP of styrene using triphenyl phosphine as ligand

Activators generated by electron transfer for atom transfer radical polymerization (AGET ATRP) is a new technique for conducting ATRP developed recently. In this work, an iron(III)-mediated AGET ATRP of styrene in bulk was carried out at 110 °C, using benzyl bromide as an initiator, oxidatively stable iron(III) chloride hexahydrate (FeCl₃·6H₂O) as a catalyst, triphenyl phosphine as a ligand, and ascorbic acid as a reducing agent. The polymerizations demonstrated the features of “living”/controlled free-radical polymerization, such as the number–average molecular weights increasing linearly with monomer conversion and narrow molecular weight distributions (M _w/M _n = 1.14–1.31).     

A novel perfluorocyclobutyl aryl ether-based graft copolymer via 2-methyl-1,4-bistrifluorovinyloxybenzene and styrene

A series of novel perfluorocyclobutyl aryl ether-containing graft copolymers with polystyrene side chains were synthesized by the combination of thermal step-growth [2π + 2π] cycloaddition polymerization of aryl bistrifluorovinyl ether monomer and atom transfer radical polymerization (ATRP) of styrene. We first synthesized a new aryl bistrifluorovinyl ether monomer of 2-methyl-1,4-bistrifluorovinyloxybenzene in two steps using commercially available 2-methylhydroquinone as starting material and the corresponding perfluorocyclobutyl aryl ether-based homopolymer with methoxyl end groups was prepared through the homopolymerization of this monomer in diphenyl ether. Next, the pendant methyls of this fluoropolymer were mono-brominated by N-bromosuccinimide and benzoyl peroxide so as to be converted to ATRP initiation groups. The targeted poly(2-methyl-1,4-bistrifluorovinyloxybenzene)-g-polystyrene with relatively narrow molecular weight distributions (M_w/M_n ≤ 1.38) was obtained by the combination of bulk ATRP of styrene at 110 °C using CuBr/bpy as catalytic system and the grafting-from strategy. These fluorine-containing graft copolymers show excellent solubility in common organic solvents.     

Reverse ATRP of acrylonitrile with diethyl 2,3-dicyano-2,3-diphenyl succinate/FeCl3/iminodiacetic acid

The reverse atom transfer radical polymerization (RATRP) technique using FeCl₃/iminodiacetic acid (IMA) complex as a catalyst was applied to the living radical polymerization of acrylonitrile (AN). A hexa-substituted ethane thermal initiator, diethyl 2,3-dicyano-2,3-diphenylsuccinate (DCDPS), was firstly used as the initiator in this iron-based RATRP system. The polymerization in N,N-dimethylformamide not only shows the best control of molecular weight and its distribution but also provides rather rapid reaction rate with the ratio of [AN]:[DCDPS]:[FeCl₃]:[IMA] at 500:1:2:4. The rate of polymerization increases with increasing the polymerization temperature and the apparent activation energy was calculated to be 49.9 kJ mol⁻¹. The polymers obtained were end-functionalized by chlorine atom, and they were used as macroinitiators to proceed the chain extension polymerization in the presence of FeCl₂/IMA catalyst system via a conventional ATRP process. The resultant polyacrylonitrile fibers were obtained with the fineness at 1.16 dtex and the tenacity at 6.01cN dtex⁻¹.     

Ultra high molar mass poly[2-(dimethylamino)ethyl methacrylate] via atom transfer radical polymerization

Well-defined high molecular weight poly[2-(dimethylamino)ethyl methacrylates] [poly(DMAEMA)s] with molar masses up to ∼1×10⁶ g/mol were successfully synthesized via atom transfer radical polymerization (ATRP). This was achieved by using p-toluenesulfonyl chloride(p-TsCl)/CuCl/1,1,4,7,10,10-hexamethyl-triethylenetetramine(HMTETA) initiator/catalyst complex in methanol/water mixture. Well-controlled/‘living’ behavior was demonstrated throughout the reaction, up to high monomer conversion. The PDI value remained low at 1.26 even for a polymer with very high molecular weight at 1.1×10⁶ g/mol. We believe this is the first successful case where controlled ATRP produces a polymer with molar mass exceeding a million!     

Controlled polymerization of methylmethacrylate from fumed SiO2 nanoparticles through atom transfer radical polymerization

Atom transfer radical polymerization (ATRP) is a promising method to synthesize well‐defined polymer/inorganic nanoparticles. However, the surface‐initiated ATRP from commercially mass produced inorganic nanoparticles has seldom been studied. In this study, the surface‐initiated ATRP of methylmethacrylate (MMA) from commercially mass produced fumed silica (SiO₂) nanoparticles was investigated. Unlike the ATRP of MMA initiated from a free initiator, the controllability of ATRP of MMA from the surface of fumed silica nanoparticles was much better using ligand 2,2'‐bipyridine (bpy) than N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine (PMDETA) as the initiator was immobilized on the surface of the SiO₂ nanoparticles and the presence of the SiO₂ nanoparticles made the CuCl/bpy catalyst system a homogeneous catalyst system and CuCl/PMDETA a heterogeneous one. The appropriate molar ratio of monomer and initiator was essential for preparing controlled PMMA/SiO₂ nanoparticles. The entire process of ATRP of MMA from the surface of SiO₂ nanoparticles was controllable when using bpy as ligand, xylene as solvent and with a monomer to initiator ratio of 300:1. The ¹H NMR results indicated that the PMMA on the surface of the SiO₂ was prepared via ATRP initiated from 4‐(chloromethyl)phenyltrimethoxysilane. The well‐defined PMMA/SiO₂ nanoparticles obtained have good thermal stability and are well dispersed in organic media as proved by TGA, dynamic light scattering and transmission electron microscopy. © 2013 Society of Chemical Industry     

Solvothermal oxidation of gallium metal

Solvothermal oxidation of gallium metal in various organic solvents at 300 °C under the autogenous vapor pressure of the solvents was examined. The reaction of gallium metal in 1-butanol or 2-methoxy-ethanol at 300 °C did not proceed and unreacted gallium metal was recovered even with prolonged reaction time. On the other hand, gallium metal reacted in aminoalcohols such as 2-aminoethanol, 2-methylaminoethanol, 2,2′-iminodiethanol and 2,2′,2″-nitrilotriethanol yielding γ-Ga₂O₃. The product obtained by this reaction has a relatively large crystallite size as compared with γ-Ga₂O₃ prepared by the conventional method.     

原子转移自由基乳液聚合研究进展

原子转移自由基聚合(ATRP)作为一种可控/活性聚合方法,可对聚合物结构进行精确控制;乳液聚合以水作为分散介质,具有经济、环保等特点。因此,乳液ATRP结合了两者的优点,具有工业化生产的潜力。首先分析了影响乳液ATRP的各种因素,然后综述了正向ATRP、RATRP(反向ATRP)、SR&NI ATRP(正向/反向同时进行的ATRP)和AGET ATRP(电子转移活化剂ATRP)等机制及研究进展,最后对乳液ATRP的发展方向进行了展望。     

还原剂对AGET ATRP乳液体系制备含氟涂料性能的影响

利用电子活化再生原子转移自由基聚合(AGETATRP)法,在Tween-80乳化体系下合成了甲基丙烯酸甲酯(MMA)-丙烯酸丁酯(BA)-丙烯酸六氟丁酯(HFBA)的三元共聚物。由于AGETATRP反应体系中加入了还原剂来还原Cu2+,所以研究了还原剂的用量对聚合反应可控性的影响以及对共聚物涂料性能的影响。研究发现增加还原剂用量,涂料的防水性、防油性、力学性能略有降低,但仍然表现出优异的防水性和良好的力学性能。     

Radically crosslinked branched poly(N-allylethylenimine) with lithium triflate as a solid state polymer electrolyte

Branched poly(N-allylethylenimine) (BPAEI), a solid state polymer electrolyte host, was synthesized by allylation of branched poly(ethylenimine) (BPEI). Allylation was essentially complete with the 2 and 1° nitrogen atoms of BPEI being mono-allylated and di-allylated, respectively, and with little or no quaternization. BPAEI can be radically cross-linked with and without lithium trifluoromethanesulfonate (LiTf) present to form free-standing, homogeneous, minimally hygroscopic films. BPAEI has a glass transition temperature (T_g) of −65 °C, as measured by differential scanning calorimetry (DSC), which increases with the concentration of initiator upon cross-linking using V-50 (2,2-azobis(2-amidino-propane) dihydrochloride) to −15 °C at a 10:1 nitrogen to initiator molar ratio (N:initiator). BPAEI with 20:1 N:Li⁺ (molar ratio) LiTf has a T_g of −48 °C, which increases with the concentration of radical initiator upon cross-linking using V-50 to 3 °C at 10:1 N:initiator. At compositions near 60:1 N:initiator, an unusual decrease in the rate at which T_g changes with cross-linking was observed, both with and without LiTf present, indicating that some undefined morphological changes occur. The effect of this morphological change resulted in the highest Ac conductivities at 60:1 N:initiator for all LiTf concentrations studied. At 20:1 N:Li⁺ LiTf and 60:1 N:initiator, the room temperature Ac conductivity was 1×10⁻⁸ S/cm which increased to 1×10⁻⁵ S/cm at 80 °C, the highest conductivity observed in the concentration ranges studied. Infrared spectroscopy (IR) showed that the concentrations of the individual ionic species present were largely independent of either LiTf concentration or cross-linking density, suggesting that changes in ion mobility, likely resulting from morphological changes, substantially control the ionic conductivity.