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     

Fabrication of block copolymer brushes on hollow sphere surface via reverse iodine transfer polymerization

The block copolymer brushes grafted from hollow sphere surface via reverse iodine transfer polymerization (RITP) were investigated in this work. A sufficient amount of azo initiator was introduced onto hollow sphere surface firstly. Then the monomer methyl methacrylate (MMA) was polymerized via surface-initiated reverse iodine transfer polymerization (RITP) using azo group modified hollow sphere as initiator. The microstructure of the samples was characterized by FT-IR, (1)H NMR, respectively. Results indicated that the poly(methyl methacrylate) (PMMA) with end functionality of alkyl iodine group had grafted from hollow sphere surface. TEM observations showed that the average diameter of hollow core was central at 1.3-1.4 μm and the average wall thickness increased from 103 nm to 138 nm and 172 nm after grafting polymerization of MMA and Tb complex, respectively. The closely linear plots of molecular weight (M(n)) versus conversion, linear kinetic plots for the free polymer formed in solution and the ability to extend the chains by sequential addition of monomer indicated that the RITP was a controlled process with a "living" characteristic.     

Surface-initiated living radical polymerization from silica particles functionalized with poly(ethylene glycol)-carrying initiator

A novel yet versatile approach is described for surface-initiated living radical polymerization (SI-LRP) from silica particles (SiPs). Monodisperse SiPs were surface-modified with a newly designed surface-fixable initiator (BPEGE) having three components: a triethoxysilane moiety, a poly(ethylene glycol) (PEG) unit, and an initiation site for atom transfer radical polymerization (ATRP) in the form of a 2-bromoisobutyryl group. The surface-initiated ATRP of methyl methacrylate (MMA) mediated by a copper complex was carried out with the BPEGE-fixed SiPs. The polymerization proceeded in a living manner, producing SiPs coated with well-defined poly(MMA) of a target molecular weight with a graft density as high as 0.5 chains/nm². Thanks to the amphiphilic property of PEG, the system was successfully applied for SI-ATRP of PEG methacrylate and sodium p-styrenesulfonate in aqueous media in which the BPEGE-fixed SiPs were highly dispersed without causing any aggregations. The formation of colloidal crystals with the polymer brush-afforded SiPs demonstrated the high uniformity and perfect dispersibility of the hybrid particles.     

Fluorocarbon‐ended polymers: Metal catalyzed radical and living radical polymerizations initiated by perfluoroalkylsulfonyl halides

Perfluoroalkylsulfonyl chlorides and bromides initiate metal catalyzed free radical polymerization of both hydrocarbon and fluorocarbon monomers affording polymers with perfluoroalkyl end groups. In the case of styrene (S) and methyl methacrylate (MMA) with Cu‐based catalysts the process affords polymers with a relatively narrow molecular weight distribution and linear dependence of molecular weight on conversion, suggesting that a living radical polymerization mechanism occurs. The orders of reaction in monomer, initiator and catalyst for these polymerizations were determined. In the case of PMMA, the detailed structure of a perfluorobutane chain‐end was determined by NMR analysis. Perfluoroalkylsulfonyl chlorides are stable in neutral aqueous media. This permits their use as initators for fluoroolefin polymerizations in H₂O. Poly(tetrafluoroethylene‐co‐hexafluoropropylene) was obtained in good yield with few ionic end groups. The aqueous fluoroolefin polymerization appears to be catalyzed by metal zero species from the reactor walls. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3313–3335, 2000     

Atom transfer radical polymerization initiated by N‐bromosuccinimide

N‐Bromosuccinimide (NBS) was used as the initiator in the atom transfer radical polymerizations of styrene (St) and methyl methacrylate (MMA). The NBS/CuBr/bipyridine (bpy) system shows good controllability for both polymerizations and yields polymers with polydispersity indexes ranging from 1.18 to 1.25 for St and 1.14 to 1.41 for MMA, depending on the conditions used. The end‐group analysis of poly(MMA) and polystyrene indicated the polymerization is initiated by the succinimidyl radicals formed from the redox reaction of NBS with CuBr/bpy. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5811–5816, 2004     

In situ radical transfer addition polymerization of styrene from silica nanoparticles

The in situ radical transfer addition polymerization of styrene from silica nanoparticles was carried out by the free radical polymerized of styrene in the presence of mercaptopropyl-modified silica nanoparticles as chain-transfer agent. The effects of the amount of the initiator, polymerizing temperature and polymerizing time on the convention of styrene (C) and the percentage of grafting were investigated. Results of elemental analysis, IR, X-ray photoelectron spectrometer and transmission electron microscope demonstrated that the desired polymer chains have been covalently bonded to the surface of the silica nanoparticles. A C of 42.56% and a PG of 38.10% could be achieved with the optimal condition. The polystyrene grafted silica nanoparticles could be separated and used as nanofiller for polymers.     

The use of the DPE radical polymerization method for the synthesis of chromophore-labelled polymers and block copolymers

Two analogues of diphenylethene carrying phenanthrene (1-(9-phenanthryl)-1-phenylethene (PPE)) and anthracene (1-(2-anthryl)-1-phenylethene (APE)) units were used in radical polymerization of styrene (St) and methyl methacrylate (MMA) at 80 °C using AIBN as initiator. Because of the nature of the polymerization, the resulting polymers possess the corresponding chromophoric groups. Using the methodology of a DPE system, these labelled polymers were further used for the synthesis of block copolymers. In this way poly(methyl methacrylate)-b-poly(styrene) and poly(methyl methacrylate)-b-poly(acrylonitrile) with molar masses of 60,000-90,000 g/mol were synthesized. Incorporation of the chromophoric groups into both homo- and block copolymers was confirmed by spectral measurements.     

Grafting of polymers onto and/or from silica surface during the polymerization of vinyl monomers in the presence of γ‐ray‐irradiated silica

The effects of radicals on silica surface, which were formed by γ‐ray irradiation, on the polymerization of vinyl monomers were investigated. It was found that the polymerization of styrene was remarkably retarded in the presence of γ‐ray‐irradiated silica above 60 °C, at which thermal polymerization of styrene is readily initiated. During the polymerization, a part of polystyrene formed was grafted onto the silica surface but percentage of grafting was very small. On the other hand, no retardation of the polymerization of styrene was observed in the presence of γ‐ray‐irradiated silica below 50 °C; the polymerization tends to accelerate and polystyrene was grafted onto the silica surface. Poly(vinyl acetate) and poly(methyl methacrylate) (MMA) were also grafted onto the surface during the polymerization in the presence of γ‐ray‐irradiated silica. The grafting of polymers onto the silica surface was confirmed by thermal decomposition GC‐MS. It was considered that at lower temperature, the grafting based on the propagation of polystyrene from surface radical (“grafting from” mechanism) preferentially proceeded. On the contrary, at higher temperature, the coupling reaction of propagating polymer radicals with surface radicals (“grafting onto” mechanism) proceeded to give relatively higher molecular weight polymer‐grafted silica. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2972–2979, 2006     

Densely grafting copolymers of ethyl cellulose through atom transfer radical polymerization

Densely grafting copolymers of ethyl cellulose with polystyrene and poly(methyl methacrylate) were synthesized through atom transfer radical polymerization (ATRP). First, the residual hydroxyl groups on the ethyl cellulose reacted with 2‐bromoisobutyrylbromide to yield 2‐bromoisobutyryloxy groups, known to be an efficient initiator for ATRP. Subsequently, the functional ethyl cellulose was used as a macroinitiator in the ATRP of methyl methacrylate and styrene in toluene in conjunction with CuBr/N,N,N′,N″,N″‐pentamethyldiethylenetriamine as a catalyst system. The molecular weight of the graft copolymers increased without any trace of the macroinitiator, and the polydispersity was narrow. The molecular weight of the side chains increased with the monomer conversion. A kinetic study indicated that the polymerization was first‐order. The morphology of the densely grafted copolymer in solution was characterized through laser light scattering. The individual densely grafted copolymer molecules were observed through atomic force microscopy, which confirmed the synthesis of the densely grafted copolymer. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4099–4108, 2005     

Reverse Atom Transfer Radical Polymerization of MMA in the Presence of CaCO3/SiO2 Two-Component Composite Particles

Summary: We previously discovered that structurally well-defined polymer/inorganic composite particles, i.e., poly(methyl methacrylate) (PMMA)/CaCO₃/SiO₂ three-component composite particles, can be achieved via reverse atom transfer radical polymerization (ATRP), using 2,2′-azo-bis-isobutyronitrile as initiator and Cu^II bromide as catalyst. In the present study, the influence of the mass ratio of CaCO₃/SiO₂ two-component composite particles to methyl methacrylate (MMA) on the rate and behavior of the polymerization was studied in detail. The results illustrate that increasing the mass ratio of CaCO₃/SiO₂ two-component composite particles will decrease the overall rate of polymerization of MMA under standard reverse ATRP conditions. Thermal properties of the obtained well-defined particles were characterized and determined by thermogravimetric analysis (TGA). The results indicate that well-defined PMMA chains grafted on the surface of CaCO₃/SiO₂ particles were only degraded by random chain scission of C C linkages within the PMMA chain, which is different from the degradation of PMMA chains prepared via traditional radical polymerization. This difference is reasonably ascribed to the difference between the end groups of PMMA prepared via reverse ATRP and that via traditional radical polymerization, which has been confirmed by end group analysis measured by ¹H–NMR spectroscopy.     

On the rate of soapless emulsion polymerization of methyl methacrylate

The rate of soapless emulsion polymerization is studied experimentally and theoretically. The soapless emulsion polymerization of methyl methacrylate (MMA) in water is carried out with potassium persulfate as initiator. It is shown that the soapless emulsion polymerization of MMA gives different time-conversion and time-average molecular weight curves from those of bulk and emulsion polymerizations. Comparing the experimental results with those of the other types of polymerization, features of the rate of soapless emulsion polymerization are discussed and a kinetic model is proposed to apply the soapless emulsion polymerization of MMA in water. The experimental results can be well expressed by this model.     

Copolymerization of butyl vinyl ether and methyl methacrylate by combination of radical and radical promoted cationic mechanisms

Butyl vinyl ether (BVE) and methyl methacrylate (MMA) mixtures were polymerized by using free radical initiators in conjunction with a cationic initiator such as diphenyl iodonium salt. Polymerization mechanism involves free radical polymerization of MMA which is switched to cationic polymerization of BVE by addition of growing poly(MMA) radicals to BVE and subsequent oxidation of electron donating polymeric radicals to the corresponding cations by iodonium ions. Two representative bifunctional monomers, ethylene glycol divinyl ether (EGDVE) and ethylene glycol dimethacrylate (EGDMA) were also used together with MMA and BVE, respectively, in photo and thermal crosslinking polymerizations. Vinyl ether and methacrylate type monomers can successfully be copolymerized by this double-mode polymerization under photochemical conditions.     

Study on radiation-induced polymerization of vinyl monomers adsorbed on inorganic substances. II. Radiation-induced polymerization of methyl methacrylate adsorbed on several inorganic substances

The radiation-induced polymerization of methyl methacrylate (MMA) absorbed on such inorganic substances as silica gel, white carbon, silicic acid anhydride, zeolite, and activated alumina was carried out to compare with the case of styrene. The rate of radiation-induced polymerization adsorbed on inorganic substances was high compared with that of radiation-induced bulk state polymerization, as was the case with styrene. Inorganic substrates which contain aluminum as a component element are more likely to be grafted than those which consist of SiO₂ alone, as with styrene. The molecular weight distribution of unextractable polymer and extractable polymer differs, depending on the type of inorganic substance. Experiments by a preirradiation method were carried out in case of silica gel, white carbon, and silicic acid anhydride. GPC spectra of the polymer obtained were different from those of polymer formed by the simultaneous irradiation method. It appears that all the unextractable polymer is grafted to the inorganic surface with chemical bond.     

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     

ARGET ATRP of methyl methacrylate with 2-(8-heptadecenyl)-4,5-dihydro-1H-imidazole-1-ethylamine (OLC) as both ligand and reducing agent in the presence of air

Copper(II)-mediated activators regenerated by electron transfer for atom transfer radical polymerization of methyl methacrylate (MMA) was successfully carried out in a limited amount of air in the presence of 2-(8-heptadecenyl)-4,5-dihydro-1H-Imidazole-1-ethylamine as ligand that served not only as ligand but also as reducing agents. Reduction of Cu(II) to Cu(I) by an excess amount of nitrogen-based ligand was followed by UV–visible spectroscopy. The kinetics of the polymerizations and effect of different polymerization conditions are investigated. It is found that the polymerization of MMA can be conducted well even if the amount of Cu(II) is as low as 1 mol% catalyst relative to initiator. The results of the polymerizations demonstrate the features of “living”/controlled free-radical polymerization, such as the number-average molecular weights being close to their corresponding theoretical values and increasing linearly with monomer conversion, and narrow molecular weight distributions. Chain extension of poly(methyl methacrylate)s with MMA was successful and demonstrated well-maintained end-group functionality.     

活性正离子聚合与原子转移自由基聚合转换合成聚β-蒎烯接枝共聚物

通过活性正离子聚合与原子转移自由基聚合(ATRP)转换合成了β-蒎烯与甲基丙烯酸甲酯(MMA)、丙烯酸丁酯(BA)、苯乙烯(St)的新型接枝共聚物.首先以α-氯代乙苯/TiCl4/Ti(OiPr)4/nBu4NCl体系引发β-蒎烯活性正离子聚合,合成预定分子量大小和窄分子量分布的聚β-蒎烯,然后经N-溴代琥珀酰亚胺(NBS)定量溴化,得到溴化聚β-蒎烯大分子引发剂(Br/β-蒎烯链节摩尔比为0.5).然后将该大分子引发剂与溴化亚铜(CuBr)/2,2′-联吡啶(bpy)复合,引发MMA、BA、St进行ATRP接枝聚合.接枝反应显示一级动力学特征,且产物的分子量及分子量分布可控,表明上述ATRP接枝聚合反应具有可控聚合特征.接枝产物的结构经1H-NMR分析得到进一步证实.     

Optimization of the synthesis of poly(octadecyl acrylate) by atom transfer radical polymerization and the preparation of all comblike amphiphilic diblock copolymers

The atom transfer radical polymerization of octadecyl acrylate (ODA) has been investigated and optimized to produce polymers with predetermined molecular weights and narrow polydispersities (<1.2). The poor solubility of the catalytic system formed with conventional ligands such as the N‐(n‐propyl)‐2‐pyridylmethanimine and 2,2′‐bipyridine with Cu(I)Br in nonpolar reaction conditions gave poor control over molecular weight characteristics in ODA polymerizations. The use of N‐(n‐octyl)‐2‐pyridylmethanimine in combination with Cu(I)Br yielded a more soluble catalyst that improved control over the polymerization. The products from the polymerizations were further improved when an initiator, octadecyl 2‐bromo‐2‐methyl‐propanoate, similar in structure to the monomer, was used. Together, these modifications produced polymerizations that showed true controlled character as well as products with predetermined molecular weights and narrow polydispersities. Diblock copolymers of PODA were prepared with methyl methacrylate (MMA) and olig(oethylene glycol) methyl ether methacrylate (OEGMA). The PODA‐block‐POEGMA copolymers are the first examples of all comblike amphiphilic block copolymers. One of PODA‐block‐POEGMA copolymer samples has been shown to self‐assemble as micelles in a dilute aqueous solution. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1129–1143, 2005     

Control of the Colloidal Stability of Polymer-Grafted-Silica Nanoparticles Obtained by Atom Transfer Radical Polymerization

Polymer chains are grafted from silica nanobeads. The method consists in grafting first the initiator molecules on the silica surface. Then, the polymerization of styrene or n-butyl methacrylate using Atom Transfer Radical Polymerization, is conducted. The nanoparticles are kept in solution during the whole process to avoid irreversible aggregation. The state of dispersion of the grafted silica nanoparticles is followed by Small Angle Neutron Scattering, as well as the quantity and the spatial organisation of the polymer. This is done during the functionalisation and the polymerization, but also after purification where free polymer chains are eliminated. This permits to reach a quantitative level of SANS analysis from these purified particles, which is compared to chemical data given by Size Exclusion Chromatography and Thermogravimetric analysis.     

N‐Bromosuccinimide as a thermal iniferter for radical polymerization

N‐Bromosuccinimide (NBS) was used as a thermal iniferter for the initiation of the bulk polymerizations of methyl methacrylate, methyl acrylate, and styrene. The polymerizations showed the characteristics of a living polymerization: both the yields and the molecular weights of the resultant polymers increased linearly as the reaction time increased. The molecular weight distributions of the polymers were 1.42–1.95 under the studied conditions. The resultant polymers could be used as macroiniferters to reinitiate the polymerization of the second monomer. The copolymers poly(methyl methacrylate)‐b‐polystyrene and polystyrene‐b‐poly(methyl methacrylate) were obtained and characterized. End‐group analysis of the resultant poly(methyl methacrylate), poly(methyl acrylate), and polystyrene confirmed that NBS behaved as a thermal iniferter. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2567–2573, 2005     

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.