A dynamic Monte Carlo model was developed to simulate ATRP with bifunctional initiators in a batch reactor. Model probabilities were calculated from polymerization kinetic parameters and reactor conditions. The model was used to predict monomer conversion, average molecular weight, polydispersity and the complete CLD as a function of polymerization time. The Monte Carlo model was compared with simulation results from a mathematical model that uses population balances and the method of moments. We also compared polymerizations with monofunctional and bifunctional initiators to illustrate some of the advantages of using bifunctional initiators in ATRP. In addition, we used the model to investigate the effect of the control volume and several polymerization conditions on simulation time, monomer conversion, molecular weight averages and CLD. Our results indicate that computational times can be reduced without sacrificing the quality of the results if we run several simulations with small control volumes rather than one single simulation with a large control volume.
Furan ring‐functionalized solid surfaces are achieved by the initiated chemical vapor deposition (iCVD) method, a solvent‐free process to form films under mild conditions. The polymerization of furfuryl methacrylate monomer is initiated by a resistively heated filament wire. The functionality of the furan group in the iCVD film enabled Diels–Alder chemistry with 4‐phenyl‐1,2,3‐triazolin‐3,5‐dione (N‐PTD).
Kinetic modeling is used to better understand and optimize initiators for continuous activator regeneration atom‐transfer radical polymerization (ICAR ATRP). The polymerization conditions are adjusted as a function of the ATRP catalyst reactivity for two monomers, methyl methacrylate and styrene. In order to prepare a well‐controlled ICAR ATRP process with a low catalyst amount (ppm level), a sufficiently low initial concentration of conventional radical initiator relative to the initial ATRP initiator is required. In some cases, stepwise addition of a conventional radical initiator is needed to reach high conversion. Under such conditions, the equilibrium of the activation/deactivation process for macromolecular species can be established already at low conversion.
The iron(III)‐catalyzed atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) was successfully employed using tributylphosphine (TBP) and trimethylphosphite (TMP) as ligands in the absence of a reducing agent. The effects of solvent and initiator on polymerization of MMA were investigated. Most of the polymerizations with these ligands were well controlled with a linear increase in the number average molecular weights ( ) versus conversion and relatively low molecular weight distribution ( = 1.2–1.4) throughout the reactions, and the measured weights matched with the predicted values. The ethyl 2‐bromoisobutyrate (EBriB) initiated ATRP of MMA with the FeBr3/TBP or FeBr3/TMP catalytic system was better controlled in toluene than in the other solvents used in this study at 80 °C.
A PTFE film surface was modified using a combined plasma/ozone‐activated process. The modified PTFE film was further reacted with 2‐bromoisobutyryl bromide to incorporate ATRP initiators in the film surface. Surface‐initiated ATRP on PTFE films was performed using sodium styrene sulfate as a monomer. The poly(sodium styrene sulfate) chain length grafted onto PTFE film surfaces increased with increasing reaction time. Analysis using X‐ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy and a contact angle analyzer gave evidence of the success of the PTFE surface modifications.
The metal catalyzed polymerization of methyl methacrylate using Cu(0) as the catalyst source has been investigated in toluene. This work looks at polymerizations in a non‐polar medium allowing control over the molecular weight and polydispersity with a 4‐fold reduction in catalyst concentration versus conventional ATRP, while the use of an active ligand allows the reaction to proceed at room temperature. The use of an excess of PMDETA ligand allows for high conversions, and the addition of a small amount of CuBr2 enhances living characteristics, enabling efficient chain extension.
The hemoprotein horseradish peroxidase (HRP) catalyzes the polymerization of N‐isopropylacrylamide with an alkyl bromide initiator under conditions of activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) in the absence of any peroxide. This is a novel activity of HRP, which we propose to name ATRPase activity. Bromine‐terminated polymers with polydispersity indices (PDIs) as low as 1.44 are obtained. The polymerization follows first order kinetics, but the evolution of molecular weight and the PDI upon increasing conversion deviate from the results expected for an ATRP mechanism. Conversion, and PDI depend on the pH and on the concentration of the reducing agent, sodium ascorbate. HRP is stable during the polymerization and does not unfold or form conjugates.
Summary: Atom transfer radical polymerization (ATRP) and reversible addition‐fragmentation transfer (RAFT) polymerization of N‐methyl methacrylamide and methyl methacrylate were investigated in the presence of rare‐earth triflates known to enhance polymer isotacticity. Poly(N‐methyl methacrylamide) with controlled molecular weight, low polydispersity, and enhanced isotacticity was prepared by ATRP and RAFT in the presence of catalytic amounts of yttrium trifluoromethanesulfonate or ytterbium trifluoromethanesulfonate. The tacticity of poly(N‐methyl methacrylamide) depends on the Lewis acid concentration: well‐defined polymers with predominantly either syndiotactic, atactic, or isotactic triads were prepared by adjusting the concentration of the Lewis acid. Simultaneous control of molecular weights, polydispersities, and tacticities in the polymerization of methyl methacrylate was less successful.
Free radical propagation in the presence of a Lewis acid (LA) giving rise to chelate control. 相似文献
A dynamic MC model was developed to simulate the polymerization kinetics and the detailed microstructure of copolymers made with ATRP in a batch reactor. The model was used to predict monomer conversion, average molecular weight, polydispersity index, and copolymer composition as a function of polymerization time. The model can also predict the distribution of molecular weight, chemical composition, and comonomer sequence length at any polymerization time or comonomer conversion. The simulation was used to explore the effects of rate constants and reactant stoichiometry on the microstructure of chains. Two copolymerization systems were chosen to demonstrate the effect of reactivity ratios and comonomer feed compositions on the final chemical composition distribution.
Simulations of polymerization rate, molecular weight development and evolution of the concentrations of species participating in the reaction mechanism over a range of operating conditions, and a parameter sensitivity analysis showing the effects of temperature, activation/deactivation equilibrium constant and initial concentrations of controller and initiator (if present) on these variables are presented for the nitroxide‐mediated radical polymerization of styrene. The simulations were performed with a computer program based on a detailed reaction mechanism. The simulated profiles of conversion, number average molecular weight ( ), and polydispersity agree well with experimental data. Previously unknown activation energies for reactions involved in the mechanism are estimated. The temperature dependence of the kinetic rate constants obtained in this study will be useful for future modeling and optimization studies.
Summary: The recently developed initiation system, activators generated by electron transfer (AGET), is used in atom transfer radical polymerization (ATRP) in the presence of a limited amount of air. Ascorbic acid and tin(II ) 2‐ethylhexanoate are used as reducing agents in miniemulsion and bulk, respectively. An excess of reducing agent consumes the oxygen present in the system and, therefore, provides a deoxygenated environment for ATRP. ATRP of butyl acrylate is successfully carried out in miniemulsion and in the presence of air. During polymerization the radical concentration remains constant. The polymerization reaches over 60% monomer conversion after 6 h, which results in polymers with a predetermined molecular weight = 14 000 g · mol−1 and a low polydispersity ( = 1.23). AGET ATRP of styrene is also successful in bulk in the presence of air, as evidenced by linear semi‐logarithmic kinetics, which leads to polystyrene with an of 13 400 g · mol−1 and a low polydispersity index ( = 1.14).
Appearance of miniemulsion before and after the reducing agent ascorbic acid was added (left); and GPC traces representing molecular weights during the AGET ATRP of BA in miniemulsion in the presence of air (right). 相似文献
Synthesis of a water‐soluble polydiacetylene has been achieved by topochemical polymerization in the solid state of the bis(N‐methylimidazolium)diacetylene monomer. Structural characterization for the monomer by X‐ray diffraction and NMR spectroscopy supports a photopolymerization initiated at the surface. Characterization of the polymer (NMR, UV and Raman spectroscopy, and dynamic light scattering) is given along with a molecular modelling interpretation of the polymerization in the solid state.
Summary: Plasma‐initiated controlled/living radical polymerization of methyl methacrylate (MMA) was carried out in the presence of 2‐cyanoprop‐2‐yl 1‐dithionaphthalate. Well‐defined poly(methyl methacrylate) (PMMA), with a narrow polydispersity, could be synthesized. The polymerization is proposed to occur via a RAFT mechanism. Chain‐extension reactions were also successfully carried out to obtain higher molecular weight PMMA and PMMA‐block‐PSt copolymer.
Dependence of ln([M]0/[M]) on post‐polymerization time (above), and \overline M _{\rm n} and PDI against conversion (below) for plasma initiated RAFT polymerization of MMA at 25 °C. 相似文献
Summary: Mesoporous silica was used as substrate for the grafting of alkyl halides initiators. The control over the surface‐initiated polymerization of styrene and MMA, in terms of molar mass and molar mass distribution, was successfully achieved using an ATRP mechanism. The occurrence of the polymerization inside the mesopores was confirmed by thermogravimetric analysis.
Transmission electron microscopy and schematic representation of mesoporous silica functionalized by the anchored iniator (left) and the grafted polymer (right). 相似文献
Amphiphilic star shaped polymers with poly(ethylene oxide) (PEO) arms and cross‐linked hydrophobic core were synthesized in water via either conventional free radical polymerization (FRP) or atom transfer radical polymerization (ATRP) techniques using a simple “arm‐first” method. In FRP, PEO based macromonomers (MM) were used as arm precursors, which were then cross‐linked by divinylbenzene (DVB) using 2,2′‐azoisobutyronitrile (AIBN). Uniform star polymers ( < 1.2) were achieved through adjustment of the ratio of PEO MM, DVB, and AIBN. While in case of ATRP, both PEO MM, and PEO based macroinitiator (MI) were used as arm precursors with ethylene glycol diacrylate as cross‐linker. Even more uniform star polymers with less contamination by low MW polymers were obtained, as compared to the products synthesized by FRP.
A series of organic‐inorganic hybrid particles were synthesized by a self‐assembled layer of different initiators, immobilized on silica particles and used for controlled radical polymerization. We use three different initiator systems for atom‐transfer radical polymerization (ATRP), unimolecular nitroxide mediated polymerization (NMP), and bimolecular NMP, for the development of the hybrid inorganic/organic particles. After preliminary qualitative characterization by X‐ray spectroscopy (XPS) and Fourier‐transformed infrared (FT‐IR) measurements, the hybrid nanoparticles were studied by thermogravimetric analysis (TGA) to determine and discuss the initiator graft density in terms of steric hindrance.
The coupling agents employed for the various approaches used here: a) NMP1‐bimolecular system, b) NMP2‐unimolecular system, and c) ATRP. 相似文献
A facile strategy for synthesis of α‐heterobifunctional polystyrenes is reported. The novel functional polystyrenes have been successfully synthesized via a combination of atom transfer radical polymerization (ATRP) and chemical modification of end‐functional groups. First, ε‐caprolactone end‐capped polystyrenes with controlled molecular weight and low polydispersity were prepared by ATRP of styrene using α‐bromo‐ε‐caprolactone (αBrCL) as an initiator. Then, removal of the terminal bromine atom was performed with iso‐propylbenzene in the presence of CuBr/PMDETA. Finally, ring‐opening modifications of the caprolactone group were carried out with amines, n‐butanol and H2O to produce novel polystyrenes containing two different functional groups at one end.
Water‐soluble single‐ and multi‐walled carbon nanotubes (CNTs) were prepared by grafting polyacrylamide chains from the graphitic surface via ceric ion‐induced redox radical polymerization. The reducing functionalities were covalently attached to the tubes by peroxide‐assisted radical reaction. The results showed that polymer chains were grafted onto CNTs by the redox process. The redox radical polymerization initiated by carbon nanotube‐bearing functionalities not only provides a powerful strategy for modifying the carbon nanostructures but also gives us the knowledge of their sidewall chemistry.
A method for growing polymers directly from the surface of graphene oxide is demonstrated. The technique involves the covalent attachment of an initiator followed by the polymerization of styrene, methyl methacrylate, or butyl acrylate using atom transfer radical polymerization (ATRP). The resulting materials were characterized using a range of techniques and were found to significantly improve the solubility properties of graphene oxide. The surface‐grown polymers were saponified from the surface and also characterized. Based on these results, the ATRP reactions were determined to proceed in a controlled manner and were found to leave the structure of the graphene oxide largely intact.
The synthesis of diblock copolymers of aromatic polyether and polyacrylonitrile (PAN) was conducted by chain‐growth condensation polymerization (CGCP) and atom transfer radical polymerization (ATRP) from an orthogonal initiator. When CGCP for aromatic polyether was carried out from a PAN macroinitiator obtained by ATRP with an orthogonal initiator, decomposition of the PAN backbone occurred. However, when ATRP of acrylonitrile was conducted from an aromatic polyether macroinitiator obtained by CGCP followed by introduction of an ATRP initiator unit, the polymerization proceeded in a well‐controlled manner to yield aromatic polyether‐block‐polyacrylonitrile (polyether‐b‐PAN) with low polydispersity. This block copolymer self‐assembled in N,N‐dimethylformamide to form bundle‐like or spherical aggregates, depending on the length of the PAN units in the block copolymer.
