Photo-mediated atom transfer radical polymerization (ATRP) of acrylonitrile (AN) was carried out at 25°C in N,N-dimethyl formamide (DMF) with aniline as photoinitiator. Polyacrylonitrile (PAN) with predictable average molecular weight and narrow molecular weight distribution was synthesized with 2-Bromopropionitrile (BPN) as ATRP initiator and FeCl3·6H2O/Triphenylphosphine (PPh3) as the catalyst. The obtained kinetics showed that the photoinduced Fe-mediated ATRP of AN provided a route to synthesize well defined PAN with narrow molecular weight distribution (Mw/Mn). The living character of photoinduced Fe-mediated ATRP of AN was verified by the linear increase of molecular weights with monomer conversion and the molecular weights are in good agreement with the theoretic values. In addition, the chain extension experiments were successfully conducted under the same conditions. The periodic light on-off process was investigated for the photoinduced Fe-mediated ATRP of AN. The obtained PAN was characterized by 1H nuclear magnetic resonance and gel permeation chromatography. The brominated PAN was used to perform chain-extension with AN as macroinitiator in order to verify the living nature of photoinduced ATRP of AN-Br. 相似文献
High‐pressure atom transfer radical polymerization (ATRP) of n‐butyl acrylate (BA) is performed in acetonitrile (MeCN) with CuIBr/TPMA [TPMA: tris(2‐pyridylmethyl)‐amine] as the catalyst up to 5 kbar. Increasing either pressure or temperature significantly enhances the rate of polymerization, while retaining control over the polymerization. The polymerizations under high pressure could be efficiently performed with very low levels of Cu catalyst in the absence of any reducing agents. For example, 100 ppm Cu is sufficient to catalyze the polymerization of BA with targeted degree of polymerization (DPT) = 1000. The conversion reached 79% in 3.0 h at 80 °C providing PBA with Mn = 112 000, Mw/Mn = 1.12. Since the initial CuI‐to‐initiator molar ratio is 0.05:1, the molar percentage of terminated chains should remain <5%. For DPT = 10 000 using only 50 ppm Cu catalyst, a polymer with molecular weight Mn = 612 000 (DP = 4800) was obtained at 67% conversion.
Ultrasound‐mediated atom transfer radical polymerization (sono‐ATRP) in miniemulsion media is used for the first time for the preparation of complex macromolecular architectures by a facile two‐step synthetic route. Initially, esterification reaction of sucrose or lactulose with α‐bromoisobutyryl bromide (BriBBr) is conducted to receive multifunctional ATRP macroinitiators with 8 initiation sites, followed by polymerization of n‐butyl acrylate (BA) forming arms of the star‐like polymers. The brominated lactulose‐based molecule was examined as an ATRP initiator by determining the activation rate constant (ka) of the catalytic process in the presence of a copper(II) bromide/tris(2‐pyridylmethyl)amine (CuIIBr2/TPMA) catalyst in both organic solvent and for the first time in miniemulsion media, resulting in ka = (1.03 ± 0.01) × 104 M?1 s?1 and ka = (1.16 ± 0.56) × 103 M?1 s?1, respectively. Star‐like macromolecules with a sucrose or lactulose core and poly(n‐butyl acrylate) (PBA) arms were successfully received using different catalyst concentration. Linear kinetics and a well‐defined structure of synthesized polymers reflected by narrow molecular weight distribution (Mw/Mn = 1.46) indicated 105 ppm wt of catalyst loading as concentration to maintain controlled manner of polymerization process. 1H NMR analysis confirms the formation of new sugar‐inspired star‐shaped polymers. 相似文献
A concept based on diffusion‐regulated phase‐transfer catalysis (DRPTC) in an aqueous‐organic biphasic system with copper‐mediated initiators for continuous activator regeneration is successfully developed for atom transfer radical polymerization (ICAR ATRP) (termed DRPTC‐based ICAR ATRP here), using methyl methacrylate (MMA) as a model monomer, ethyl α‐bromophenylacetate (EBrPA) as an initiator, and tris(2‐pyridylmethyl)amine (TPMA) as a ligand. In this system, the monomer and initiating species in toluene (organic phase) and the catalyst complexes in water (aqueous phase) are simply mixed under stirring at room temperature. The trace catalyst complexes transfer into the organic phase via diffusion to trigger ICAR ATRP of MMA with ppm level catalyst content once the system is heated to the polymerization temperature (75 °C). It is found that well‐defined PMMA with controlled molecular weights and narrow molecular weight distributions can be obtained easily. Furthermore, the polymerization can be conducted in the presence of limited amounts of air without using tedious degassed procedures. After cooling to room temperature, the upper organic phase is decanted and the lower aqueous phase is reused for another 10 recycling turnovers with ultra low loss of catalyst and ligand loading. At the same time, all the recycled catalyst complexes retain nearly perfect catalytic activity and controllability, indicating a facile and economical strategy for catalyst removal and recycling.
The first well‐controlled aqueous atom‐transfer radical polymerization (ATRP) conducted in the open air is reported. This air‐tolerant ATRP was enabled by the continuous conversion of oxygen to carbon dioxide catalyzed by glucose oxidase (GOx), in the presence of glucose and sodium pyruvate as sequential sacrificial substrates. Controlled polymerization using initiators for continuous activator regeneration (ICAR) ATRP of oligo(ethylene oxide) methyl ether methacrylate (OEOMA, Mn=500) yielded polymers with low dispersity (1.09≤?≤1.29) and molecular weights (MWs) close to theoretical values in the presence of pyruvate. Without added pyruvates, lower MWs were observed due to generation of new chains by H2O2 formed by reaction of O2 with GOx. Successful chain extension of POEOMA500 macroinitiator with OEOMA300 (?≤1.3) and Bovine Serum Albumin bioconjugates (?≤1.22) confirmed a well‐controlled polymerization. The reactions in the open air in larger scale (25 mL) were also successful. 相似文献
The potential of initiators for continuous activator regeneration atom transfer radical polymerization (ICAR ATRP) for the synthesis of well‐defined poly(n‐butyl acrylate) is analyzed by means of simulations. The kinetic model accounts for reactivity differences between secondary and tertiary macrospecies and considers the possible influence of diffusional limitations. CuBr2 is used as transition metal salt and the commercially available N,N,N′,N″,N″‐pentamethyldiethylenetriamine as ligand. For targeted chain lengths (TCLs) up to 1000, the ICAR ATRP can be performed relatively quickly, and with ppm levels of ATRP catalyst. For moderate TCLs, slightly higher ppm levels are required if excellent control over chain length is also desired. In all cases, limited loss of end‐group functionality (EGF) results.
High molecular weight polystyrene (PS) was synthesized by ATRP. Under atmospheric pressure (1 bar), PS with Mn up to 200,000 was prepared using either ARGET or ICAR ATRP. Under high pressure (6 kbar), higher molecular weight PS could be obtained due to accelerated radical propagation and diminished radical termination in polymerization of styrene. Therefore, it was possible to synthesize PS with Mn > 1,000,000 and Mw/Mn < 1.25 using AGET ATRP under a pressure of 6 kbar at room temperature. This is the highest molecular weight linear PS prepared by a controlled radical polymerization. 相似文献
NIR‐sensitized photoinduced atom‐transfer radical polymerization (ATRP) is possible by using ppm of CuII/tris(2‐pyridylmethyl)amine (TPMA) as the catalyst, a polymethine as the photosensitizer, and α‐bromophenylacetate as the alkyl halide initiator. Among the polymethines investigated with cationic, zwitterionic, or anionic structures, only the zwitterionic 2 exhibited sensitization activity under NIR light at room temperature resulting in the formation of polymers with controlled molecular weight characteristics and functionalities. The barbital group placed at the meso‐position of 2 caused the activity in this photo‐ATRP framework. The chain‐end fidelity of the polymers was confirmed by chain extension and block copolymerization experiments. The polymerization system exhibits high photostability under NIR light exposure and irradiation dependency as demonstrated by light on/off experiments. 相似文献
Controlled polymerization of (meth)acrylamides was achieved by ATRP using the initiating system methyl 2‐chloropropionate/CuCl/tris(2‐dimethylaminoethyl)amine. Linear increase of molecular weights with conversion and low polydispersity (Mw/Mn < 1.2) were obtained in toluene, at room temperature, when N,N‐dimethylacrylamide was used as a monomer. However, the polymerization reached limited conversion, which could be enhanced by increasing the catalyst/initiator ratio. The limited conversion is not due to the loss of the active chains, but rather to the loss of activity of the catalytic system. 相似文献
Low concentration limitations of the catalyst and conventional free radical polymerization are investigated in the system of initiators for continuous activator regeneration atom transfer radical polymerization (ICAR ATRP) of butyl methacrylate (BMA), in which 2,2-azobisisobutyronitrile (AIBN) is used as a reducing agent, pentamethyldiethylenetriamine (PMDETA) as a ligand, copper bromide (CuBr2) as a catalyst and ethyl 2-bromoisobutyrate (EBiB) as an initiator. Results show that conventional radical polymerization happens in the early stage of the ICAR ATRP of BMA when the amounts of AIBN are 3~25 times of the catalyst. And with the increase of the conversion, the BMA polymerization solely conducts the controlled radical polymerization (CRP). The low concentration limitations (based on monomer) of the catalyst required in ICAR ATRP of BMA with good controllability are found to be closely related to the molar ratio of initiator to catalyst, which is determined by the stability of the catalyst/ligand complex. The smaller molar ratio of initiator to catalyst allows lower concentration limitations of the catalyst. 相似文献
Environmentally friendly iron(II) catalysts for atom‐transfer radical polymerization (ATRP) were synthesized by careful selection of the nitrogen substituents of N,N,N‐trialkylated‐1,4,9‐triazacyclononane (R3TACN) ligands. Two types of structures were confirmed by crystallography: “[(R3TACN)FeX2]” complexes with relatively small R groups have ionic and dinuclear structures including a [(R3TACN)Fe(μ‐X)3Fe(R3TACN)]+ moiety, whereas those with more bulky R groups are neutral and mononuclear. The twelve [(R3TACN)FeX2]n complexes that were synthesized were subjected to bulk ATRP of styrene, methyl methacrylate (MMA), and butyl acrylate (BA). Among the iron complexes examined, [{(cyclopentyl)3TACN}FeBr2] ( 4 b ) was the best catalyst for the well‐controlled ATRP of all three monomers. This species allowed easy catalyst separation and recycling, a lowering of the catalyst concentration needed for the reaction, and the absence of additional reducing reagents. The lowest catalyst loading was accomplished in the ATRP of MMA with 4 b (59 ppm of Fe based on the charged monomer). Catalyst recycling in ATRP with low catalyst loadings was also successful. The ATRP of styrene with 4 b (117 ppm Fe atom) was followed by precipitation from methanol to give polystyrene that contained residual iron below the calculated detection limit (0.28 ppm). Mechanisms that involve equilibria between the multinuclear and mononuclear species were also examined. 相似文献