Radical Polymerization of Methyl Methacrylate in the Presence of Aromatic Nitroso Compounds

Features of radical polymerization of methyl methacrylate in the presence of various aromatic nitroso compounds (nitrosobenzene, nitrosodurene, 2,4,6-tribromonitrosobenzene) as potential sources of stable nitroxyl radicals controlling the chain propagation were studied.     

甲基丙烯酸甲酯自由基聚合反应的统计理论研究

在自由基聚合反应中,每个聚合物分子都是经历成百上千次加成聚合形成。由于聚合次数不完全相同造成实际链长的不等性,故由稳态近似法所获得的结果只是一个平均的概念,对反应未达平衡态时不适用。本文运用统计的方法,克服了非稳态方法的限制。通过从任意时间微元扩展至反应结束,获得了甲基丙烯酸甲酯聚合反应相应的统计关系式,如聚合物的数量、重量分布及聚合物的平均分子量等,对深入了解高分子化学反应的本质具有重要的价值和意义。     

Homogeneous Solution Reverse Atom Transfer Radical Polymerization of Methyl Methacrylate

A homogeneous reverse atom transfer radical polymerization (RATRP) of methyl methacrylate (MMA) was successfully carried out in N, N-dimethylformamide(DMF) (25%, v/v) at 69°C, using an initiating system azobisisobutyronitrile (AIBN)/CuBr₂/N, N, N′, N″, N″-pentamethyldiethylenetriamine (PMDETA). The kinetics of homogeneous solution polymerizations showed linear first-order rate plots, indicating a constant number of growing species throughout the polymerization as well as a negligible contribution of termination or transfer reactions; a linear increase of the number-average molecular weight with conversion, and relatively low polydispersities, but low initiator efficiency. The dependence of the rate of polymerization on the concentrations of initiator, catalyst, ligand and temperature were presented.     

Effect of Some Solvents on the Radical Polymerization of Methyl Methacrylate Studied by Differential Scanning Calorimetry

The course of the isothermal polymerization of methyl methacrylate in different concentrated solutions in toluene, n-butyl acetate, cyclohexanone, and dimethylformamide was measured at four temperatures by differential scanning calorimetry. The conversions at the sharp increase of the reaction rate were found to increase with dilution of the reaction mixture. The polymerization enthalpies and the composite rate constants were calculated. The polymerization enthalpies seem to be solvent independent. The composite rate constants for polymerization in butyl acetate are lower and those for polymerization in toluene are equal to the constants for bulk polymerization. They are independent of the concentration of the reaction system. The constants for polymerization in cyclohexanone and dimethylformamide are, however, concentration dependent. An interrelation between the composite rate constants and solubility parameters of the solvents and methyl methacrylate was found. The relative molecular weight averages decrease with decreasing concentration of the reaction mixture. The MW distributions were very broad.     

Some Peculiarities of the Radical Polymerization of Methyl Methacrylate in the Presence of Low Molecular Weight Liquid Crystals

Abstract

Radical polymerization of methyl methacrylate (MMA) in the presence of propylbenzene, benzonitrile, their equimolar mixture, and a mixture of nematic liquid crystals (LC) was studied. Chain transfer reaction and unexpected dependence of the initial polymerization rate on LC concentration were revealed by means of UV spectrophotometry, viscometry, and dilatometry. The chain transfer reaction which occurred at the boundary of LC domains in the polymer matrix caused binding of some of the LC molecules to the macromolecules of PMMA. An increase in the initial rate of polymerization and a decrease of polydispersity were explained with formation of the LC phase because growth of the macroradicals continued not only in the homogeneous polymer phase but simultaneously also at the interfacial boundary between the polymer matrix and the LC phase. It is assumed that the LC molecules anchored to the PMMA matrix can affect the mobility of free LC molecules in the LC domains when an external electric field is applied to LC/polymer composite films.     

Aqueous Polymerization of Methyl Methacrylate Initiated by Potassium Pervanadate

The aqueous polymerization of methyl methacrylate was kinetically studied using acidic (H₂SO₄) potassium pervanadate as initiator. The initiator exponent was 0.3 and the monomer exponent was 1.0. Polymerization is considered to proceed by a radical mechanism, and termination takes place quite measurably by a degradative initiator transfer mechanism.     

室温下甲基丙烯酸甲酯原子转移自由基乳液聚合反应研究

以卤化亚铜（CuX）/1,10-邻二氮菲（phen）配合物为催化剂、2-溴代异丁酸 乙酯（EBiB）为引发剂、十二烷基磺酸钠（SLS）为乳化剂,进行了甲基丙烯酸甲 酯（MMA）的原子转移自由基乳液聚合（ATRP）反应。结果表明,与较高温度（70 - 90 ℃）下的聚合反应相比,室温（25 ℃）时聚合反应有更好的可控性,通过 外加钝化剂的复合催化引发体系CuBr/CuBr_2/phen/EBiB或利用CuCl/phen/EBiB催 化引发体系的“卤素交换反应”,可进一步改善聚合反应的可控性。紫外发光谱测 定结果表明,CuBr/phen配合物在MMA相中的分配倾向随着温度的降低而增大,使得 室温下MMA的乳液ATRP保持了较好的可控性和较快的反应速度。     

新引发体系引发MMA活性自由基聚合

近年来 ,关于活性自由基聚合的研究极为活跃 ,已经发现了多种基于增长链自由基被可逆钝化形成休眠种的活性自由基聚合方法[1,2 ] .它们主要包括引发转移终止剂 ( Iniferter) ,稳定自由基聚合( SFRP) ,原子转移自由基聚合 ( ATRP) ,可逆加成 -断链链转移聚合 ( RAFT)等 .其中 ATRP因其具有可聚合单体多 ,反应条件相对缓和等优点而成为该领域的研究热点 [3～ 5] .ATRP活性自由基聚合的实现主要是在过渡金属催化剂的作用下 ,通过循环往复的碳 -卤键的活化、加成、碳 -卤键的再形成而得到最终活性的聚合物 ,引发体系由引发剂、过渡金属…     

Some Studies on the Plasma-Initiated Polymerization of Methyl Methacrylate in the Liquid State

Previous results obtained for the free radical polymerization of methyl methacrylate were used to predict the mechanism of plasmainitiated polymerization of this monomer in the liquid state. The data obtained by use of high resolution NMR spectra strongly predict a free radical mechanism for the plasma-initiated polymerization of methyl methacrylate.     

Active Centers for the Stereospecific Polymerization of Methyl Methacrylate by Organomagnesium Compounds

New evidence on the polymerization kinetics of methyl methacrylate and molar mass distributions is presented which together with earlier work on the stereochemistry of the polymerization of α,β-dideuteroacrylates shows that these are not typical anionic polymerizations. The persistence and stability of the active centers, together with evidence that the α-carbon of the monomer assumes the tetrahedral configuration it takes in the polymer chain as it becomes the active chain end, suggests that the active centers are covalent magnesium-carbon bonds. Existing hypotheses about the mechanism of steric control in homogeneous polymerizations are examined. Kinetic evidence confirms that complexing of the monomer to the active center does occur. However, intramolecular complexing of the penultimate or antepenultimate chain carbonyl group to the metal is not a prerequisite for isotactic polymerization though it may be involved in controlling the in-chain configuration of the β-carbon. Gel-permeation chromatography shows that in some systems more than one active center operates independently. These centers are established in the initiation stages and persist. The proportions of active centers of different reactivity and stereo-specificity are determined by conditions prevailing during initiation and it is these that primarily determine the structure of the polymers formed. Evidence is reported that confirms this.     

Employing Imine Macrocycle Ligand in the Atom Transfer Radical Polymerization of Methyl Methacrylate

Imine macrocycle M₁ was successfully used in conjunction with CuBr as a catalytic system in the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA). The role of the reaction conditions was clearly observed. Such reaction conditions were found to be the molar ratios of the reactants, the chosen initiating systems, and some additional ambient conditions (e.g. temperature, solvent). MMA homopolymers were successively prepared via ATRP by using benzhydrylbromide, diethylmethylbromomalonate initiating systems under the appropriate reaction conditions. Definite well‐known structures of the formed polymers were unambiguously identified with ¹H NMR.     

Modeling of the Methyl Methacrylate Atom Transfer Radical Suspension Polymerization Process: Polymerization and Particle Kinetics

In this work, a mathematical model is developed to characterize the batch atom transfer radical suspension polymerization (batch suspension ATRP). For the first time, the morphological and molecular properties of particles, as well as their dynamics in methyl methacrylate ATRP can be simultaneously simulated by solving the model that consists of ATRP kinetic equations, moment equations, a phase equilibrium equation for calculating equilibrium monomer distributions in various phases, and a particle population balance model. The proposed model is verified using the open experimental data. Based on the verified model, two key operating factors including the ratios of monomer to initiator and water to monomer are studied in order to investigate the batch suspension ATRP kinetics. In addition, the model is also used to predict the droplet/particle size distribution. The effects of breakage rate, coalescence rate, and agitation speed on the droplet volume density distribution and the Sauter mean diameter are discussed in details. The simulated results demonstrate that the coupled model can describe the batch suspension ATRP kinetics and its droplet kinetics.

     

Controlled Radical Polymerization of Methyl Methacrylate Catalyzed by Hybrid Supported Iron Catalyst

A supported iron catalyst, which was prepared by anchoring FeCl2/FeCl3 on the cross-linking macroporous polyacrylate ion exchange resin, was evaluated via the controlled radical polymerization. When a small amount of CuCl2/ Me6TREN was added, the controllability of the polymerization over the iron-mediated catalyst was significantly improved（Mw/Mn = 1.23-1.73 ）, affording a polymer with a low residual metal via a simple catalyst separation procedure. After suitable regeneration, the supported iron catalyst could also he recycled. UV-Vis analysis showed that the additional copper catalyst could facilitate the radical deactivation process.     

Controlled Polymerization of Methyl Methacrylate in the Presence of C-Phenyl-N-tert-Butylnitrone and Commercial Radical Initiators

Radical polymerization of methyl methacrylate initiated by dicyclohexyl peroxydicarbonate in the presence of a chain-terminating agent, C-phenyl-N-tert-butylnitrone, as a potential source of stable nitroxyl radicals, was studied.     

Atom Transfer Radical Polymerization of Methyl Methacrylate Using Telechelic Tribromo Terminated Polyurethane Macroinitiator

Novel telechelic tribromo terminated polyurethane (Br₃-PU-Br₃) was used as a macroinitiator in atom transfer radical polymerization (ATRP) of methyl methacrylate using CuBr as a catalyst and NN,N',N”,N”-pentamethyldiethylenetriamine (PMDETA) as a ligand. During the course of polymerization, poly(methyl methacrylate)-b-polyurethane-b-poly(methyl methacrylate) (PMMA-b-PU-b-PMMA) tri-block copolymers were formed. The resulting tri-block copolymers were characterized by gel permeation chromatography (GPC) and ¹H nuclear magnetic resonance (NMR) spectroscopy. Molecular weight of the tri-block copolymers increases with increasing conversion. This result shows Br₃-PU-Br₃/CuBr/PMDETA initiating system polymerized methyl methacrylate through ATRP mechanism. NMR spectroscopy results revealed that apart from bromine atom transfer from Br₃-PU-Br₃ to PMDETA-CuBr complex, bromine atom transfer from the initially formed tri-block copolymer to PMDETA-CuBr complex also takes place, and, as a result, double bond terminated copolymer formed. Mole ratio of polyurethane and poly(methyl methacrylate) present in the PMMA-b-PU-b-PMMA tri-block copolymers was calculated using ¹H-NMR spectroscopy and it was found to be comparable with the mole ratio calculated through GPC results. Differential scanning calorimetric results confirmed the presence of two different phases in the tri-block copolymers.     

新型引发体系引发MMA"活性"自由基聚合

传统的原子转移自由基聚合(ATRP)引发体系是由卤化物(引发剂)、低价过渡金属和合适的配体组成的络合物(催化剂)[1,2],即RX/Mnt/LX,三部分组成的.但由于卤化物的毒性和低价过渡金属易被空气中的氧气氧化,因此Matyjaszewski等[3,4]和Teyssié等[5]提出了新的引发体系反向ATRP.反向ATRP用传统引发剂(如AIBN)代替卤化物,用高价过渡金属络合物代替原来的催化体系,即AIBN/Mn+1t/LX,就避免了上述两个缺点.反向ATRP的引发反应机理表述如下:　　目前已见诸报道的关于反向ATRP的文献甚少[3～5],所使用的引发剂均为AIBN.Wang和Matyja…     

Facile Soap‐Free Miniemulsion Polymerization of Methyl Methacrylate via Reverse Atom Transfer Radical Polymerization

A facile soap‐free miniemulsion polymerization of methyl methacrylate (MMA) was successfully carried out via a reverse ATRP technique, using a water‐soluble potassium persulfate (KPS) or 2,2′‐azobis(2‐methylpropionamidine) dihydrochloride (V‐50) both as the initiator and the stabilizer, and using an oil‐soluble N,N‐n‐butyldithiocarbamate copper (Cu(S₂CN(C₄H₉)₂)₂) as the catalyst without adding any additional ligand. Polymerization results demonstrated the “living”/controlled characteristics of ATRP and the resultant latexes showed good colloidal stability with average particle size around 300–700 nm in diameter. The monomer droplet nucleation mechanism was proposed. NMR spectroscopy and chain‐extension experiments under UV light irradiation confirmed the attachment and livingness of UV light sensitive  S C(S) N(C₄H₉)₂ group in the chain end.     

四丁基碘化铵催化甲基丙烯酸甲酯的可逆-休眠自由基溶液聚合

以四丁基碘化铵(BNI) 为有机催化剂, 碘单质(I₂) 与偶氮二异庚腈(ABVN) 原位生成的碘代异庚腈为引发剂, 进行甲基丙烯酸甲酯(MMA) 的溶液聚合. 以甲苯为溶剂, MMA:I₂:ABVN的摩尔比为200:1:1.7, 考察了催化剂用量对聚合的影响. 结果表明, 加入催化剂可以缩短诱导期, 当I₂:BNI摩尔比为1:1时聚合反应的诱导期最短(1.7 h); 当BNI:I₂摩尔比为0.25:1~2:1之间时, 聚合物实测分子量与理论值十分接近, 分子量分布较窄, 分子量分布指数(M_w/M_n) 多在1.2以下. 考察了在N,N'-二甲基甲酰胺(DMF)、 四氢呋喃(THF)、 苯甲醚、 苯和甲苯5种溶剂中的聚合反应, 发现在苯和甲苯中聚合可控性最佳, M_w/M_n多在1.2以下; 苯甲醚和THF中聚合速率较快, 聚合物分子量分布较苯中的略宽. 以DMF为溶剂时所得聚合物分子量分布很宽, 聚合可控性差. 核磁共振分析聚合物为碘封端结构, 碘原子封端的聚合物链所占比为91.6%.     

Atom Transfer Radical Polymerization of Methyl Methacrylate High Efficiently Initiated by Azo-containing Iniferter

Two novel azo-containing iniferters, (4,4′-(diazene-1,2-diyl) bis(4,1-phenylene) bis(2-(diethylca-rbamothioylthio)-2-methylpropanoate (BDCMP) and 4-((4-bromophenyl)diazenyl)phenyl-2-(diethylcarbamothioylthio)-2-methylpropanoate (PDCMP) were synthesized and used successfully as the initiators for atom transfer radical polymerization of methyl methacrylate (MMA). The kinetic plots were first order and the molecular weights of the polymers with narrow molecular weight distributions increased with the monomer conversions. Furthermore, the results showed that the apparent initiation efficiencies (f was close to 0.90 defined as M _n(th)/M _n(GPC)) of BDCMP and PDCMP were both higher than that (f was lower than 0.5) of 2-N,N-(diethylamino)dithiocarboyl-isobutyrate (EDCIB), which was reported previously by us (14 Zhang, W., Zhu, X. L., Cheng, Z. P. and Zhu, J. 2007. J. Appl. Polym. Sci., 106: 230–7. [Crossref] , [Google Scholar]). The obtained mono- and bi-functional PMMAs containing azo and N,N-diethyldithiocarbamate (DC) groups were confirmed by ¹H-NMR and ultraviolet absorption spectra, respectively. The block copolymer, poly (methyl methacrylate)-b-polystyrene (PMMA-b-PS), was also successfully prepared via the ATRP chain-extension experiment using the obtained PMMA as a macroinitiator.