KINETICS OF SUSPENDED EMULSION POLYMERIZATION OF METHYL METHACRYLATE*

 The kinetics of suspended emulsion polymerization of methyl methacrylate (MMA), in which water acted as the dispersed phase and the mixture of MMA and cyclohexane as the continuous phase, was investigated. It showed that the initial polymerization rate (R_p0) and steady-state polymerization rate (R_p) were proportional to the mass ratio between water and oil phase, and increased as the polymerization temperature, the potassium persulphate concentration ([I]) and the Tween20 emulsifier concentration ([S]) increased. The relationships between the polymerization rate and [I] and [S] were obtained as follows: R_p0∝[I]^0.71[S]^0.23.The above exponents were close to those obtained from normal MMA emulsion polymerization. It also showed that the average molecular weight of the resulting poly(methylmethacrylate) decreased as the polymerization temperature,[I]and [S] increased. Thus, MMA suspended emulsion polymerization could be considered as a combination of many miniature emulsion polymerizations proceeding in water drops and obeyed the classical kinetics of MMA emulsion polymerization.     

N-甲基-N-(2-羟乙基)-对-甲苯胺存在下甲基丙烯酸甲酯的自由基聚合

测定了在N-甲基-N-(2-羟乙基)-对-甲苯胺(HMT)存在下,MMA以过氧化物引发的聚合速率和聚合表观活化能.发现HMT对BPO、LPO引发的MMA聚合有促进作用,提高聚合速率.由聚合物端基分析证实了含有HMT的碎片,表明由芳叔胺HMT与BPO反应产生的自由基能引发单体聚合,BPO-HMT引发聚合为一氧化还原引发聚合.     

受阻胺对甲基丙烯酸甲酯聚合的影响

本文研究了受阻胺TMP、TMPM、TUV-770对MMA、St本体聚合的影响。无论用BPO或AlBN引发MMA聚合时,TMPM或TUV-770都能延长诱导期,但对R_p的影响较小,而TMP能使R_p略增。测定了聚合反应的表观活化能和动力学方程。     

Cu~(2+)离子浓度对Cu~(2+)-Na_2SO_3体系引发甲基丙烯酸甲酯聚合机理的影响

<正> 氧化还原体系引发乙烯类单体自由基聚合过程中,氧化剂或还原剂浓度的变化可能引起聚合机理的改变,Reddy等研究“铜(Ⅱ)——维生素C-氧”体系引发甲基丙烯酸甲酯的自由基聚合时,发现随着Cu~(2+)离子浓度增加,聚合速度由上升至下降;单体反应级数从3/2增至2.0,我们在空气气氛下,对Cu~(2+)-Na_2SO_3体系引发甲基丙烯酸甲酯聚合进行了研究,亦发现Cu~(2+)离子浓度对聚合速度和聚合机理有很大影响,在较低的Cu~(2+)离子浓     

含胺基功能性单体的聚合研究——Ⅶ.N-(4-N′,N′-二甲氨基苯基)代丙烯酰胺作为氧化还原引发体系组分的研究

<正> 我们曾报道过甲基丙烯酸-4-N,N-二甲氨基苄酯(DMABMA),4-N,N-二甲氨基苯乙烯(DMAS)等含芳香叔胺基的烯类衍生物不仅可以作为氧化还原引发体系组分引发烯类单体如甲基丙烯酸甲酯(MMA)的聚合,而且还进入MMA的聚合物链中。在另文中报道了两个芳香叔胺取代的丙烯酰胺:N-(4-N′,N′-二甲氨基苯基)丙烯酰胺(DMAPAA)和N-(4-N′,N′-二甲氨基苯基)甲基丙烯酰胺(DMAPMA)的合成及其聚合的研究,本文研究了这两个丙烯酰胺衍生物与过氧化苯甲酰(BPO)组成的氧化还     

有机过氧化物-芳叔胺体系引发甲基丙烯酸甲酯聚合的研究

以过氧化二酰(BPO、LPO)或有机过氧化氢物(TBH、CHP)和芳叔胺如DMA或对位具有不同取代基的衍生物组成的引发体系进行MMA聚合,研究过氧化物与胺的结构对聚合的影响。结果表明,过氧化二酰的活性要比有机过氧化氢物大,其顺序为BPO>LPO>CHP>TBH。对于BPO-芳叔胺或LPO-芳叔胺体系,芳叔胺中给电子取代基能提高聚合速度,而吸电子取代基能降低聚合速度。测定了MMA聚合的总活化能E_α,BPO-芳叔胺体系时E_α=36-54kJ/mole,LPO-芳叔胺体系时E_α=56-71kJ/mole;还研究聚合动力学。     

可见光敏引发聚合甲基丙烯酸甲酯的动力学研究

本论文用膨胀计法进行了甲基丙烯酸甲酯在氯仿溶液中可见光光敏引发聚合动力学的研究。此光敏引发体系由光敏剂1,3,3-三甲基-2-[5-(1,3,3-三甲基-2-吲哚叉)-1,3-戊二烯]吲哚碘盐(简称NK-529),引发剂邻氯代六芳基双咪唑(简称o-Cl-HABI),氢给体3-巯基-4-甲基-4氢-1,2,4-三氮唑(简称MTA)组成。研究结果表明,此光敏聚合体系的光聚合速率与各组分的动力学方程如下:R_p=K(NK-529)^0.51(HABI)^0.41(MTA)^0.36(MMA)^1.0.     

哌嗪-二氧化硫电荷转移复合物引发的甲基丙烯酸甲酯光聚合

本文研究了哌嗪 (PPZ)与二氧化硫 (SO2 )电荷转移复合物 (CTC)的制备及其作为光引发剂引发甲基丙烯酸甲酯 (MMA)的聚合 ,发现PPZ/SO2 摩尔比对聚合速率影响甚大 .当PPZ/SO2 为 1∶2时 ,形成了具有潜在引发能力的复合物 (Ⅰ ) .Ⅰ引发MMA光聚合的动力学关系式为Rp =Kp [Ⅰ ] 0 .34[MMA] 1.0 6 ,表观活化能为 2 3 7kJ/mol.并对引发机理进行了探讨     

Propagation kinetics of free‐radical polymerizations in ionic liquids

Propagation rate coefficients, k_p, of methyl methacrylate (MMA) and glycidyl methacrylate (GMA) homopolymerizations were measured at ambient pressure in four ionic liquids (ILs): 1‐ethyl‐3‐methylimidazolium ([emim]) ethyl sulfate and [emim] hexyl sulfate as well as butyl‐3‐methylimidazolium ([bmim]) hexafluorophosphate and [bmim] tetrafluoroborate via the pulsed‐laser polymerization size‐exclusion chromatography technique. In passing from bulk polymerization at 40 °C polymerization in IL solution containing 20 vol % monomer, k_p is enhanced by up to a factor of 4 with MMA and by a factor of 2 with GMA. This enhancement of k_p primarily results from a lowering of activation energy upon partial replacement of monomer by ionic liquid species. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1460–1469, 2008     

以阳离子乳化剂进行丙烯酸丁酯－苯乙烯乳液共聚的动力学研究

采用十二烷基二甲基苄基氯化铵（１２２７）乳化剂，对丙烯酸丁酯（ＢＡ）－苯乙烯（Ｓｔ）进行乳液共聚，研究了影响聚合速度的各种因素，得出了聚合速率方程和表观活化能．     

甲基丙烯酸甲酯水溶性对其悬浮均聚动力学的影响

通过比较在大水油比下的甲基丙烯酸甲酯 (MMA)悬浮均聚的实验数据以及本体聚合实验结果 ,发现单体的水溶性对其聚合动力学有影响 ,不能用本体聚合动力学代替其悬浮聚合动力学 .为了能更好了解单体的水溶性对其悬浮聚合动力学的影响以及影响动力学的原因 ,在MMA本体聚合动力学模型基础上 ,进一步提出 3个假设 :扣除溶于水相部分的单体量、增长和终止速率参数降低、少部分的油溶性引发剂被带到水相中 ,得到改进的悬浮聚合动力学模型 .运用该模型能很好预测水油比、聚合温度、引发剂浓度等对MMA悬浮聚合动力学的影响 ,且与实验数据能较好吻合     

过硫酸盐-N,N,N′,N′-四甲基乙二胺体系引发乙烯基类单体聚合动力学的研究

研究了过硫酸盐-TMEDA体系引发丙烯酰胺、丙烯腈、甲基丙烯酸甲酯水溶液聚合的规律.发现[TMEDA]/[过硫酸盐]的比值起始增大时,聚合速度R_p与转化率都增大,但达到某一值后,如>5,R_p虽然增大而转化率反而下降.聚合物的分子量则总是下降,测定了三种单体聚合的表观活化能E_α和聚合速度方程。     

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.     

胺对有机过氧化物引发聚合的影响

<正> 有机过氧化物引发烯类单体的聚合,可以加入芳叔胺促进过氧化物的分解,提高聚合速度。其中最常用的芳叔胺有N,N-二甲苯胺(DMA)、N,N-二甲基对甲苯胺(DMT),本文采用过氧化二苯甲酰(BPO)、过氧化二月桂酰(LPO)、叔丁基过氧化氢(TBH)和过氧化苯甲酸叔丁酯(TBPB)四种过氧化物为引发剂进行甲基丙烯酸甲酯(MMA)的本体聚合,测得其聚合速度R_p的顺序为LPO>BPO>TBH>TBPB,但在添加芳叔胺DMT或脂环叔胺N-乙基哌啶(NEP)时,则聚合速度的顺序变为BPO-胺>LPO-胺>TBH-胺>TBPB-胺。添加这两种叔胺虽然都能促进聚合,但只对BPO引发剂有显著的影响,研究结果如下:     

Ionic Liquids - New Solvents in the Free Radical Polymerization

Summary: The analysis of the influence of ionic liquids (ILs) in polymer synthesis as an alternative for common organic solvents is still an active field of research. 1 Using ILs as solvents for free radical polymerizations implies a significant increase in polymerization rates and molecular weights which can be observed. In this work we examined the copolymerization behaviour of styrene (S) and methyl methacrylate (MMA), glycidyl methacrylate (GMA) and 2-hydroxypropyl methacrylate (HPMA) with acrylonitrile (AN) in 1-etyhl-3-methylimidazolium ethylsulfate ([EMIM]EtSO₄). ILs are liquids with comparable high polarities and viscosities. These two characteristic properties are strongly correlated with the rate coefficients of propagation k_p and termination k_t. 2 - 4 The rate constant of termination k_t decreases when the IL concentration and therefore the viscosity of the reaction mixture is increased, whereas the propagation rate coefficient k_p increases with increasing IL content. The viscosity of the IL can be varied by either working with mixtures of IL with conventional organic solvents – here the IL [EMIM]EtSO₄ was mixed with DMF – or by variation of the temperature. The influence of the viscosity of the IL ([EMIM]EtSO₄) on polymerization kinetics of methyl methacrylate (MMA) and styrene/acrylonitrile (S/AN) was investigated.     

Polymerizable bis(2-ethylhexyl)sulfosuccinate: application in microemulsion polymerization

A hygroscopic and polymerizable salt ([2-methacryloyloxy]ethyl trimethylammonium chloride) is used to ion exchange the sodium ion in AOT (bis[2-ethylhexyl]sulfosuccinate, sodium salt) to produce a polymerizable form of AOT, MDOS ([2-methacryloyloxy]ethyl trimethylammonium bis[2-ethylhexyl]sulfosuccinate). A partial ternary phase diagram of water, MDOS, and methyl methacrylate (MMA) was determined at room temperature (22 +/- 1 degrees C). A relatively large L2 domain is obtained, but this domain is smaller than that obtained with AOT. Microemulsion polymerization in this domain at 70 degrees C, using AIBN (azoisobutyronitrile) as an initiator, produces an optically clear copolymer solid domain nearly as large as the L2 domain. This interesting behavior contrasts with similar studies of Pavel and Mackay [Langmuir 2000, 16, 8528] using a polymerizable surfactant DDAMA (didecyldimethylammonium methacrylate) that produced a much larger L2 domain than MDOS but yielded a much smaller optically clear domain after thermally initiated polymerization. Thermogravimetric analysis indicates that optically clear composites obtained at an MDOS/MMA weight ratio of 1:4 and containing 5% water (w/w; weight % water in microemulsion) released the water in a transition commencing around 160 degrees C and continuing to 250 degrees C. Thereafter, the thermal decomposition was substantially impeded relative to poly(methyl methacrylate) as a control, which was due to the fire-resistant nature of the MDOS monomer. Molecular weight measurements indicate MDOS/MMA copolymers form substantially higher molecular weights as the proportion of MDOS increases. At a given radius of gyration, higher MDOS-containing copolymers exhibit higher molecular weights, suggesting a more compact structure with increasing MDOS.     

新型乳液聚合制备疏松PMMA树脂及成粒机理

采用以水相为分散相、甲基丙烯酸甲酯 (MMA) 环己烷混合物为连续相的新型乳液聚合制备PMMA树脂 .发现 ,在未加乳化剂和加入少量Tween2 0乳化剂时 ,均可制备由初级粒子凝聚而成、无明显皮膜结构的疏松PMMA粒子 ,初级粒子粒径小于环己烷存在下MMA悬浮聚合得到的PMMA粒子的初级粒子 .根据聚合体系相构成、PMMA在MMA 环己烷混合液的溶解性及PMMA粒子粒径分布和形态的演变 ,提出了在分散水滴内乳液聚合形成初级粒子 生长 凝聚的新型乳液聚合成粒机理     

以阳离子乳化剂进行丙烯酸丁酯－苯乙烯乳液共聚的动力学研究

采用十二烷基二甲基苄基氯化铵（１２２７）乳化剂，对丙烯酸丁酯（ＢＡ）－苯乙烯（Ｓｔ）进行乳液共聚，研究了影响聚合速度的各种因素，得出了聚合速率方程和表观活化能。     

Kinetics of dispersion polymerization: Effect of medium composition

The effect of the medium composition (monomer and solvent) on the kinetics of dispersion polymerization of methyl methacrylate (MMA) was studied via reaction calorimetry. It was found that increasing the monomer concentration increased the reaction rate; the exponent of the dependency of the initial reaction rate on the MMA concentration was found to be 0.93. Narrow particle size distributions were achieved at the lower monomer concentrations (0.24–0.81 mol/L) and a minimum size (2.45 μm) was found at an intermediate concentration (0.44 mol/L). The average molecular weight of the PMMA increased and the molecular weight distribution broadened with increasing monomer concentration. During a dispersion polymerization, the MMA concentration was found to decrease linearly with conversion in both phases, whereas the ratio of concentrations in the particles and continuous phase ([M]_p/[M]_c) remained constant (0.47) with partitioning favoring the continuous phase. The average number of free radicals per particle in MMA dispersion polymerization was estimated to be high from the nucleation stage onward (>5000). The increasing rate during the first ～ 40% conversion was primarily caused by the increasing volume of the polymer particle phase. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3638–3647, 2008     

RAFT Polymerization: Adding to the Picture

SUMMARY: Factors affecting the choice of RAFT agent [RSC(Z) = S] for a given polymerization are discussed. For polymerization of methyl methacrylate (MMA), tertiary cyanoalkyl trithiocarbonates provide very good control over molecular weight and distribution and polymerizations show little retardation. The secondary trithiocarbonate RAFT agents with R = CHPh(CN) also gives good control but an inhibition period attributed to slow reinitiation is manifest. Radical induced reduction with hypophosphite salts provides a clean and convenient process for removal of thiocarbonylthio end groups of RAFT-synthesized polymers. Two methods providing simultaneous control over stereochemistry and molecular weight distribution of chains formed by radical polymerization are reported. Polymerization of MMA in the presence of scandium triflate provides a more isotactic PMMA. A similar RAFT polymerization with trithiocarbonate RAFT agents also provides control and avoids issues of RAFT agent instability seen with dithiobenzoate RAFT agents in the presence of Lewis acids. RAFT polymerization of tetramethylammonium methacrylate at 45 °C provides a more syndiotactic PMMA of controlled molecular weight and distribution (after methylation; mm:mr:rr 2:21:77 compared to 3:35:62 when formed by bulk polymerization of MMA).