Kinetics of emulsifier–free emulsion polymerization of methyl methacrylate

The influences of polymerization temperature, initiator and monomer concentrations, ionic strength of the aqueous phase, as well as ethylene glycol dimethacrylate (EGDM) co-monomer, on the kinetics of the emulsifier-free emulsion polymerization of methyl methacrylate (MMA) and on the properties of the resulting poly(methyl methacrylate) (PMMA) lattices were studied. The polymerizations were carried out using potassium persulfate (KPS) as the initiator. Monodisperse PMMA lattices with particle diameters varying between 0.14–0.37 μm and polymer molecular weights of the order 0.4 × 10⁶ to 1.2 × 10⁶ g/mol were prepared. The initial rate of polymerization increases with increasing temperature, KPS-MMA mole ratio, EGDM content, or with decreasing ionic strength of the aqueous phase. It was shown that the bead size can be limited by reducing the monomer concentration or by using the cross-linking agent EGDM. The ionic strength of the aqueous phase has a dominant effect on final particle diameter and polymer molecular weight. The uniformity of the latex particles increases as the temperature increases or as the initiator concentration decreases. The experimental results can be reasonably interpreted by the homogeneous nucleation mechanism of the emulsifier-free emulsion polymerization of MMA. © 1996 John Wiley & Sons, Inc.     

Preparation of raspberry‐like poly(methyl methacrylate) particles by seeded dispersion polymerization

The facile preparation of nonspherical raspberry‐like poly(methyl methacrylate) (PMMA) particles by seeded dispersion polymerization of methyl methacrylate (MMA) on micron‐sized PMMA seed particles was described. Various polymerization parameters influencing the particle morphology, as well as the polymerization kinetic and morphological stability, were investigated in detail. It was found that the following polymerization conditions were necessary to prepare this kind of nonspherical particles: a relatively low temperature, an appropriate ratio of seed/MMA, an initiator with a relatively low decomposition rate, and a relatively low initiator concentration. These particles showed very good morphological stability at room temperature, but they changed to the spherical ones when heat treated at 60°C in methanol solution of MMA. The experimental results suggest that the prepared PMMA particles were kinetically favored and the localized polymerization of the MMA monomer on PMMA seed particle surface was responsible for the formation of the raspberry‐like particles. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

聚苯乙烯-聚甲基丙烯酸甲酯核-壳粒子的制备

由种子乳液聚合法制备了聚苯乙烯-聚甲基丙烯酸甲酯核-壳粒子。以过硫酸钾(KPS)为引发剂,辛基酚聚氧乙烯醚(OP-10)为乳化剂,合成了聚苯乙烯(PS)种子核;连续滴加甲基丙烯酸甲酯(MMA),在核表面富集MMA,制备了粒径范围在0.16~0.67μm的核-壳粒子;当单体苯乙烯与甲基丙烯酸甲酯(St/MMA)的比为30∶70(质量比)时,所得粒径在0.18μm,粒径分布为0.012。差示扫描量热(DSC)研究显示,复合粒子的玻璃化转变温度(Tg)为97.2℃,峰形单一,表现出良好的热性能。     

Emulsion polymerization of methyl methacrylate in concentration of emulsifiers below their CMCs—polymerization rate,particle size,and particle-size distribution

The emulsion polymerization of methyl methacrylate (MMA) in concentration of emulsifiers below their critical micelle concentrations (CMCs) initiated by K₂S₂O₈ (KPS) was studied. It was observed that the initiator concentration has little effect on both polymerization rate and particle size. However, the polymerization rate is faster and particle size is smaller obviously when decreasing the ratio of the water/monomer or increasing the temperature of polymerization or the amount of the emulsifier. In the range of a 200–400 rpm stirring speed, the polymerization rate is almost unchanged although the particle size become larger with increase in the stirring speed. The monodisperse particle (size about 100–200 nm) can be obtained using this process. The mechanism of emulsion polymerization of MMA in the emulsifier concentration below its CMC is discussed. © 1995 John Wiley & Sons, Inc.     

Particle features of a poly(methyl methacrylate) resin prepared by a new emulsion polymerization process

A new emulsion polymerization process, in which water acted as the dispersed phase and a mixture of methyl methacrylate (MMA) and cyclohexane acted as the continuous phase, was applied to the preparation of a poly(methyl methacrylate) (PMMA) resin. The primary (latex) particles were formed in the early stage of polymerization and coagulated as the polymerization conversion increased. Scanning electron micrographs showed that the final PMMA particles were porous and composed of loosely aggregated primary particles. The porosity characterized by cold di(2‐ethylhexyl) phthalate absorption increased as the water/oil and cyclohexane/MMA mass ratios increased. The PMMA primary particles were smaller than the primary particles in the PMMA resin prepared by suspension polymerization in the presence of cyclohexane. Because of the phase composition of the reaction system, the solubility of PMMA in a mixture of cyclohexane and MMA, and the particle morphology of PMMA, a particle formation mechanism, including the formation, growth, and coagulation of primary particles in dispersed water droplets, was proposed. The primary particles formed mainly through a homogeneous nucleation mechanism and increased in size as MMA diffused from the oil phase to the water phase to the primary particles. The coagulation of the primary particles occurred because of the lower colloidal stability and the space limitations of the primary particles. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1905–1911, 2004     

Comparison of RAFT polymerization of methyl methacrylate in conventional emulsion and miniemulsion systems

In this study, we have conducted the reversible addition-fragmentation chain transfer (RAFT) polymerization of methyl methacrylate (MMA) in two heterogeneous systems, i.e. conventional emulsion and miniemulsion, with identical reaction conditions. The main objective is to compare the living character in both systems according to the nucleation mechanism, the latex stability, the particle sizes and particle size distributions of latexes, the molecular weights and molecular weight distributions (or polydispersity index, PDI) of PMMA, and the kinetics of the RAFT polymerization. The RAFT agent used in both systems was 2-cyanoprop-2-yl dithiobenzoate (CPDB). The effects of an oil-soluble initiator 2,2′-azobisisobutyronitrile (AIBN) and a water-soluble initiator kalium persulfate (KPS) on the RAFT/emulsion and RAFT/miniemulsion polymerizations were investigated. Methyl-β-cyclodextrin (Me-β-CD) was used as a solubilizer. The average molecular weights and molecular weight distributions (PDIs) of dried PMMA samples were characterized by gel permeation chromatography (GPC). The experimental results showed that the RAFT/miniemulsion polymerization of MMA exhibited better living character than that of RAFT/emulsion polymerization under the conditions of our experiment. The PDI of PMMA in RAFT/miniemulsion polymerization was decreased with the addition of Me-β-CD. However, Me-β-CD did not have influence on the PDI of PMMA prepared in RAFT/emulsion polymerization.     

Polymerization of methyl methacrylate in 3-component cationic microemulsion

Methyl methacrylate has been polymerized in three-component o/w microemulsions made with the cationic surfactant dodecyltrimethylammonium bromide (DTAB). The effects of temperature type and concentration of initiator (AIBN or potassium persulfate), and surfactant and monomer concentration on polymerization kinetics are investigated. Final conversions and reaction rates increase with increasing monomer and initiator concentrations and with higher reaction temperatures. The rate of polymerization shows initiation and termination intervals, but no constant rate interval is observed. Both molecular weight and particle size decrease as the concentration of initiator increases, regardless of type of initiator. Latexes with small particle size (< 70 nm) and high molecular weights (>10⁶) were obtained in all cases. Activation energies for the microemulsion polymerization of MMA with AIBN (10.3 kcal/mol) and KPS (13.4 kcal/mol) are smaller than that of bulk polymerization using AIBN (20 kcal/mol). © 1993 John Wiley & Sons, Inc.     

Synthesis of chitosan‐modified poly(methyl methacrylate) by emulsion polymerization

Emulsion polymerization of methyl methacrylate (MMA) in the presence of chitosan was studied and a reaction mechanism was proposed. It was proved in the companion article that potassium persulfate (KPS) free radicals can degrade chitosan chains into chain free radicals. Therefore, it is possible to produce a chitosan copolymer when the monomer and the KPS initiator are added into the chitosan solution. According to the proposed mechanism, concentrations of different species such as the initiator, total free radicals, and degraded chitosan chain were calculated with the reaction time. All the results agreed with the experimental observation. The results showed that the polymerization rate varied with 0.83‐ and 0.82‐order of the total free‐radical concentration and chitosan repeating unit concentration, respectively. It was also verified that chitosan played multiple roles in the reaction system. If the monomer was added into the chitosan solution before the addition of KPS, chitosan served mainly as a surfactant. Consequently, the polymer particle number was increased with the chitosan addition and so was the polymerization rate. However, if the monomer was added into the solution where the chitosan was already degraded by KPS, the polymerization rate was decreased with the predegradation time of chitosan. In both cases, the final polymer particles consisted of the poly(methyl methacrylate) (PMMA) homopolymer and the chitosan‐PMMA copolymer. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3047–3056, 2002     

Preparation of polystyrene/poly(methyl methacrylate) core‐shell composite particles by suspension‐emulsion combined polymerization

Suspension‐emulsion combined polymerization process, in which methyl methacrylate (MMA) emulsion polymerization constituents (EPC) were drop wise added to styrene (St) suspension polymerization system, was applied to prepare polystyrene/poly(methyl methacrylate) (PS/PMMA) composite particles. The influences of the feeding condition and the composition of EPC on the particle feature of the resulting composite polymer particles were investigated. It was found that PS/PMMA core‐shell composite particles with a narrow particle size distribution and a great size would be formed when the EPC was added at the viscous energy dominated particle formation stage of St suspension polymerization with a suitable feeding rate, whereas St‐MMA copolymer particles or PS/PMMA composite particles with imperfect core‐shell structure would be formed when the EPC was added at the earlier or later stage of St suspension polymerization, respectively. It was also showed that the EPC composition affected the composite particles formation process. The individual latex particles would exist in the final product when the concentrations of MMA monomer, sodium dodecyl sulfate emulsifier, and potassium persulfate initiator were great in the EPC. Considering the feature of St suspension polymerization and the morphology of PS/PMMA composite particles, the formation mechanism of PS/PMMA particles with core‐shell structure was proposed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis of well‐defined poly(methyl methacrylate) nanoparticles by reverse atom transfer radical polymerization in a microemulsion

Well‐defined poly(methyl methacrylate) (PMMA) with an α‐isobutyronitrile group and an ω‐bromine atom as the end groups was synthesized by the microemulsion polymerization of methyl methacrylate (MMA) at 70°C with a 2,2′‐azobisisobutyronitrile/CuBr₂/2,2′‐bipyridine system. The conversion of the polymerization reached 81.9%. The viscosity‐average molecular weight of PMMA was high (380,000), and the polydispersity index was 1.58. The polymerization of MMA exhibited some controlled radical polymerization characteristics. The mechanism of controlled polymerization was studied. The presence of hydrogen and bromine atoms as end groups of the obtained PMMA was determined by ¹H‐NMR spectroscopy. The shape and size of the final polymer particles were analyzed by scanning probe microscopy, and the diameters of the obtained particles were usually in the range of 60–100 nm. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3670–3676, 2006     

甲基丙烯酸甲酯/改性纳米碳酸钙原位非均相聚合

将偶氮二氰基戊酸螯合到纳米碳酸钙表面，引发甲基丙烯酸甲酯非均相聚合，对聚合动力学和聚甲基丙烯酸甲酯(PMMA)在纳米碳酸钙表面的包覆进行了研究。差热扫描量热分析表明偶氮引发剂与纳米碳酸钙螯合后分解温度略有降低；随着螯合引发剂浓度和聚合温度增加，聚合速率增加；随着碳酸钙含量增加，聚合速率降低；PMMA接枝率随聚合转化率增加而增加，而接枝效率下降；随聚合进行，纳米粒子团聚体会剥离成较小粒子，复合粒子的粒径减小。     

ZrO2/聚甲基丙烯酸甲酯纳米复合物:制备及其在聚合物阵列中的分散（英文）

ZrO2/PMMA nanocomposite particles are synthesized through an in-situ free radical emulsion polymerization based on the silane coupling agent (Z-6030) modified ZrO2 nanoparticles, and the morphology, size and its distribution of nanocomposite particles are investigated. Scanning electron microscopy (SEM) images demonstrate that the methyl methacrylate (MMA) feeding rate has a significant effect on the particle size and morphology. When the MMA feeding rate decreases from 0.42ml·min-1 to 0.08ml·min-1 , large particles (about 200-550nm) will not form, and the size distribution become narrow (36-54nm). The average nanocomposite particles size increases from 34nm to 55nm, as the MMA/ZrO2 nanoparticles mass ratio increased from 4:1 to 16:1. Regular spherical ZrO2/PMMA nanocomposite particles are synthesized when the emulsifier OP-10 concentration is 2mg·ml-1. The nanocomposite particles could be mixed with VAc-VeoVa10 polymer matrix just by magnetic stirring to prepare the ZrO2 /PMMA/VAc-VeoVa10 hybrid coatings. SEM and atomic force microscopy (AFM) photos reveal that the distribution of the ZrO2 /PMMA nanocomposite particles in the VAc-VeoVa10 polymer matrix is homogenous and stable. Here, the grafted-PMMA polymer on ZrO2 nanoparticles plays as a bridge which effectively connects the ZrO2 nanoparticles and the VAc-VeoVa10 polymer matrix with improved comparability. In consequence, the hybrid coating with good dispersion stability is obtained.     

Mechanism of microemulsion polymerization of methyl methacrylate: Experimental evidence

Free radical polymerization of methyl methacrylate in emulsion and microemulsion media was studied for the understanding of the mechanism of the polymerization process. Average particle size of the poly(methyl methacrylate) (PMMA) latex formed during microemulsion polymerization was observed to be ≈ 45 nm. Nuclear magnetic resonance data indicated a larger number of interactions for β-methylene protons of PMMA synthesized in microemulsion, indicating dominant isotaciticity in the polymer. Activation energy of degradation of the products was calculated by Broido's method and was found to be 44.70 kJ/mol and 65.47 kJ/mol for PMMA synthesized from microemulsion and emulsion media, respectively. Solution properties of the above polymers were also studied. Intramolecular expansion factors indicate a more rigid structure for PMMA synthesized from microemulsion medium. © 1996 John Wiley & Sons, Inc.     

纳米级PU-PMMA LIPN的制备与结构研究

以异佛尔酮二异氰酸酯(IPDI)、聚四氢呋喃醚二醇(PTMG)、聚醚多元醇(PPG3010)、二羟甲基丙酸(DMPA)等为主要原料,甲基丙烯酸甲酯(MMA)为降粘剂合成了聚氨酯(PU)-MMA乳液;采用无皂原位乳液聚合的方法,MMA在PU-MMA乳液内部聚合,制备了纳米级的PU-聚甲基丙烯酸甲酯(PMMA)乳液互穿聚合物网络(LIPN)。对PU-PMMA复合乳液的结构、乳胶粒子粒径、成膜后PU和PMMA两相的相容性进行了讨论。结果表明,PU-PMMA复合结构已经形成;乳胶粒子的粒径分布多在20 nm,由于比表面积较大,部分小粒径粒子发生了团聚;复合体系只有一个Tg且介于PU和PMMA的Tg之间;成膜后PU和PMMA的相畴小于50 nm。     

Preparation and properties of chitosan‐graft‐poly(methyl methacrylate) nanoparticles using potassium diperiodatocuprate (III) as an initiator

Graft copolymer nanoparticles prepared from chitosan (CS) and methyl methacrylate (MMA) monomer were synthesized in aqueous solution by using potassium diperiodatocuprate [Cu(III)] as an initiator and characterized in terms of particle size, zeta potential, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy, thermal stability, and X‐ray diffraction spectrometry. The results indicated that CS was covalently linked to poly(methyl methacrylate) (PMMA), and the resulting copolymers formed nanoparticles. These nanoparticles [prepared at 35°C, in a weight ratio of MMA/CS of 5 : 1 and with a Cu(III) concentration of 1.5 × 10⁻³ mol/L] were 54–350 nm in size, with a mean hydrodynamic diameter of 183 ± 3 nm and were highly uniform in particle‐size distribution, with a rather spherical shape and an obvious positive charge surface. The effect of reaction conditions such as Cu(III) concentration, reaction temperature, and the weight ratio of MMA/CS on the mean particle size was also investigated. Insulin‐loaded nanoparticles were prepared, and their maximal association efficiency was up to 85.41%. The experiment of release in vitro showed that the nanoparticles gave an initial burst release followed by a slowly sustained one. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

PMMA/PAN核-壳粒子制备工艺研究

加入适量的引发剂,通过无皂乳液聚合,以聚甲基丙烯酸甲酯( PMMA)核体为种子乳液,制备了PMMA/PAN核-壳乳液.实验中分别对引发剂量、丙稀腈( AN)滴加量对PMMA/PAN壳层厚度及其粒径和粒径分布的影响进行了较详细的研究,确定了种子乳液聚合法制备PMMA/PAN核-壳结构聚合物粒子的实验方法及条件.通过激光粒度仪、扫描电镜和透射电镜对核-壳粒子的形态结构进行了表征,证明了PMMA/PAN复合粒子的核-壳结构.     

“胶乳共混法”制备天然橡胶／二氧化硅纳米复合材料及其性能

采用γ-甲基丙烯酰氧基丙基三甲氧基硅烷（KH570）改性纳米二氧化硅（SiO2）,然后通过乳液聚合接枝上聚甲基丙烯酸甲酯（PMMA）,再将其与甲基丙烯酸甲酯（MMA）改性的天然胶乳,通过胶乳共混法制备天然橡胶／二氧化硅纳米复合材料,结果显示,纳米二氧化硅表面接枝上了PMMA,二氧化硅在橡胶基体中分散良好,粒径在60～100nm之间,得到的胶膜力学性能有很大的提高。     

Mechanistic study of the formation of amphiphilic core-shell particles by grafting methyl methacrylate from polyethylenimine through emulsion polymerization

The mechanism for the formation of amphiphilic core-shell particles in water is elucidated via a kinetic study of semi-batch polymerization of methyl methacrylate (MMA) grafted from polyethylenimine (PEI) initiated with tert-butyl hydroperoxide in an emulsion polymerization. The monomer conversion, the polymerization kinetics, the particle size, the particle number density, the poly(methyl methacrylate) (PMMA) core diameter, the percentage of unbound PEI, and the grafting efficiency of PMMA were determined at various times during the polymerization. The particle number density and the percentage of unbound PEI were almost independent of the controllable variables. The particle sizes and the core diameters increased with each consecutive batch of monomer addition, while the grafting efficiency of PMMA decreased. These data supported the hypothesis that the PEI-g-PMMA graft copolymers were formed early in the polymerization and later self-assembled to a new phase, micellar microdomains. These microdomains act as loci for subsequent MMA polymerization as the monomer is fed into the reaction, without subsequent formation of new particles. The size of the resulting highly uniform core-shell particles (99-147 nm) can be controlled by choosing the amount of monomer charged. Thus, this polymerization method is viable for a large scale production of core-shell particles with high solids content.     

Online monitoring of drop/particle size and size distribution in liquid–liquid dispersions and suspension polymerizations by optical reflectance measurements

Evolutions of drop/particle size and size distribution in liquid–liquid dispersions and suspension polymerizations of methyl methacrylate (MMA) were monitored by using an online optical reflectance measurement (ORM), and effects of operating parameters such as the agitation rate, concentration of poly(vinyl alcohol) (PVA) dispersant, and initial concentration of poly(methyl methacrylate) (PMMA) in MMA monomer on the Sauter mean diameter (d₃₂) and size distribution of drop/particle were investigated. According to the variations of d₃₂ of drops/particles with time, four characteristic particle formation stages can be identified for suspension polymerization process. The factors that lead to increase the rate of drop break up, such as increasing of concentration of PVA and decreasing of viscosity of dispersed phase, would postpone the particle growth stage. The d₃₂ and size distribution breadth of drops/particles were significant increased when the liquid–liquid dispersions or suspension polymerizations were conducted at low PVA concentrations or MMA/PMMA solutions with high PMMA contents were used as the dispersed phase, in consistent with the scanning electron micrograph observation on final PMMA particles. It is clear that ORM can be effectively applied in online monitoring of size and size distribution of drops/particles in the liquid–liquid dispersions and suspension polymerizations. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43632.     

Octadecyl acrylate - Methyl methacrylate block and gradient copolymers from ATRP: Comb-like stabilizers for the preparation of micro- and nano-particles of poly(methyl methacrylate) and poly(acrylonitrile) by non-aqueous dispersion polymerization

Three random and three block copolymers of methyl methacrylate (MMA) and octadecyl acrylate (ODA) were synthesized by atom transfer radical polymerization. These copolymers were assessed for their application as stabilizers in the one-step non-aqueous dispersion (NAD) polymerization of MMA and of acrylonitrile (AN) in a non-polar solvent mixture of hexane and dodecane. In all cases stable spherical micro-particle colloidal dispersions were formed with particle diameters in the range of 62-2725 nm for PMMA. Uniform monodisperse PMMA particles with standard deviations in size distributions of less than 5% were obtained in two cases demonstrating the utility of ODA:MMA copolymers as replacement preformed stabilizers in the one-step synthesis of MMA micro-spheres. Overall the block copolymer PMMA₆₄-block-PODA₃₆ gave greater control over size when varying the solvent:monomer ration than a related gradient PMMA-PODA copolymer. These copolymers were further used as stabilizers in the one-step NAD polymerization of MMA with ethylene glycol dimethacrylate (EGDMA) under similar conditions allowing for the preparation of monodisperse cross-linked PMMA particles with diameters ranging from 110 to 1700 nm. The general utility of the copolymers as stabilizers was demonstrated by the NAD polymerization of acrylonitrile (AN) in non-polar solvent mixture of hexane and dodecane giving ‘crumpled’ latex dispersions with particle diameters in the range 85-483 nm.