Semi-continuous emulsion polymerization of styrene in the presence of poly(methyl methacrylate) seed particles. Polymerization conditions giving core-shell particles

This work reports the morphology of two-phase latex particles prepared by semi-continuous seed emulsion polymerization of styrene in the presence of polar poly(methyl methacrylate), PMMA, seed particles, using different conditions of non-polar styrene feed rate, rate of initiation, seed particle concentration and temperature of polymerization.The expected latex particle morphology at thermodynamic equilibrium is an inverted core-shell structure where the non-polar polystyrene would form the core. However, depending on the set of process conditions used the morphology of the resulting two-phase particles varied from that of a pure core-shell structure, over intermediate structures in which a shell of PS surrounded a PMMA core containing an increasing number of PS phase domains, to a structure in which the entire PS phase was present as discrete PS phase domain, more or less evenly distributed in a matrix of PMMA.By the use of a caloirimetric reactor system the monomer concentration in the particles during the different polymerization experiments could be calculated by comparing the integral of the polymerization rate curve with the integral of the monomer feed rate. A comparison between particle morphology and the calculated concentration of plasticizing monomer in the polymerizing particles strongly suggested that the diffusivity of the entering oligo radicals determined by the difference between polymerization temperature and the glass transition temperature of the monomer-swollen core polymer is a key factor determining the morphology of two-phase particles prepared by semi-continuous seed emulsion polymerization.Two-phase particles with a true core-shell structure were obtained in experiments where the estimated glass transition temperature of the PMMA phase was only a few degrees below the polymerization temperature. The results show that such particles can be obtained under conditions of high as well as low styrene feed rates, provided that the rate of initiation is properly adjusted.     

EFFECT OF THE PHASE STRUCTURE EVOLUTION ON THE PROPERTIES OF FILMS FORMED FROM PBA/P(St-co-MMA) COMPOSITE LATEX

A group of heterogeneous latexes poly(butyl acrylate)/poly(styrene-co-methyl methacrylate)(PBA/P(St-co-MMA)) were prepared by a semi-continuous seeded emulsion polymerization process under monomer starved conditions.The glass transition temperature(T_g)and the mechanical properties of the film formed from the composite latex changed with the evolution of the particle morphology.A photon transmission method was used to monitor the phase structure evolution of films which were prepared from core-shell PBA/...     

Preparation of silica-coated poly(styrene-co-4-vinylpyridine) particles and hollow particles

This paper presents a novel method for preparation of polymer-silica colloidal nanocomposites based on emulsion polymerization and subsequent sol-gel nanocoating process. The polystyrene latex particles bearing basic groups on their surfaces were successfully synthesized through emulsion polymerization using 4-vinylpyridine (4VP) as a functional comonomer and polyvinylpyrrolidone (PVP) as a surfactant. A series of poly(styrene-co-4-vinylpyridine)/SiO2 nanocomposite particles with smooth or rough core-shell morphology were obtained through the coating process. The poly(styrene-co-4-vinylpyridine) particles could be dissolved subsequently or simultaneously during the sol-gel coating process to form hollow particles. The effects of the amount of 4VP, PVP, NH(4)OH, and tetraethoxysilane (TEOS) on both the nanocomposite particles and hollow particles were investigated. Transmission electron microscopy showed that the morphology of the nanocomposite particles and hollow particles was strongly influenced by the initial feed of the comonomer 4VP and the coupling agent PVP. The conditions to obtain all hollow particles were also studied. Thermogravimetric analysis and energy dispersive X-ray spectroscopy analyses indicated that the interiors of hollow particles were not really "hollow".     

荧光探针法研究核壳结构有机硅-丙烯酸酯乳液的聚合行为

以芘为荧光探针,探讨了有机硅-丙烯酸酯核壳乳液聚合过程中,芘的第一振动峰(373 nm处)与第三振动峰(384 nm处)荧光强度的比值I1/I3与乳化剂、有机硅单体(D4)和引发剂(KPS)用量之间的关系,并结合聚合过程中探针芘的I1/I3峰值与单体转化率及乳胶粒形态演变之间的关系,研究了核壳结构有机硅-丙烯酸酯乳液的聚合行为.研究结果表明,探针芘的I1/I3峰值随乳化剂用量,D4用量,KPS用量不同发生相应的变化,随单体转化率的增加而增大.当乳化剂用量、D4用量、KPS与总单体的质量比依次为2 g、8 g、0.7%时,得到的乳液具有优良的综合性能.聚合反应过程中,当种子乳胶粒转变为核壳乳胶粒时,芘的I1/I3峰值仍呈现出明显的转变,说明有机硅-丙烯酸酯核壳乳液具有互穿聚合物网络结构.因此,荧光探针可用于研究有机硅-丙烯酸酯核壳乳液聚合反应进程.     

单分散聚丙烯酸丁酯-二氧化硅核壳粒子的制备

近年来,有机-无机核壳材料因其具有可调的光、电、磁等特性而备受关注．无机物外壳可以增强粒子的热力学稳定性、机械强度和抗拉性能．高分子乳胶粒内核具有弹性,且易成膜,外部包覆无机物的乳胶粒可结合两者特性并产生协同效应．     

核/壳乳液聚合工艺中乳化剂的定量研究

以十二烷基硫酸钠(SDS)为乳化剂,采用多步种子乳液聚合方法制备了核/壳结构乳液,研究了乳化剂加入量以及加料速率对核壳乳液聚合的影响,并推导了核及壳乳液聚合阶段所需乳化剂量的计算公式.研究表明,当种子、核、壳乳液聚合阶段单体量分别为12g、50g和50g,种子乳液聚合阶段加入的乳化剂量为0.44g时,控制核、壳乳液聚合阶段乳化剂的加入量分别在0.64～2.07g及0.04～2.12g之间,且预乳化单体的滴加速度低于2.3g/min时,可以防止二次成核及新乳胶粒子的形成,制得粒径分布窄、核/壳结构明显的乳胶粒子.利用透射电镜(TEM)对所制备的核壳结构乳胶粒子的结构形态进行了验证,试验结果与理论预测结果一致.     

Double-responsive polymer brushes on the surface of colloid particles

Well-defined poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) brushes were synthesized on the surface of polystyrene latex particles by atom transfer radical polymerization (ATRP). It was found that the surface-initiated polymerization of DMAEMA catalyzed by CuCl/CuCl(2)/bpy was under good control in the solvent of acetone/water at ambient temperature (35 degrees C). High-density PDMAEMA brushes with low polydispersity (PDI 1.21) were obtained. TEM results demonstrate that the PDMAEMA-grafted particles have core-shell structure. Dynamic light scattering studies indicate that the particles with PDMAEMA brushes are both pH and temperature responsive.     

MORPHOLOGY EVOLUTION OF POLY（St-co-BuA）/SILICA NANOCOMPOSITE PARTICLES SYNTHESIZED BY EMULSION POLYMERIZATION

Poly（St-co-BuA）/silica nanocomposite latexes were synthesized via conventional emulsion polymerization in the presence of 3-（trimethoxysilyl）propyl methacrylate modified colloidal nano-silica. The effects of surface property, particle size and content of colloidal nano-silica as well as the concentrations of monomer and surfactant on the morphology of nanocomposite latex particles were investigated by transmission electron microscope （TEM） and scanning electron microscope （SEM） in detail. Various interesting morphologies such as grape-like, Chinese gooseberry-like, pomegranate-like and normal core-shell structures were observed. Droplet nucleation mechanism competing with micelle nucleation mechanism was proposed to explain the morphological evolution of the nanocomposite particles.     

Preparation of Bowl-Like Polymer Particles via Multi-Step Emulsion Polymerization and Alkali Post-Treatment

Summary : Monodisperse P(BA-MMA-MAA-EGDMA)/P(St-MAA-DVB) core/shell latex particles were first synthesized by a four-step emulsion polymerization, and a new kind of latex particles with “bowl-like” morphology were obtained by post-treating the resultant core/shell particles under alkali condition. Results indicated that the feeding rates of the monomer mixture and initiator aqueous solution were the key parameters to obtain monodisperse core/shell latex particles in the emulsion polymerization process, and the latex particles with “bowl-like” morphology could be generated only when the treatment temperature was equal or higher than 70 °C.     

Synthesis and characterization of a novel silane-based vinylic monomer and its application in the multilayer core-shell latex

A novel monomer methacrylamidophenoxy dimethylsiloxy phenylphthalimide was obtained by a reaction of 4,4′-bis-aminophenoxy dimethylsilane, phthalic anhydride and methacryloyl chloride. Then it has been used in the synthesis of phase-separated polymer latex with a multilayer core-shell morphology by surface cross-linking emulsion polymerization. Poly(butyl acrylate) was used for the seed and the core of the latex, the inner shell was poly(butyl acrylate/styrene) cross-linked with divinylbenzene to avoid phase inversion, and the poly(methyl methacrylate/butyl acrylate/methacrylamidophenoxy dimethylsiloxy phenylphthalimide) was the outer shell. The structural elucidation of monomer was carried out by elemental analysis, FTIR, ¹H NMR, and ¹³C NMR spectroscopic techniques. The morphology and glass transition temperatures of the synthesized product were investigated by transmission electron microscopy and differential scanning calorimetry, respectively. The multilayer core-shell structure was clearly shown in TEM micrographs, and the three-phase separation was confirmed by DSC analysis. The obtained results demonstrated that the average particle size is 81.8, 108 and 132 nm for the core, core-shell and multilayer core-shell particles, which agrees with the TEM micrograph measurement of 75, 103, and 131 nm, respectively.     

苯乙烯和N-乙烯基吡咯烷酮共聚物/Ag复合微球的制备及性能研究

首先用无皂乳液聚合法制备了单分散聚苯乙烯(PSt)乳液,以此为种子乳液,使用N,N-亚甲基双丙烯酰胺(MBA)为交联剂,过硫酸钾(KPS)为引发剂,进行苯乙烯和N-乙烯基吡咯烷酮(NVP)共聚合制备了以PSt为核、St和NVP共聚物为壳的具有核-壳结构的聚合物微球(P(St-NVP)).以此微球为模板通过化学沉积法得到了粒径分布均匀、单分散的P(St-NVP)/Ag复合微球.傅里叶红外光谱、X-射线衍射、扫描电镜、透射电镜、激光粒度仪和紫外-可见光谱对复合微球的结构、形貌、物相及催化性能进行了表征.结果表明,P(St-NVP)/Ag复合微球具有规则的球形结构,粒径在400～700 nm之间,随交联剂浓度或种子乳液浓度的增加,复合微球粒径减小.粒径在十几个纳米左右的银粒子均匀分布在微球表面和内部.载银复合微球在NaBH4还原4-硝基苯酚为4-氨基苯酚的模型反应中表现出较高的催化活性.     

Block copolymers prepared by emulsion polymerization with poly(ethylene oxide)–azo-initiators

Poly(ethylene oxide)-b-poly(styrene) block copolymers were prepared in the form of latex particles by emulsion polymerization of styrene with poly(ethylene glycol)–azo-initiators as well as with the redox initiation system poly(ethylene glycol)/Ce⁴⁺. The emulsion polymerization can be carried out in the absence of additional stabilizers if the chain length of the poly(ethylene glycol) is greater than 40. The latex particles as well as the copolymers were characterized by capillary hydrodynamic fractionation, ¹³C-nuclear magnetic resonance (NMR) spectroscopy and Fourier transform infrared spectroscopy. By ¹³C-NMR spectroscopy a side reaction of the primary radicals arising from the azo-initiator was found which can contribute to the low efficiency of azo-initiators in emulsion polymerization.     

Comparative study between core-shell and interpenetrating network structure polyurethane/polyacrylate composite emulsions

Anionic aqueous polyurethane dispersion was prepared by using carboxyl acid group to make the polyurethane dispersible, and then nanograde core-shell and crosslinked IPN structure polyurethane/polyacrylate composite latex (PUA) were synthesized by soap-free emulsion polymerization method with polyurethane dispersion as seed. FTIR, DSC, dynamic light scattering, TEM, ESCA, TGA, electronic tensile machine were employed to investigate the structures and properties of the composite latex and their polymers. Meanwhile the core-shell composite PUA emulsion and the crosslinked IPN composite PUA emulsion were compared. The results showed that the particle morphology of PUA composite emulsion is inverted core-shell structure with polyacrylate as the core and with polyurethane as the shell. The morphology of the crosslinked PUA emulsion was multi-core structure. The surface in core-shell PUA contains rich PU phase. The phase structure of the crosslinked PUA is more uniform. Three transition temperatures are observed for the core-shell composite PUA, two transitions are observed for the film from the crosslinked PUA. The TGA curves of core-shell PUA and crosslinked PUA exhibit two stages, the first stage corresponds to the thermal decomposition of hard segments in seed polyurethane; the second stage corresponds to the decomposition of soft segments in PUA and decomposition of polyacrylate. With the increase of glycidyl methacrylate (GMA) amounts in PUA composite emulsions, the tensile strength of the PUA films as well as the average diameter of the PUA composite emulsion particles increase, the elongation at break of the PUA films decreases.     

Morphology and grafting in polybutylacrylate-polystyrene core-shell emulsion polymerization

The morphology of polybutylacrylate–polystyrene (PBA–PS) core-shell latex particles prepared by seeded emulsion polymerization was investigated as a function of the addition method of styrene (St). The thin layer chromatography/flame ionization detector (TLC–FID) technique was used to characterize the morphology of the core-shell latexes. It was found that grafting PS to the PBA core occurs during seeded emulsion polymerization. The percentage of grafting depended on the method of addition of St, being greatest for the batch reaction, less for the preswollen batch reaction, and least for the semibatch reaction. Upon aging the PBA core-polymer migrated out of the latex particles with a low degree of grafting to form dumbellshaped particles, whereas the PBA–PS core-shell particles with a high degree of grafting remained spherical because of the emulsifying ability of graft copolymer.     

A polymer thin-film technique to study the micromorphology of core/shell latexes

A series of poly(styrene)/poly(styrene-co-acrylonitrile) core-shell latexes were synthesized by seeded emulsion polymerization. The dried latex was dissolved in toluene and then cast on the surface of water to form a very thin film (60–90 nm). Phase separation in the thin film was studied by transmission electron microscopy (TEM). Electron micrographs of these thin films yielded fine structure and interesting morphology that was unattainable by ultramicrotoming of the corresponding compression-molded specimens. Glass transition temperatures and percent grafted polystyrene were correlated with the TEM results. As grafting increases, mixing of the two phases improves, with the resulting T_g value being between the two T_g's of poly(styrene) and poly(styrene-co-acrylonitrile).     

Synthesis and Structure Control of A New Kind of Inelastomer Impact Modifier with Core-shell Structure and Impact Modification to PVC/CPE

Introduction　　 As a structure material,a polymer has two important mechanical properties,i.e.,strength and toughing.Therefore,plastic toughening isalwaysa fundamental study on poly-mer materials.Traditionally,toughnessmodification isto make rubberasan elastomerimpactmodifier dispersed to plastic matrix which is hence toughened[1 ,2 ] .But as the toughness ofplastic is improved,the elastomerimpactmodifieralso reducesthe othermechanical propertiesof the material.Consequently,whether rigid par…     

DESIGN AND CONTROL OF SOAP-FREE HYDROPHILIC-HYDROPHOBIC CORE-SHELL LATEX PARTICLES WITH HIGH CARBOXYL CONTENT IN THE CORE OF THE PARTICLES

Soap-free hydrophilic-hydrophobic core-shell latex particles with high carboxyl content in the core of the particles were synthesized via the seeded emulsion polymerization using methyl methacrylate(MMA),butyl acrylate(BA), methacrylic acid(MAA),styrene(St)and ethylene glycol dimethacrylate(EGDMA)as monomers,and the influences of MMA content used in the core preparation on polymerization,particle size and morphology were investigated by transmission electron microscopy,dynamic light scattering and conductometric titration.The results showed that the seeded emulsion polymerization could be carried out smoothly using "starved monomer feeding process" when MAA content in the core preparation was equal to or less than 24 wt%,and the encapsulating efficiency of the hydrophilic P(MMA-BA-MAAEGDMA) core with the hydrophobic PSt shell decreased with the increase in MAA content.When an interlayer of P(MMAMAA -St)with moderate polarity was inserted between the P(MMA-BA-MAA-EGDMA)core and the PSt shell,well designed soap-free hydrophilic-hydrophobic core-shell latex particles with 24 wt%MAA content in the core preparation were obtained.     

氯丁胶乳-聚甲基丙烯酸甲酯复合乳胶粒结构形态

以氯丁胶乳（Pa）为种子乳液,甲基丙烯酸甲酯（Pb）为第二单体,采用种子乳液聚合法,制备了氯丁胶乳-聚甲基丙烯酸甲酯复合乳胶粒。 热力学分析表明,当Pb的体积分数Φb＜0.69时,可同时形成Pa-Pb型正核-壳和（Pa＋Pb）分离型乳胶粒,当Φb＞0.69时,形成Pb-Pa型翻转型核壳结构乳胶粒,并伴有Pa-Pb型正核-壳结构乳胶粒的形成。 动力学分析表明,引发剂类型、第二单体的加入方式、种子乳胶粒的交联、单体/聚合物质量比是影响乳胶粒形态的主要因素。 采用水溶性引发剂过二硫酸钾（KPS）,以饥饿态方式加入单体,氯丁胶乳 聚甲基丙烯酸甲酯(PCR-PMMA)复合乳胶粒呈现正核-壳结构,以充溢态方式加入单体则不能形成明显的核-壳结构;而以油溶性偶氮二异丁腈（AIBN）为引发剂时,单体无论以充溢态方式加入还是饥饿态加入均倾向于形成翻转核-壳型粒子。 在种子乳胶粒中加入一定量交联剂二缩三乙二醇二甲基丙烯酸酯,有利于形成明显的正核壳结构。 以饥饿态进料,KPS为引发剂时,随着单体用量增加,壳层变厚,仍呈正核-壳结构,与热力学分析结果相吻合;以AIBN为引发剂时,随着单体用量增加,PCR-PMMA复合乳胶粒逐渐由翻转核壳型结构变为互穿结构。     

Synthesis of core-shell polystyrene nanoparticles by surfactant free emulsion polymerization using macro-RAFT agent

Novel approach for the synthesis of core-shell polystyrene nanoparticles by living hydrophilic polymer consisting of thiocarbonyl thio end group is reported. The surfactant free emulsion polymerization of styrene in the presence of macro-RAFT (reversible addition fragmentation chain transfer) agent is carried out to synthesize stable latex particles with smaller particle size. A macro-RAFT agent is prepared by homopolymerization of sodium styrene sulfonate (NaSS) in aqueous phase by using dithioester as chain transfer agent. This synthesized polystyrene sulfonate-sodium (PSS-Na) based macro-RAFT agent, which is essentially water soluble macromolecular chain transfer agent used for the surfactant-free batch emulsion polymerization of styrene. Transmission electron microscopy (TEM) study of the synthesized colloids shows the narrow particle size distribution with core-shell morphology.     

Synthesis and Characterization of Large Dimension PBA-P(MMA-ITA) Latex Particles with Core-Shell Morphology

In this paper, a novel large dimension poly(n-butyl acrylate)-poly(methyl methacrylate-itaconic acid) (PBA-P(MMA-ITA)) core-shell latex particles (CSR) with diameter of 200 nm～300 nm were successfully synthesized via pre-emulsion and semi-continuous seeded emulsion polymerization process. The analysis on the surface tension and coagulation rate of polymeric system, size and distribution of latex particles indicated that the composite emulsifier of sodium dodecyl sulfonate/polyoxyethylene nonyl phenyl ether (SDS/OP-10) had the best emulsified effect. The optimal ratio of SDS/OP-10 was 1:1 and its optimum dosage was 1.0% of monomer amount. FTIR analysis results confirmed that ITA participated in the copolymerization reaction and the chemical bond between P(MMA-ITA) copolymer and PBA core existed in the interfacial of core and shell. DSC analysis results showed that the glass transition temperature (T _g) of P(MMA-ITA) copolymer increased with the increase of the ITA dosage and decreased with the increase of the core shell mass ratio. TEM images revealed that CSR particles had core-shell morphology indeed, but the particles’ core-shell morphology would be changed at higher ITA dosage and core shell mass ratio. The size of CSR particles was 330 nm, and the diameter of PBA core was 290 nm. ITA content in the shell of CSR particles was analyzed by non-aqueous acid-base titration. ITA content was the highest at 6% of ITA dosage, ITA amount which chemically bonded with PBA core was the highest at 8% of ITA dosage. When the core shell mass ratio was 60/40, ITA content and ITA amount which grafted onto PBA core were both the highest. ITA content of CSR particles achieved above 1.11% in this work, and it is completely possible for using CSR particles toughening and compatibilizing polyamide 6 (PA 6).