Preparation of monodispersed hollow polymer particles by seeded emulsion polymerization under low emulsifier conditions

In a low emulsifier system, the MMA‐BA‐MAA copolymer emulsions were prepared as seed latices and the seeded emulsion polymerization of MMA‐MAA‐DVB was consequently carried out to prepare carboxylated core particles. The hydrophobic shell was then synthesized onto the core using styrene, acrylonitrile, and divinylbenzene as comonomers. The hollow latex particles were obtained by alkalization treatment of the core‐shell latex particles. The effects of the feeding rate of monomer mixture, contents of emulsifier SDBS and crosslinking agent DVB, and ratio of the monomers during the core stage and shell stage on the morphology and volume expansion of the latex particles were investigated. The results show that the monodispersed hollow latex particles with large size can be obtained when the feeding rate is 0.1 g/min, SDBS content is 0.15 and 0.2 wt % during the core stage and shell stage, respectively, DVB contents are 1% during the preparation of shell copolymers, and the monomer ratio of the core particle to shell layer is 1 : 8. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1505–1510, 2005     

Enhancing formation and retention of hollow structural integrity through intermediate and outermost layer design in seeded emulsion polymerization of hollow latex particles

The synthesis of hollow latex particles through seeded emulsion polymerization involves a series of intricate steps, including the formation of distinct polymer layers with specific properties. Despite extensive research, preserving the desired hollow structure remains challenging due to the unclear role of the encapsulating polymer layers. This study systematically adjusts the glass transition temperature (T_g) of the intermediate layer by varying the butyl acrylate (BA) ratio in the monomer feed mixture. By controlling the reaction temperature during alkali swelling, we explore the critical influence of T_g on hollow latex particle formation from carboxylated core latex particles. To ensure long-term hollow structure retention after drying, a rigid outer layer is polymerized onto the intermediate layer. Surprisingly, higher divinylbenzene (DVB) mass ratios (5.0 and 10.0 wt%) do not result in a highly crosslinked hollow shell due to DVB self-nucleation. This paper emphasizes the importance of precise design parameters for both intermediate and outermost layers in achieving and maintaining hollow latex particle structures. Understanding each layer's role and optimizing their compositions contribute to advancing hollow latex particle synthesis through seeded emulsion polymerization.     

中空聚合物微球的制备——种子及核乳胶粒的制备

为了制得具有中空结构的聚合物微球,首先以十二烷基苯磺酸钠(SDBS)为乳化剂,在其用量低于CMC的条件下,进行甲基丙烯酸甲酯(MMA)、甲基丙烯酸(MAA)和丙烯酸丁酯(BA)的乳液聚合,制备了带羧基的种子乳胶粒.然后采用MMA、MAA和二乙烯基苯为单体进行种子乳液聚合,制备了轻度交联的带羧基的核乳胶粒.该核乳胶粒经过核-壳乳液聚合和适当的碱处理工艺就可成为具有中空结构的聚合物微球.采用粒度仪测定了乳胶粒的直径及其分布,采用TEM对乳胶粒结构形态进行了表征.研究了种子及核乳胶粒制备过程中单体加料方式、乳化剂用量及羧基单体种类等因素对聚合稳定性、乳胶粒直径及其分布以及最终的中空聚合物微球结构形态的影响,确定了制备种子及核乳胶粒的最佳工艺条件.在制备种子阶段,SDBS用量为单体总量的0.5%,采用一次性加入单体的进料工艺;在核乳胶粒制备阶段,以MAA为羧基单体,所有单体采用"饥饿式"加料,半连续补加乳化剂并使乳化剂用量为核单体总量的0.15%时可保持聚合稳定性并保证无新乳胶粒生成.     

Preparation and characterization of core‐shell nanoparticles containing poly(chlorotrifluoroethylene‐co‐ethylvinylether) as core

Core shell latex particles with a glassy core and a low T_g polymeric shell are usually preferred. More so, the glassy core happens to be a fluoropolymer with a shell polymer that helps in processability. We describe here the preparation and characterization of core shell nanoparticles consisting of poly(chlorotrifluoroethylene‐co‐ethylvinylether) as core encapsulated in poly(styrene‐acrylate) copolymer shell using seeded emulsion polymerization method under kinetically controlled monomer starved conditions. Properties of the emulsion using surfactants (fluoro/conventional) and surfactant free conditions were investigated. Average size (100 nm), spherical shape and core–shell morphology of the latex particles was confirmed by dynamic light scattering and transmission electron microscopy. Absence of C? F and C? Cl peaks in X‐ray photoelectron spectroscopy proves that cores are completely covered. Polymerization in the presence of fluorocarbon surfactant was found to give optimum features like narrow size distribution, good shell deposition and no traces of agglomeration. Films of core shell latex particles exhibited improved transparency and enhanced water contact angles thus making them suitable for applications in various fields including coatings. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Particle morphology and NMR structure of polymethylmethacrylate/polystyrene emulsifier‐free core–shell cationic latices in the presence of DBMEA

In the absence of emulsifier, we prepared stable emulsifier‐free polymethylmethacrylate/polystyrene (PMMA/PSt) copolymer latex by batch method with comonomer N,N‐dimethyl, N‐butyl, N‐methacryloloxylethyl ammonium bromide (DBMEA) by using A1BN as initiator. The size distribution of the latex particles was very narrow and the copolymer particles were spherical and very uniform. Under the same recipe and polymerization conditions, PMMA/PSt and PSt/PMMA composite polymer particle latices were prepared by a semicontinuous emulsifier‐free seeded emulsion polymerization method. The sizes and size distributions of composite latex particles were determined both by quasi‐elastic light scattering and transmission electron microscopy (TEM). The effects of feeding manner and staining agents on the morphologies of the composite particles were studied. The results were as follows: the latex particles were dyed with pH 2.0 phosphotungestic acid solution and with uranyl acetate solution, respectively, revealing that the morphologies of the composite latex particles were obviously core–shell structures. The core–shell polymer structure of PMMA/PSt was also studied by ¹H, ¹³C, 2D NMR, and distortionless enhancement by polarization transfer, or DEPT, spectroscopy. Results showed that PMMA/PSt polymers are composed of PSt homopolymer, PMMA homopolymer, and PMMA‐g‐PSt graft copolymers; results by NMR are consistent with TEM results. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1681–1687, 2005     

Kinetic study on the poly(methyl methacrylate) seeded soapless emulsion polymerization of styrene. III. Seeds with crosslinking

In this work, a seeded soapless emulsion polymerization was carried out with crosslinking (XL) poly(methyl methacrylate) (PMMA) as seeds, styrene as monomer, and potassium persulfate (K₂S₂O₈) as initiator to synthesize the PMMA XL–PS composite latex, which we knew as the latex interpenetrating polymer network (IPN). The morphology of the latex IPN was observed by transmission electron microscopy (TEM). It showed a core–shell structure. The kinetic data from the early stages of the reaction of seeded soapless emulsion polymerization showed that the square root of polymer yield (W_p)^1/2 was proportional to the reaction time. The reaction rate decreased with the increase of crosslinking density of PMMA seeds. The core–shell model proposed in our previous work^1–2 was modified to predict the conversion of polymerization over the entire course of the synthesis of PMMA (XL)–PS composite latex. Our modified core–shell kinetic model fitted well with the experimental data. © 1997 John Wiley & Sons, Inc. J Appl Polm Sci 65:425–438, 1997     

电导滴定研究中空聚合物微球的制备

采用渗透溶胀法制备中空聚合物微球。首先用种子乳液聚合制备了3种不同粒径的酸核S1、S2、S3,然后在酸核上包裹不同质量分数的壳层聚合物,形成一系列核/壳质量比不同的乳胶粒子。通过电导滴定,分析了不同核/壳质量比乳胶粒子表面羧酸的变化,由此来研究壳核包裹过程和确定中空微球形成的最佳核/壳质量比。对不同核/壳质量比的乳胶粒子进行了流变学、遮盖性和TEM分析。实验结果表明,电导滴定所确定的S1、S2、S3形成中空微球的最佳核/壳质量比分别为1/9、1/12、1/9,这与流变学、遮盖性、TEM分析得到的最佳核/壳质量比一致。     

Effect of the intermediate layer–core ratio on the morphology and opacity ability of hollow latex particles

In this study, well‐monodispersed hollow latex particles were synthesized through semicontinuous seed emulsion polymerization, and the effect of the hollow latex particles' intermediate layer–core ratios on their morphology and opacity ability were studied. The results show that when the intermediate layer–core ratios increased from 6 to 10, the swelling degree of the hollow latex particles decreased, and the intensity gradually increased, but the opacity ability increased first and then decreased. When the intermediate layer–core ratio was 8, the opacity ability of the hollow latex particles was the best. When the intermediate layer–core ratios were 6 and 7, the surface of the hollow latex particles was rough, and they showed a great swelling degree, big cavity, and thin shell, and few of latex particles collapsed or ruptured. When the intermediate layer–core ratios were 9 and 10, the hollow latex particles had a smooth surface, thick shell, and small swelling degree and cavity, and roughly, there was no collapse or rupture of the hollow latex particles. When the intermediate layer–core ratio was 8, the swelling degree of the hollow latex particles was moderate. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42268.     

Self‐assembly of pH‐responsive acrylate latex particles at emulsion droplets interface

The self‐assembly of pH‐responsive poly (methyl methacrylate‐co‐acrylic acid) latex particles at emulsion droplet interfaces was achieved. Raising pH increases the hydrophilicity of the latex particles in situ and the latex particle acts as an efficient particulate emulsifier self‐assembling at emulsion droplet interface at around pH 10–11 but exhibits no emulsifier activity at higher pH. This effect can be reversibly induced simply by varying the aqueous phase pH and thus the latex emulsifier can be reassembled. The effect factors, including the aqueous phase pH, the surface carboxyl content, ζ‐Potential of the latex particles and oil phase solvent have been investigated. Using monomer as oil phase, the latex particles could stabilize emulsion droplets during polymerization and cage‐like polymer microspheres with hollow core/porous shell structure were obtained after polymerization. The mechanism of the latex particles self‐assembly was discussed. The morphologies of emulsion and microspheres were characterized by optical microscopy, scanning electron microscopy, and transmission electron microscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

中空聚合物微球的制备——溶胀处理条件的影响

采用种子乳液聚合法合成不同核壳比的聚甲基丙烯酸（MAA）-丙烯酸丁酯（BA）一甲基丙烯酸甲酯（MMA）／聚苯乙烯（St）-丙烯腈（AN）核壳乳液,经碱／酸溶胀法处理制备了中空聚合物微球。结果表明,中空聚合物的形态不仅与核壳比有关,也与溶胀处理时碱的种类、温度、溶胀剂及其用量、乳液pH值等因素有关,当核壳比为1：10,溶胀剂用量为核壳乳胶粒质量的1.5倍时,可以得到最大中空度接近30％的中空聚合物微球。     

Preparation and characterization of poly(butadiene-stat-styrene)/poly(styrene-stat-acrylonitrile) structured latex particles

In rubber toughening of thermoplastics, core/shell polymers have been used extensively. This work introduces the synthesis and characterization of polybutadiene based core/shell latex particles with controlled particle size and crosslinking density of the core. A lithium soap recipe was employed to prepare a series of poly(butadiene-stat-styrene) (90/10 by wt) core particles by conventional emulsion polymerization through a batch process. The shell polymer, poly(styrene-stat-acrylonitrile) (72/28 by wt), was polymerized by a semicontinuous process in the presence of the core particles to form a core/shell morphology. The effects of initiator concentration, monomer feeding rate, core/shell ratio, and gel-fraction of the core on the core/shell particle morphology were studied. The degree of grafting of the shell polymer on the core particles was determined as well. The morphology and glass transitions of these particles were characterized by transmission electron microscopy, differential scanning calorimetry, and dynamic mechanical spectroscopy. These latex particles can be used specifically in toughening polycarbonate. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1123–1134, 1997     

Synthesis and characteristics of poly(methyl methacrylate-methacrylic acid-3,3-(trimethoxysilyl) propyl methacrylate) hollow latex particles and their application to drug carriers

In this study, the hollow latex particle was synthesized by three processes. The first process was to synthesize the poly(methyl methacrylate-co-methacrylic acid) (poly(MMA-MAA)) copolymer latex particles by the method of soapless emulsion polymerization. Following the first process, the second process was to polymerize MMA, MAA, 3,3-(trimethoxysilyl) propyl methacrylate (MPS), and ethylene glycol dimethacrylate in the presence of poly(MMA-MAA) latex particles to form the linear poly(MMA-MAA)/crosslinking poly(MMA-MAA-MPS) core–shell latex particles. In the third process, the core–shell latex particles were heated in the presence of ammonia to form the poly(MMA-MAA-MPS) hollow latex particles. A sufficient heating time and high-heating temperature were necessary for the ammonia to dissolve the linear poly(MMA-MAA) core to form a perfect hollow structure. The crosslinking poly(MMA-MAA-MPS) shell was a barrier for the ammonia to diffuse into the latex particles so that the latex particle with the high-crosslinking shell showed an imperfect hollow structure. Besides, the hollow poly(MMA-MAA-MPS) latex particles reacted with ZnO nanoparticles, which were synthesized by a traditional sol-gel method, to form the polymer/inorganic poly(MMA-MAA-MPS)/ZnO composite hollow latex particles. With the increase of crosslinking degree would increase the amount of ZnO bonding. Moreover, the poly(MMA-MAA-MPS) hollow latex particles were used as carriers to load with the model drug, caffeine. The release of caffeine from poly(MMA-MAA-MPS) hollow latex particles was investigated.     

Preparation and properties of polydimethylsiloxane/polyacrylate composite latex initiated by 60Co γ‐ray irradiation

In this study, polydimethylsiloxane (PDMS)/polyacrylate composite polymer latex was synthesized via polymerization of the acrylate monomer in the presence of vinyl‐containing PDMS seeded latex. The polymerization was initiated by ⁶⁰Co γ‐ray irradiation. The morphology of the PDMS/polyacrylate composite polymer latex was a core–shell structure with PDMS as the core and polyacrylate as the shell. There was an interpenetration layer between the PDMS core and the polyacrylate shell. The composition of the vinyl‐containing PDMS and the PDMS/polyacrylate composite latex were investigated with NMR and Fourier transform infrared spectroscopy, respectively. The effect of irradiation dose on the seeded emulsion polymerization conversion is discussed. Finally, the mechanical properties of latex film, such as water‐absorption ratio, tensile strength, pendulum hardness, and heat‐decomposed temperature, were tested. The results showed that the mechanical properties of the PDMS/polyacrylate film were remarkably improved when compared to the polyacrylate film. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2732–2736, 2003     

Morphology control of hollow polymer latex particle preparation

Hollow polymer latex particles containing a hydrophilic core fully encapsulated with a hydrophobic shell were prepared by multistage polymerization followed by neutralization with a base. The diameters of the particles were monodispersed and void fractions of the prepared latex particles as high as 50% were achieved. High instantaneous monomer conversion was found to be the key point to minimize the interdiffusion of the core–shell polymer chains. The influences of the shell crosslinking agent and shell carboxyl content on the hollow morphology were also investigated. The maximum hollow diameter was observed with crosslinking agent contents of 7.5–12.5 wt %. The shell carboxyl content had an appropriate value, and an excess of it resulted in an excentric hollow structure. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 860–863, 2005     

Self film‐forming and opaque hollow latexes fabricated via seeded emulsion polymerization followed by alkali post‐treatment

In order to obtain novel hollow latexes with both opaque and self film‐forming properties, the four‐layer core/shell latex particles—sequentially consisting of a high carboxyl‐containing soft core, a transition layer, a rigid supporting layer, and an outermost film‐forming layer—are first designed and prepared by emulsion polymerization, and then treated with alkali to fabricate self film‐forming hollow latexes. On the basis of the previous research on the three‐layer core/shell latex, influences of the composition and thickness of the film‐forming layer on the properties and morphologies of the four‐layer core/shell and the final hollow latexes are investigated. Results show that under optimized conditions with butyl acrylate/styrene (BA/St) mass ratio of 2/1, divinyl benzene (DVB) content of 1 wt %, and core/film‐forming layer mass ratio of 1/6 in the film‐forming layer preparation, the final hollow latex particles exhibit best morphology considering both light scattering efficiency and film‐forming capability at room temperature. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42541.     

Study on emulsion and suspension in situ polymerization

A novel and simple method of emulsion and suspension in situ polymerization was designed for preparing a composite of polystyrene containing core–shell emulsion particles. The advantage of this method was that it did not need a complex process, such as emulsion breaking, washing, drying, and so on, during transforming from emulsion polymerization to suspension polymerization. First, the core–shell particles of poly(styrene/bisphenol A dimethyl methacrylate)/polystyrene [P(St/BPADA)/PS] with crosslinking structure were synthesized by emulsion polymerization. Then the latex was broken with electrolyte dripping and the emulsion particles became swollen and transformed into the monomer in the suspension polymerization system. Thus the emulsion and suspension in situ polymerization could be carried out successfully. The mechanism of the process was investigated in detail. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 404–412, 2005     

Grafting behavior of n-butyl acrylate onto poly(butadiene-co-styrene) latexes

The radical-induced grafting of n-butyl acrylate (BA) onto poly(butadiene-co-styrene) [(P(Bd-S)] latexes during seeded emulsion polymerization was studied. This P(Bd-S)/PBA rubber/rubber core/shell latex system exhibited unique grafting behavior as compared to other extensively studied rubber/glass core/shell latex systems, such as poly(butadiene-co-styrene)/poly(methyl methacrylate) [P(Bd-S)/PMMA], poly(butadiene-co-styrene)/polystyrene [P(Bd-S)/PS] and poly(butadiene-co-styrene)/poly(acrylonitrile)[P(Bd-S)/PAN]. These composite latexes were characterized by the formation of a highly grafted/crosslinked P(Bd-S)/PBA interphase zone generated during the seeded emulsion polymerization process. Although both of the individual core and shell polymers studied were “soft” themselves, the resulting P(Bd-S)/PBA composite latex particles were found to be rather “hard.” The formation of the interphase zone was studied by using techniques such as solvent extraction, differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:511–523, 1997     

Trilayer Composite Poly(styrene/butyl acrylate/acrylic acid) Terpolymer Microspheres with Fe2O3 Middle Layer: Synthesis and Characterization

Fe₂O₃ particles with diameter of 3–5 nm were encapsulated in polymer spheres (styrene/butyl acrylate/acrylic acid terpolymer latex) by emulsion polymerization. Control of the pH value of the medium and modification of the latex prior to the second polymerization were of importance in determining the microstructure and morphology of the composite particles. The interaction between Fe₂O₃ and seed latex was confirmed by IR spectral changes of the surface groups of the latex particles. Mossbauer spectra gave evidence for the changes of electric density and electric field symmetry around Fe₂O₃, and surface photovoltage spectra indicated that the Fe₂O₃ particles were encapsulated in polymer. It was shown by all the results that the composite microspheres of size 80 nm had a core–shell structure with trilayers of seed latex core, Fe₂O₃ nanoparticles middle layer and polymer shell. © 1997 SCI.     

Influence of unsaturated acid monomer on the morphology of latex particles in the preparation of hollow latex via the alkali post‐treatment

Multistage hydrophilic core/hydrophobic shell latexes containing carboxyl groups were prepared via multistep seeded emulsion copolymerization, and particles with different morphologies were obtained after alkali post‐treatment. Influences of the type and content of unsaturated acid monomer on the polymerization and the particle morphology were investigated based on conductometric titration and TEM observation. Results showed that the hydrophilic core/hydrophobic shell particles could be easily formed using methacrylic acid (MAA) instead of acrylic acid. When MAA was 12.2 wt % in the core latex preparation, only fine pores existed inside the alkali‐treated particles. With MAA increased from 20.0 to 30.0 wt %, the alkali‐treated particle morphology evolved from porous, hollow to collapse structure. When MAA further increased to 40.0 wt %, it was difficult to prepare uniform multistage particles and distinct morphologies including solid, deficient swelling, hollow and collapse structure were coexistent in the alkali‐treated particles. Moreover, the forming mechanism of different morphologies was proposed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of amount of emulsifier added in the second stage on morphology of composite latex particles

In this article, PBA/P(MMA–crosslinking agent)-composite particle latexes were prepared by semicontinuous seeded emulsion polymerization. To determine the seed emulsion's saturating capacity of an emulsifier, a mathematical model was built to simulate the changes of the seed PBA emulsion's surface tension with the amount of emulsifier added dropwise. The effects of the emulsifier amount added in the second stage and the addition method on the morphology of the composite particles were studied. The results were shown as follows: If the amount of emulsifier added in one batch to the seed emulsion in the second stage was less than or equal to the saturating capacity of emulsifier of the seed emulsion (Cs), the morphology of the particles was “core–shell”; otherwise, a few particles were of a core–shell structure. However, if shell materials were preemulsified and added dropwise at an appropriate rate, the latex particles were still of a core–shell structure, even when the amount of emulsifier added to the seed emulsion was greater than the Cs. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 969–975, 1998