Phase separation of poly (methyl methacrylate) / poly (styrene-co-acrylonitrile) blends in the presence of silica nanoparticles

The effects of silica nanoparticles on the phase separation of poly (methyl methacrylate)/poly (styrene-co-acrylonitrile) (PMMA/SAN) blends are studied by the rheological method. The binodal temperatures of near-critical compositions were obtained by the gel-like behavior during spinodal decomposition, which is a character of polymer blends with co-continuous morphology. The shifted Cole–Cole plot method was introduced to determine the binodal temperatures of off-critical compositions based on the appearance of shoulder-like transition in the terminal regime of blends with droplet morphology. Such method is found also applicable in nanoparticle filled polymer blends. Moreover, a new method to determine the spinodal temperature from Fredrickson-Larson mean field theory was suggested, where the concentration fluctuation's contribution to the storage modulus is used instead of the whole dynamic moduli. This method was also successfully extended to nanoparticle filled polymer blend. The influences of the concentration and the average diameter of silica particles on the phase separation temperature were studied. It was found that the small amount of the silica nanoparticles in PMMA/SAN blends will significantly change the phase diagram, which is related to the selective location of silica in PMMA. The comparisons with thermodynamic theory of particle-filled polymer blends are also discussed.     

Synthesis and characterization of poly(butyl acrylate)/silica and poly(butyl acrylate)/silica/poly(methyl methacrylate) composite particles

Poly(butyl acrylate)/poly(methyl methacrylate) (PBA/PMMA) core–shell particles embedded with nanometer‐sized silica particles were prepared by emulsion polymerization of butyl acrylate (BA) in the presence of silica particles preabsorbed with 2,2′‐azobis(2‐amidinopropane)dihydrochloride (AIBA) initiator and subsequent MMA emulsion polymerization in the presence of PBA/silica composite particles. The morphologies of the resulting PBA/silica and PBA/silica/PMMA composite particles were characterized, which showed that AIBA could be absorbed effectively onto silica particles when the pH of the dispersion medium was greater than the isoelectric potential point of silica. The critical amount of AIBA added to have stable dispersion of silica particles increased as the pH of the dispersion medium increased. PBA/silica composite particles prepared by in situ emulsion polymerization using silica preabsorbed with AIBA showed higher silica absorption efficiency than did the PBA/silica composite particles prepared by direct mixing of PBA latex and silica dispersion or by emulsion polymerization in which AIBA was added after the mixing of BA and silica. The PBA/silica composite particles exhibited a raspberrylike morphology, with silica particles “adhered” to the surfaces of the PBA particles, whereas the PBA/silica/PMMA composite latex particles exhibited a sandwich morphology, with silica particles mainly at the interface between the PBA core and the PMMA shell. Subsequently, the PBA/silica/PMMA composite latex obtained had a narrow particle size distribution and good dispersion stability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3425–3432, 2006     

Novel polymer composites based on a mixture of preformed nanosilica‐filled poly(methyl methacrylate) particles and a diepoxy/diamine thermoset system

In this work, a new material based on an epoxy thermoset modified with a thermoplastic filled with silica nanoparticles was investigated. When thermoplastic particles are filled with nanoparticles with unique properties such as high efficiency for absorbing ultraviolet light, electric or magnetic shielding, high electrical conductivity, and high dielectric constants, more than an enhancement of the mechanical properties is expected to be achieved for modified epoxy‐based thermosets. Particles of poly(methyl methacrylate) (PMMA) filled with silica nanoparticles were used to modify a thermoset based on a full reaction between diglycidyl ether of bisphenol A and 3‐(aminomethyl)benzylamine. When the preformed thermoplastic particles were mixed with the reactive constituents of the epoxy system under certain curing conditions in which total miscibility was avoided, uniform particle dispersions could be obtained. The relationships between the composition, morphology (nanoscale and microscale), glass‐transition temperature, mechanical properties, and fracture toughness were considered. Four main results were obtained for consideration of the potential of silica‐filled PMMA as an important modifier of brittle epoxy thermoset systems: (1) a good dispersion of the silica nanoparticles in the PMMA domains, (2) a good dispersion of the silica‐filled PMMA microparticles in the epoxy matrix, (3) the possibility of partial dissolution of the PMMA‐rich domains into the epoxy system, and (4) a slight increase in properties such as the hardness, indentation modulus, and fracture toughness. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis of poly(butyl acrylate)—laponite nanocomposite nanoparticles for improving the impact strength of poly(lactic acid)

This work aims at preparing and characterizing poly(butyl acrylate) (PBA)—laponite (LRD) nanocomposite nanoparticles and nanocomposite core (PBA‐LRD)‐shell poly(methyl methacrylate) (PMMA) nanoparticles, on the one hand, and the morphology and properties of poly(lactic acid) (PLA)‐based blends containing PBA‐LRD nanocomposite nanoparticles or (PBA‐LRD)/PMMA core–shell nanoparticles as the dispersed phase, on the other hand. The PBA and (PBA‐LRD)/PMMA nanoparticles were synthesized by miniemulsion or emulsion polymerization using LRD platelets modified by 3‐methacryloxypropyltrimethoxysilane (MPTMS). The grafting of MPTMS onto the LRD surfaces was characterized qualitatively using FTIR and quantitatively using thermogravimetric analysis (TGA). The amounts of LRD in the PBA‐LRD nanocomposites were characterized by TGA. The PBA/PMMA core–shell particles were analyzed by ¹H‐NMR. Their morphology was confirmed by SEM and TEM. Mechanical properties of (PBA‐LRD)/PLA blends and (PBA‐LRD)/PMMA/PLA ones were tested and compared with those of the pure PLA, showing that core–shell particles allowed increasing impact strength of the PLA while minimizing loss in Young modulus and tensile strength. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation of poly(methyl methacrylate)‐Silica nanoparticles via differential microemulsion polymerization and physical properties of NR/PMMA‐SiO2 hybrid membranes

Poly(methy methacrylate) (PMMA)‐SiO₂ nanoparticles were prepared via differential microemulsion polymerization. The effects of silica loading, surfactant concentration, and initiator concentration on monomer conversion, particle size, particle size distribution, grafting efficiency, and silica encapsulation efficiency were investigated. A high monomer conversion of 99.9% and PMMA‐SiO₂ nanoparticles with a size range of 30 to 50 nm were obtained at a low surfactant concentration of 5.34 wt% based on monomer. PMMA‐SiO₂ nanoparticles showed spherical particles with a core‐shell morphology by TEM micrographs. A nanocomposite membrane from natural rubber (NR) and PMMA‐SiO₂ emulsion was studied for mechanical and thermal properties and pervaporation of water‐ethanol mixtures. PMMA‐SiO₂ nanoparticles which were uniformly dispersed in NR matrix, significantly enhanced mechanical properties and showed high water selectivity in permeate flux. Thus, the NR/PMMA‐SiO₂ hybrid membranes have great potential for pervaporation process in membrane applications. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers     

Morphology and rheology of immiscible polymer blends filled with silica nanoparticles

The effect of silica nanoparticles on the morphology and the rheological properties of an immiscible polymer blend (polypropylene/polystyrene, PP/PS 70/30) was investigated. Two types of pyrogenic nanosilica were used: a hydrophilic silica with a specific surface area of 200 m²/g and a hydrophobic silica having a specific surface area of 150 m²/g. First, a significant reduction in the PS droplet volume radius, from 3.25 to nearly 1 μm for filled blends with 3 wt% silica, was observed. More interestingly, image analysis of the micrographs proved that the hydrophilic silica tends to confine in the PS phase whereas hydrophobic one was located in the PP phase and at the PP/PS interface (interphase thickness ≈ 100-200 nm). Furthermore, a migration of hydrophilic silica from PP phase toward PS domains was observed.An analysis of the rheological experimental data was based on the framework of the Palierne model, extended to filled immiscible blends. Due to the partition of silica particles in the two phases and its influence on the viscosity ratio, limited cases have been investigated. The rheological data obtained with the hydrophobic silica were more difficult to model since the existence of a thick interphase cannot be taken into account by the model. Finally, the hypothesis that hydrophilic silica is homogeneously dispersed in PS droplets and that hydrophobic silica is dispersed in PP matrix was much closer to the actual situation. It can be then concluded that stabilization mechanism of PP/PS blend by hydrophilic silica is the reduction in the interfacial tension whereas hydrophobic silica acts as a rigid layer preventing the coalescence of PS droplets.     

Morphology of latex particles formed by poly(methyl methacrylate)-seeded emulsion polymerization of styrene

Poly(methyl methacrylate)–polystyrene composite particle latexes were prepared by poly(methyl methacrylate)-seeded emulsion polymerization of styrene employing batch, swelling-batch, and semibatch methods. The changes in particle morphology taking place during the polymerization reaction were followed by electron microscopy. Anchoring effect exerted by ionic terminal groups introduced by ionic initiator was found to be the main factor in controlling the particle morphology. The polymer particles obtained by oil-soluble hydrophobic initiators such as azobisisobutyronitrile and 4,4′-azobis-(4-cyanovaleric acid) gave the inverted core-shell morphology. Water-soluble hydrophilic initiator, K₂S₂O₈, also gave the inverted core-shell morphology. However, in this case the occurrence of the halfmoonlike, the sandwichlike, and the core-shell morphologies were also observed depending upon the polymerization conditions. The distribution of terminal ? SO groups on the surface area of polystyrene particles could be controlled by initiator concentration and polymerization temperature. Viscosity of polymerization loci dictated the movement of polymer molecules, thus causing the unevenness of particle shape and phase separation at high viscosity state. Viscosity was controlled by the styrene/poly(methyl methacrylate) ratio, the addition of a chain transfer agent or a solvent which is common to polystyrene and poly(methyl methacrylate).     

The preparation of carbon nanotube/poly(ethylene oxide) composites using amphiphilic block copolymers

Polymer/multiwall carbon nanotube (MWCNT) composites were prepared by using amphiphilic block copolymers as dispersant. First, MWCNTs were wrapped with amphiphilic block copolymers in aqueous solution. Poly(ethylene oxide) was selected as the hydrophilic block because of its strong affinity with water while one of the following polymers: poly(ethylene), poly(butadiene), poly(styrene), poly(propylene oxide), or poly(thiophene) was used as the hydrophobic block of the copolymers. The dispersions were characterized by optical microscopy and transmission electron microscopy along with UV–Visible adsorption and dynamic light scattering. Based on the results, we could assess the effect on CNT dispersion quality of both, the molar mass of copolymers, the nature of the hydrophobic block and the length of hydrophilic block. The crystallization behavior of composites prepared from these dispersions was investigated. Results were related to the dispersion of the nanoparticles in the polymer matrix.     

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.     

Application of the dry‐spinning method to produce poly(ε‐caprolactone) fibers containing bovine serum albumin laden gelatin nanoparticles

We designed and manufactured a polymeric system with combined hydrophilic–hydrophobic properties by loading gelatin nanoparticles (GNPs) containing bovine serum albumin (BSA) into poly(ε‐caprolactone) (PCL) fibers. Our ultimate goal was to create a device capable of carrying and releasing protein drugs. Such a system could find several biomedical applications, such as those in controlled release systems, surgical sutures, and bioactive scaffolds for tissue engineering. A two‐step desolvation method was used to produce GNPs, whereas PCL fibers were produced by a dry‐spinning method. The morphological, mechanical, and thermal properties of the produced system were investigated, and the distribution of nanoparticles both inside and on the surface of the fibers was examined. The effect of the particles on the biodegradability of the fibers was also evaluated. In vitro preliminary tests were performed to study the release of BSA from nanoparticle‐laden fibers and to compare this with its release from free nanoparticles. Our results indicate that the distribution of particles inside the fibers was quite homogeneous and only a few of them were present on the surface. The presence of the particles in the fibers did not affect the thermal properties of the PCL polymer matrix, although it created voids that affected the degradation characteristics so the PCL fibers favored faster erosion compared to the plain fibers. Preliminary results indicate that the release from GNP‐laden fibers occurred much more slowly compared to that in the free GNPs. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44233.     

水性聚氨酯/聚甲基丙烯酸甲酯杂化乳液的合成

用异佛尔酮二异氰酸酯(IPDI)、聚丙二醇(PPG)和二羟甲丙酸(DMPA)合成了水性聚氨酯分散体(WPU),讨论了PPG摩尔质量,NCO/OH及PPG/DMPA比例对WPU乳液和涂膜性能的影响。以WPU为种子与甲基丙烯酸甲酯进行乳液聚合制备杂化乳液,研究了不同PU/PMMA物质的量比例对杂化乳液及涂膜性能的影响,并采用TEM对WPU及杂化乳液粒子进行了表征。结果表明,在以PPG1000为原料,NCO与OH物质的量比为1.4∶1,PPG与DMPA物质的量比为1∶0.8条件下制备的WPU杂化乳液,随着PMMA比例增加,杂化乳液的稳定性和成膜性变差,聚合物膜断裂伸长率降低,但铅笔硬度、耐水性及耐乙醇性均得到了改善。     

Production of filled hydrogels by mechanochemically induced polymerization

Silica nanoparticles functionalized with polyvinylpyrrolidone (PVP) were obtained by the grinding/mechanical activation of quartz or nonfunctionalized silica nanoparticles in a stirred media mill in the presence of 1‐vinyl‐2‐pyrrolidone, as proven by Fourier transform infrared spectroscopy. The polymer layer thickness formed on the silica nanoparticles after 8 h of mechanical activation in the absence of polymerization initiators amounted to about 10 nm, as derived from shear rheology. The silica nanoparticles functionalized with the hydrophilic PVP by mechanochemical polymerization reaction were used as fillers for hydrogels based on poly(hydroxyethyl methacrylate) (polyHEMA). The water absorption, release properties, and mechanical properties of the polyHEMA–silica composites were measured as functions of the filler content and particle size of the filler. PolyHEMA samples containing 20 wt % of the functionalized silica particles exhibited a higher maximum water absorption than the unfilled polymer; this showed that the hydrophilic interface between the filler and the matrix improved the water absorption. The release of methylene blue from the polyHEMA–silica composites was governed by diffusion and was almost unaffected by the silica particles. The values for the storage modulus and loss modulus of the polyHEMA–silica composites increased with growing filler content. For constant filler content, the storage modulus increased with decreasing particle diameter of the filler; this showed that the reinforcing effect increased with the interface between the filler particles and the matrix polymer. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Temperature-dependent interaction parameters of poly(methyl methacrylate)/poly(2-vinyl pyridine) and poly(methyl methacrylate)/poly(4-vinyl pyridine) pairs

Temperature-dependent interaction parameters (α) of poly(methyl methacrylate)/poly(2-vinyl pyridine) (PMMA/P2VP) pair and PMMA/poly(4-vinyl pyridine) (PMMA/P4VP) pair were obtained from the SAXS profiles at various temperatures, and curve fitting to the random phase approximation theory. For this purpose, symmetric P2VP-block-PMMA and P4VP-block-PMMA copolymers were synthesized anionically. The molecular weights of both block copolymers were controlled to exhibit the disordered state over the entire experimental temperatures. We found that the value of α for PMMA/P4VP was larger than PMMA/P2VP, similar to polystyrene (PS)/poly(vinyl pyridine) pairs. However, the difference between in α between PMMA/P2VP and PMMA/P4VP was much smaller than that between PS/P2VP and PS/P4VP. This might be attributed to the hydrophilic PMMA block compared with hydrophobic PS block. Finally, the order-to-disorder transition temperature for symmetric P2VP-block-PMMA copolymers was determined by small angle X-ray scattering and birefringence methods.     

Investigation of polymer blends of polyamide-6 and poly(methyl methacrylate) synthesized by RAFT polymerization

Morphological and thermal properties of immiscible and incompatible polymer blends of commercial polyamide-6 (PA-6) and poly(methyl methacrylate) (PMMA) synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization have been studied in the presence of a compatibilizer consisting of either a random copolymer of styrene-maleic anhydride (SMA) or a diblock copolymer poly(methyl methacrylate) and polystyrene (PMMA-PS) also synthesized via RAFT polymerization. Blends of PA-6/PMMA were obtained by extrusion mixing. During melt compounding in the extruder, the functional groups of the polymer components were reacted in the presence of a compatibilizer, which changed considerably the morphology of the blend. After compatibilization, particles of PMMA in the PA-6 were smaller and better dispersed. The morphology and thermal properties of the blends were characterized using scanning electron microscopy (SEM) and differential scanning calorimetry (DCS).     

Fumed silica filled poly(dimethylsiloxane-urea) segmented copolymers: Preparation and properties

Novel fumed silica filled thermoplastic poly(dimethylsiloxane-urea) (TPSU) segmented copolymers were synthesized and characterized. TPSU copolymers were prepared from a cycloaliphatic diisocyanate, aminopropyl terminated PDMS oligomers with number average molecular weights of 3,200, 10,800 and 31,500 g/mol and 2-methyl-1,5-diaminopentane chain extender. Two different types of fumed silica HDK H2000 (hydrophobic) and HDK N20 (hydrophilic) were utilized and incorporated into silicone-urea copolymers in amounts of 1-60% by weight. Influence of the silica type (hydrophilic versus hydrophobic), amount of silica loading and the PDMS soft segment molecular weight on the morphology, tensile properties and modulus-temperature behavior of the nanocomposites were determined. Major observations of this study were: (i) under the blending conditions used, incorporation of silica does not seem to interfere significantly with the hydrogen bonding between urea groups, (ii) incorporation of silica does not affect the glass transition temperature of PDMS, (iii) incorporation of silica influences the tensile and thermomechanical properties of silicone-urea segmented copolymers significantly, (iv) average molecular weight of the PDMS soft segment in the silicone-urea copolymer plays a critical role on the improvement of the tensile properties of the fumed silica/TPSU composites.     

Enhanced physical aging of polymer nanocomposites: The key role of the area to volume ratio

The physical aging process, namely the spontaneous evolution of the thermodynamic state occurring in glasses, has been monitored in poly(methyl methacrylate) (PMMA)/silica and polystyrene (PS)/silica nanocomposites following the time evolution of the enthalpy by means of differential scanning calorimetry (DSC). The effect on physical aging of the content of silica particles has been investigated in detail varying it over a wide range. Our results indicate accelerated physical aging in the nanocomposites in comparison to the corresponding pure polymer. Furthermore the acceleration is generally more pronounced in nanocomposites presenting a high silica content. This result cannot be attributed to a difference in molecular mobility of the polymers in the nanocomposites in comparison to pure PMMA and PS, since broadband dielectric spectroscopy (BDS) indicates no effect of silica nanoparticles on the polymer segmental dynamics. Moreover, calorimetric measurements reveal a reduction of the heat capacity jump at T_g for the nanocomposites, as well as lower experimentally recoverable enthalpy values. This may result from the faster non-isothermal evolution of the glass state when cooling down the samples from their liquid state. To account for these experimental results the acceleration of physical aging has been rationalized in the framework of the diffusion of free volume holes model as previously proposed. This is able to adequately catch the dependence of the physical aging rate on silica content, determining the area of nanoparticles to the volume of polymer, that is the relevant variable within the diffusion model.     

Study on the synthesis of poly(methyl methacrylate)–poly(methacrylic acid) composite latex and their humidity sensitive properties

The composite latex particles of poly(methyl methacrylate)–poly(methacrylic acid) [poly(MMA–MAA)] were synthesized through either soapless seeded emulsion polymerization or a soapless emulsion copolymerization technique. The reaction kinetics, morphology, and size of latex particles, composition, glass transition temperature (T_g), and molecular weight of polymer products were studied under different experimental conditions. Moreover, this work also focused on the humidity‐sensitive properties of the polymer films fabricated by melting under the temperature of 200°C and followed by chemical modification with aqueous solution of NaOH. It is confirmed that there exists both an optimum ratio of hydrophilic to hydrophobic monomers and the initial structure of the latex particle to provide the humidity‐sensitive polyelectrolyte film with excellent water resistivity and good sensitivity to humidity. Besides, little hysteresis and quick response were observed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 47–57, 1999     

Effect of noncovalent chemical modification on the electrical conductivity and tensile properties of poly(methyl methacrylate)/carbon nanotube composites

Noncovalent chemical modification by initiated chemical vapor deposition technique is applied to carbon nanotubes (CNTs) to reduce average agglomerate size of the nanoparticles in the polymer matrix and to improve surface interaction between the composite constituents. CNT surfaces are coated conformally with thin poly(glycidyl methacrylate) (PGMA) polymer film and coated nanoparticles are incorporated in poly(methyl methacrylate) (PMMA) polymer matrix using solvent casting technique. Conformal PGMA coatings around individual nanotubes were identified by scanning electron microscopy analysis. Transmission electron microscopy and optical microscopy analyses show homogeneous composite morphology for composites prepared by using PGMA coated nanotubes. Fourier Transform Infrared and X‐ray photoelectron spectroscopy analyses show the successful deposition of polymer with high retention of epoxide functionality. PGMA coating of CNTs exhibits improvement in electrical conductivity and tensile properties of PGMA‐CNT/PMMA systems when compared with uncoated nanoparticles. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Polymer compatibility III. The system poly(methyl methacrylate)–poly(vinyl acetate). Characterization studies

Blends of poly(methyl methacrylate) (PMMA) and poly(vinyl acetate) (PVAc) were prepared by mixing the polymers in the melt and in the absence of a solvent. PMMA was the major constituent of the blend. The polymer blends were tested, using various methods, to determine if they are compatible as solids. Data obtained from dynamic mechanical and DSC measurements show that, when they are mixed under given Brabender mix conditions, the blends exhibit properties characteristic of polymer pairs compatible as solids. If the mix conditions are altered, a two-phase system is evidenced. Using micrographs obtained by light microscopy in phase contrast as criteria, two companion blends containing PMMA/PVAc 80/20 would be classified as incompatible as solids because of the differences in refractive index of PMMA and PVAc. The micrographs also show that, in the system that would otherwise be listed as compatible, the PVAc domains appear to be relatively uniform in size and distribution through the PMMA matrix. In its companion blend, large, irregularly shaped particles of PVAc which are poorly dispersed in the PMMA matrix are evident.     

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