Semi-continuous Seeded Emulsion Polymerization Research Articles

Influencing Mechanism of Methacrylic Acid on the Redispersion Properties of Redispersible Polymer Powders

Acrylic polymer emulsions were synthesized by semi-continuous seeded emulsion polymerization and the corresponding redispersible polymer powders were prepared by spray drying. Methacrylic acid (MAA) was used as the hydrophilic shell monomer. The influences of the amount of MAA on the average particle size of the original emulsion, the dispersion stability, zeta potential, and size distribution of the redispersion emulsion were investigated. The results show that with an increase in the amount of MAA, the particle size of original emulsion, the dispersion stability, and the zeta potential of the redispersion emulsion increased significantly. The size distribution of the redispersion emulsion with a high amount of MAA was unimodal and similar to the original emulsion indicating excellent water-redispersibility. Transmission electron microscopy (TEM) was used to characterize the internal microtopography of the redispersible polymer powder, and results showed that with a higher amount of MAA, millipores with larger pore sizes were present in the transection of the redispersible polymer powder. When polymer powders are redispersed in an aqueous phase, large micropores provide a more convenient channel for water permeation, which optimizes the redispersibility. The hairy structure and higher zeta potential endow the redispersion emulsion with excellent redispersion stability.

Hydrazine‐functionalized latexes

AbstractThe noncommercial functional monomer 4‐vinylbenzyl hydrazine (VBH) was synthesized and subsequently copolymerized with styrene (St) by means of different batch and semicontinuous seeded emulsion polymerization processes, so as to obtain hydrazine‐functionalized nanoparticles. The effect of pH, surfactant and initiator amounts, ratio VBH/St, reaction temperature, and ratio acetone/water were studied. Due to the amphiphilic character of VBH at acid pH, the hydrazine groups of the functionalized comonomer were masked with acetone to form hydrazone groups. Secondary nucleations were avoided by using the protected VBH comonomer; however, a decreased radical efficiency achieving limited conversion was observed. Controlling the cationic initiator concentration, complete conversions together with the neat growth of the seed particles were obtained in the semicontinuous seeded emulsion polymerization of styrene and VBH protected with acetone. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6201–6213, 2009

Synthesis of Crosslinkable Core-Shell Emulsion and Rheology of the Core-Shell/Amine Crosslinking Process

Starve feed and semi-continuous seed emulsion polymerization were used to control the morphology of core shell latex particles with a vinyl acetate (VAc)/vinyl ester of versatic acid 10(VeoVa10) copolymer core surrounded by a poly(glycidyl methacrylate) (PGMA) shell. Pure core and core-shell structures were confirmed by TEM. The results suggest that core-shell morphology of the two stage emulsion was favoured by higher concentration of emulsifier in the seed latex: the particle size distribution of core-shell latex was broader than that of the core latex, and the average particle size of core-shell latex was larger than that of the core latex. The core-shell structure was not produced using seed emulsion with emulsifier concentration at or below the critical micelle concentration. The core shell emulsion containing epoxy functional group with added ethylene diamine showed an abrupt increase in dynamic shear moduli, G' and G'' and complex viscosity η* (several orders of magnitude) at about 35oC, during temperature ramps, over a wide range of angular frequencies. The time ramps showed that the crosslinking reaction did not occur at 15oC for the core-shell emulsion/amine system. The time for gel formation decreased with increase in temperature.

Preparation of Core/Shell Composite Latex Particles and Toughening Modification for Polyamide 6

In this paper, a novel poly(butyl methacry1ate)/poly(methyl methacrylate-itaconic acid)(PBA/P(MMA-ITA)) latex particles with core/shell structure (CSR) was synthesized by the method of pre-emulsion semi-continuous seeded emulsion polymerization. The core/shell structure of CSR was characterized by TEM and confirmed that the average size of CSR particles was about 330 nm and that of PBA core was about 290 nm. The polyamide 6 (PA 6)/CSR blends (N/CSR) were prepared by the melt-blending technique, and its impact strength reached 40kJ•m-2 (more than 7 times higher than neat PA 6) when the ITA dosage was in the range of 4%~10%. The results of SEM showed that the high toughness of N/CSR blends was the result of the shear deformation of PA 6 matrix induced by cavitation of dispersed phase CSR.

Synthesis and property investigation of three core‐shell fluoroacrylate copolymer latexes

AbstractThree core‐shell fluoroacrylate copolymer latices with different fluorinated side chain structure were synthesized in this article by semicontinuous seed emulsion polymerization, using butyl acrylate (BA) and methyl methacrylate (MMA) as acrylate monomer and trifluoroethyl methacrylate (TFEM, C6H7O2F3), hexafluorobutyl methacrylate (HFBM, C8H8O2F6), and dodecafluoroheptyl methacrylate (DFHM, C11H8O2F12) as fluorine‐containing acrylate monomer. The core‐shell fluoroacrylate copolymer latices were named as BA/MMA/TFEM, BA/MMA/HFBM, and BA/MMA/DFHM, respectively. The latex particle morphology and the particle size were determined by transmission electron microscopy and differential scanning calorimetry. The final chemical structure of the latex was analyzed by NMR. The effect of the fluorinated side chain on the core‐shell copolymer latex and film properties, as well as on the superiority of core‐shell copolymer latex to general fluoroacrylate copolymer latex was investigated by energy dispersive X‐ray detector, thermogravimetric analysis, and the determination of contact angle. The analysis results indicated that the particle of fluoroacrylate copolymer latex presented uniform sphere core‐shell structure. Compared with core‐shell BA/MMA/TFEM and BA/MMA/HFBM, BA/MMA/DFHM exhibited not only better surface property as increasing temperature but also better thermal stability. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Preparation of self-crosslinked acrylate emulsion with high elasticity and its rheological properties

Using butyl acrylate(BA), methyl methacrylate(MMA), methacrylic acid(MAA) and mixed emulsifier as raw materials, the self-crosslinked emulsion was prepared via pre-emulsified and semi-continuous seeded emulsion polymerization technology in the presence of N-hydroxymethyl acrylamide and poly solidum maleate. The influence of mass ratio of BA to MMA, amount of N-hydroxymethyl acrylamide and poly solidum maleate on the rheological properties of the self-crosslinked emulsion was studied. Possible cross-linked mechanism of self-crosslinked monomer was investigated. And the relationship between emulsion viscosity and shear rate was investigated. The results show that the self-crosslinked acrylate emulsion with high elasticity can be synthesized when the mass fractions of BA is 60%, MMA is 40%, and added amount of N-hydroxymethyl acrylamide is 2.5%–3.0% and added amount of poly solidum maleate is 0.3%–0.4%. The self-crosslinkage process of N-hydroxymethyl acrylamide involves two steps. One is copolymerization of N-hydroxymethyl acrylamide and acrylate, the other is cross-linkage among polymer molecules via condensation reaction of methylol. The emulsion is of rheological properties of pseudo-plastic fluid and belongs to non-Newtonian fluid.

Synthesis, modification and characterization of core–shell fluoroacrylate copolymer latexes

Core–shell fluoroacrylate copolymer latex, typically used for the protection of ancient stone monument, was synthesized in this paper by semi-continuous seed emulsion polymerization with butyl acrylate (BA) served as the core, methyl methacrylate (MMA), BA and dodecafluoroheptyl methacrylate (DFHMA, C 11H 8O 2F 12) served as the shell. At the same time, the above core–shell fluoroacrylate latex was modified by hydrolysis of tetraethyl orthosilicate (TEOS, Si(OC 2H 5) 4) in the presence of silane coupling agent dodecyltrimethoxysilane (DTMS, C 12H 25Si(OCH 3) 3). The chemical component of the final latex was analyzed by FT-IR. Morphology structure and the particle size of core–shell latex were determined by TEM. The effect of DFHMA and TEOS content on the latex and film properties was characterized by SEM-EDX, AFM, TEM, DSC and UV–vis. The analysis results indicated that the copolymer latex particle presented uniform sphere core–shell structure with 40–50 nm in diameter. About 30 wt% DFHMA gave favorable characteristics both in latex and in film properties. Compared with core–shell fluoroacrylate latex, the modified fluoroacrylate copolymer displayed, when TEOS was controlled in 2.2–3.8 wt%, sound performances in hydrophobic, mechanics, thermodynamics and resistance to ultraviolet.

Preparation and Characterization of Polymer Core Shell Latex Particles

Stable core‐shell latex was synthesized by semicontinuous seeded emulsion polymerization with core monomers consisting of styrene (St), butyl acrylate (BA), and shell monomers consisting of methyl methacrylate (MMA), eutyl acrylate (EA), and methacrylic acid (MAA). The effects of compound emulsifier amount, mass ratio of anionic/nonionic emulsifier, and initiator amount on latex performance were investigated. By particle size analysis and transmission electron microscopy (TEM) observation, results suggest that final latex particles have clearly core shell structures.

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 (Tg) 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/P(St-co-MMA) latex at room temperature and annealed at 383 K above Tg of the polymers. In addition, the changes of the surface of the film formed from the composite latex with time at 383 K were observed by AFM. The evidence illustrated that the film formed from the core-shell latex particles was metastable. The rearrangement of the phases could occur under proper conditions.

Preparation of the stable core–shell latex particles containing organic-siloxane in the shell

In this study, the latex particles with a polyacrylate core and a polydimethylsiloxane shell via 3-(methacryloxypropyl)-trimethoxysilane as the space arm to link the core and shell have been prepared by semi continuous seeded emulsion polymerization. And several key polymerization reaction conditions such as the emulsifier concentration, 3-(methacryloxypropyl)-trimethoxysilane dosages, feeding sequence and the acrylates/siloxanes ratio were detailedly discussed. Then, the optimal condition to prepare stable core/shell particles was selected and a proper preparation process has been established. The as-synthesized particles were characterized by TEM and XPS. The clear core/shell structure of the particles could be observed through analysis TEM. In addition, the results of XPS analyses manifested that siloxanes had been grafted on the surface of the polyacrylate particles and they distributed on the outmost layer of the particles. Finally, the surface hydrophobicity of the film formed by latex particles was investigated by the water absorption ratio measurement. The results indicated the developed latex particle provided with a fair water-repellency property.

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.

Preparation and Characterization of Core-Shell Latex Containing PDMS in the Shell

AbstractIn this paper, the composite latex particles with a polyacrylate (PA) core and a polydimethylsiloxane (PDMS) shell via 3-(methacryloxypropyl)- trimethoxy silane (MPS) as the medium to link the core and shell were prepared by semicontinuous seeded emulsion polymerization and were characterized by transmission electron microscopy (TEM), FT-IR, particle size analyzer and X-ray photoelectron spectroscopy (XPS). The TEM images indicated that the particles containing organic siloxane (D-40) displayed an evident core/shell structure. Additionally, the study by FT-IR and XPS also revealed that D4 could be grafted onto the surface of polyacrylate core because there appeared the characteristic peaks of Si-O-Si group and Si 2s and Si 2p in the spectra of FT-IR and XPS respectively. Besides, the atomic ratio of C/Si on the surface of the core/shell particles (D-40) was close to the ratio of C/Si in the latex of pure PDMS that could prove the PA particles were fully covered by PDMS and the properties of PDMS should be embodied in a maximal level. In order to testify the result, the surface properties of the films produced from the core/shell particles were also investigated by the static contact angle method. Compared with the copolymer of PA, the core/shell particles were more effective to create hydrophobic surface, so, the introduction of D4 was capable of obvious increase in water repellency.

Preparation and properties of novel plastisols based on acrylic core-shell lattices

A series of core-shell lattices comprising a core portion of rubbery acrylic homo- or copolymers and a surrounding shell portion of glassy methyl methacrylate (MMA) homo- or copolymers were designed as plastisols for automotive underbody coatings. The lattices were synthesized by a semi-continuous seeded emulsion polymerization and characterized by using differential scanning calorimetry (DSC) and scanning electronic microscopy (SEM). DSC investigations demonstrated that the incorporation of a hard segment of MMA into the core portion and strongly polar monomer methyl acrylic acid (MAA) or cross-linker allyl methacrylate (ALMA) into the shell portion resulted in an improvement of the glass transition temperatures. SEM micrographs verified that the latex particles were always spherical with regular structure throughout the polymerization stage. Novel plastisols were developed based on the abovementioned core-shell polymers with dioctyl phthalate (DOP) or tricresyl phosphate (TCP) plasticizers, whose core portions were compatible with the employed plasticizer and whose shell portions were incompatible with the plasticizer. Evaluation of the viscosity as a function of the storage time revealed that the storage stability of the plastisols could be obtained through incorporation of the strongly polar monomer MAA or the cross-linker ALMA into the shell portions. The mechanical properties of the plastigels were improved by incorporating MMA into the core portion or by incorporating MAA or ALMA into the shell portion of the lattices. A balance between the mechanical properties of plastigels and the storage stability of plastisols should be considered during selection of the monomers both for the core and shell.

Morphologies of polybutylacrylate/poly(styrene‐co‐methyl methacrylate) latex prepared by starved emulsion polymerization Part I. Thermodynamics equilibrium morphology

AbstractHeterogeneous latexes were prepared by a semicontinuous seeded emulsion polymerization process under monomer starved conditions at 80 °C using potassium persulfate as the initiator and sodium dodecyl sulfate as the emulsifier. Poly(butyl acrylate) latexes were used as seeds. The second‐stage polymer was poly(styrene‐co‐methyl methacrylate). By varying the amounts of methyl methacrylate (MMA) in the second‐stage copolymer, the polarity of the copolymer phase could be controlled. Phase separation towards the thermodynamic equilibrium morphology was accelerated either by ageing the composite latex at 80 °C or by adding a chain‐transfer agent during polymerization. The morphologies of the latex particles were examined by transmission electron microscopy (TEM). The morphology distributions of latex particles were described by a statistical method. It was found that the latex particles displayed different equilibrium morphologies depending on the composition of the second‐stage copolymers. This series of equilibrium morphologies of [poly(butyl acrylate)/poly(styrene‐co‐methyl methacrylate)] (PBA/P(St‐co‐MMA)) system provides experimental verification for quantitative simulation. Under limiting conditions, the equilibrium morphologies of PBA/P(St‐co‐MMA) were predicted according to the minimum surface free energy change principle. The particle morphology observed by TEM was in good agreement with the predictions of the thermodynamic model. Therefore, the morphology theory for homopolymer/homopolymer composite systems was extended to homopolymer/copolymer systems.© 2002 Society of Chemical Industry

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

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