Two-stage Seeded Emulsion Polymerization Research Articles

Fabrication and evaluation of one-component core/shell structured latex adhesives containing poly(styrene) cores and poly(acrylate) shells

A one-component, non-crosslinked, and ambient temperature-cured core/shell (CS) structured waterborne poly(styrene-acrylate) (PStA) latex adhesive was prepared by two-stage seeded emulsion polymerization. The first-stage polymers were non-polar styrene-based copolymers with Tgs ranging from 86°C to 41°C and the second-stage polymer was polar acrylate-based copolymer having a Tg of 8°C. The effect of latex particle morphology and film microstructure on the CS structured PStA latex adhesive was examined by evaluating film thermal properties and mechanical performance. The results have shown that incorporation of soft shell polymers into hard core polymers can improve adhesive properties without compromising film-forming ability. Wood adhesive performances of latex adhesive were measured by shear strength and boiling water resistance of glued wood blocks. The utilization performances of the one-component CS structured PStA latex adhesive were found to largely depend on CS morphological character and the interfacial compatibility between various polymeric constituents, demonstrating that fabrication of CS latex particles provides a promising approach to realize high-performance latex adhesives.

Synthesis and characterization of HALS/UV-absorbers bifunctionalized core-shell elastomer and Its application in polyoxymethylene

Poly(BA-MMA-PMPA-BPMA), a core-shell polyacrylate elastomer containing hindered amine light stabilizer (HALS) and benzophenone UV-absorber (UVA) in the shell phase, was prepared by two-stage seeded emulsion polymerization from n-butyl acrylate (BA), methyl methacrylate (MMA), 1,2,2,6,6-pentamethylpiperidin-4-ylacrylate (PMPA) and 2-hydroxy-4-(3-methacryloxy-2-hydroxyl-proroxy) benzophenone (BPMA). Poly(BA-MMA-PMPA-BPMA) was characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (1H-NMR), transmission electron microscopy(TEM), differential scanning calorimetry(DSC), thermogravimetric analysis (TG) and UV-visible (UV-vis) absorption spectroscopy. Furthermore, the obtained Poly(BA-MMA-PMPA-BPMA) was melt-blended with polyoxymethylene (POM). The effect of Poly(BA-MMA-PMPA-BPMA) on POM was compared with that of Poly (BA-MMA-PMPA) and Poly(BA-MMA-BPMA). Scanning electron microscope (SEM), metallographic microscopy, DSC and mechanical properties were employed to characterize POM blends before and after UV irradiation. The results showed that the size of surface cracks and changing degree of melting point of POM/poly(BA-MMA-PMPA-BPMA) were lower than that of POM/poly(BA-MMA-PMPA) and POM/poly(BA-MMA-BPMA). The percentage retention of elongation at break and notched impact strength of POM/poly(BA-MMA-PMPA-BPMA) was 63 % and 80 % respectively after 800 h UV irradiation, which was higher than that of POM/poly(BA-MMA-PMPA) and POM/poly(BA-MMA-BPMA). Therefore, it could conclude that the photostabilizing of Poly(BA-MMA-PMPA-PBMB) was greatly enhanced, attributing to the synergistic effect between HALS and UVA.

Convenient synthesis and morphology of latex particles composed of poly (methyl methacrylate)-b-poly (n-butyl acrylate) by 1, 1-diphenylethylene (DPE) seeded emulsion polymerization

Methyl methacrylate-butyl acrylate structural latexes were synthesized by two-stage seeded emulsion polymerization using 1,1-diphenylethylene (DPE) as a control reagent. In the first stage, the seed latex particles with the precursor poly (methyl methacrylate-DPE) (P(MMA-DPE)) were prepared, and then the second monomer n-butyl acrylate (nBA) was swollen into the seed latex particles under stirring at room temperature. In the second stage, the polymerization of nBA was thermally initiated at 80 °C, and the latex particles composed of block copolymer were synthesized. The size and morphology of the latex particles were investigated by light scattering and TEM. The contact angles of different latex films were also measured. The block copolymer was characterized by size exclusion chromatography, nuclear magnetic resonance spectroscopy, and differential scanning calorimetry. Microphase separation of the block copolymer was examined using atomic force microscopy.

Synthesis and characterization of core–shell polyacrylate particles containing hindered amine light stabilizers

A polymerizable hindered amine light stabilizer (HALS) 1,2,2,6,6-pentamethylpiperidin-4-yl acrylate (PMPA) was synthesized through transesterification of 1,2,2,6,6-pentamethylpiperidin-4-ol (PMP) with methyl acrylate (MA). Core–shell latex particles containing HALS moieties in the shell phase were prepared by two-stage seeded emulsion polymerization from n-butyl acrylate (BA), methyl methacrylate (MMA) and PMPA. The Fourier transformed infrared (FTIR) and nuclear magnetic resonance ( 1H NMR) analysis showed that PMPA monomer was successfully prepared and was effectively involved in the polyacrylate particles. The surface composition was studied by X-ray photoelectron spectroscopy (XPS), and the results indicated that HALS-containing groups could be distributed on the surfaces of the particles. Transmission electron microscopy (TEM) analysis revealed that the particles obtained presented a core–shell structure with a particle size around 100 nm. Two glass transition temperatures ( T g), assigned to the core phase and the shell phase of the particles, respectively, were observed for both HALS-containing and HALS-free particles, as determined by differential scanning calorimetry (DSC). In addition, the T g value for the shell phase of HALS-containing particles was 13 °C lower than that of HALS-free particles, indicating the presence of random copolymer between MMA monomer and PMPA comonomer in the shell phase. The thermogravimetry analysis (TGA) and differential thermal gravimetric (DTG) results showed that HALS-containing particles provided an improvement in thermal stability in comparison to HALS-free particles.

Preparation of ASA (acrylonitrile-styrene-acrylate) structural latexes via seeded emulsion polymerization

Acrylonitrile-styrene-acrylate (ASA) structural latexes were synthesized in a two-stage seeded emulsion polymerization. In the first-stage, partially cross-linked poly ( n-butyl acrylate) (P nBA) and poly ( n-butyl acrylate-stat-2-ethyl hexyl acrylate) P ( nBA-stat-2EHA) (75/25 by wt) rubber cores were synthesized, and then in the second-stage, a hard poly (styrene-stat-acrylonitrile) (SAN) (70/30 by wt) shell was grafted on to the rubber seeds. The effects of surfactant type and second-stage monomer addition mode have been investigated on the final morphology of two-stage emulsion particles. The results indicated that an application of anionic surfactant, that is, sodium dodecyl sulfonate (SDS), along with sodium persulfate (KPS) initiator for both stages, and with first-stage tert-butyl hydroperoxide ( t-BHP) and second-stage KPS initiators led to a hemisphere particle morphology. On the other hand, raspberry and core–shell structures were observed for the structural latexes, which were prepared using a non-ionic surfactant, that is, nonylphenol ethoxylated polyethylene glycol (Igepal CO-850), accompanying KPS initiator for both stages. It is clear, however, that the relative surface hydrophilicity of the core phase, altered by the surfactant type considerably affected the type of morphology formed. For obtained structural latexes, the gradual addition of the second-stage monomers to the core latexes resulted in a fairly real core–shell structure with a higher shell thickness. On the contrary, a raspberry structure in which the rubber phase was enlarged by the second-stage polymer microdomains was observed for the second-stage monomer addition batch. In fact, the shell semi-batch polymerization conditions lower the shell plasticizing effect, and increase the kinetic barrier to prevent from further second-stage monomer diffusion and microdomain formation within the rubbery phase.

Luminescence techniques and characterization of the morphology of polymer latices: 2. Fluorescence lifetime, phosphorescence and fluorescence anisotropy studies

Five poly(n-butyl methacrylate), PBMA, latex dispersions have been prepared, each incorporating a different fluorescent label, via a two-stage seeded emulsion polymerization. The resultant latices contain ca. 35% by weight total solids and are of 80 (±10) nm diameter as determined by photon correlation spectrometry. Luminescence spectroscopic techniques, namely fluorescence (and phosphorescence) excited state lifetime measurements in addition to time-resolved anisotropy experiments have provided useful information regarding the morphology, microviscosity and water permeability of the resultant particles. A picture of the PBMA colloid emerges of an interior which is highly viscous and water impermeable in nature. Indeed, the environment is protective enough to sustain room temperature stabilized phosphorescence from both an acenaphthylene and 9-phenanthrylmethyl methacrylate labeled dispersion through simple nitrogen purging of the solutions. However, the current spectroscopic measurements should be viewed with the knowledge that each luminescent label may fashion its own distinctive microenvironment within the latex during polymerization.

Morphology and electrokinetic behavior of styrene-2-ethylhexyl acrylate copolymer latex for coatings prepared by two-stage seeded emulsion polymerization

The styrene (ST)-2-methylhexyl acrylate (EHA) copolymer latexes were synthesized through two-stage seeded emulsion polymerization (TSSEP) technique which were compared with the conventional emulsion polymerization (CEP) technique. The morphologies, particle size and electrokinetic behaviors of TSSEP and CEP latexes were studied through transmission electron microscopy (TEM) and Zetasizer respectively. It was found that the latex particles of TSSEP were all uniform and almost spherical in morphology. The particle size as well as polydispersity of TSSEP latex was smaller than that of CEP latex, and the particle size measurement of TEM corresponded with that of Zetasizer. Electrokinetic studies showed that all latexes were negative systems, and the particles exhibited colloidal stability under basic conditions. The negative value of ζ-potential for TSSEP latex was larger than that for CEP latex over the whole range of measured pH and NaCl concentrations, i.e. TSSEP latex demonstrated higher electrostatic stability than CEP latex. The ζ-potential reached the maximum value at approximately 3 × 10 - 3 mol dm - 3 of NaCl concentration indicating the highest colloidal stability of TSSEP and CEP latexes. At very high salt concentration ([NaCl] = 0.1 M), we obtained very small ζ-potential values, thus the colloidal stability of ST-EHA copolymer latexes was much low.

Synthesis of acrylic core–shell composite polymers and properties of plastisol–gels

Heterogeneous latices of acrylic core–shell polymers were designed and prepared via a two-stage seeded emulsion polymerization for plastisol–gel of automotive underbody coatings and body sealers. 1,6-Hexanediol diacrylate (HDDA) was introduced to the rubbery core and/or the glassy shell with interpenetrating polymer network (IPN). The latices were characterized by submicron particle sizer, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The properties of plastisol–gels prepared by mixing the core–shell polymers and DOP/TCP plasticizers were investigated by testing the storage stability of plastisols and the mechanical properties of plastigels. These novel core–shell polymers represent a highly positive innovation and a wide application in automotive industry instead of the hazardous material PVC plastisol.

Simple method of related sensitivity range to predict the thermodynamic equilibrium morphology of a core-shell latex particle

The equilibrium morphologies of different core–shell latices are predicted, and a related sensitivity analysis is given for the predictions. This article proposes a related sensitivity range for estimating the accuracy of predictions, made with the simple method, of the thermodynamically preferred morphology of a core–shell latex particle in two-stage seeded emulsion polymerization. The related sensitivity range of the predictions is defined and calculated, and the results show that different core–shell latices have different sensitivity ranges. The wider the sensitivity range is, the more reliable the prediction is of the morphology of the core–shell latex. The simple method of related sensitivity range has been verified in the literature and with experiments. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3144–3152, 2004

Morphology of poly(isoprene-co-styrene-co-methacrylic acid) latex prepared by two-stage seeded emulsion polymerization

Heterogeneous latexes were prepared by a two-stage seeded emulsion polymerization process at 80°C using potassium persulfate as the initiator and sodium dodecyl sulfate as the emulsifier. Poly(styrene-co-methacrylic acid) latexes containing varying amounts of methacrylic acid (MAA) were used as seeds. The second-stage polymer was poly(isoprene-co-styrene-co-methacrylic acid). By using different methods for the addition of the MAA and by varying the amount of MAA, the hydrophilicity of the polymer phases could be controlled. The morphologies and size distributions of the latex particles were examined by transmission electron microscopy. The latexes were in all cases unimodal, and had narrow particle size distributions. The particles displayed different morphologies depending on the polymerization conditions and monomer composition. The hydrophilic properties of the two phases in combination with the internal particle viscosity and crosslinking of the second phase during polymerization were found to be the major factors influencing the particle morphology. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1543–1555, 1997