Baijun Liu

Crosslinking network structure effects on particle coagulation in the emulsion polymerization of styrene in methanol solution

This work is an extension of previous research results reported by our team (Colloid Polym Sci 292:519–525; 1347–1353), where how to control particle size distribution by adjusting particle coagulation has been investigated. There is limitation in previous studies, that is, the particles taking part in coagulation only possess a linear structure. However, the crosslinking network structure is necessary to many fields, such as rubber and plastic modifier. Thus, it is very significant to investigate the effect of the crosslinking network structure on particle coagulation for understanding the nature of particle coagulation and controlling particle size distribution. In this manuscript, dihydrodicyclopentadienyl acrylate (DCPA) is chosen as a crosslinker to copolymerize with styrene to promote particle structure shift from the linear to the crosslinking network structure and to investigate further the coagulation behavior of the particles with the crosslinking network structure. Experimental results are explained by the collision frequency of particles and stability dependence of the particle structure.

Preparation of monodisperse, sub-micrometer polymer particles by one-step emulsion polymerization under particle coagulation

The particle coagulation technology in emulsion polymerization is a novel and facile approach to prepare large-scale, narrowly dispersed latex particles. However, the formation of narrowly dispersed latex particles under particle coagulation at a high zeta potential is surprising. To elucidate this observation, a detailed investigation on the relationship between particle coagulation and particle size distribution was carried out. Unlike the conventional emulsion polymerization, a rapid decrease in the particle number and an increase in the particle size were clearly observed during the polymerization. The results confirm the occurrence of particle coagulation. The width of zeta potential and particle size distribution also decreased with particle coagulation, resulting in large-size, narrowly dispersed latex particles. These phenomena were explained by the competitive growth mechanism.

Particle Nucleation and Growth in the Emulsion Polymerization of Styrene: Effect of Monomer/Water Ratio and Electrolyte Concentration

This work is an extension of previous research results reported by our team (Colloid and Polymer Science 2013, 291: 2385-2398), where large scale and high solid content latexes of poly(n-butyl acrylate) were obtained with the particle coagulation method induced by the electrolyte. However, how to prepare controlled particle size distribution polymer latex has not been studied. Thus, in this study, the effect of the monomer/water ratios and electrolyte concentrations on particle formation and growth methods were studied by following the tracks of the evolutions of particle size, number and distribution as a function of reaction time or conversion. Experimental results showed that the length of time that particle nucleation occurred increased with increasing monomer charged for the systems without electrolyte. A point worthy of attention here is that homogeneous nucleation may occur at high monomer concentrations (30/70, 40/60). However, electrolyte added could be made the nucleation mechanism shift from micellar/homogeneous nucleation to micelle /coagulation nucleation. As a result, the final particle size distribution can be controlled by adding an appropriate electrolyte to regulate the nucleation mechanism. Spherical and uniformly sized particles could be obtained when electrolyte concentration is between 0.2 wt% and 0.4 wt% for water at the high monomer/water ratio (40/60). The effects of electrolyte concentration on nucleation mechanism mainly were expressed by decreasing the solubility of the monomer and interparticle potential, and then preventing homogeneous nucleation and enhancing particle coagulation.

Exothermal Behavior and Particle Scale Evolution in High Solid Content One-Step Batch Emulsion Polymerization

This investigation is an extension of the previous study (Colloid Polym Sci. 291: 2385–2398), where the latex of poly(butyl acrylate) with large particle scale (300–600 nm) and high solid content was obtained via batch emulsion polymerization technology according to particle coagulation mechanism induced by electrolyte. However, some technological parameters such as the variation in the maximum reaction temperature and the time at which this maximum occurs with the initial temperature and electrolyte concentrations were not been discussed in that article. These variations play important roles in determining the design of reactor and industry production. Thus, in this study, the evolution of reaction temperature, particle scale, and number as functions of reaction time are of concern in order to confirm the effect of particle coagulation on polymerization process and finally the latex properties. Experimental results indicated that the maximum value of the polymerization system decreased with decreasing the initial reaction temperature, and with increasing electrolyte concentration. The addition of electrolyte not only reduced the maximum value of reaction temperature ranging from 92.4°C to 71°C, but also made the particle scale increase to ∼650 nm from 315 nm, and the viscosity of latexes decrease to 40.2 mPa · s from 200.1 mPa · s.

Facile synthesis of large sized and monodispersed polymer particles using particle coagulation mechanism: an overview

Highly uniform polymer latex particles with controlled particle size have been widely applied in many fields such as nanotechnology, drug delivery, biomedical separation, and material templates. Since the particle size plays a critical role in determining the application fields, various technologies such as two-stage swelling method and dynamic swelling method have been used to control the particle size in the polymerization process. However, these methods usually need a multi-step polymerization reaction and long reaction time. This review focuses on a method of controlling particle size, that is, particle coagulation technology. Particle coagulation technology can be used to produce large sized, monodispersed polymer particles by soap-free emulsion polymerization, macroemulsion polymerization, and dispersion polymerization. In this review article, an overview of the concept of particle coagulation is given, followed by the description of the particle coagulation process in different polymerization systems. Some representative publications about particle coagulation were also reviewed, especially the effect of reaction parameters on the particle coagulation extent and time. Finally, the relationship between the particle coagulation and particle size distribution is reviewed extensively.

Synthesis of Sub-100 nm and Narrow Particle Size Distribution Cationic Latex by One-Step Emulsion Polymerization

A novel approach to synthesize narrow particle size distribution cationic latex particles based on styrene and butyl acrylate was proposed. The effect of monomer/water ratios, surfactant (cetyltrimethylammonium chloride) concentrations, and monomer compositions on the evolution of particle size, distribution, number, and morphology as a function of monomer conversion was concerned in order to confirm the optimum polymerization condition. As expected, the particle size of the ultima latex increased with monomer/water ratios and styrene contents decreased with increasing surfactant concentrations. Continuous nucleation phenomena occurred when monomer/water ratio was lesser than 30/70, resulting in a gradual increase in the number of particles in the whole polymerization process. Combined with the previous work (Colloid and Polymer Science, 2014, 292: 519–525), it was concluded that particle coagulation easily took place in cationic emulsion polymerization of styrene. Thus, the narrow particle size distribution cationic latexes with particle scale between 50 nm and 80 nm, 30 wt% solid content could be prepared in a short reaction time. GRAPHICAL ABSTRACT

Effect of Polymer Characteristics on Particle Formation and Growth in Batch Emulsion Polymerization

This article is an extensive investigation on particle coagulation growth in emulsion polymerization proposed by our team (Colloid and Polymer Science, 2013, 291, 2385–2398). Monodispersed, large-scale, high-solid content poly (butyl acrylate) latex was obtained by varying the reaction procedures in previous studies. However, the present method, which could be used in other monomer systems such as styrene, methyl methacrylate, or the copolymerization of different monomers, has not been reported to date. In this article, the particle formation and growth behaviors of different monomer compositions were investigated in regard to the range of application and to clarify the effect of monomer characteristics on particle coagulation. Experimental results indicated that polymer characters such as hydrophilicity play an important role in particle coagulation, which was increased with increasing monomer hydrophilicity. Moreover, particle coagulation could improve reaction system stability and enhance the likelihood of obtaining a high solid content. The optimal systems for styrene, methyl methacrylate, and butyl acrylate were 40, 50, and 60 wt%, respectively, due to variation in monomer hydrophilicity. GRAPHICAL ABSTRACT

Synthesis of large-scale, narrowly dispersed, highly cross-linked, and spherical latex particles via one-step emulsion polymerization through particle coagulation

ABSTRACT Particle coagulation technology is a facile approach to prepare large-scale and narrowly dispersed polymer particles. However, diverse shapes such as ellipsolid, snowman, dumbbell, and trimer among others were obtained if the cross-linker was directly added into the initial reaction mixtures due to the restriction of the highly cross-linking particle fusion process. In this study, we prepared sub-200 nm, narrowly dispersed, highly cross-linked, and spherical latex particles using particle coagulation technology by controlling the relation between the cross-linking net formation and particle coagulation. Depending on the addition time or feeding rate of the cross-linker (divinylbenzene, DVB), the particles with different sizes or shapes were obtained. The later the addition start time of DVB, the narrower the particle size distribution of the latex particles. Alternatively, the increase of the continuing feeding time could also be used to decrease the width of particle size distribution of the ultimate latex. In addition, narrowly dispersed and spherical latex particles also could be directly obtained by advancing the particle coagulation time using 2, 2′-Azobis (2-methylpropionamidine) dihydrochloride as a cationic initiator. Our study presents a new method that will further widen the fields of application of particle coagulation technology. GRAPHICAL ABSTRACT

Crosslinking network structure governing particle shape and size distribution by one-step emulsion polymerization in the presence of particle coagulation

ABSTRACT In this study, sub-200 nm, crosslinked latex particles with a narrow particle size distribution were prepared by one-step emulsion polymerization in the presence of particle coagulation. The relationship between the particle shape and particle coagulation was investigated by varying the time of crosslinking network structure formation and particle coagulation. Particles with irregular shapes such as doublet, triplet, and ellipsoid were obtained using divinylbenzene (DVB) and ethylene glycol dimethacrylate (EGDMA) as the crosslinking agents, because the crosslinking network structure of particles was formed before the particle coagulation. In contrast, latex particles with a uniform spherical shape were also prepared using triallyl isocyanurate (TAIC) or dihydrodicyclopentadienyl acrylate (DCPA) as the crosslinking agents by delaying the time of crosslinking network structure formation. Alternatively, uniform spherical latex particles were prepared by bringing forward the particle coagulation time using cationic initiator, 2, 2′-azobis (2-methylpropionamidine) dihydrochloride (AAPH). This study presents a new idea that would further broaden the application of particle coagulation in emulsion polymerization. GRAPHICAL ABSTRACT

A novel approach to prepare large-scale and narrow-dispersed latex particles by emulsion polymerization based on particle coagulation mechanism

Abstract In order to understand the mechanism of narrow particle size distribution of the final latex during particle coagulation, a series of experiments were performed to investigate the effect of polymer nature on particle coagulation capability. In particular, thermodynamics and kinetics in aqueous phase were considered to illustrate the detail process of particle coagulation. The final particle size decreased with the increasing side chain length of alkyl methacrylate from 181.5 nm in MMA to 131.6 nm in EMA, 119.3 nm in PMA, and 115.1 nm in BMA, indicating that the particle coagulation capability was proportional to the hydrophilicity of polymer. With increasing polymer hydrophilicity, the affinity between surfactant molecules and particle surface decreased, thus enhancing the particle coagulation capability. Moreover, the critical length of oligomer radical also increased with increasing hydrophilicity and the efficiency of radical capture decreased, thus increasing the saturation of monomer concentration in the inner part of particle, promoting particle coagulation. Combining these results and the La Mer Diagram, a novel approach was developed to prepare large-scale, narrow-dispersed, and high solid content polymer latex based on particle coagulation mechanism. Three criteria, namely, rapid nucleation, fast coagulation, and a long growth period, should be met to produce latex with a narrow particle size distribution.