Miniemulsion polymerization of styrene using alkyl methacrylates as the reactive cosurfactant

 Stable styrene miniemulsions were prepared by using alkyl methacrylates as the reactive cosurfactant. Like conventional cosurfactants (e.g., cetyl alcohol (CA) and hexadecane (HD)), alkyl methacrylates (e.g., dodecyl methacrylate (DMA) and stearyl methacrylate (SMA)) may act as a cosurfactant in stabilizing the homogenized miniemulsions. Furthermore, the methacrylate group may be chemically incorporated into latex particles in subsequent miniemulsion polymerization. The data of the monomer droplet size, creaming rate and phase separation of monomer as a function of time were used to evaluate the shelf-life of miniemulsions stabilized by sodium dodecyl sulfate in combination with various cosurfactants. Polystyrene latex particles were produced via both monomer droplet nucleation and homogeneous nucleation in the miniemulsion polymerization using CA or DMA as the cosurfactant, with the result of a quite broad particle size distribution. On the other hand, the miniemulsion polymerization with HD or SMA showed a predominant monomer droplet nucleation. The resultant particle size distribution was relatively narrow. In miniemulsion polymerization, the less hydrophobic DMA is similar to CA, whereas the more hydrophobic SMA is similar to HD. Received: 19 November 1996 Accepted: 20 February 1997     

A competitive particle nucleation mechanism in the polymerization of homogenized styrene emulsions

The effects of concentrations of surfactant (sodium lauryl sulfate [SLS]) and initiator (sodium persulfate [SPS]) on the polymerization of homogenized styrene emulsions, stabilized by SLS/lauryl methacrylate (LMA) or SLS/stearyl methacrylate (SMA), were studied. The rate of polymerization increases with increasing [SLS] or [SPS]. In addition to monomer droplet nucleation, the formation of particle nuclei in the aqueous phase (homogeneous nucleation) plays a crucial role in the polymerization kinetics. In comparison with the LMA containing polymerization system, monomer droplet nucleation becomes more important when the more hydrophobic SMA was used as the costabilizer. Furthermore, the degree of homogeneous nucleation increases with increasing [SPS].     

Synthesis of large,high‐solid‐content latexes by miniemulsion polymerization

Multiple and diverse applications have been recently found for miniemulsions and miniemulsion polymerization. In this work, miniemulsion polymerization is presented as a suitable technique for the preparation of high‐solid‐content latices with large particle sizes. Monomer miniemulsions were prepared with a high‐pressure homogenizer, and droplet sizes of 200–700 nm were obtained. Latexes with particle sizes larger than the sizes commonly accepted for miniemulsion polymerization were obtained. With fixed operational conditions of the homogenizer, the type of stabilizer was the key parameter determining the droplet size and the droplet size distribution. The particle size of the latices obtained by miniemulsion polymerization indicated that the particles were mainly formed by droplet nucleation. Latexes obtained by this process have multiple applications, including use as seeds in the polymerization of high‐solid‐content latices. This article shows that potential new applications for miniemulsion polymerization are far from being exhausted. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4222–4227, 2004     

Styrene miniemulsion polymerization initiated by 2,2′-azobisisobutyronitrile

The effects of various parameters on the dodecyl methacrylate (DMA) or stearyl methacrylate (SMA) containing styrene miniemulsion polymerizations were investigated. These parameters include the type of initiators [2,2′-azobisisobutyronitrile (AIBN) vs. sodium persulfate (SPS)], the size of the homogenized monomer droplets, the AIBN concentration, and the SDS concentration. A small quantity of a water-insoluble dye was also incorporated into the polymerization system to study the related particle nucleation mechanisms. The oil-soluble AIBN promotes nucleation in the monomer droplets, whereas homogeneous nucleation predominates in the reaction system with the water-soluble SPS. Homogeneous nucleation, however, cannot be ruled out in the DMA or SMA containing polymerizations with AIBN as the sole initiator. Increasing the level of AIBN or SDS enhances formation of particle nuclei via homogeneous nucleation. The reaction kinetics is primarily controlled by the competitive events of monomer droplet nucleation and homogeneous nucleation. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2537–2550, 1999     

Effects of 2‐hydroxyalkyl methacrylates on the styrene miniemulsion polymerizations stabilized by SDS and alkyl methacrylates

The effects of 2‐hydroxyalkyl methacrylates (HEMA and HPMA) on the styrene miniemulsion polymerizations stabilized by SDS/lauryl methacrylate (LMA) or SDS/stearyl methacrylate (SMA) were investigated. A mixed mode of particle nucleation (monomer droplet nucleation and homogeneous nucleation) is operative during polymerization. Homogeneous nucleation plays a crucial role in the polymerizations stabilized by SDS/LMA, whereas monomer droplet nucleation becomes more important in the polymerizations stabilized by SDS/SMA. The polymerization kinetics is insensitive to the type of 2‐hydroxyalkyl methacrylates, but the difference in the relative importance of monomer droplet nucleation and homogeneous nucleation is detected. Incorporation of 1‐pentanol (C₅OH) into the reaction mixture also shows a significant influence on the polymerizations stabilized by SDS/LMA or SDS/SMA. This is attributed to the formation of a close‐packed structure of SDS and C₅OH on the droplet surface, which acts as a barrier to the incoming oligomeric radicals. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3188–3199, 2000     

含氟接枝共聚物为助稳定剂的苯乙烯细乳液聚合反应

以含氟接枝共聚物(PSG)单独作为助稳定剂,十二烷基硫酸钠(SDS)为乳化剂,过硫酸钾(KPS)为引发剂引发苯乙烯(St)的细乳液聚合。考察了聚合温度、乳化剂用量、引发剂用量和PSG用量对细乳液聚合转化率的影响。结果表明,以PSG单独作为助稳定剂,细乳液聚合过程较稳定,起始单体液滴数目与成核粒子数目几乎相等。最终转化率随着乳化剂用量和反应温度的提高而增加,引发剂用量影响不明显。在相同的反应条件下,分别以相同用量(w.t.%=0.091%时,占单体和水的总质量)的PSG和十六醇为助稳定剂用于苯乙烯细乳液聚合,反应290min后,PSG体系的聚合转化率达到87.2%,而十六醇体系的聚合转化率只有78.2%。     

Miniemulsion copolymerization of vinyl acetate and butyl acrylate. IV. Kinetics of the copolymerization

The copolymerization kinetics of conventional emulsions and miniemulsions of 50:50 and 25:75 molar ratios vinyl acetate–butyl acrylate monomer mixtures were studied using sodium hexadecyl sulfate as surfactant. Hexadecane was the cosurfactant used in the preparation of the miniemulsions, and ammonium persulfate was the initiator used in the polymerizations. The rate of polymerization showed four regions which extended to different conversions depending on the type of emulsion used (conventional or miniemulsion). The rate of polymerization for the miniemulsion process was always slower than for the conventional process. The dependence of the rate on the initiator concentration was higher for the miniemulsion process. The number of particles nucleated in the miniemulsion copolymerization process was lower than in the conventional emulsion copolymerization process. The initiator and surfactant concentration dependence of the number of particles were 0.8 and 0.25 for the miniemulsion copolymerization process and 0.0 and 0.68 for the conventional emulsion copolymerization process respectively. These effects were attributed to the different particle nucleation mechanism operating in each process.     

Miniemulsion polymerization of methyl methacrylate with dodecyl mercaptan as cosurfactant

Miniemulsions of methyl methacrylate with sodium lauryl sulfate as the surfactant and dodecyl mercaptan (DDM) as the cosurfactant (or hydrophobe) were prepared and polymerized. The emulsions were of a droplet size range common to miniemulsions and exhibited long-term stability (greater than 3 months). Results indicate that DDM retards Ostwald ripening and allows the production of stable miniemulsions. When these emulsions were initiated, particle formation occurred predominantly by monomer droplet nucleation. The effects of the concentration of surfactant, cosurfactant and initiator were determined. Rates of polymerization, monomer droplet sizes, polymer particle sizes, molecular weights of the polymer, and the effect of initiator concentration on the number of particles vary systematically in ways that indicate predominant droplet nucleation in these systems. © 1996 John Wiley & Sons, Inc.     

苯乙烯RAFT细乳液聚合

活性自由基聚合研究在上世纪90年代取得突破，受到研究者的广泛关注．现今，已形成NMP(Nitroxide-medjated polymerization)、ATRP(Atom transfer radical polymerization)、RAFT(Reversible addition／fragmentation transfer)聚合等3种高效活性自由基聚合体系，其各自的聚合机理已基本探明。     

Miniemulsion polymerization of styrene costabilized with polyurethane via <Superscript>60</Superscript>Co γ-ray radiation initiation

Polyurethane (PU) was successfully synthesized and used as costabilizer in the miniemulsion polymerization of styrene (St) initiated by ⁶⁰Co γ-ray radiation at room temperature. Only 2 wt% PU based on the monomer was enough to prepare a stable miniemulsion with a shelf life of more than 12 months. Preservation of original particle size and distribution throughout the polymerization observed from dynamic light scattering measurements indicates the predominance of monomer droplet nucleation. Kinetic analysis shows that there is no constant rate stage, which also suggests a droplet nucleation mechanism. Polystyrene (PS) nanoparticles with relatively small diameters (40–70 nm) and narrow size distribution could be easily prepared. The effects of surfactant, costabilizer, and absorbed dose rate on the miniemulsion polymerization were discussed.     

The preparation of sterically stabilized polymer dispersions

The emulsion polymerizations of styrene (St) and butyl acrylate (BA) stabilized by nonionic polyoxyethylene type emulsifiers did not show the long stationary rate interval. This was discussed in terms of two opposing effects: 1) the decreased monomer concentration at the reaction loci due to the depletion of monomer droplets or depressed monomer droplet degradation and 2) the increased number of polymer particles with increasing conversion. The continuous particle nucleation is attributed to the continuous release of emulsifier from the emulsifier saturated monomer droplets and/or the presence of monomer swollen micelles (microdroplets). The limited particle flocculation operative at lower emulsifier concentrations increases the nonstationary-state polymerization. The particle agglomeration is accompanied by the increased reaction order x (N_p vs. [E]^x) above 0.6. The increased uniformity of monomer emulsion stabilized by Tween 20 by homogenization of monomer emulsion increased the final conversion and the polymerization rate as well. The polymerization rate vs. conversion curve of the homogenized emulsion characterized with broader stationary rate interval reminds the four rate intervals system typical for miniemulsion. The accumulation of polymer and nonionic emulsifier within the monomer phase preserves the monomer droplets up to high conversion. The decreased monomer droplet degradation rises the monomer-starved condition or the depressed transport of both monomer and emulsifier to the reaction loci.     

Evolution of droplet size distribution and composition in miniemulsions

A fundamental understanding of the formation, degradation and polymerization of miniemulsions has been hindered by difficulties in quantifying their monomer droplet size distribution (DSD). In this work, particle sizing techniques including capillary hydrodynamic fractionation, acoustic attenuation spectroscopy, surfactant titration, and microscopy were adapted to characterize miniemulsion DSDs. The key ingredient in miniemulsions is the costabilizer, a low water solubility compound that limits monomer diffusion from the smaller to larger droplets (Ostwald ripening). The DSD evolution of styrene miniemulsions employing hexadecane (HD) as costabilizer was characterized. With less costabilizer, droplets were initially smaller, but increased in average size with time, and their DSDs broadened. These changes were slowed with addition of extra surfactant after homogenization. After several days, the average droplet size increased to about 150 nm regardless of the amount of HD or surfactant used. The HD content of separated portions of centrifuged miniemulsions was measured and showed significant Ostwald ripening within minutes after preparation. The further evolution of the DSD is attributed primarily to droplet coalescence. Less composition change occurred with either higher HD content or post‐homogenization surfactant addition, both of which led to minimization of free energy, increasing stability. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1529–1544     

Effect of the presence of polymer in miniemulsion droplets on the kinetics of polymerization

Solution of polystyrene in styrene were dispersed in an aqueous gel phase comprising sodium lauryl sulfate, cetyl alcohol, and water using an emulsification process known to produce monomer droplet sizes inthe submicron size range (referred to as miniemulsion droplets). The shelf-life stabilities of these miniemulsions were studied to determine their relative droplet sizes, and the emulsions were concommitantly polymerized in an isothermal batch reaction calorimeter. The polymerization kinetics and final particle sizes produced were compared with miniemulsion and conventional emulsion polymerizations prepared using equivalent recipes without the addition of polystyrene. The results indicate that polymerization of miniemulsions prepared from polymer solutions produce significantly different kinetics than both miniemulsion and conventional emulsion polymerizations. In general, a small amount of polymer greatly increases the rate of polymerization and the final number of particles produced in the polymerization to the extent where even conventional polymerizations carried out above the critical micelle concentration of the surfactant polymerize more slowly. The results are explained by considering the system to be comprised of small, stable pre-formed monomer-swollen polymer particles which are able to efficiently capture aqueous phase radicals. This enables the system to produce a large final number of particles, similar to the initial number of pre-formed polymer particles, as opposed to miniemulsions and micelles in which only a relatively small fraction of the initial number of species (droplets or micelles) become polymer particles. © 1994 John Wiley & Sons, Inc.     

聚合过程中原位生成助稳定剂的细乳液聚合

以甲基丙烯酸十二氟庚酯(DFMA)、甲基丙烯酸甲酯(MMA)、丙烯酸丁酯(BA)为共聚单体,不加任何传统的助稳定剂进行细乳液聚合.在共聚体系中,由于DFMA在初期反应生成的聚合物中占有较高比例,初期形成的少量低聚物可以起到助稳定剂作用,因此DFMA作为反应单体的同时,又可以原位生成助稳定剂,维持单体液滴或乳胶粒子的稳定,以细乳液聚合的方式进行聚合.分别采用油溶性引发剂(AIBN)和水溶性引发剂(KPS)引发聚合,考察细乳液聚合过程中乳胶粒子粒径的变化规律,粒径由初始时刻的400nm左右减少到80nm左右,最终与使用传统的助稳定剂得到的粒径相当.提出了原位生成助稳定剂的细乳液聚合机理,并使用交联剂验证了提出的原位生成助稳定剂的细乳液聚合机理.     

Miniemulsion polymerization of styrene with chain transfer agent as cosurfactant

Miniemulsion polymerization of styrene with the chain transfer agent n-dodecyl mercaptan (DDM) used as cosurfactant was studied. Droplet size and shelf life for unpolymerized miniemulsions were measured and compared with those of equivalent macroemulsions. The miniemulsion monomer droplets with dodecyl mercaptan as cosurfactant were very stable. Shelf lives were from 17 h to 3 months. The kinetics of miniemulsion polymerization were studied. Unlike other miniemulsion systems where the cosurfactant does not act as a chain transfer agent, the polymerization rate falls with cosurfactant level because the chain transfer agent enhances radical desorption from the particles. The polymerization rate in all the miniemulsions was lower than that of the corresponding macroemulsions. Polymerized particles were larger than in the corresponding macroemulsions, but molecular weights were lower. Results indicate that DDM can serve as an effective cosurfactant as well as a chain transfer agent. The fact that the molecular weights are lower in the miniemulsion reactions indicates predominant droplet nucleation. © 1997 John Wiley & Sons, Inc.     

氧化-还原低温引发苯乙烯/丙烯酸丁酯细乳液共聚合动力学与成核机理的研究

详细讨论了 [(NH4 ) 2 S2 O8/NaHSO3 ]氧化 还原引发体系引发苯乙烯 (St)丙烯酸丁酯 (BuA)体系的细乳液共聚合的动力学特征及其与成核机理的关系 .细乳液的聚合速率比相同条件下的常规乳液聚合速率低 ,引发期长 .随聚合温度、引发剂浓度、乳化剂浓度的增加 ,聚合速率增大 .共乳化剂正十六烷 (HDE)的浓度在一定范围内增大 ,反应的速率增大 ,然后再增加HDE ,反应速率下降 .建立动力学曲线数学模型 ,并深入讨论了细乳液的聚合动力学特征 ,与常规乳液所得结果相比较 ,探讨了细乳液的单体液滴成核机理 .     

Kinetics and mechanism of emulsifier-free emulsion polymerization. III. Styrene/nonionic comonomer (2-hydroxyethyl methacrylate) system

The emulsifier-free emulsion polymerizations of styrene in the presence of about 0.33–2.7% (relative to styrene) of the water soluble comonomer, 2-hydroxyethyl methacrylate (HEMA), and of the initiator, potassium persulfate (KPS), were carried out. It was found that KPS plays a predominant role in the particle nucleation process, since the number density of polymer particles (N_p) was dependent on the 0.97-power of [KPS]. The nucleation ability of HEMA was weak, since N_p was dependent only on the 0.17-power of [HEMA]. The particle nucleation stage ceased quite early before 1% conversion, leading to nearly monodispersed polymer particles. The nucleation is suggested to be via the homogeneous nucleation mechanism. The particles grow via the core-shell structure mechanism (shell region polymerization), since the particle size is rather large—from 1500 to 6000 Å. The amount of HEMA can affect the shell thickness and physical properties of the shell, such as the monomer swelling capacity and monomer diffusion rate.     

八甲基环四硅氧烷正离子细乳液开环聚合动力学

以十二烷基苯磺酸钠(SDBS)为乳化剂,硫酸或盐酸为催化剂,八甲基环四硅氧烷(D4)为单体,十六烷为共稳定剂,超声预乳化,制备了聚硅氧烷细乳液,研究了超声时间、催化剂用量、乳化剂用量和温度对聚合动力学的影响.结果表明,在一定酸度范围内,聚合速度与硫酸浓度0.81次方、与盐酸浓度1.02次方、与乳化剂浓度-0.66次方成正比,反应的表观活化能为40.56kJ/mol.     

Synthesis and characterization of miniemulsion copolymers of methyl methacrylate (or styrene) and stearyl methacrylate

The copolymers of methyl methacrylate (MMA) (or styrene (ST))/stearyl methacrylate (SMA) obtained from miniemulsion polymerization were prepared and characterized. All the miniemulsions showed satisfactory colloidal stability upon aging due to the effectively retarded Ostwald ripening by the reactive costabilizer SMA. In subsequent miniemulsion copolymerizations, monomer droplet nucleation predominated in the particle formation process, but homogeneous nucleation could not be ruled out even at such high levels of SMA (20–50 wt.%). The contact angle first increased rapidly and then leveled off when the SMA content increased from 20 to 50 wt.% for both the copolymers of MMA/SMA and ST/SMA. At constant level of SMA, the copolymer of MMA/SMA with a less hydrophobic composition showed a larger contact angle compared to the ST/SMA counterpart. The contact angle (103 ± 1°) of the copolymer MMA/SMA (50/50 w/w) was comparable to that (104°) of PSMA. A schematic model was proposed to explain the experimental results.     

Kinetics of styrene emulsion polymerization in the presence of montmorillonite

The effect of the pristine sodium montmorillonite (Na⁺-MMT) on the styrene emulsion polymerizations with different concentrations of SDS ([SDS]) was investigated. At constant [SDS], the polymerization rate is faster for the run with 1 wt.% Na⁺-MMT compared to the counterpart without Na⁺-MMT. Micelle nucleation predominates in the polymerizations with [SDS] ≧ 13 mM. On the other hand, the contribution of the polymerization associated with the Na⁺-MMT platelets increases significantly when [SDS] decreases from 13 to 9 mM. At [SDS] (e.g., 2 mM) < CMC, homogeneous nucleation controls the particle formation process and polymerization kinetics. Moreover, the contribution of the Na⁺-MMT platelets that act as extra reaction loci to the polymerization kinetics is even comparable to the run in the absence of Na⁺-MMT. The resultant polymer particle size, polymer molecular weight and zeta potential were characterized and a preliminary model was developed to qualitatively study the differences between the polymerizations in the presence and absence of 1 wt.% Na⁺-MMT.