Synthesis and morphology of Fe3O4/polystyrene/poly(isopropylacrylamide‐co‐methyl acrylate acid) magnetic composite latex – 2,2′‐azobis (2‐methylpropionamidine) dihydrochloride as initiator

In this work, Fe₃O₄/polystyrene/poly(N‐isopropylacryl amide‐co‐methylacrylate acid) (Fe₃O₄/PS/P(NIPAAM‐co‐MAA)) magnetic composite latex was synthesized by the method of two stage emulsion polymerization. In this reaction system, 2,2′‐azobis(2‐methyl propionamidine) dihydrochloride (AIBA) was used as initiator to initiate the first stage reaction and second stage reaction. The Fe₃O₄ particles were prepared by a traditional coprecipitation method. Fe₃O₄ particles were surface treated by either PAA oligomer or lauric acid to form the stable ferrofluid. The first stage for the synthesis of magnetic composite latex was to synthesize PS in the presence of ferrofluid by soapless emulsion polymerization to form the Fe₃O₄/PS composite latex particles. Following the first stage of reaction, the second stage of polymerization was carried out by the method of soapless emulsion polymerization with NIPAAM and MAA as monomers and Fe₃O₄/PS latex as seeds. The magnetic composite particles, Fe₃O₄/PS/P(NIPAAM‐co‐MAA), were thus obtained. The mechanism of the first stage reaction and second stage reaction were investigated. Moreover, the effects of PAA and lauric acid on the reaction kinetics, morphology, and particle size distribution were studied. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3912–3921, 2007     

Ultrasonically initiated emulsion polymerization of methyl methacrylate

The ultrasonically initiated emulsion polymerization of methyl methacrylate (MMA) was investigated. Experimental results show that sodium dodecyl sulfonate (SDS) surfactant plays a very important role in obtaining a high polymer yield, because in the absence of SDS, monomer conversion is near zero. Thus, the surfactant serves as an initiator and as interfacial modifier in this system (MMA/H₂O), and the monomer conversion increases significantly with increasing SDS concentration. An increase in the reactor temperature also leads to an increase in the monomer conversion. An appropriate increase in the N₂ purging rate also leads to higher conversion. The conversion of MMA decreases with increasing monomer concentration because of the higher viscosity of the system. With the experimental results, optimized reaction conditions were obtained. Accordingly, a high monomer conversion of about 67% and a high molecular weight of several millions can be obtained in a period of about 30 min. Furthermore, transmission electron micrographs show that the latex particles prepared are nanosized, indicating a promising technique for preparing nanoscale latex particles with a small amount of surfactant. In conclusion, a promising technique for ultrasonically initiated emulsion polymerization has been successfully performed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3356–3364, 2001     

Kinetic and particle size studies of emulsion polymerization of methyl methacrylate and styrene with using polyamidoamine dendrimer as seed

The emulsion polymerization of methyl methacrylate (MMA) and styrene (St) were investigated with using polyamidoamine (PAMAM) dendrimer as seed, potassium persulfate as initiator and sodium dodecyl sulfate as emulsifier. The effects of 4.0GPAMAM dendrimer concentration, initiator concentration, emulsifier concentration, monomer concentration, and polymerization temperature on the monomer conversion and polymerization rate were investigated. At the same time, the influence of the generation of PAMAM dendrimer on latex particle size was studied also. The results showed that the monomer conversion and polymerization rate increased with increasing initiator concentration, emulsifier concentration, monomer concentration, and polymerization temperature. But polymerization rate increased firstly with an increase in the 4.0GPAMAM dendrimer from 0.03 g to 0.09 g and then decreased with further increase to 0.12 g. When the concentration of 4.0GPAMAM dendrimer less than 1.449 × 10^?4 mol/L, the kinetic equation can be expressed by Rp∝[4.0GPAMAM]^0.772[SDS]^0.562[KPS]^0.589[M]^0.697, and the activation energy (Ea) of emulsion polymerization is 62.56kJ/mol. In additional, the copolymer latex particle size decreased and possessed monodispersity with increasing the generation of PAMAM dendrimer. According to FT-IR spectrum analysis, PAMAM dendrimer is successfully incorporated into the poly(PAMAM-St–MMA) latex particles.     

Hydroxypropyl cellulose (HPC)-stabilized dispersion polymerization of styrene in polar solvents: Effect of reaction parameters

Dispersion polymerization of styrene in polar solvents in the presence of hydroxypropyl cellulose (HPC) produces latex particles from ca. 1 to 26 μm depending on reaction parameters. Increasing the initiator concentration or temperature decreases the molecular weight, but increases the particle size and breadth of the size distribution. The decrease in molecular weight with increasing R_i, caused by larger initiator concentration or higher temperature, is expected based of fundamental kinetic relationships. The inverse correlation between size and rate of initiation is rationalized by polarity (stabilizing ability) of the grafted HPC-polystyrene formed in situ. High polar HPC-g-PS, which contains shorter graft polystyrene chain, stabilizes particles less effectively and this leads to larger particles. The primary influence of initial styrene concentration is a solvent effect: larger particles are obtained at high styrene concentration due to high solubility of polystyrene during the initial part of the reaction. The influence of the molecular weight of HPC is to change the polarity of the HPC-g-PS stabilizer. Comparison of particle growth of three critical polymerization systems suggests that the favorable continuous-phase solubility parameter for dispersion polymerization of styrene is around 11.6 (cal/mL)^1/2. Too high or too low polarity generates particles with broad size distribution because large particles are formed during the initial stage and nucleation continues as the polymerization proceeds. © 1992 John Wiley & Sons, Inc.     

Cuso4‐amine redox‐initiated radical polymerization of methyl methacrylate mediated by a CuCl2 complex: Homogeneous reverse ATRP

Kinetic results of CuSO₄/2,2'‐bipyridine(bPy)‐amine redox initiated radical polymerization of methyl methacrylate (MMA) at 70 to 90 °C in dimethylsulfoxide suggest that such initiation is characteristic of a slow rate and a low initiator efficiency, but tertiary amines exhibit a relatively higher rate. UV‐Vis spectroscopy confirms the alpha‐amino functionality of PMMA chains. CuCl₂/bPy successfully mediates the redox‐initiated radical polymerization of MMA with aliphatic tertiary amines in a fashion of slow‐initiated reverse atom transfer radical polymerization (ATRP), i.e. both the initiator efficiency of aliphatic tertiary amines and the average molecular weight of PMMA increase gradually, while the molecular weight distribution remains narrow but become broader with the conversions. As the PMMA chains contain alpha amino and omega C‐Cl moieties, UV‐induced benzophenone‐initiated radical polymerization and Cu^ICl/bPy‐catalyzed ATRP initiated from PMMA lead to block copolymers from terminal functionalities. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2562‐2578     

Highly magnetic latexes from submicrometer oil in water ferrofluid emulsions

The synthesis of functionalized submicrometer magnetic latex particles is described as obtained from a preformed magnetic emulsion composed of organic ferrofluid droplets dispersed in water. Composite (polystyrene/γ‐Fe₂O₃) particles were prepared according to a two‐step procedure including the swelling of ferrofluid droplets with styrene and a crosslinking agent (divinyl benzene) followed by seeded emulsion polymerization with either an oil‐soluble [2,2′‐azobis(2‐isobutyronitrile)] or water‐soluble (potassium persulfate) initiator. Depending on the polymerization conditions, various particle morphologies were obtained, ranging from asymmetric structures, for which the polymer phase was separated from the inorganic magnetic phase, to regular core–shell morphologies showing a homogeneous encapsulation of the magnetic pigment by a crosslinked polymeric shell. The magnetic latexes were extensively characterized to determine their colloidal and magnetic properties. The desired core–shell structure was efficiently achieved with a given styrene/divinyl benzene ratio, potassium persulfate as the initiator, and an amphiphilic functional copolymer as the ferrofluid droplet stabilizer. Under these conditions, ferrofluid droplets were successfully turned into superparamagnetic polystyrene latex particles, about 200 nm in size, containing a large amount of iron oxide (60 wt %) and bearing carboxylic surface charges. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2642–2656, 2006     

Microemulsion polymerization of styrene

Initiation of polymerization in styrene oil-in-water microemulsions by water-soluble potassium persulfate of oil-soluble 2,2′-azobis-(2-methyl butyronitrile) at 70°C gave stable latexes which were bluish and less translucent than the original microemulsions. The effects of initiator concentration, polymerization temperature, and monomer concentration on the kinetics, particle size distributions, and molecular weight distributions were investigated. The kinetics of polymerization were measured by dilatometry. In all cases, the polymerization rate shows only two intervals, which increased to a maximum and then decreased. There was no apparent constant rate period and no gel effect. A longer nucleation period was found for polymerizations initiated by potassium persulfate as compared to 2,2′-azobis-(2-methyl butyronitrile). The small latex particle size (20–30 nm) and high polymer molecular weight (1–2 × 10⁶) implies that each latex particle consists of two or three polystyrene molecules. The maximum polymerization rate and number of particles varied with the 0.47 and 0.40 powers of potassium persulfate concentration, and the 0.39 and 0.38 powers of 2,2′-azobis-(2-methyl butyronitrile) concentration, respectively. This is consistent with the 0.4 power predicted by Smith–Ewart Case 2 kinetics. Microemulsion polymerizations of styrene–toluene mixtures at the same oil-water phase ratio gave lower polymerization rates and lower molecular weights, but the same latex particle size as with styrene alone. A mechanism is proposed, which comprised initiation and polymerization in the microemulsion droplets, by comparing the kinetics of microemulsion polymerization with conventional emulsion and miniemulsion polymerization systems.     

Polystyrene/Fe3O4 composite latex via miniemulsion polymerization‐nucleation mechanism and morphology

In this research, oil‐based Fe₃O₄ nanoparticles were prepared by means of coprecipitation method followed by a surface modification using lauric acid. Oil‐based Fe₃O₄ could disperse in styrene, and polystyrene/Fe₃O₄ (PS/Fe₃O₄) composite particles were prepared via miniemulsion polymerization in the presence of potassium peroxide (KPS) as an initiator, sodium dodecyl sulphate as a surfactant, hexadecane or sorbitan monolaurate(Span 20) as a costabilizer. The effects of Fe₃O₄ content, homogenization energy, amount of initiator, amount of surfactant and costabilizer on the conversion, size distributions of droplets and latex particles, nucleation mechanism and morphology of composite latex particles were investigated. The results showed that different nucleation mechanisms dominated during the course of reaction when polymerization conditions changed. The most important two key factors to influence the nucleation mechanism were homogenization energy and initiator. High homogenization energy provided critically stabilized size of droplets. Otherwise, secondary nucleation, including micellar and/or homogeneous nucleation, would take place rather than droplet nucleation when a water‐soluble initiator, KPS, was used. It resulted in two populations of latex particles, pure PS particles in smaller size and PS/Fe₃O₄ composite particles in larger size. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1014–1024, 2008     

Emulsifier-free emulsion polymerization of the comonomer system styrene/tetrahydrofurfuryl metacrylate

 The emulsifier-free emulsion copolymerization of styrene and tetrahydrofurfuryl methacrylate (TMA) in aqueous phase is described. Monodisperse latex particles with diameters from about 280 to 620 nm are obtained consisting of a hydro-phobic polystyrene core and a hydrophilic poly-TMA shell. The influence of a variation of TMA, styrene and initiator (potassium persulfate) concentration in the original emulsion on particle size, molecular weight and composition of the copolymer is described. The concentration of TMA and initiator affects the number of primary particles but not the size of the final particles, whereas the styrene concentration strongly influences the particle diameter, a large size being favored by a high styrene concentration. The molecular weights of the polymers are between 6.2×10⁴ and 7.0×10⁵ g/mole. Size exclusion chromatography of polymer solutions in tetra-hydrofuran shows that high molecular weights are especially found in large particles, which are preferentially formed in emulsions with a high concentration of styrene. ¹H-NMR spectroscopy of the polymer shows that only about 50% of the initial TMA concentration are polymerized in the particles. Thus the copolymers prepared at increasing styrene concentration and constant initiator concentration of the emulsion show an increasing polystyrene content and are formed in particles of increasing size. Received: 4 June 1997 Accepted: 19 August 1997     

Polymerization of styrene with tetramethylthiuram disulfide as an initiator in the presence of 2,2,6,6‐tetramethyl‐1‐piperidinyloxy

The bulk polymerization of styrene was investigated with tetramethylthiuram disulfide (TMTD) as an initiator in the presence of 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO) at 123 °C. The polymerization proceeded in a controlled/living way; that is, the polymerization rate was first‐order with respect to the monomer concentration, and the molecular weight increased linearly with conversion. The molecular weights of the polymers obtained were close to the theoretical values, and the molecular weight distributions were relatively low (weight‐average molecular weight/number‐average molecular weight = 1.1–1.3). The rate of polymerization with TMTD as an initiator was faster than that with benzoyl peroxide, and the rate was independent of the initial concentration of TMTD in the presence of TEMPO. The obtained polystyrene was functionalized with ultraviolet‐light‐sensitive ? SC(S)N(CH₃)₂ groups, which was characterized with ¹H NMR spectroscopy. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 543–551, 2005     

Polymerization of vinyl chloride at reduced monomer accessibility. II. Polymerization at subsaturation pressure with emulsion PVC as seed

Vinyl chloride was polymerized at 59–92% of saturation pressure in a water-suspended system at 45–65°C with an emulsion poly(vinyl chloride) (PVC) latex as a seed. A water-soluble initiator was used in various concentrations. The monomer was continuously charged as vapor from a storage vessel kept at lower temperature. Characterization included determination of molecular-weight distribution and degree of long-chain branching by gel permeation chromatography (GPC) and viscometry, thermal dehydrochlorination, and microscopy. The polymerization rate decreases with decreasing pressure but is reasonable even at the lowest pressure. The molecular weight decreases with decreasing pressure and increasing initiator concentration and also with increasing polymerization temperature, if the initiator concentrations are chosen to give a constant initiator radical concentration. The degree of long-chain branching increases with increasing initiator concentration and decreasing monomer pressure but is unaffected by the polymerization temperature, if the initiator radical concentration is kept constant. The thermal stability decreases with decreasing M _n, while the degree of long-chain branching has only a minor influence. The most important factor in the system influencing the molecular parameter is the monomer accessibility.     

Reversible addition–fragmentation chain transfer/miniemulsion polymerization of butyl methacrylate in the presence of β‐cyclodextrin

In the presence of β‐cyclodextrin (β‐CD), reversible addition–fragmentation chain transfer (RAFT) polymerization has been successfully applied to control the molecular weight and polydispersity [weight‐average molecular weight/number‐average molecular weight (M_w/M_n)] in the miniemulsion polymerization of butyl methacrylate, with 2‐cyanoprop‐2‐yl dithiobenzoate as a chain‐transfer agent (or RAFT agent) and 2,2′‐azoisobutyronitrile (AIBN) as an initiator. β‐CD acted as both a stabilizer and a solubilizer, assisting the transportation of the water‐insoluble, low‐molecular‐weight RAFT agent into the polymerization loca (i.e., droplets or latex particles) and thereby ensuring that the RAFT agent was homogeneous in the polymerization loca. The polymers produced in the system of β‐CD exhibited narrower polydispersity (1.2 < M_w/M_n < 1.3) than those without β‐CD. Moreover, the number‐average molecular weight in the former case could be controlled by a definite amount of the RAFT agent. Significantly, β‐CD was proved to have a favorable effect on the stability of polymer latex, and no coagulum was observed. The effects of the concentrations of the RAFT agent and AIBN on the conversion, the molecular weight and its distribution, and the particle size of latices were investigated in detail. Furthermore, the influences of the variations of the surfactant (sodium dodecyl sulfate) and costabilizer (hexadecane) on the RAFT/miniemulsion polymerization were also studied. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2931–2940, 2005     

Fabrication and Characterization of Sulfonate‐containing Polystyrene/CaCO3 Core‐shell Nanoparticles

Polystyrene (PSt) seed latex was first prepared via soap‐free emulsion polymerization in the presence of a small amount of methacrylic acid using ammonium persulfate as initiator, and then seeded emulsion polymerization of sodium 4‐styrenesulfonate (NaSS) and St was carried out to synthesize P(St‐NaSS) core latex using 2,2′‐azobisisobutyronitrile as initiator. After that, P(St‐NaSS)/CaCO₃ core‐shell nanoparticles were fabricated by sequentially introducing Ca(OH)₂ aqueous solution and CO₂ gas into the core latex. The morphology of the core and core‐shell nanoparticles was characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM), and the state of CaCO₃ shell was confirmed with high‐resolution scanning transmission electron microscope (HR‐STEM) and selected area electron diffraction (SAED). Results showed that PNaSS chains were successfully grafted onto the PSt seed surface, and length of the PNaSS "hairs" could be modulated by adjusting NaSS amount. Sulfonic groups of the PNaSS hairs served as additives in the formation and stabilization of amorphous CaCO₃(ACC) and prevented ACC from sequent transformation into crystalline states. The amount of the anchored CaCO₃ increased with the growth of PNaSS hair length, and reached 51 wt% (by thermalgravimetric analysis) under the optimal encapsulating temperature of 45°C. Moreover, the forming mechanism of P(St‐NaSS)/CaCO₃ core‐shell nanoparticles was proposed.     

Synthesis and morphology of an iron oxide/polystyrene/poly(isopropylacrylamide‐co‐methacrylic acid) thermosensitive magnetic composite latex with potassium persulfate as the initiator

In this work, an iron oxide (Fe₃O₄)/polystyrene (PS)/poly(N‐isopropylacryl amide‐co‐methacrylic acid) [P(NIPAAM–MAA)] thermosensitive magnetic composite latex was synthesized by the method of two‐stage emulsion polymerization. The Fe₃O₄ particles were prepared by a traditional coprecipitation method and then surface‐treated with either a PAA oligomer or lauric acid to form a stable ferrofluid. The first stage for the synthesis of the thermosensitive magnetic composite latex was to synthesize PS in the presence of a ferrofluid by emulsion polymerization to form Fe₃O₄/PS composite latex particles. Following the first stage of reaction, the second stage of polymerization was carried out with N‐isopropylacryl amide and methacrylic acid as monomers and with Fe₃O₄/PS latex as seeds. The Fe₃O₄/PS/[P(NIPAAM–MAA)] thermosensitive magnetic particles were thus obtained. The effects of the ferrofluids on the reaction kinetics, morphology, and particle size of the latex were discussed. A reaction mechanism was proposed in accordance with the morphology observation of the latex particles. The thermosensitive property of the thermosensitive magnetic composite latex was also studied. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3062–3072, 2007     

Emulsion polymerization of styrene. I. Review of experimental data and digital simulation

Isothermal emulsion polymerization at 60°C of styrene in a batch reactor were studied by using sodium lauryl sulfate as surfactant and potassium persulfate as initiator source. The concentrations of surfactant and initiator were varied during the runs. The polymerization evolution was followed as samples were taken at regular intervals. These emulsion samples were analyzed for monomer conversion, rate of polymerization, as well as for the size and the size distribution of the particles. The molecular weight and molecular weight distribution were obtained by gel permeation chromatography. Our study showed that fresh nucleation takes place even at high conversion, causing a continuous shifting toward broadening of particle size distribution. Contrary to the theory of Smith and Ewart, which assumes a constant number of particles during interval II of the polymerization reaction, our digital simulation of the reaction presents better experimental results with a variable number of particles, and indicates that the Hui–Hamielec model for termination constant k_t as function of conversion is not applicable under our working conditions.     

In situ Cu(0) catalyzed SET‐LRP: The first attempt

In this work, single electron transfer‐living radical polymerization (SET‐LRP) was catalyzed by in situ Cu(0) generated from copper sulphate pentahydrate (CuSO₄·5H₂O) and hydrazine hydrate (N₂H₄·H₂O) at 25 °C. The polymerization occurred smoothly with moderate controllability: the polymerization rates increased by the increases of N₂H₄·H₂O, and the initiator concentration had an optimal value on the polymerization rate; the number‐average molecular weights (M_n,GPC) increased with monomer conversions and polydispersities were below 1.40. The M_n,GPC deviated much from theoretical ones with about 50% polymer chain‐end fidelities. Some side reactions stemming from the strong reduction performance of N₂H₄·H₂O were responsible for the mildly controlled polymerizations. This polymerization can be conducted in SET‐LRP unfavorable solvents or in bulk, such as toluene and tetrahydrofuran, owing to the H₂O contained in CuSO₄·5H₂O and N₂H₄·H₂O. On account of the utilization of CuSO₄·5H₂O, an inactive Cu(II) compounds in LRP area, this work confirmed from experimental level that it was Cu(0) which acted as activator and mediator in SET‐LRP. This work provided a first example of in situ Cu(0) catalyzing SET‐LRP with CuSO₄·5H₂O as a copper source. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Developing a hybrid emulsion polymerization system to synthesize Fe3O4/polystyrene latexes with narrow size distribution and high magnetite content

A hybrid emulsion polymerization was formulated for synthesizing Fe₃O₄/polystyrene composite latex. This system, containing binary droplets that are magnetic (Mag)‐droplets with a diameter of 100–200 nm and styrene (St)‐droplets with a diameter of 3–4 μm, was obtained by mixing Mag‐miniemulsion and St‐macroemulsion. With extremely low surfactants concentration (?critical micelle concentration, CMC), the nucleated loci are selectively controlled in the Mag‐droplets, as the result of smaller droplet size and larger surface ratio. Both water‐soluble potassium persulfate (KPS) and oil‐soluble 2,2′‐azobis(2‐isobutyronitrile) was adopted to initiate the polymerization. In the presence of KPS, magnetic polystyrene latices with particles size of 60–200 nm, narrow size distribution, and high magnetite content (86 wt % measured by TGA) were attained successfully. The synthesized magnetic Fe₃O_4/polystyrene latices assembled into well‐ordered hexagonal structure in the surface of a carbon supported copper grid. The influence of various parameters on various aspects of the as‐synthesized Fe₃O₄/polystyrene was investigated in detail: type of initiator on composite morphology, feed ratio of Mag‐miniemulsion and St‐macroemulsion on magnetite content, and hydrophobic agent or amount of surfactant on size and size distribution. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5285–5295, 2007     

Polymerization of styrene with ionic comonomer,nonionic comonomer,or both

Nanosized polystyrene latexes with high polymer contents were obtained from an emulsifier-free process by the polymerization of styrene with ionic comonomer, nonionic comonomer, or both. After seeding particles were generated in an initial emulsion system consisting of styrene, water, an ionic comonomer [sodium styrenesulfonate (NaSS)] or nonionic comonomer [2-hydroxyethyl methacrylate (HEMA)], and potassium persulfate, most of the styrene monomer or a mixture of styrene and HEMA was added dropwise to the polymerizing emulsion over 6 h. Stable latexes with high polystyrene contents (≤25%) were obtained. The latex particle weight-average diameters were largely reduced (41 nm) by the continuous addition of monomer(s) compared with those (117 nm) obtained by the one-pot polymerization method. Latex particles varied from about 30 to 250 nm in diameters, whereas their molar masses were within 10⁴ to 10⁵ g/mol. The effect of the comonomer concentration on the number of polystyrene particles per milliliter of latex and the weight-average molar masses of the copolymers during the polymerization are discussed. The surface compositions of the latex particles were analyzed by X-ray photoelectron spectroscopy, which indicated that the surface of the latex particles was significantly enriched in NaSS, HEMA, or both. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1634–1645, 2001     

氧化-还原引发剂引发苯乙烯超浓乳液聚合的研究

以过氧化羟基二异丙苯(CHPO)和四乙烯五胺(TEPA)为氧化-还原引发剂,以十二烷基硫酸钠(SDS)为乳化剂,十六醇(CA)为共乳化剂,通过超浓乳液聚合方法制备了聚苯乙烯乳胶粒子.探讨了乳化剂浓度及配比、分散相体积分数、引发剂种类、引发剂浓度及配比和温度等各因素对乳液稳定性、聚合速率、乳胶粒子大小、形态及分布的影响.用透射电子显微镜(TEM)观察了乳胶粒子的形态,用粘度法测定了聚苯乙烯的粘均分子量.考察了苯乙烯进行超浓乳液聚合的反应动力学,求得在30℃时聚合速率方程为Rp=K[M]^0.36[I]^0.49[E]^0.72,表观活化能为19.72kJ/mol.所得乳胶粒子的直径在0.1～0.3μm之间,粘均分子量在2×10⁶～4×10⁶之间.为低温下实现超浓乳液薄层聚合提供了参考数据.     

Preparation of monodispersed polystyrene microspheres uniformly coated by magnetite via heterogeneous polymerization

Composite microspheres of core-shell type were prepared by a seeded polymerization using monodispersed polystyrene seed latex (Ps) combined with an in situ dispersion of magnetite (Fe₃O₄) fine particles. The heterogeneous polymerization was carried out in aqueous dispersions of the Fe₃O₄ particles modified with sodium oleate. All the synthetic processes were carried out in a wet state to avoid serious agglomeration. The morphology of the composite particle and the size distribution were examined to discuss the effects on the polymerization parameters, such as monomer concentration, type and concentration of an initiator, magnetite particle concentration and the method of surface modification of Fe₃O₄.