Batch and semicontinuous emulsion copolymerization of vinyl acetat–butyl acrylate. I. Bulk,surface, and colloidal properties of copolymer latexes

Vinyl acetate (VAc)–butyl acrylate (BuA) comonomer mixtures with various composition were polymerized by batch and semicontinuous emulsion polymerization processes. PVAc and PBuA homopolymer latexes as well as the (VAc-BuA) copolymer latexes were characterized with respect to particle size, molecular weight, acid end groups on particle surfaces, and colloidal stability against electrolytes. The surface and colloidal properties of these latexes were also compared before and after aging and acid hydrolysis. The average particle size of batch latexes was independent of copolymer composition, whereas for semicontinuous latexes it decreased with increasing BuA content and was always lower than that of the corresponding batch latex. The molecular weight distribution (MWD) for batch latexes was narrower and much less dependent on composition than that of the semicontinuous latexes; bimodal MWD was found in most semicontinuous latexes with a substantial amount of low MW fraction. The total weak and strong acid end groups on particle surfaces for semicontinuous latexes is higher, and more dependent on composition, than the batch latexes. Acid-induced hydrolysis results in a drastic change in the type and concentration of the surface groups of the semicontinuous latex particles. Colloidal stability against electrolytes showed that both electrostatic (due to surface acid groups) and steric [due to surface poly(vinyl alcohol)] mechanisms are contributing. However, for semicontinuous latexes, increasing PVAc content above 50 mol % resulted in a proportional increase and ultimately dominant role of steric stabilization. The results were interpreted in terms of differences in reactivity ratios and water solubilities of the two monomers and their effects on the locus of initiation and growth in the two polymerization processes, as well as the monomer sequence within the polymer chain and degree of homogeniety of the copolymer composition within the particle.     

Studies on the Preparation of Stable and High Solid Content Emulsifier-Free Poly(MMA/BA/HEA) Latex with the Addition of AMPS and Characterization of the Obtained Copolymers

The 2-acrylamido -2-methylpropane sulfonic acid (AMPS) was used as a reactive comonomer for the methyl methacrylate (MMA), n-butyl acrylate (BA) and 2-hydroxyethyl acrylate (HEA) emulsifier-free emulsion copolymerization system to obtain latices of stable and high-solid content (50 wt%).The polymerization and storage process is very stable, and the emulsion could store at room temperature for more than six months with the addition of AMPS. Properties of the latices, such as stability, flow behavior, particles diameter and morphology were studied. In addition, physical properties of the obtained copolymers, such as water resistance, glass transition temperature (T_g) were also investigated. The final size of the latex particles is 200～300 nm in diameter. Compared with the copolymers that were prepared by surfactant emulsion polymerization water resistance is greatly improved.     

Stable aqueous film coating dispersion of zein

The effects of plasticizers, pH, and electrolytes on film formation and physical stability of aqueous film coating dispersions (pseudolatexes) of zein were evaluated. The influence of plasticizer on film formation mechanism and minimum film-formation temperature (MFT) were monitored by means of hot stage microscopy (HSM). Furthermore, the effects of pH and electrolytes on the short-term physical stability of pseudolatexes were investigated by measuring relative absorbance, zeta potential, and particle size of the dispersions. With aqueous coating dispersions of zein, stages of film formation were identified. The dispersions plasticized with 20% (w/w) PEG 400 or glycerol formed mechanically strong and flexible films with the lowest glass transition temperature (T(g)). Physical stability of the aqueous zein dispersions was dependent on both pH and electrolyte content. At a pH ranging from 3 to 4, the aqueous dispersions of zein were stable for at least 2 months exhibiting the highest values for zeta potential, the smallest particle size, and a low volume of aggregates. The stable dispersion could be obtained containing a lower concentration of electrolytes (e.g., 10(-5) M). The physical stability of aqueous zein dispersions can be determined by the combined measurements of relative absorbance, zeta potential, and particle size.     

Colloidal stability of aqueous polymeric dispersions: effect of pH and salt concentration

Aqueous film coatings often contain some electrolytes, organic acids, and pigments to give functions of sustained release, time-controlled release, or protection against light. Additions of some electrolytes or organic acids into latex dispersion for an aqueous film coating affect its colloidal stability. We characterized the aqueous polymeric latexes used in the pharmaceutical industry by measuring zeta potential and particle size, and evaluated this colloidal stability using DLVO theory. Three polymethacrylate-based aqueous polymeric latexes, Eudragit L30D-55, Eudragit RS30D and Eudragit NE30D, having anionic, cationic, and neutral polymer, respectively, were used in this study. The Hamaker constant of the polymethacrylate-based latex was determined to be 6.35 x 10(-21) J, and the total potential energy of the latex dispersion was calculated. The total potential energy of interaction between pairs of latex particles changes by altering the salt concentration and pH. The experimental results of stability in the anionic and the cationic latex dispersions can be explained by the total interaction energies. However, the stabilization of the neutral latex did not match the calculated result. The steric interaction produced by the surfactant likely resulted in the stable dispersion of this latex.     

新型水性环氧树脂的合成研究

以2-丙烯酰胺基-2-甲基丙磺酸(AMPS)为改性剂,过氧化苯甲酰(BPO)为引发剂,通过溶液聚合,使环氧树脂获得水分散性。以改性环氧树脂的收率、粒径分布、反应体系酸值随时间的变化为指标,对反应历程进行了推断,并对改性产物的结构进行了红外光谱分析。结果表明,在整个反应中,AMPS与环氧树脂主链接枝反应和与环氧树脂的环氧基团的开环反应同时进行。高聚物收率可达76.72%,体系中的环氧基团约70%被保留下来。改性环氧树脂体系不需中和即可分散于水中。     

Effect of different surfactants on colloidal and polymer properties of fluorinated acrylate latex

Fluorinated acrylate latex was successfully prepared by semi-continuous seeded emulsion polymerization of dodecafluoroheptyl methacrylate (DFMA) with butyl acrylate (BA), methyl methacrylate (MMA) initiated by potassium persulfate in the water. The resultant latexes and their films are characterized with Fourier transform infrared (FTIR) spectrometry, contact angle determinator, dynamic light scattering detector and surface tension determinator. Effect of different surfactants on colloidal and polymer properties of fluorinated acrylate latex was studied. Results show that the latex prepared with sodium dodecyl benzene sulfonate surfactant has the smallest particle size and contact angle but the moderate surface tension. The latex prepared with perfluorooctanesulfonic acid potassium surfactant has the smallest surface tension, moderate particle size but the biggest contact angle. The latex prepared with sodium 2-hydroxy-3-(methacryloyloxy) prop- ane-1-sulfonate surfactant has the biggest particle size and surface tension but moderate contact angle. In addition, the latex prepared with sodium 2-hydroxy-3-(methacryloyloxy) prop- ane-1-sulfonate has higher electrolyte stability.     

The effect of electrolyte on the colloidal properties of poly(N-isopropylacrylamide-co-dimethylaminoethylmethacrylate) microgel latexes

Monodisperse cationic thermosensitive latex microgels prepared by radical-initiated precipitation copolymerization of N-isopropylacrylamide (NIPAM), methylenebisacrylamide, and dimethylaminoethylmethacrylate (DMAEMA) have been reported (Zha LS, Hu JH, Wang CC, Fu SK, Elaissari A, Zhang Y 2002 Colloid Polym Sci 280:1) and we suggested (Zhang Y, Zha LS, Fu SK J Appl Polym Sci) that the polyelectrolyte chains are rich in their expanded shell layers. The effect of a range of electrolytes on several colloidal properties of these cationic latexes (such as particle size, zeta potential and colloidal stability) has been investigated. The ability of the anions to induce the particle deswelling and flocculation is related to their position in the Hofmeister series. Owing to the DMAEMA-rich layer on the latex particles, the ionic-strength dependence of the particle hydrodynamic size and the zeta potential become more profound with increasing amount of DMAEMA incorporated into the microgel. It is suggested that the effect of electrolytes on the colloidal properties of the copolymer microgel latexes is attributed to the dehydration of the poly(NIPAM) segment and the screening of the electrostatic interaction between the charged DMAEMA units induced by electrolytes.     

乳液聚合法制备P(St/BA)-KAl(OH)2CO3纳米复合物

利用乳液聚合法制备了一种含KAl(OH)2CO3纳米粒子的聚苯乙烯／丙烯酸丁酯复合物．Zeta电位、粒径分布、扫描电镜(SEM)和透射电镜(TEM)等分析表明KAl(OH)2CO3粒子能够稳定地分散于苯丙乳液的乳胶粒中,形成核一壳结构．热失重(TG)分析表明KAl(OH)2CO3粒子的加入能提高复合物的热稳定性,使其在阻燃涂料领域有着潜在的应用前景．     

聚硅氧烷/丙烯酸酯核/壳复合胶乳的粒径分布与成核机理

通过种子乳液法合成出具有高有机硅含量核 壳结构的聚硅氧烷 丙烯酸酯复合粒子 .研究了聚合方法、乳化剂浓度、引发剂浓度、单体滴加速度等工艺条件对复合乳液粒径尺寸、分布与形态的影响 ,并对复合乳液的成核机理进行了探讨 .研究表明 ,乳化剂浓度对乳液粒子的粒径分布和形态、结构有显著影响 ,引发剂浓度增加将使粒子粒径减小 ;相对一次投料法 ,种子乳液法生成的粒子分布窄 ,具有明显核壳结构 ,通过壳层单体滴加速度可以控制粒子的粒径尺寸和分布 ;而壳层丙烯酸酯聚合物主要是在聚硅氧烷种子表面的“过渡层”聚合、富集而成 .     

超浓反相聚合物乳液的粒径双峰分布特征及其与稳定性的关系

以丙烯酸、丙烯酰胺、2-丙烯酰胺基-2-甲基丙磺酸作为混合单体,Span-80和Tween-60作为复合乳化剂、采用氧化还原引发体系在常温下引发聚合,制备了稳定的超浓反相聚合物乳液,同时制备了低分散相体积分数的普通乳液及由普通乳液离心得到的超浓反相聚合物乳液作为对比研究.用显微镜观察了乳胶粒的形态,统计计算了乳胶粒粒径...     

Solvent effects on Pt-Ru/C catalyst for methanol electro-oxidation

Alloying degree, particle size and the level of dispersion are the key structural parameters of Pt-Ru/C catalyst in fuel cells. Solvent(s) used in the preparation process can affect the particle size and alloying degree of the object substance, which lead to a great positive impact on its properties. In this work, three types of solvents and their mixtures were used in preparation of the Pt-Ru/C catalysts by chemical reduction of metal precursors with sodium borohydride at room temperature. The structure of the catalysts was characterized by X-ray diffraction (XRD) and Transmission electron microscopy (TEM). The catalytic activity and stability for methanol electro-oxidation were studied by Cyclic Voltammetry (CV) and Chronoamperometry (CA). Pt-Ru/C catalyst prepared in H₂O or binary solvents of H₂O and isopropanol had large particle size and low alloying degree leading to low catalytic activity and less stability in methanol electro-oxidation. When tetrahydrofuran was added to the above solvent systems, Pt-Ru/C catalyst prepared had smaller particle size and higher alloying degree which resulted in better catalytic activity, lower onset and peak potentials, compared with the above catalysts. Moreover, the catalyst prepared in ternary solvents of isopropanol, water and tetrahydrofuran had the smallest particle size, and the high alloying degree and the dispersion kept unchanged. Therefore, this kind of catalyst showed the highest catalytic activity and good stability for methanol electro-oxidation.     

Miniemulsion copolymerization of vinyl acetate and butyl acrylate. I. Differences between the miniemulsion copolymerization and the emulsion copolymerization processes

Differences between the emulsion copolymerization and miniemulsion copolymerization processes, in terms of emulsifier adsorption, emulsion stability, polymerization kinetics, copolymer composition and dynamic mechanical properties were studied for the comonomer mixture of 50:50 molar ratio vinyl acetate (VA+)—butyl acrylate (BuA), using sodium hexadecyl sulfate (SHS) as a surfactant and hexadecane (HD) as a co-surfactant. The use of hexadecane with the appropriate SHS initial concentration led to a higher adsorption of surfactant, smaller droplet size, higher stability of the emulsions, lower polymerization rates, and larger latex particle size. The copolymer composition during the initial 70% conversion was found to be less rich in Vac monomer units for the miniemulsion process. The dynamic mechanical properties of the copolymer films showed less mixing between the BuA-rich core and the VAc-rich shell in the miniemulsion latexes compared to the conventional latex films.     

Synthesis of TiO2 nanoparticles utilizing hydrated reverse micelles in CO2

Titanium dioxide nanoparticles were produced by the controlled hydrolysis of titanium tetraisopropoxide (TTIP) in the presence of reverse micelles formed in CO2 with the surfactants ammonium carboxylate perfluoropolyether (PFPECOO-+NH4) (Mw = 587) and poly(dimethyl amino ethyl methacrylate-block-1H,1H,2H,2H-perfluorooctyl methacrylate) (PDMAEMA-b-PFOMA). Based on dynamic light scattering measurements, the amorphous TiO2 particles formed by injection of TTIP are larger than the reverse micelles, indicating surfactant reorganization. The size of the particles and the stability of dispersions in CO2 were affected by the molar ratio of water to surfactant headgroup (w(o)), precursor concentration, and injection rate. The amorphous particle size did not change upon depressurization and redispersion in CO2. PDMAEMA-b-PFOMA provided greater stability against particle aggregation at higher reactant concentration compared with PFPECOO-+NH4. The crystallite size after calcination, which was examined by X-ray diffraction and transmission electron microscopy, increased with w(o).     

Emulsifier-free latex of fluorinated acrylate copolymer

Emulsifier-free latices of fluorinated acrylate copolymers were prepared by semicontinuous polymerization method, with perfluoroalkylethyl methacrylate (Zonyl TM) as a fluoromonomer. Ultrasonic at 40 kHz was adopted to help monomers disperse well in water. The relationships of polymerization conditions between the final conversion and polymerization stability were discussed in detail and the optimal polymerization condition was given. A fluorinated acrylate copolymer was finally obtained and its T_g was 54 °C. The average particle size of the latex was about 601 nm and the particle size distribution of the latex was narrow. The latex film exhibited a low surface free energy and good surface property. By using 6% Zonyl TM, the water contact angle of the film-air interface increased significantly and reached to 110.2°. Compared with the latex film of fluorine-free polyacrylate prepared under the similar polymerization condition, the fluorinated latex film had a better water-resistance and thermal stability.     

On the preparation of stable poly(2-hydroxyethyl methacrylate) nanoparticles

A comprehensive experimental study of aqueous heterophase homopolymerization of 2-hydroxyetyl methacrylate revealed special conditions that must be fulfilled in order to obtain stable latex particles in the nanometer size range. The results clearly show that the formation and the stability of this kind of hydrophilic latex particle strongly depends on the hydrophobic-hydrophilic properties of both the initiating radicals and the stabilizers. Hydrophobic initiators in combination with sodium alkyl sulfate surfactants of proper chain lengths or ionic surface-active initiators lead to stable latex particles. In the latter case the particles keep their identity and spherical shape even after drying of the aqueous dispersion.     

单分散交联聚（4—乙烯吡啶／丙烯酸丁酯）无皂正电性共聚乳胶

以偶氮二异丙基脒盐酸盐（V50)为引发剂,采用4－乙烯吡啶（4－VP）／丙烯酸丁酯（BA）为混合单体,分别以二乙烯苯（DVB）或双甲基丙烯酸乙二醇酯（EGDMA）为交联剂,用无皂乳液聚合的方法合成了一系列正电性共聚乳液,并用扫描电镜（SEM）、Zeta电位测定仪详细研究了单体配比、交联剂种类和交联度对粒径大小及其分布、粒子形态和乳液电性能的影响,并探讨了该三元无皂乳液聚合的成核机理。结果表明：4VP／BA的无皂乳液聚合遵循均相成核机理。当BA含量低或者微球交联度较小时,高分子亲水性强,临界链长度大,生成粒子数目少,所以粒径大;随着BA含量的增加或者交联度的增大,高分子疏水性增强,临界链长度沽小,生成粒子数目增多,粒径变小,当BA／4VP＝1／4（g/g)时,得到单分散共聚乳胶,少量BA与4VP共聚可以明显提高乳液的稳定性。     

Fabrication of core/shell hybrid organic–inorganic polymer microspheres via Pickering emulsion polymerization using laponite nanoparticles

Oil-in-water (o/w) emulsions of styrene, as monomer oil in water, were achieved successfully via Pickering emulsification with laponite nanoparticles as the sole inorganic stabilizers. The formed emulsions showed excellent stability not only against droplets coalescence (before polymerization) but also against microparticles coagulation (after polymerization). Generally, the number of composite polystyrene microparticles (PS) increased and their sizes decreased with the content of solid nanoparticles used in stabilizing the precursor o/w emulsions. This is consistent with the formation of rigid layer(s) of the inorganic nanoparticles around the PS microparticles thus a better stability was achieved. The composite microparticles were characterized using various techniques such as surface charge, stability, transmission electron microscope (TEM), scanning electron microscope (SEM) and Fourier transform infra-red (FT-IR). Coating films of the prepared latexes were applied to flat glass surfaces and showed reasonable adhesion compared to PS latex particles prepared with conventional surfactants. The effect of employed conditions on the features of the resulting emulsions in terms of stability and particle size has been discussed.     

Emulsion copolymerization of styrene with a nonionic styrenic polymerizable surfactant

Among the variety of possible structures for polymerizable surfactants, it seems clear that the most interesting should be those with the reactive group located in the hydrophobic part of the molecule. We report here a study based on such a surfactant. Its general formula is A set of surfactants has been produced with m varying from 23 to 48 and n = 6 or 12. The compounds have been characterised by ¹H-NMR (nuclear magnetic resonance), size exclusion chromatography, surface tension measurements and turbidimetry. These surfactants have been copolymerized with styrene in emulsion polymerization. The coagulum is rather important, except if m is large enough. Although the incorporation of the surfactant in the latex is rather high. Most of the anchored surfactant remains at the surface and is not too buried inside. The particle size decreases with both the amount of surfactant and the length of its hydrophilic part. The use of these polymerizable surfactants leads to an excellent stability of the latex against the addition of electrolytes, and also against freeze-thawing constraints.     

Dependency of particle sizes and colloidal stability of polyelectrolyte complex dispersions on polyanion structure and preparation mode investigated by dynamic light scattering and atomic force microscopy

Polyelectrolyte complex (PEC) dispersions were prepared by controlled mixing of three random copolymers of sodium 2-acrylamido-2-methylpropanesulfonate (AMPS) with either t-butyl acrylamide (TBA) [P(AMPS54-co-TBA46) and P(AMPS37-co-TBA63)] or methyl methacrylate (MM) [P(AMPS52-co-MM48)] with an ionene-type polycation, containing 95 mol % N,N-dimethyl-2-hydroxypropyleneammonium chloride repeat units (PCA5), with their structural characteristics being deeply investigated by dynamic light scattering (DLS) and atomic force microscopy (AFM). Shape, size, and polydispersity of the PEC dispersions were directly observed by AFM as a function of polyanion structure, the ratio between charges, n-/n+, and the titrant addition rate (TAR). The particle sizes increased and the colloidal stability decreased with the increase of the nonionic comonomer content and with the decrease of TAR. It was demonstrated that the medium particle sizes of the complex nanoparticles adsorbed on silicon wafers measured by AFM, in the dry state, were close but always lower than those measured by DLS, both before and after the complex stoichiometry.     

The Effect of Weight Fraction of H-PDMS on the Latex Membrane and the Stability of Composite Emulsion of H-PDMS/Acrylate

High hydrogen-containing polymethylsiloxane(H-PDMS)/polyacrylate composite emulsion was synthesized by a drop-adding method for monomer emulsion. The effects of weight fraction of H-PDMS on the stability of composite emulsion, water resistance and heat-aging resistance of the latex membrane have been investigated. The TEM demonstrated that latex particles are a core-shell structure. By analyzing the spectrums of FTIR and ¹H-NMR, it can be indicated that H-PDMS had reacted with acrylate monomer resulting chemical bond formation. The core-shell structure and chemical bond play an important role to restrain phase separation of composite emulsion and enhance the stability of the emulsion. By analyzing the surface tension, apparent viscosity and morphological structure, the results showed that the stable composite emulsion system can be obtained in which the average latex particle size was smaller than 90 nm when weight fraction of H-PDMS is below 16% (based on the weight of acrylate monomer), the stable emulsion system can be obtained in which the average latex particle size becomes larger than 90 nm when the weight fraction of H-PDMS is above 20% of the acrylate monomer. The DSC demonstrated that the T_g of pure polyacrylate is 49°C, and there is only one T_g (35°C) when the weight fraction of H-PDMS is 13%, but there are two T_g (15°C and 25°C) when the weight fraction of H-PDMS is 16%. In addition, the water resistance and heat-aging resistance of composite latex membrane enhanced gradually with the increase of amount of H-PDMS.