Pigment encapsulation by emulsion polymerisation,redespersible in water

Emulsion Polymerization was carried out in the presence of inorganic pigments such as TiO2, black FexOy, yellow FexOy, and red FexOy, and NP 30 as surfactants, and water soluble AZO compounds or KPS as initiator. Monomers with specific hydrogen bonding interaction must be used in the initial steps of polymerisation, methylmethacrylate and vinylacetate being the most convenient. Then a semi continuous feed of a mixture of monomers was carried out in starved conditions. In order to make the covered pigments water-redispersible a mixture of hydrophobic and hydrophilic monomers should be chosen with proper pH conditions. The amount of surfactant has to be chosen so that no agglomeration of the covered pigments take place. The covered pigments were dried upon lyophylisation, then formulation of powder paints was carried out using commercial powder binders and other additives. Good properties of the paints, such as brightness were obtained in that way.     

Preparation and characterization of graft copolymerization of ethyl acrylate onto hydroxypropyl methylcellulose in aqueous medium

Graft copolymerization of ethyl acrylate (EA) onto water-soluble hydroxypropyl methylcellulose (HPMC) was investigated with potassium persulfate (KPS) as initiator in an aqueous medium. The effects of monomer concentration, initiator concentration, matrix concentration, reaction temperature, reaction time and pre-interacting time in terms of percentage of grafting (G) and grafting efficiency (G _E) are discussed. The graft copolymers were characterized by Fourier transform infrared spectra (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction analysis (XRD) and differential scanning calorimetry (DSC). In addition, equilibrium humidity adsorption behavior of the pure grafted copolymers was also studied.     

Radical desorption in the emulsion polymerisation of vinyl monomers

The dependence of emulsion polymerisation rates on a number of important parameters is considered. Attention is paid to the use of seeded emulsion systems for the evaluation of radical desorption coefficients (k _o). Experimental conditions are shown to be important. When the average number of radicals per particle is low, large changes in the rate coefficient for chain termination do not have a large effect on the kinetics. With styrene and methylmethacrylate, radical re-absorption by the polymer particles is shown to be important and radical capture efficiences can be high. Consistency is established between the results of a number of workers and values fork _o are shown to be lower than those calculated from chain transfer rates.     

Synthesis of polyfluorophenyl substituted-4,5-dihydropyrazole derivatives via 1,3-dipolar cycloaddition of nitrile imine with ethyl acrylate

Oxidation of aldehyde 4-chloro-2,3,5,6-tetrafluorophenylhydrazones (1) with [bis(acetoxy)iodo]benzene leads to the formation of nitrile imines (2) which reacted in situ with ethyl acrylate to produce 3-substituted-1-(4-chloro-2,3,5,6-tetrafluorophenyl)-5-ethoxycarbonyl-4,5-dihydropyrazoles (3) in moderate to good yields. The structures of new compounds were fully confirmed by their spectral data, elemental analyses and X-ray diffraction (XRD) analysis. A plausible reaction mechanism for the synthesis of title compounds is presented.     

Kinetic and mechanistic aspects of metallocene polymerisation catalysts

The nature of the counteranion is an essential component of metallocene polymerisation catalysts. Detailed mechanistic investigations show how the anion is able to determine the activity and, in many cases, also the stereoselectivity of the catalyst. This review summarises recent advances in mechanistic understanding of well defined metallocene catalysts based on ion pairs [L₂ZrR⁺ ?X⁻] and describes recent insights in ion mobility and kinetics of alkene polymerisation processes. The interplay of ligand structure and nature of the counteranions demonstrates a fascinating versatility and subtlety that continually challenge our ability to rationalise and predict catalyst performance.     

Effect of dimethylaminoethyl methacrylate on the graft copolymerization of ethyl acrylate onto hydroxypropyl methylcellulose in aqueous medium

Graft copolymerization of an ethyl acrylate (EA) and dimethylaminoethyl methacrylate (DMAEMA) monomer mixture onto water-soluble hydroxypropyl methylcellulose was investigated with potassium persulfate (KPS) as the initiator in an aqueous medium. The effects of introducing DMAEMA onto the graft copolymerization and the properties of the resulting latex that was produced were studied systematically. The optimum conditions for the graft copolymerization in terms of percentage of grafting and grafting efficiency were determined. The graft copolymer was characterized by Fourier transform infrared spectra, elemental analyses, nuclear magnetic resonance, transmission electron microscopy, and dynamic light scattering methods. The results suggest that the introduction of the DMAEMA monomer clearly accelerates the initial rate of the graft copolymerization, whereas the grafting parameters decrease significantly with increasing amounts of DMAEMA. These results can be attributed to the relatively large size of the DMAEMA molecule, its redox reaction with KPS, its hydrophilicity in water, and its chain transfer effect. The equilibrium humidity adsorption behavior and acid solubility of graft the copolymer films were also studied.     

Determination of residual monomers in acrylate dispersions by gas chromatography

The content of residual monomers is one of the most important characteristics of polymer dispersions. As a result of the similar physicochemical parameters of ethyl acrylate and methyl methacrylate, it is very difficult to determine the residual monomers in acrylate dispersions obtained by emulsion polymerization of both monomers. Gas chromatography with capillary columns, however, permits separation of these monomers and their quantitative determination in acrylate dispersions.     

Mechanistic studies on particle nucleation in the batch emulsion polymerisation of<Emphasis Type="Italic"> n</Emphasis>-butyl acrylate containing multifunctional monomers

This paper reports the mechanistic details concerning the synthesis of crosslinked poly(n-butyl acrylate) dispersions intended to be used as seeds in the preparation of core-shell emulsions. The influence of crosslinking comonomers and the amount and type of surfactants on the kinetics, particle nucleation, particle size and particle size distribution in the batch emulsion polymerisation of n-butyl acrylate (BA) is explored. In the case of EGDA (ethylene glycol diacrylate) crosslinker the particle number decreased with increasing crosslink density, whereas the opposite trend was observed in the case of m-diisopropenylbenzene (m-DIPB) in the presence and absence of the surfactant sodium dodecyl sulfate (SDS). The observed behaviour is mainly attributed to the variation in the aqueous phase kinetics caused by the water solubility of the comonomer, which influences the formation rate of precursor particles during the nucleation stage. Only for the less water soluble crosslinker, DIPB, could the increase of particle number be explained within the Smith–Ewart theory by assuming prolonged nucleation due to reduced swelling of growing particles with monomer as a result of the crosslinking reaction.Abbreviations EGDA ethylene glycol diacrylate - m-DIPB meta-diisopropenylbenzene - SDS sodium dodecyl sulfate - PBA poly(n-butyl acrylate) - AFFF asymmetric field flow fractionation - MALLS multiangle laser light scattering - CMC critical micelle concentration     

Kinetics of the potassium persulfate-initiated inverse emulsion polymerization of sodium acrylate solutions

The kinetics of the K₂S₂O₈-initiated inverse emulsion polymerization of aqueous sodium acrylate solutions in kerosene with Span 80 as the emulsifier has been studied. The conversion-time curves are S-shaped. The following expressions have been obtained for the maximum rate of polymerization and the molecular weight of the polymers under the experimental conditions investigated: R_max ∞ [K₂S₂O₈]^0.78[sodium acrylate]^1.5[Span 80]^0.1, (OVERLINE)M(/OVERLINE)_u ∞ [K₂S₂O₈]^−0.37[sodium acrylate]^2.9[Span 80]^−0.2. The activation energy for the maximum rate of polymerization is 94.8 kJ mol^−1. The results suggest a monomer–droplet–nucleation mechanism for the system studied. © 1996 John Wiley & Sons, Inc.     

Preparation of PEG-modified urethane acrylate emulsion and its emulsion polymerization

In order to improve stability and reduce droplet size, the PEG-modified urethane acrylates were synthesized by the reaction of polyethylene glycol (PEG) with residual isocyanate groups of urethane acrylate to incorporate hydrophilic groups into the molecular ends. The droplet sizes of the PEG-modified urethane acrylate emulsions were much smaller than those of unmodified urethane acrylate emulsions at the same surfactant composition, and the droplet sizes of these emulsions were significantly effected not by surfactant compositions and types, but by the reaction molar ratio of PEG, because the urethane acrylate containing polyoxyethylene groups as terminal groups aided the interfacial activity of surfactant molecules and acted as a polymeric surfactant. The actions of PEG-modified urethane acrylate were confirmed by the investigation of adsorption of urethane acrylate in a water/benzene interface.For polymerization of emulsions, the stability of emulsion in the process of emulsion polymerization was changed by the type of surfactant or initiator. In the case of emulsion polymerization with a water soluble initiator (K₂S₂O₈), the emulsions prepared using TWEEN 60 were broken in the process of polymerization. However, polymerization of these emulsions could be carried out using an oil soluble initiator (AIBN). The conversion of emulsion polymerization changed with the type of urethane acrylates, that is, the reaction molar ratio of PEG to 2-HEMA.     

Capsules from Pickering emulsion templates

Following the resurgence of interest in particle-stabilised or Pickering emulsions recently, the preparation of capsules from such templates has become feasible. We review some of the recent activity in this area and focus on both the methods used to reinforce the particle shell and the applications of these novel capsules, which may be empty or liquid-filled. The methods reported include interfacial polymerisation or crystallisation, interfacial cross-linking, the use of a sacrificial template, formation of polymer layers, gelation and evaporation from multiple emulsions. Potential applications are in the areas of wastewater treatment, perfume encapsulation, drug/dye release and as self-healing coatings.     

An effective new access to ethyl 2-[(alkylamino)(cyano)methyl] acrylates: first synthesis of ethyl 3-cyano-2-(hydroxymethyl) acrylate

A regioselective coupling of ethyl 2-(bromomethyl)-3-cyanoacrylate and primary amines is described to give ethyl 2-[(alkylamino)(cyano)methyl] acrylates in good yields. Whereas the conversion of allyl bromide in the presence of TEAF leads to the first synthesis of ethyl 3-cyano-2-(hydroxymethyl) acrylate.     

Semicontinuous emulsion copolymerization of methyl methacrylate and ethyl acrylate

The monomer addition policies required to produce homogeneous methyl methacrylateethyl acrylate copolymers of different compositions were determined by means of a semiempirical approach. This approach is useful for systems about which only a limited information is available. Applying this method only three reactions were needed to obtain homogeneous copolymers in a minimum process time. Comparisons were made between the results obtained using this monomer addition strategy and those from copolymerizations carried out under the classical starved conditions.     

Kinetic studies on the addition of dipropylamine to glucose acrylate

The kinetics of the nucleophilic addition reaction of dipropylamine to the vinyl double bonds of glucose acrylate (GA) has been investigated. The reactions were carried out under pseudo first-order conditions in tetrahydrofuran with excess amine within the temperature range from 25 to 45 °C. The activation energy of dipropylamine addition to the vinyl groups of GA is 21.1 kJ/mol.     

A kinetic investigation of styrene/ethyl acrylate copolymerization

An experimental study of the bulk-free radical copolymerization of styrene (STY)/ethyl acrylate (EA) initiated by 2,2′-azobisisobutyronitrile was conducted. Reactivity ratios were evaluated using both nonlinear least-squares (NLLS) and error-in-variables model (EVM) techniques. A thorough study of the kinetics over the full conversion range was subsequently carried out at a variety of feed compositions, initiator concentrations, and temperatures, with and without added chain transfer agent (CTA). © 1996 John Wiley & Sons, Inc.     

Kinetic studies on the addition of dipropylamine to starch acrylate

Summary The kinetics of nucleophilic addition of dipropylamine to vinyl groups of starch acrylate has been investigated. The reactions were carried out under pseudo-first order conditions in tetrahydrofuran with excess amine within the temperature range from 25 to 45^oC. Pseudo-first-order rate constants for addition and the activation energy have been determined.     

Kinetics and mechanism of base catalysed ethyl cyanoformate addition to aldehydes

The mechanism by which tertiary amines catalyse the formation of cyanohydrin carbonates from aldehydes and alkyl cyanoformates is investigated by means of a kinetic study. The reaction rate shows a second order dependence on amine concentration unless the amine is sterically hindered, when the rate has a first order dependence on amine concentration. The catalytic activity of the amine correlated with its pK_aH. On the basis of these results, a mechanism is proposed in which the amine acts as a base to activate a water molecule, which reacts with the ethyl cyanoformate generating cyanide in situ.     

Polyurethane acrylate microgel synthesized by emulsion polymerization using unsaturated self-emulsified polymer

Polyurethane (PU) acrylate microgels were obtained by emulsion polymerization of self-emulsified PU acrylate terminated by 2-hydroxyethyl methacrylate without any extra emulsifier and crosslinker. Moreover, the PU acrylate was also used as stabilizer and crosslinker to synthesize poly(methyl methacrylate) (PMMA)–PU composite microgels via emulsion polymerization, which provided a new method to synthesize PU microgels and their composite microgels. The kinetics of microgel synthesis was studied by gel permeation chromatography. The dynamic rheological behaviors indicated that a crosslinked structure was formed. The frequency dependency of the loss tangent and complex viscosities showed strong relationships with the microgel structure. Those microgels with rigid PMMA core showed higher ability to slide than the soft PU acrylate microgel, which had influence on the changing of loss tangent with frequency. All the microgels swollen in tetrahydrofuran exhibited high viscosities and strong shear-thinning behaviors. As a sort of flexible microgel, the PU microgel was able to form a coherent film at room temperature, which was distinct from hard microgels.     

Emulsions Stabilized with poly(Hydroxyethyl Acrylate-co-Coumaryl Acrylate-co-2-Ethylhexyl acrylate)

Thermo- and photo-responsive emulsions were prepared using mineral oil as an oil phase and a thermo- and-photo-sensitive polymer as an emulsifier. Hydroxyethyl acrylate (HEA) was copolymerized with Coumaryl acrylate (CA) and 2-Ethylhexyl acrylate (EHA) by a free radical reaction with the content of CA in the reaction mixture being varied (0, 0.5, 1, 2, 3 mol%) and the content of EHA being kept constant (2 mol%). CA was used as a photo-responsive comonomer and EHA was used as a hydrophobic comonomer to endow the copolymer with amphiphilicity. The copolymers prepared using the HEA/CA/EHA mixture where CA content was 1, 2, 3 mol% exhibited a phase transition in the range of 20°C– 45°C, and the phase transition temperature decreased with increasing the content. The CA of the copolymers was readily dimerized under the irradiation of UV (365 nm. 400 W) and the dimerization degree was 27%–47% in 60 min. The droplet size of emulsions significantly increased with increasing the temperature from 27°C- 50°C, possibly due to the thermal contraction of the copolymers. Also, the size markedly increased by 60 min-irradiation of the UV light, possibly because of the photo collapse of the copolymers.     

Thermal degradation of poly(ethyl methacrylate) and its copolymer with poly(ethyl acrylate)

The thermal degradation behaviour of poly(ethyl methacrylate) homopolymers and poly(ethyl methacrylate) and poly(ethyl acrylate) copolymers synthesized by using the benzoyl peroxide-di-methyl aniline redox pair at different temperatures (18–35C) was investigated. Contrary to some reports in the literature, the thermal degradation of PEMA was observed to take place in multi steps. These are assigned to be loss of labile end groups, side chain scission, anhydride formation and main chain degradation steps. Dominating chemical formations at the end of these steps were characterized by FTIR spectroscopy.The homopolymer samples synthesized at 18C showed a greater thermal stability against degradation. Copolymerization with small amounts of ethyl acrylate was observed to impart thermal stability to PEMA by stabilizing mainly the end groups against degradations.