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     

Polymerization of high‐solids‐content acrylic latexes using a nonionic polymerizable surfactant

Stable high‐solids‐content methyl methacrylate/butylacrylate latexes with small particle sizes (in the range of 150–180 nm) were obtained with a nonionic polymerizable surfactant (surfmer). Three percent of surfmer with respect to monomer was proven to be enough for the stabilization of the latexes. The influence of different operational variables on the stabilization of the final latex was analyzed, and the conditions needed to obtain coagulum‐free latex were assessed. The inorganic potassium persulfate/sodium metabisulfite initiator system provided better stability than the organic tert‐butyl hydroperoxide/ascorbic acid as a result of the end groups. In addition, the feeding of acrylic acid during the second half of the polymerization improved the stability of the final latex. The reduction of the feeding time was effective in the stabilization. Proof of the surfmer incorporation into the particles is presented. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1552–1559, 2002     

High solids content latexes with low viscosity

The effect of particle size distribution (PSD) on the solids content and viscosity of the multi-sized latex was investigated by blending mono-sized latexes and measuring their rheological properties. The results showed that the maximum packing (highest solids content) was observed at a weight fraction 80% of large particles with respect to total solids content for both bi-modal and tri-modal latexes, and the lowest viscosity was obtained when the ratio of large to medium to small particles was approximately 80/10/10 (by weight). A two-stage technique to prepare high solids multi-sized polymer latex was developed by using a polymer latex previously made as seed and by adding small amount of additional surfactants and/or second group of polymer particles. The PSD of the latex was optimized by varying the amount of the seed, the additional surfactants, and the second group of particles. Film forming latexes with high solids (>65%) and low viscosity were obtained. Received: 18 February 2000 Accepted: 30 September 2000     

Thermosensitive and control release behavior of poly (N‐isopropylacrylamide‐co‐acrylic acid) latex particles

In this work, poly(N‐isopropylacrylamide‐co‐acrylic acid) (poly(NIPAAm‐AA)) copolymer latex particles (microgels) were synthesized by the method of soapless emulsion polymerization. Poly(NIPAAm‐AA) copolymer microgels have the property of being thermosensitive. The concentration of acrylic acid (AA) and crosslinking agent N,N′‐methylenebisacrylamide were important factors to influence the lower critical solution temperature (LCST) of poly(NIPAAm‐AA) microgels. The effects of AA and crosslinking agent on the swelling behavior of poly(NIPAAm‐AA) microgels were also studied. The poly(NIPAAm‐AA) copolymer microgels were then used as a thermosensitive drug carrier to load caffeine. The effects of concentration of AA and crosslinking agent on the control release of caffeine were investigated. How the AA content and crosslinking agent influenced the morphology and LCST of the microgels was discussed in detail. The relationship of morphology, swelling, and control release behavior of these thermosensitive microgels was established. A new scheme was proposed to interpret the control release of the microgels with different morphological structures. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5734–5741, 2008     

New routes to high solid content latexes: a process for in situ particle nucleation and growth

A means of generating latices with solid contents well over 70% (v/v) without the use of intermediate seeds is proposed. It is demonstrated that the use of an electrically neutral initiation system (hydrogen peroxide) in the initial stages of the process, followed by an initiator yielding negatively charged free radicals (ammonium persulphate) changes the way in which the system generates stable particles. The reason for this change is the need to avoid stabilising small, homogeneously nucleated particles during the first portion of the process, and the desire to generate controlled quantities of them during the second portion. The processes are highly reproducible, as are the particle size distributions and rheological properties of the final latices.     

Hydrazine‐functionalized latexes

The noncommercial functional monomer 4‐vinylbenzyl hydrazine (VBH) was synthesized and subsequently copolymerized with styrene (St) by means of different batch and semicontinuous seeded emulsion polymerization processes, so as to obtain hydrazine‐functionalized nanoparticles. The effect of pH, surfactant and initiator amounts, ratio VBH/St, reaction temperature, and ratio acetone/water were studied. Due to the amphiphilic character of VBH at acid pH, the hydrazine groups of the functionalized comonomer were masked with acetone to form hydrazone groups. Secondary nucleations were avoided by using the protected VBH comonomer; however, a decreased radical efficiency achieving limited conversion was observed. Controlling the cationic initiator concentration, complete conversions together with the neat growth of the seed particles were obtained in the semicontinuous seeded emulsion polymerization of styrene and VBH protected with acetone. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6201–6213, 2009     

Polystyrene microspheres with narrow particle size distribution

Crosslinked polystyrene microspheres of a diameter of the order of more than 2 μm and a narrow particle diameter distribution were synthesized by emulsifier-free emulsion polymerization. The dependence of various parameters such as an electrolyte (NaCl), an initiator (K₂S₂O₈), the phase volume ratio, the reaction temperature and time on the diameter and the particle size distribution has been discussed.     

Batch emulsion copolymerization of 3‐O‐methacryloyl‐1,2:5,6‐di‐O‐isopropylidene‐α‐D‐glucofuranose and butyl acrylate: Synthesis and properties of the sugar latices

To obtain new polymer latices based on sugar derivative, batch emulsion copolymerizations of 3‐O‐methacryloyl‐1,2:5,6‐di‐O‐isopropylidene‐α‐D ‐glucofuranose (3‐MDG) and n‐butyl acrylate (BA) were carried out at 70 °C, with potassium persulfate as the initiator. 3‐MDG polymerizes faster than BA because of its higher reactivity ratio, r_(3‐MDG) = 1.94 versus r_(BA) = 0.54. The effect of the initial monomer composition on the polymerization rate and the thermal properties of the end copolymers was investigated. The overall rate of polymerization increases by enhancing the sugar content in the initial monomer composition. The glass‐transition temperature is linearly related to the sugar content in the copolymer. The influence of the type of surfactant showed that the particle size increases by changing from ionic to nonionic surfactant. Furthermore, the effect of the added acrylic acid (AA) on the rheological properties suggests that the sugar latices exhibit different non‐Newtonian flows depending on the pH of the latex and on the AA concentration on the particle surface. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 788–803, 2003     

煤浆浓度和颗粒分布对煤浆黏度预测的影响

采用神华煤制备煤浆,分析了颗粒粒径比λ和小颗粒体积分数ξ对双峰分布浆体黏度的影响,根据浆体黏度的关联式预测了煤浆的黏度并且与实验结果进行了比较。结果表明,采用双峰分布的颗粒制浆可以有效地降低浆体的黏度,同时可以获得较大的浆体体积分数 。在相同体积分数下,随着颗粒粒径比λ的增加,浆体的黏度迅速下降。当小颗粒体积分数ξ_dp1为35%时,浆体的黏度最小。采用Ouchiyama模型计算浆体的最大体积分数Φ_m与实验值较为吻合,而浆体的本质黏度[μ]基本保持不变。考虑λ和小颗粒体积分数ξ对双峰分布浆体的最大体积分数Φ_m的影响,可以采用单峰分布浆体的黏度关联式预测双峰分布浆体的黏度。     

Knowledge‐based choice of the initiator type for monomer removal by postpolymerization

The mechanisms involved in monomer removal by postpolymerization were investigated to establish a criterion to select the most effective initiator systems. Three redox systems yielding radicals of different hydrophobicities were studied. Efficiency in monomer removal by postpolymerization increased with the hydrophobicity of the radical formed from the initiator system. This result was independent of the water solubility of the residual monomer. The mechanistic reasons for this finding are discussed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4245–4249, 2002     

Atypical transition temperature dependence of poly(N‐isopropylacrylamide) and poly(N‐isopropylacrylamide‐co‐acrylamide) nanocomposites on the content of exfoliated montmorillonites

Exfoliated montmorillonite (MMT)/poly(N‐isopropylacrylamide) (PNIPAAm) and MMT/poly(N‐isopropylacrylamide‐co‐acrylamide) [P(NIPAAm‐co‐AAm)] nanocomposites were fabricated by soap‐free emulsion polymerization. Interestingly, as the content of MMT was increased from 0 to 10 wt %, the glass transition temperature of MMT/PNIPAAm was decreased from 145 to 122 °C, whereas that of the MMT/P(NIPAAm‐co‐AAm) increased from 95 to 153 °C. Although the lower critical solution temperature (LCST) of 32 °C for the MMT/PNIPAAm nanocomposites in aqueous solutions was slightly increased with the content of MMT, that of the MMT/P(NIPAAm‐co‐AAm) was decreased from 70 to 65 °C. A mechanism that the hydrogen bonds between the amide groups of PNIPAAm were interfered by the exfoliated MMT nano‐platelets for the MMT/PNIPAAm nanocomposites and the preferred absorption of acrylamide units to the MMT nanoplatelets rather than N‐isopropylacrylamide in the MMT/P(NIPAAm‐co‐AAm) nanocomposites was suggested to interpret these unusual transition behavior. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 524–530, 2009     

Sugar latexes as a new type of binder for water-based paint and coating

Sugar latexes based on saccharid derivatives, such as 3-MDG, 1- or 3-MDF and ITDF, have been synthesized in batch and semi-continuous emulsion polymerization. The polymerizations were carried out at 60 or 70°C, initiated by potassium peroxodisulfate, (KPS), in the presence of either ionic or non-ionic surfactant. The effect of the type and concentration of the surfactant and the type of polymerization process on the colloidal and rheological properties was studied. It was found that the particles size increased with using a non-ionic surfactant. Monodisperse particles were obtained by using SDS below its CMC, and smaller polydisperse latexes were observed when the SDS conc. was above the CMC. The latexes exhibit different non-Newtonian flows depending on the solid content and on the additives.     

Starch‐graft‐copolymer latexes initiated and stabilized by ozonolyzed amylopectin

A method is presented for synthesizing surfactant‐free latexes comprising a starch‐graft‐vinyl polymer, (1) starting with a suspension of the highly branched starch amylopectin, either native or degraded, (2) then using ozonolysis to create free‐radical initiation sites on this amylopectin scaffold, and (3) finally adding the monomer and inducing polymerization. The ozone simultaneously thins the starch and creates initiating/grafting sites on the starch, from which starch‐graft‐copolymer latexes can be grown. The encapsulation of starch inside the hydrophobic polymer particles created by a heterogeneous free‐radical polymerization process is demonstrated with energy‐dispersive spectroscopy; this is the first time that the particle morphology of such a latex has been so characterized. The data unambiguously prove that low‐molar‐mass degraded starch can be encapsulated within a latex particle. The underlying mechanisms have been explored, and data quantifying the rates of production of hydroperoxides by ozone, the thermal decomposition of the starch hydroperoxides so formed, and the degradation of amylopectin by ozone are reported. The activation energy for the thermal decomposition of the starch macroinitiator, determined in this work to be 125 ± 8 kJ mol⁻¹, is consistent with the proposition that the initiating species are mainly hydroperoxides. Colloidally stable poly(styrene‐co‐n‐butyl acrylate) latexes based on high‐molar‐mass amylopectin have been developed. These are stable against electrolytes (several months in 4 mol L⁻¹ NaCl), with 20% of the starch effectively grafted to the particles. Films cast from such latexes are more pliable than starch films and are readily redispersed in water. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5832–5845, 2006     

Influence of polymer particle size on the percolation threshold of electrically conductive latex‐based composites

Monodispersed copolymer emulsions, each with a different polymer particle size, were used to investigate the effect of particle size on the electrical and thermomechanical properties of carbon black (CB)‐filled segregated network composites. These emulsions were synthesized with equal moles of methyl methacrylate and butyl acrylate, with latex particle size ranging from 83 to 771 nm. The electrical percolation threshold was found to decrease from 2.7 to 1.1 vol % CB as the latex particle size was increased. Microstructural images reveal diminished latex coalescence, and improved CB segregation, with increasing latex particle size. In general, coalescence is shown to increase for all systems with increasing CB concentration. Furthermore, all systems exhibited a similar maximum electrical conductivity plateau of 0.7 S cm^?1, albeit at lower concentration for larger latex particle size. This ability to tailor percolation threshold with latex particle size provides an important tool for manipulating electrical and mechanical properties of polymer nanocomposites. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1547–1554, 2011     

Study on the shear viscosity behavior of keratin/PEO blends for nanofibre electrospinning

Graessley's theory has been applied to keratin/PEO concentrated aqueous solutions giving qualitative insight to the rheology of these polymer blends in electrospinning. The shear rate dependent viscosity of different blends was compared with that of pure polymer solutions. The characteristic time τ_η was calculated by the minimum value of at the beginning of the non‐Newtonian viscosity behavior. Flow curves of PEO (at concentration from 1.0 to 7.0 wt %) reduce to a single curve by plotting η/η₀ against . Moreover, PEO solutions exhibit a linear proportionality between zero‐shear viscosity and the characteristic time η₀ ∝ τ_η. Keratin/PEO blend solutions follow the same proportionality at very high and low keratin content, whereas linearity drops when the keratin content range from 50 to 70%. The departure from the theory has been interpreted as a sign of some interaction between the macromolecules of keratin and PEO. It was supposed that keratin displaces solvent molecules and expands the PEO chain coils increasing the relaxation time of the polymer solution. This behavior was correlated with changes in the morphology of the nanofibres produced by electrospinning from these polymer blends. Finally, additive rules to zero‐shear viscosity were applied to keratin and PEO solutions, indicating that the experimental η₀ values were higher than the theoretical ones for all the proportions of the blends, especially for high keratin amount. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1193–1201, 2008     

Study of poly(St/BA/MAA) copolymer latexes with trimodal particle size distribution

A new strategy was developed for producing a polymer latex with trimodal particle size distribution by adding a second seed of polymer particles and some additional surfactants during polymerization. The polymerization was investigated by following the variation of the particle size, the size distribution, the number of particles, the surface tension and surfactant surface coverage at different stages of the polymerization process. The results showed that both the size and the size distribution can be easily controlled by varying the amount of additional surfactants and the second seed of polymer particles. The secondary nucleation was achieved when the surface coverage of particles was over 70%, and the amount of small particles formed increased with increasing amount of additional surfactants. The introduction of the additional surfactants had no significant effect on the size and number of middle particles, but reduced the size of large particles and caused the number of large particles to remain more stable because of the suppression of limited flocculation. Copyright © 1998 John Wiley & Sons, Ltd.     

Synthesis,characterization, and utilization of itaconate‐based polymerizable surfactants for the preparation of surface‐carboxylated polystyrene latexes

Two polymerizable surfactants (surfmers), namely, monododecyl itaconate (MDDI) and monocetyl itaconate (MCI), were synthesized by reacting itaconic anhydride with 1‐dodecanol and cetyl alcohol, respectively. A series of uncrosslinked and crosslinked surface‐carboxylated latexes were prepared from styrene and styrene–divinylbenzene, respectively, using varying amounts of these two surfmers. The latexes were characterized by gravimetry, dynamic light scattering, and conductometric titration in order to obtain the conversion, particle size distribution, and concentration of surface carboxyl groups, respectively. The size of latex varied between 41–72 nm and was seen to depend inversely on the surfmer concentration. In the case of the soluble polystyrene latexes, solution ¹H NMR spectra provided conclusive evidence for surfmer incorporation into the polymer chain. Comparison of the incorporation levels determined by NMR with the surface carboxylic acid concentrations in the latexes, determined by conductometric titrations, revealed that the majority of the surfmers, as ancticipated, were present on the latex surface. The study of the stability of the latexes to varying salt concentrations clearly demonstrated that the smaller‐size latexes having higher surface carboxyl group density exhibited far improved stability when compared with the larger‐size ones having lower surface carboxyl group density. Similarly, enhanced freeze‐thaw stability was also observed for the smaller‐size latexes. MCI‐based latexes exhibited marginally improved stability compared with those prepared using MDDI, which again seems to be because of the higher surface functional group density in the former. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3257–3267, 2005     

Carboxylic‐group distribution of carboxylated acrylate copolymer latexes with their properties in the presence of acrylic acid and monobutyl itaconate

A series of carboxylated acrylate copolymer latexes were prepared via two different emulsion polymerization technologies with different carboxylic‐group distribution and morphologies. The effects of the emulsifier, the initiator, and the carboxylic monomers [acrylic acid (AA) or monobutyl itaconate (MBI)] on the total conversion of the monomers and the properties of acrylate latexes and films have been investigated. The distribution of carboxylic groups (?COOH) measured by conductometric titration shows that the concentration of surface –COOH (C_s) and embedded –COOH (C_b) both increase with the increase of the amount of carboxylic monomers. For the latexes containing AA, –COOH tends to distribute on the surface of latex particles and in the aqueous phase, whereas –COOH tends to concentrate inside the core of latex particles for the latexes containing MBI. Transmission electron microscopy demonstrates that the latex particles are regular with narrow size distribution and have significant differences in morphologies when different carboxylic monomers and polymerization technologies were used. The stability of latex is satisfactory through the results of common stability and zeta potential tests. Moreover, the water absorption and contact angle experiment tests also revealed that the water resistance of the latex films is good. Copyright © 2011 John Wiley & Sons, Ltd.     

Acrylic polymer/silica hybrids prepared by emulsifier‐free emulsion polymerization and the sol–gel process

Acrylic polymer/silica hybrids were prepared by emulsifier‐free emulsion polymerization and the sol–gel process. Acrylic polymer emulsions containing triethoxysilyl groups were synthesized by emulsifier‐free batch emulsion polymerization. The acrylic polymer/silica hybrid films prepared from the acrylic polymer emulsions and tetraethoxysilane (TEOS) were transparent and solvent‐resistant. Atomic force microscopy studies of the hybrid film surface suggested that the hybrid films did not contain large (e.g., micrometer‐size) silica particles, which could be formed because of the organic–inorganic phase separation. The Si? O? Si bond formed by the cocondensation of TEOS and the triethoxysilyl groups on the acrylic polymer increased the miscibility between the acrylic polymer component and the silica component in the hybrid films, in which the nanometer‐size silica domains (particles) were dispersed homogeneously in the acrylic polymer component. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 273–280, 2006     

Epoxy‐functionalized,low‐glass‐transition‐temperature latex. II. Interdiffusion versus crosslinking in the presence of a diamine

This article describes the results of experiments examining the competition between the polymer diffusion rate and the crosslinking rate in low‐glass‐transition‐temperature, epoxy‐containing latex films in the presence of a diamine. We examined films formed from donor‐ and acceptor‐labeled poly(butyl acrylate‐co‐methyl methacrylate‐co‐glycidyl methacrylate) copolymer latex and studied the influence of several parameters on the growth rate of gel content and the rate of polymer diffusion. These factors include the molecular weight of the latex polymer, the presence or absence of a diamine crosslinking agent, and the cure protocol. The results were compared to the predictions of a recent theory of the competition between crosslinking and polymer diffusion across interfaces. In the initially formed films, polymer diffusion occurs more rapidly than the chemical reaction rate. Therefore, these films fall into the fast‐diffusion category of this model. In our system (unlike in the model), the latex polymer has a broad distribution of molecular weights and a distribution of diffusivities. The shortest chains contribute to the early time diffusion that we measure. At later stages of our experiment, slower diffusing species contribute to the signal that we measure. The diffusion time decreases substantially, and we observe a crossover to a regime in which the chemical reaction dominates. The increases in chain branching and gel formation bring polymer diffusion to a halt. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4098–4116, 2002