Semi-continuous Emulsion Polymerization Process Research Articles

Effect of dodecafluoroheptyl methacrylate (DFMA) on the comprehensive properties of acrylate emulsion pressure sensitive adhesives

Fluorinated acrylate emulsion pressure sensitive adhesives (PSA) based on butyl acrylate (BA), fluorine monomer dodecafluoroheptyl methacrylate (DFMA), acrylic acid (AA) and 2-hydroxyethyl acrylate (HEA) were synthesized via a monomer-starved seeded semi-continuous emulsion polymerization process. The influences of DFMA on the resultant latex and PSA properties were comprehensively investigated. FTIR analysis indicated that DFMA could be successfully introduced into the latex PSA copolymer through emulsion polymerization. DSC and TG analyses showed that Tg and thermal stability of the PSA were both improved as DFMA content increased. XPS analysis indicated that fluoroalkyl groups had a tendency to enrich on the surface of the film, and the more DFMA added the more F content on the film surface. Moreover, the surface roughness and contact angle of the acrylate latex PSA film were both increased with the introduction of DFMA. Dynamic mechanical analysis (DMA) and adhesive property tests showed that the storage modulus (Gʹ) and shear holding power were improved with DFMA content while at the sacrifice of loop tack. Finally, 180° peel strength of fluorinated acrylate latex PSAs on different substrates (PP, SS) as a function of DFMA content was evaluated.

Preparation and characterization of self-crosslinking fluorinated polyacrylate latexes and their pressure sensitive adhesive applications

Self-crosslinking fluorinated polyacrylate latexes based on butyl acrylate (BA), fluorine monomer octafluoropentyl methacrylate (OFPMA), self-crosslinking functional monomers acrylic acid (AA) and 2-hydroxyethyl acrylate (HEA) were synthesized by a monomer-starved seeded semi-continuous emulsion polymerization process. The latexes and their corresponding films were characterized by laser particle size analyser, Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), contact angle goniometer, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Results indicated that the particle size of the latexes and the gel content of the films were both independent of the amount of OFPMA employed. On the other hand, the particle size of the latexes decreased and the gel content of the films increased with the incorporation of AA and HEA as expected. Glass transition temperature (Tg) and the thermal stability of the copolymer were both improved gradually as OFPMA content increased. XPS, AFM and water contact angle measurement indicated that the fluoroalkyl groups had a tendency to enrich on the surface of the films. However, this enrichment of fluorine on the film surface was reduced after the introduction of self-crosslinking functional monomers into the system. Finally, the adhesive property of the latexes was evaluated for application as a pressure sensitive adhesive (PSA).

Investigations of addition of low fractions of nanoclay/latex nanocomposite on mechanical and morphological properties of cementitious materials

In this study, we report the synthesis, characterization and performance of organic-inorganic hybrid (OIH) cementitious nanocomposites. OIH was synthesized by the insertion of polymer latex particles in the structure of clay nanoplates. Polymer latex particles were prepared by the polymerization of three different organic monomer comprising styrene monomer (St), 2-ethyl hexyl acrylate (EHA), and methacrylic acid (MAA). Poly(St/EHA/MAA) was prepared by a semi-continuous emulsion polymerization process. The prepared OIH was used to modify the cement paste properties. For the fabrication of latex structure various composition of methacrylic acid as a functional monomer was examined. The effect of the variety of the percentage of MAA on latex composition, and also the OIH to cement ratios were optimized. The optimum conditions were applied to the fabrication of nanoclay based blends. The effects of OIH onto the cement paste properties were evaluated by measuring of the compressive and flexural strength analyses. The obtained results showed that the best composition in cementitious matrix was related to the sample of OIH namely CP565, in which comprises of five percent nanoclay. Also FT-IR, XRD, and SEM analyses were performed to exactly identify the effects of OIH onto the cementitious matrix properties.

Preparation and characterization of fluorine-containing acrylic latex PSAs using a reactive surfactant

Fluorinated acrylic pressure sensitive adhesive (PSA) latexes based on butyl acrylate (BA), acrylic acid (AA), 2-hydroxyethyl acrylate (HEA) and 2,2,2-trifluoroethyl methacrylate (TFMA) were synthesized via a monomer-starved seeded semi-continuous emulsion polymerization process using a reactive emulsifier. Effects of TFMA on the resultant PSA properties were comprehensively investigated. IR analysis indicated that TFMA can be introduced into the latex particles successfully through emulsion polymerization. Gel content and sol molecular weight of the PSA were not significantly affected by the addition of TFMA. It was also found that Tg and thermal stability of the PSA were both improved remarkably as TFMA content increased. Water resistance of the PSA was enhanced, while surface energy of the PSA was decreased with TFMA concentration increased, which were confirmed by XPS analysis. Moreover, the storage modulus (G’) and loss modulus (G”) of the PSA increased with TFMA content. Peel strength of the PSA on PP surface was not affected by the presence of TFMA, while peel strength of the PSA on SS and PC surfaces were first decreased and then increased with the TFMA content. Besides, the influences of reactive surfactant SR-10 and conventional surfactant CO-436 on the acrylic latex PSA were also compared.

Effect of trifunctional cross-linker triallyl isocyanurate (TAIC) on the surface morphology and viscoelasticity of the acrylic emulsion pressure-sensitive adhesives

Acrylic pressure sensitive adhesive (PSA) latexes were synthesized via a starved monomer-seeded semi-continuous emulsion polymerization process with butyl acrylate (BA), methyl methacrylate, acrylic acid (AA), 2-hydroxyethyl acrylate and trifunctional cross-linker, triallyl isocyanurate (TAIC). Influences of TAIC on the resultant latex and PSA properties were comprehensively investigated. The results indicated that latex particle size was independent of the amount of TAIC in the pre-emulsion feed, while the viscosity of the latex increased remarkably with TAIC content increased. Thermal gravimetric analysis result showed that the thermal stability of the polymers was improved significantly with the addition of TAIC. Besides, with the increase in TAIC content, gel content of the polymer increased significantly, while molecular weight between cross link points (Mc) and sol molecular weight (Mw, Mn) of the polymer decreased remarkably. Moreover, for the cross-linked adhesive film, the shear strength was improved greatly while at the sacrifice of loop tack and peel strength, when compared with the uncrosslinked counterparts. Finally, dynamic mechanical analysis and atomic force microscopy were also used to evaluate the viscoelastic properties and surface morphology of the acrylic emulsion PSA film, respectively.

Effect of N,N-dimethylacrylamide (DMA) on the comprehensive properties of acrylic latex pressure sensitive adhesives

Acrylic pressure sensitive adhesive (PSA) latexes were synthesized via a monomer-starved seeded semi-continuous emulsion polymerization process with butyl acrylate (BA), methyl methacrylate (MMA), N,N-dimethylacrylamide (DMA), acrylic acid (AA) and 2-hydroxyethyl acrylate (HEA) as monomers. Impacts of DMA on the resultant latex and PSA properties were comprehensively investigated. Results indicated that latex particle size was independent of the amount of DMA in the pre-emulsion feed with excessive and constant surfactant concentration. Latex viscosity increased with DMA concentration. It was also found that water resistance of acrylic latex PSA became worse by the presence of DMA, confirmed by water contact angle measurements. Besides, DSC results showed that as the amount of DMA increased, glass transition temperatures (Tg) of the polymers were elevated significantly. TGA results showed that thermal stability of PSA was improved with DMA as a co-monomer. Furthermore, as DMA amount increased, gel content slightly increased, while sol molecular weight (Mw, Mn) of the polymer decreased. Finally, with respect to the adhesive properties of the PSA, it was observed that loop tack initially increased and then decreased with the addition of DMA from 0 to 4wt%, and the maximum value appeared at 1wt%. Peel strength reduced, while shear strength improved with increased DMA concentration.

Emulsion Polymerization of Vinyl Acetate in the Presence of a New Cationic Surfactant

In this study, the emulsion homopolymerization system containing vinyl acetate, potassium persulfate, a new cationic polymeric surfactant and water was studied by the applying semi-continuous emulsion polymerization process. The effects of new polymeric emulsifier on the physicochemical properties of obtained vinyl acetate latexes were investigated depending on vinyl acetate percentage in the polymerization recipe, and two thermal initiators in homopolymerization.

Structure and Properties of Modifier for Heat Transfer Printing on Cotton Fabric

Modifier for heat transfer printing on cotton fabrics was prepared by semi-continuous emulsion polymerization process with butyl acrylate (BA), styrene (St), acrylonitrile (AN) and cross-linking monomer. FT-IR characterization of modifier groups showed that individual monomer well carried out polymerization. Transmission electron microscopy (TEM) photos demonstrated that latex particles had regular spherical shape and uniform distribution. TGA curves indicated that thermal decomposition temperature of modifier was 439 oC. As for the transfer printing products had good colour fastness, high transfer rate and no formaldehyde.

Nanostructured latexes made by a sequential multistage emulsion polymerization

AbstractA series of linear and lightly crosslinked nanostructured latices was prepared by a sequential multistage semicontinuous emulsion polymerization process alternating styrene (S) and n‐butyl acrylate (BA) monomer feeds five times, that is ten stages, and vice versa, along with several control latices. Transmission electron micrographs of the RuO4‐stained cross sections of nanostructured and copolymer latex particles and films showed that their particle morphologies were not very different from each other, but the nanostructured latex particles were transformed into a nanocomposite film containing both polystyrene (PS) and poly(n‐butyl acrylate) (PBA) nanodomains interconnected by their diffuse polymer mixtures (i.e. interlayers). The thermal mechanical behaviors of the nanostructured latex films showed broad but single Tgs slightly higher than those of their counterpart copolymer films. These single Tgs indicated that their major component phases were the diffuse interlayers and that they behaved like pseudopolymer alloys. The minimum film formation temperatures of nanostructured latices capped with PBA and PS, respectively, were 15 °C lower than and equal to those of their counterpart copolymer latices, but their Tgs were about 10 °C higher. Consequently, nanostructured latices enabled us to combine good film formation with high strengths for adhesives and coatings applications. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2826–2836, 2006

Studies of Dimethyl Meta‐Isopropenylbenzyl Isocyanate (TMI) for Preparation of Ambient Cross‐linkable Latexes—Film Formation and Cross‐Linking

Single‐pack, ambient cross‐linkable acrylic latexes containing dimethyl meta‐isopropenylbenzyl isocyanate (TMI) repeat units were prepared by batch and semicontinuous emulsion polymerization processes at 40°C using methyl methacrylate (MMA) and n‐butyl acrylate (BA) as the principal comonomers and methacrylic acid (MAA) as a functional comonomer. Degree of cross‐linking and mechanical properties of films from batch latexes increased as the level of TMI increased from 0–5 wt%. Increasing latex pH (from 1–4) to 9 by adding dilute aqueous NaOH brings about an increase in degree of cross‐linking and mechanical properties of films. This effect is further enhanced by incorporation of MAA repeat units, which also give rise to physical cross‐linking through associations between MAA repeat units. Thus, by use of both TMI and MAA, a synergy is achieved in which the TMI repeat units provide for chemical cross‐linking that is accelerated by the effect of MAA repeat units, which also provide for physical cross‐linking, leading to greater improvements in film mechanical properties than when only TMI or MAA is incorporated. Core‐shell particles with an outer TMI/MAA‐containing layer are more susceptible to aliphatic isocyanate (NCO) hydrolysis, which can be detrimental if the rate of hydrolysis is too high. Although the rate of NCO hydrolysis in the TMI/MAA‐containing phase can be reduced by having an outer phase of unreactive poly(MMA/BA), this also prevents development of strong interfaces between particles during film formation. The TMI latexes are colloidally stable during storage for one year, but suffer from extensive NCO hydrolysis and substantial intraparticle cross‐linking, which converts the particles into microgels. The mechanical properties of films from the stored latexes are far inferior to films cast just after latex preparation due to the poor film integrity resulting from the low level of interparticle chemical cross‐linking. Thus, in order to obtain optimum properties in films, TMI latexes should be used soon after preparation and NCO hydrolysis must proceed at a rate that is synchronized with the particle integration stage of film formation. Dedicated to Professor John L. Stanford on the occasion of his 60th birthday.

Studies of Dimethyl Meta‐Isopropenylbenzyl Isocyanate (TMI) for Preparation of Ambient Cross‐linkable Latexes—Stability of NCO Groups in Latex Form

Single‐pack, ambient cross‐linkable acrylic latexes containing dimethyl meta‐ isopropenylbenzyl isocyanate (TMI) repeat units were prepared by batch and semicontinuous emulsion polymerization processes at 40°C using methyl methacrylate (MMA) and n‐butyl acrylate (BA) as the principal comonomers. The semicontinuous processes were used to prepare structured latexes in which the locus of functional groups within the particles was controlled. In some polymerizations, methacrylic acid (MAA) was incorporated at similar levels to TMI (2 and 5 wt%). An FT‐IR method was established for monitoring loss of isocyanate (NCO) groups during latex storage and was shown to give reliable values of rate coefficients. The results showed that NCO functionality was lost gradually over a period of 1–2 weeks depending on latex parameters. Inclusion of MAA repeat units increased the rate of loss of NCO groups by an order of magnitude when the TMI and MAA were uniformly incorporated. The rate also increased significantly on changing latex pH from acidic (pH 1–4) to basic (pH 9) using NaOH. Particle morphology and functional group location also were important. Loss of NCO groups was fast for core‐shell latexes in which the NCO groups were incorporated only in the shell (with more direct access to water from the continuous phase), but much slower when a core containing the TMI and MAA repeat units was protected from the continuous phase by an unreactive poly(MMA/BA) shell layer. The observations show that TMI‐containing latexes have a relatively short shelf‐life and emphasize the importance of casting films soon after latex preparation for optimum cross‐linking during film formation. Dedicated to Professor John L. Stanford on the occasion of his 60th birthday.

Synthesis and characterization of functionalized polymer latex particles through a designed semicontinuous emulsion polymerization process

AbstractMonodispersed noncarboxylated and carboxylated poly(n‐butyl methacrylate‐co‐n‐butyl acrylate) latices were synthesized with a well‐defined semicontinuous emulsion polymerization process. A modified theory to correlate the polymerization rate to the instantaneous conversion of the monomer or comonomer mixture was developed. The resulting equation was used to determine the maximum polymerization rate only below or equal to which the polymerization could be operated in the highly monomer‐starved regime, which corresponded to an instantaneous conversion of 90% or greater. Experimental data from reaction calorimetry supported that the polymerization was under highly monomer‐starved conditions when the model latices were synthesized with the modified model. The estimation of the average number of free radicals per latex particle(n̄) during the feeding stage revealed that n̄ was as high as 1.4 in the actual polymerization, which showed that the original selection of 0.5 as the n̄ value was not accurate in the developed model. From the conductimetric titration experiments, we found that most of the carboxyl groups from the methacrylic acid (MAA) were buried inside the latex particles, and the surface carboxyl group coverage increased as the MAA concentration in the comonomer feed increased. The glass‐transition temperatures of the synthesized polymers were close to the designed value from the Pochan equation, and only one glass transition was observed in the polymer samples in the differential scanning calorimetry measurements, indicating a homogeneous copolymer composition in the functionalized shell. Particle size characterization and transmission electron microscopy confirmed the uniformity in the latex particle size. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 248–256, 2005

Synthesis and phase separation during film formation of novel methyl methacrylate/ n-butyl acrylate/methacrylic acid (MMA/BA/MAA) hybrid urethane/acrylate colloidal dispersions

Hybrid acrylic/urethane colloidal dispersions were prepared by incorporation of a novel multifunctional urethane castor vinyl ether (UCVE) macromonomer derived from castor oil in acrylic latexes. Single-stage and two-stage semi-continuous emulsion polymerization processes were utilized to control placement of UCVE in colloidal dispersions with core/shell and spherical particle morphologies. While the single-stage process resulted in optically clear and chemically homogeneous films, the two-stage process led to heterogeneous film formation. Internal reflection infrared imaging (IRIRI) spectroscopic analysis of the film-air (F-A) interfaces revealed phase-separated urethane- and urea-rich domains ranging in size from approximately 4–40 μm. Based on these measurements, a model of film formation is proposed which incorporates the effect of exceedingly high shear conditions to achieve fine dispersions of UCVE. These experiments indicate that features of the single-stage process facilitate uniform dispersion of UCVE and efficient grafting between UCVE and the acrylic polymer matrix resulting in intimately mixed networks and homogeneous films.

Synthesis of well‐defined, functionalized polymer latex particles through semicontinuous emulsion polymerization processes

AbstractThe design of a semicontinuous emulsion polymerization process, primarily based on theoretical calculations, has been carried out with the objective of achieving overall independent control over the latex particle size, the monodispersity in the particle size distribution, the homogeneous copolymer composition, the concentration of functional groups (e.g., carboxyl groups), and the glass‐transition temperature with n‐butyl methacrylate/n‐butyl acrylate/methacrylic acid as a model system. The surfactant coverage on the latex particles is very important for maintaining a constant particle number throughout the feed process, and this results in the formation of monodisperse latex particles. A model has been set up to calculate the surfactant coverage from the monomer feed rate, surfactant feed rate, desired solid content, and particle size. This model also leads to an equation correlating the polymerization rate to the instantaneous conversion of the monomer or comonomer mixture. This equation can be used to determine the maximum polymerization rate, only below or at which monomer‐starved conditions can be achieved. The maximum polymerization rate provides guidance for selecting the monomer feed rate in the semicontinuous emulsion polymerization process. The glass‐transition temperature of the resulting carboxylated poly(n‐butyl methacrylate‐co‐n‐butyl acrylate) copolymer can be adjusted through variations in the compositions of the copolymers with the linear Pochan equation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 30–41, 2003

Synthesis and characterization of model carboxylated latexes for studies of film formation from latex blends

Poly(n-butyl methacylate-co-n-butyl acylate) [P(BMA/BA)] soft latexes (carboxylated and noncarboxylated) were synthesized using a semicontinuous emulsion polymerization process that was designed on the basis of a theoretical calculation to determine the suitable surfactant [i.e., sodium dodecyl sulfate (SDS)], monomer, and water feed rates to maintain a constant particle number throughout the polymerization (guaranteeing monodispersity in the particle size), to obtain a homogeneous copolymer composition, and to independently control the particle size and carboxyl group concentration. The experimental results support the theoretical calculation. The surface coverage of the carboxyl groups present on the soft latex particles ranges from 7.6 to 21.9% for a series of latexes with particle sizes around 120 nm. In another series of latexes, the particle size was varied over a range from 120 to 450 nm. Monodisperse carboxylated polystyrene hard latexes were synthesized by shot growth (batch) and semicontinuous processes. The shot growth method is somewhat inflexible in providing more choices in surfactant, particle size, and surface carboxyl coverage. A semicontinuous process designed using a similar method used for the synthesis of P(BMA/BA) latexes successfully eliminated the drawbacks of the shot growth process. In this way, the changes in the surface carboxyl coverage (varies from 0 to 77.2%) was independent of the particle size, which was precisely controlled by the amount of styrene fed under suitable styrene and SDS feed rates. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 644–659, 2000

Synthesis and characterization of model carboxylated latexes for studies of film formation from latex blends

Poly(n-butyl methacylate-co-n-butyl acylate) (P(BMA/BA)) soft latexes (car- boxylated and noncarboxylated) were synthesized using a semicontinuous emulsion polymerization process that was designed on the basis of a theoretical calculation to determine the suitable surfactant (i.e., sodium dodecyl sulfate (SDS)), monomer, and water feed rates to maintain a constant particle number throughout the polymerization (guaranteeing monodispersity in the particle size), to obtain a homogeneous copolymer composition, and to independently control the particle size and carboxyl group concen- tration. The experimental results support the theoretical calculation. The surface coverage of the carboxyl groups present on the soft latex particles ranges from 7.6 to 21.9% for a series of latexes with particle sizes around 120 nm. In another series of latexes, the particle size was varied over a range from 120 to 450 nm. Monodisperse carboxylated polystyrene hard latexes were synthesized by shot growth (batch) and semicontinuous processes. The shot growth method is somewhat inflexible in providing more choices in surfactant, particle size, and surface carboxyl coverage. A semicontinu- ous process designed using a similar method used for the synthesis of P(BMA/BA) latexes successfully eliminated the drawbacks of the shot growth process. In this way, the changes in the surface carboxyl coverage (varies from 0 to 77.2%) was independent of the particle size, which was precisely controlled by the amount of styrene fed under suitable styrene and SDS feed rates. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 644 - 659, 2000

Impact modification of thermoplastics by methyl methacrylate and styrene‐grafted natural rubber latexes

AbstractThe preparation and characterization of polymer blends with structured natural rubber (NR)‐based latex particles are presented. By a semicontinuous emulsion polymerization process, a natural rubber latex (prevulcanized or not) was coated with a shell of crosslinked polymethylmethacrylate (PMMA) or polystyrene (PS). Furthermore, core–shell latexes based on a natural rubber/crosslinked PS latex semi‐interpenetrating network were synthesized in a batch process. These structured particles were incorporated as impact modifiers into a brittle polymer matrix using a Werner & Pfleiderer twin screw extruder. The mechanical properties of PS and PMMA blends with a series of the prepared latexes were investigated. In the case of PMMA blends, relatively simple core (NR)–shell (crosslinked PMMA) particles improved the mechanical properties of PMMA most effectively. An intermediate PS layer between the core and the shell or a natural rubber core with PS subinclusions allowed the E‐modulus to be adjusted. The situation was different with the PS blends. Only core–shell particles based on NR‐crosslinked PS latex semi‐interpenetrating networks could effectively toughen PS. It appears that microdomains in the rubber phase allowed a modification of the crazing behavior. These inclusions were observed inside the NR particles by transmission electron microscopy. Transmission electron photomicrographs of PS and PMMA blends also revealed intact and well‐dispersed particles. Scanning electron microscopy of fracture surfaces allowed us to distinguish PS blends reinforced with latex semi‐interpenetrating network‐based particles from blends with all other types of particles.

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

AbstractVinyl 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.