Semibatch Emulsion Polymerization Research Articles

Real-Time Monitoring of Particle Size in Emulsion Polymerization: Simultaneous Turbidity and Photon Density Wave Spectroscopy.

Particle size evolution in seeded semibatch emulsion polymerization is monitored by two real-time monitoring techniques: online turbidity spectroscopy (TUS) and inline photon density wave spectroscopy (PDWS). An automatic dilution system that withdraws a sample from the reactor and upon dilution transfers to the measurement cell is used for the online TUS analysis. A PDWS probe is immersed in the reactor and collects inline the scattered light directly from the reacting latex. The particle sizes retrieved from TUS and PDWS are compared to offline dynamic light scattering (DLS) values. The particle size obtained by TUS is close to the intensity-average particle size obtained offline by DLS, while the particle size obtained by PDWS lies closer to the number-average particle size from DLS.

Efficient incorporation of protein into waterborne hybrid acrylic based nanoparticles

The use of raw materials from natural sources as substitutes for petrochemical monomers is of high interest in the polymer science, to comply with the increasing social awareness of pollution and environmental regulations. Natural proteins emerge as particularly promising candidates to be combine with synthetic polymers, offering the prospect of enhancing the product sustainability. Nonetheless, protein-based hybrid materials still present some drawbacks such as high susceptibility to water, due to the incorporation of hydrophilic protein and the resulting morphology of hybrid particles. In the present study, we propose a novel approach for synthesizing biphasic hybrid particles with a controlled morphology that tend to optimize the synergy between both phases. Here, protein phase forms the core of hybrid particles, which is surrounded by an acrylic polymer phase. To achieve this particular morphology, a seeded semibatch emulsion polymerization strategy was designed by employing preformed zein-casein bioparticles (BPs) as seed. This paper encompassed a comprehensive exploration of the key variables impacting on both the synthesis of BPs and the subsequent formation of hybrid latex particles. The outcomes of this research not only contribute to a deeper understanding of the synthesis process but also broaden the potential applications of acrylic-protein hybrid films, particularly as coatings.

Influence of cellulose nanocrystal surface chemistry and dispersion quality on latex nanocomposite stability, film formation and adhesive properties

The different surface functional groups on carboxylated and sulfated cellulose nanocrystals (CNCs) affect the latex CNC–polymer interactions.

Effect of molecular weight and its modality on pressure-sensitive adhesives behavior of plant oil-based latexes

Semibatch emulsion polymerization of high oleic soybean oil-based monomer (HO-SBM), 2–ethylhexyl acrylate (2-EHA), and styrene (St) was applied to synthesize pressure-sensitive latex adhesives with up to 40 wt% of plant oil-based content. Ternary latex copolymers with similar chemical composition and broadly different molecular weight distribution (MWD) and modality were synthesized at varying temperatures and the mechanism of free-radical initiation. Conventional thermal initiation with ammonium persulphate at 80 °C and ascorbic acid/tert-butyl hydroperoxide redox system of lower reaction temperature up to 20 °C were employed. Linear, short-chain, and long-chain branched macromolecules are formed due to chain-breaking reactions of HO-SBM (chain transfer on allyl groups) and 2-EHA (inter- and intramolecular chain transfer on the polymer). The dominant effect of chain transfer on allyl group protons and subsequent decrease in molecular weight was observed at higher reaction temperatures, while extensively branched polymer with high molecular weight was obtained at reaction temperature close to 20 °C.The effect of MWD and branching on the PSAs performance of synthesized biobased latexes was studied using loop tack and peel strength and lap shear testing and compared to two commercial PSA tapes as a benchmark. A significant increase in shear strength (up to 0.23 MPa) was observed for latex adhesives due to high molecular weight fractions, maintaining satisfactory level of tack (3–7 N) and peel (3–6 N/in). Broad MWD of the copolymers can be beneficial for providing materials with high shear strength (0.25–0.33 MPA) while preserving the significant level of tack (2–4 N) and peel strength (9–12 N/in) on both glass and steel substrates.

Multi-hierarchical nanoparticles with tunable core by emulsion polymerization processes

Nanoparticles (NPs) with functional cores are gaining research interest due to their advanced architecture. However, exposed reactive groups on NP surfaces can lead to material side reactions and biomedical tissue damage. NPs with multi-hierarchical morphologies can be synthesized by various methods; however, controlling the size and position of the functional groups using conventional and scalable methods is still a challenge. This study explores emulsion-based polymerization methods for producing multi-hierarchical NPs with varying sizes and compositions. We compared micro-, macro-, and semi-batch emulsion polymerization using 2-hydroxyethyl methacrylate (HEMA) and pentafluorophenyl methacrylate (PFMA) as co-monomers. The components present in PFMA can be substituted and are used for post-synthetic functionalization. The results suggest that the architecture of the synthesized NPs is multi-hierarchical, with the substitutable pentafluorophenyl units surrounded by HEMA monomers. Additionally, we evaluated the NPs' ability to enhance dermal drug penetration using nile red as a hydrophobic drug model. Significant variations in skin permeation enhancement properties were observed among the NPs, underscoring the impact of the synthesis method on nanocarriers' drug delivery performance.

Wavelength exponent based calibration for turbidity spectroscopy: Monitoring the particle size during emulsion polymerization reactions

Particle size and particle size distribution (PSD) are important properties of polymer latexes because they strongly affect the film formation and the rheological properties of the latexes. Thus, monitoring the particle size is of paramount importance during the production of waterborne polymeric dispersions, for which online/inline measurements of the particle size are required. Herein, turbidity spectroscopy (TUS) is used to measure the particle size of nanoparticles in dispersed media. Calibration curves based on a modified wavelength exponent method are introduced and assessed to monitor the evolution of a broad range of particle sizes in seeded semibatch emulsion polymerizations of methyl methacrylate, butyl acrylate, methacrylic acid (MMA/BA/MAA 51/47/2) terpolymers. It is shown that the wavelength exponent based calibration curves can be successfully used to retrieve the particle size during the polymerization process.

Film formation of high poly(vinyl chloride) content latex particles

Although poly(vinyl chloride) (PVC) is produced on a large scale industrially by emulsion and suspension polymerization, it is usually processed from the dry state and is seldom directly used as an aqueous polymer dispersion. In this work we demonstrate that by control of particle morphology and particle size distribution it is possible to produce latexes with high PVC content from which polymer films can be cast directly. A series of hybrid PVC/acrylic latexes with a core-shell structure are produced by semi-batch emulsion polymerization using a preformed PVC latex as a seed. Although monomodal particles of this type have a minimum film formation temperature in excess of 80 °C when the content of PVC is high, it is shown that through the use of a bimodal particle size distribution the packing efficiency of the spherical PVC domains is increased such that room temperature film formation is possible with PVC content up to 80 wt%.

Development of waterborne anticorrosive coatings by the incorporation of coumarate based corrosion inhibitors and phosphate functionalization

Waterborne coatings are more industrially appealing for corrosion protection due to their low toxicity when compared to traditional solvent based coatings. In waterborne latex systems, the presence of surfactants is crucial, which can nevertheless contribute later to a poor performance of the final films in terms of barrier protection. This can be avoided by the use of polymerizable surfactants covalently bonded to the polymeric chains. In this work, particles of a latex loaded with an organic corrosion inhibitor, methoxy p-coumaric acid (H1), are further functionalized by the incorporation of a polymerizable surfactant, Sipomer® PAM-200 (SIP), by semibatch emulsion polymerization. The proposed system was hypothesized to ideally have higher barrier and corrosion protection properties due to the combination of H1 and SIP. However, the Electrochemical Impedance Spectroscopy results of the latexes cast on metal substrates indicate an antagonistic effect on the corrosion inhibition process rather than synergistic, as both species compete for the same moieties of the metallic surface. Thus, while the control coating with SIP (13.3 mg of SIP/g of polymer) showed impedances of 107.1–106.4 Ω and phase angles of 84–88 degrees over 24 h, the coating with H1 (3.3 mg of H1/g polymer) and SIP (13.3 mg of SIP/g of polymer) showed a less stable behavior with changes in impedances with time from 107.1 to 105.5 Ω and in phase angle from 86 to 72 degrees. The production of a bi-layer system avoids this antagonistic effect.

Preparation and characterization of high solid content acrylate latex pressure sensitive adhesives with difunctional cross-linker EGDMA

Cross-linked acrylate latex pressure sensitive adhesives (PSAs) were synthesized via unseeded semi-batch emulsion polymerization processes with butyl acrylate (BA), acrylic acid (AA), 2-hydroxyethyl acrylate (HEA) and difunctional cross-linker, ethylene glycol dimethacrylate (EGDMA). The influences of EGDMA on the comprehensive properties of the acrylate latex PSAs were investigated. The results indicated that both viscosity and particle size of the latexes were independent of the amount of EGDMA in the pre-emulsion feed when unseeded semi-batch emulsion polymerization process was employed. It was also found that water resistance of the latex PSA was improved with increasing EGDMA content, further confirmed by water contact angle measurements. DSC and TGA results showed that Tg of the copolymer was elevated, plus thermal stability was increased with introduction of EGDMA. Besides, with the increase of EGDMA content, the gel content of the polymer increased. 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 uncross-linked counterparts.

Thiol‐ene emulsion polymerization using a semi‐continuous approach

AbstractThe thermally initiated thiol‐ene emulsion polymerization of diallyl phthalate (DAP) diene and ethylenedioxy diethanthiol (EDDT) dithiol monomers in batch and semibatch emulsion polymerization is investigated. The batch process leads to larger and broader particle sizes than when the polymerization is carried out in semibatch. The evolution of the particle size and the final particle size distribution indicate that the stability of the latexes is limited and, hence, aggregation phenomena occurred in both processes. In particular, the evolution of the particle size distribution (PSD) in the semibatch process indicates nucleation, growth, and aggregation occurring simultaneously that produced a bimodal particle size. When the diene monomer was changed to diallyl terephthalate (DATP), the semibatch polymerization yielded smaller particles and narrow distribution without any indication of aggregation. The partial substitution of the dithiol by a trithiol monomer that is substantially more water insoluble affected nucleation of the particles, yielding for both systems smaller particles. The polythioether polymers synthesized present low glass transition temperatures (~ −30/−40°C) and those containing the therephthalate yield crystalline films. The potential application of the polymers as pressure sensitive adhesives (PSAs) was preliminarily assessed.

POSS increased the toughness and mechanical modulus of acrylic copolymers by increasing the entanglement density

Polyhedral oligomeric silsesquioxane copolymerized with butyl acrylate (BA), methyl methacrylate (MMA), and acrylic acid (AA) induced ca. twofold increase of fracture energy Γ and of Young's modulus E of cast films at only 1 wt% content. The copolymer of composition BA:MMA:AA:POSS 56:41:2:1 mol% was synthesized in situ by seeded semi-batch emulsion polymerization. Films cast from the corresponding emulsions were optically transparent and transmission electron microscopy (TEM) showed that POSS was predominantly dispersed at nearly single unit in the acrylic matrix. Shear rheology and time-temperature superposition (TTS) analysis demonstrated an entangled state with the absence of terminal regime, and POSS increased the segmental relaxation time τe and the rubbery modulus Ge, hence the free volume and packing length p decreased, relative to the neat copolymer. The efficient dispersion of POSS and its size smaller than the virtual tube diameter suggests that POSS is intercalating the molecular mesh. Therefore, the entanglement density increased and induced an increase of tensile mechanical modulus. The mesh intercalation by POSS means that it did not act as stress concentrator and consequently the critical fracture strain ε* and the fracture energy Γ also increased. These results evidenced the topological constraints imposed by the bulky POSS to hinder chains past each other thus inducing an increase of entanglement density and this manifested in simultaneous mechanical reinforcement and resistance to fracture.

Towards improved performance of waterborne polymer dispersions through creation of dense ionic interparticle network within their films

To overcome the main challenge of low performance of the waterborne polymer coatings due to the particulate nature of the polymer dispersions and the complex film formation process, in this work we implemented the strategy of ionic complexation between oppositely charged waterborne polymer particles. For that aim, doubled charged ionic monomers ithaconic acid (IA) and styrenic 1,4-diazabicyclo[2.2.2]octane (DABCO) were used to densely functionalize (meth)acrylic film forming polymer particles, synthesized by seeded semi-batch emulsion polymerization to produce high solids content anionically and cationically charged polymer dispersions, respectively. The main advantage of the double charges in the selected ionic monomers is that they provide high ionic charge density onto charged particles at lower content of ionic monomers.The blending of these oppositely, densely charged and concentrated dispersions resulted in instantaneous coagulation. To postpone the immediate complexation, water-soluble non-ionic polymeric stabilizing species as steric obstacles around the colloids were employed, which allowed to prepare colloidally stable blends and to prepare ionic complexed films. Certainly, the established ionic complexes between carboxylic acids of IA anionic monomer and quaternary ammonium groups of DABCO units within the films improved substantially the mechanical properties and the water sensitivity of the ionic complexed polymeric films with respect to individual films and the reference blend, in which ionic bonding was prevented by pH control. Moreover, the dense ionic network formed within the film actuated as a strong barrier to the leakage of all the water-soluble species during film immersion in water. Beside simple strategy towards improved performance of waterborne coatings, these results offer further extension of their application potential.

Incorporation of a Coumarate Based Corrosion Inhibitor in Waterborne Polymeric Binders for Corrosion Protection Applications

AbstractThe incorporation of organic corrosion inhibitors into waterborne coatings is optimized in this work. Herein, p‐coumaric acid (4‐hydroxycinnamic acid) is modified by a butyl radical and its effectiveness as an anticorrosive free inhibitor in solution is confirmed by potentiodynamic polarization (PP). The molecule is then successfully incorporated into waterborne polymeric binders by employing different polymerization techniques in dispersed media. Whenever possible, the inhibitor is also blended into the bare latexes to compare the effect of the incorporating method. The anticorrosion performance of the obtained coatings is tested and compared by electrochemical analysis. Promising results are obtained for the coatings produced by semibatch emulsion polymerization even at the low concentration of 1.5 mg of inhibitor g−1 latex. The intact control coating without inhibitor shows an impedance of up to 106 Ω and a phase angle of 72° after 1 h of immersion in the corrosive medium, meanwhile the coating with inhibitor shows higher values, 106.7 Ω and 80°. Active corrosion inhibition is observed in the coating with inhibitor in which a defect has been done, as the impedances drop to 103.9 Ω after 24 h of immersion in the saline solution while in the control scratched coating it drops to 103.6 Ω.

Strategies to incorporate a fluorinated acrylate monomer into polymer particles: from particle morphology to film morphology and anticorrosion properties

Four strategies to incorporate a fluorinated monomer (perfluoro octyl acrylate, POA) into a waterborne polymeric dispersion are investigated. Due to the very low water solubility of the POA monomer, three of the strategies use miniemulsion droplets containing the whole POA monomer in the initial charge. The rest of the comonomers of the formulation (methyl methacrylate, MMA, and n-butyl acrylate, BA) are partially incorporated in the initial miniemulsion or fed to the reactor as a preemulsion. In the fourth strategy, a conventional seeded semibatch emulsion polymerization is carried out using cyclodextrin in the seed and feeding the POA/MMA/BA preemulsion to the reactor. Each process strategy led to a distinct particle morphology and hence a particular film morphology. We found that the strategy that produced core–shell particles with the core composed by pure polyPOA yielded the films that showed the best corrosion protection as measured in salt-spray test (1200 h standing without damage).

Incorporation of Polymer-Grafted Cellulose Nanocrystals into Latex-Based Pressure-Sensitive Adhesives.

While the improvement of water-based adhesives with renewable additives is important as industry shifts toward more sustainable practices, a complete understanding of how the compatibility between additives and polymers affects adhesive performance is currently lacking. To elucidate these links, cellulose nanocrystals (CNCs) were first functionalized via surface-initiated atom-transfer radical polymerization with the hydrophobic polymers poly(butyl acrylate) (PBA) and poly(methyl methacrylate) (PMMA) to facilitate their incorporation into latex-based pressure-sensitive adhesives (PSAs). Next, PBA latexes were synthesized using seeded semibatch emulsion polymerization with unmodified or polymer-grafted CNCs added in situ at a loading of 0.5 or 1 phm (parts per hundred parts of monomer). Viscosity and electron microscopy suggested that the polymer-grafted CNCs were incorporated inside or on the latex particles. PSAs containing any CNC type had one or more improved properties (compared to the no-CNC "base case"); CNCs with a low degree of polymerization (DP) grafts exhibited improved tack (up to 2.5-fold higher) and peel strength (up to 6-fold higher) relative to PSAs with unmodified CNCs. The best performing PSA contained the low DP PMMA-grafted CNCs, which is attributed to the higher glass transition temperature and the higher wettability of the PMMA grafts compared to PBA, and the more uniform dispersion of polymer-grafted CNCs throughout the PSA film. In contrast, PSAs containing CNCs with high DP grafts resulted in reduced tack and peel strength (compared to low DP grafts) due to enhanced CNC aggregation. Unfortunately, all PSAs containing polymer-grafted CNCs exhibited inferior shear strength relative to PSAs with unmodified CNCs (and comparable shear strength to the no-CNC "base case"). Collectively, these results provide guidelines for future optimization of more sustainable latex-based PSAs.

Copolymerization of Styrene with 2-Ethylhexyl Acrylate and 2-Ethylhexyl Methacrylate by Semibatch Emulsion Polymerization Using BlocBuilderMA as Macroinitiator

Copolymerization of Styrene with 2-Ethylhexyl Acrylate and 2-Ethylhexyl Methacrylate by Semibatch Emulsion Polymerization Using BlocBuilderMA as Macroinitiator

Single-Ion Conducting Polymer Nanoparticles as Functional Fillers for Solid Electrolytes in Lithium Metal Batteries

Composite solid electrolytes including inorganic nanoparticles or nanofibers which improve the performance of polymer electrolytes due to their superior mechanical, ionic conductivity, or lithium transference number are actively being researched for applications in lithium metal batteries. However, inorganic nanoparticles present limitations such as tedious surface functionalization and agglomeration issues and poor homogeneity at high concentrations in polymer matrixes. In this work, we report on polymer nanoparticles with a lithium sulfonamide surface functionality (LiPNP) for application as electrolytes in lithium metal batteries. The particles are prepared by semibatch emulsion polymerization, an easily up-scalable technique. LiPNPs are used to prepare two different families of particle-reinforced solid electrolytes. When mixed with poly(ethylene oxide) and lithium bis(trifluoromethane)sulfonimide (LiTFSI/PEO), the particles invoke a significant stiffening effect (E′ > 106 Pa vs 105 Pa at 80 °C) while the membranes retain high ionic conductivity (σ = 6.6 × 10–4 S cm–1). Preliminary testing in LiFePO4 lithium metal cells showed promising performance of the PEO nanocomposite electrolytes. By mixing the particles with propylene carbonate without any additional salt, we obtain true single-ion conducting gel electrolytes, as the lithium sulfonamide surface functionalities are the only sources of lithium ions in the system. The gel electrolytes are mechanically robust (up to G′ = 106 Pa) and show ionic conductivity up to 10–4 S cm–1. Finally, the PC nanocomposite electrolytes were tested in symmetrical lithium cells. Our findings suggest that all-polymer nanoparticles could represent a new building block material for solid-state lithium metal battery applications.

Ambient temperature cross-linkable acrylic latexes: effect of cross-link density, glass transition temperature and application temperature difference on mechanical properties

This study focuses on the mechanical properties of ambient temperature cross-linkable acrylic latex polymers synthesized via the semibatch emulsion polymerization reaction. Various combinations of monomers including common acrylates and diacetone acrylamide (DAAM) were used to prepare functional polymers. DAAM cross-linkable monomer in 0.5, 1, 2, and 3 wt% of the monomers and theoretical glass transition temperatures at 5 °C and 15 °C (as the representative temperatures under the application temperature) were considered in designing different emulsions. Adipic dihydrazide was added to the emulsion as a cross-linking agent at the stoichiometric ratio. The mixtures were then applied on the plates and leave to dry at 25 °C. ATR-FTIR and NMR spectroscopies and dynamic light scattering (DLS) were used to characterize the latexes. DLS results revealed the storage stability of the mixtures composed of the latex and cross-linking agent in one pot even after 2 months. Mechanical performance of dry films was assessed through hardness and abrasion resistance measurements, dynamic mechanical thermal analysis, and stress–strain analysis. Mechanical assessments resulted that the higher DAAM percentage in polymer synthesis does not necessarily lead to mechanical improvement and the difference between ambient temperature and glass transition temperature (Ta–Tg) in the film formation process has more importance than the cross-link density of the dry films in the mechanical performance of the latex films.

High Solids Hydroxy‐TEMPO Mediated Radical Semibatch Emulsion Polymerization of Styrene

AbstractStable polystyrene latexes having controlled molecular weight distribution (MWD) with solids contents up to 40 wt% are obtained using potassium persulfate as initiator with the nitroxides 4‐hydroxy‐2,2,6,6‐tetramethylpiperidine‐N‐oxyl (hydroxy‐TEMPO) and 4‐amino‐2,2,6,6‐tetramethylpiperidine‐N‐oxyl (amino‐TEMPO). Using different concentrations of styrene (St) in the nucleation step, it is possible to create colloidal dispersions with particle size ranging from ≈57 to ≈390 nm, conversions up to ≈96%, nitroxide efficiencies (NEff) up to ≈0.76, and number average molecular weight (Mn) ranging from ≈10 000 to ≈85 000 g mol−1. The effect of the monomer feed rate in the semibatch step is also studied. These polymerizations do not require a separate macroinitiator synthesis, since this is formed in situ during the heating ramp. A mathematical model is used to compare the mechanistic understanding of the system with the experimental results.

Pushing the Limits with Cellulose Nanocrystal Loadings in Latex‐Based Pressure‐Sensitive Adhesive Nanocomposites

AbstractCellulose nanocrystals (CNCs) are a naturally sourced, nontoxic, nanoparticle known to improve tack, peel strength, and shear resistance simultaneously when incorporated into nanocomposite latexes produced for pressure‐sensitive adhesive (PSA) applications. In this study, methods for incorporating CNCs into a butyl acrylate/styrene/acrylic acid (91.5/4.5/4.0 wt%) seeded semibatch emulsion polymerization for the production of PSAs are presented. Past work has revealed a limit of 1.0–2.0 wt% (based on monomer) CNC loadings due to latex instability. In this work, CNC loadings of up to 4.0 wt% in a stable latex with 40 wt% solids are achieved by utilizing all of the available water in the formulation to maximize CNC redispersion. The CNC addition method is studied (i.e., in the seed, in the feed, or partitioned in both) and adhesive performance results indicate that there are no significant benefits to where the CNCs are dispersed in situ during polymerization. However, the quality of the CNC‐water dispersion is pivotal to ensuring latex homogeneity and therefore, adhesive film quality. Though CNCs improved adhesive strength at low concentrations, their enhancing effects are modest when used with a commercially competitive base‐case PSA formulation.