Starved Feed Emulsion Polymerization Research Articles

Polymer/C.I. Pigment Red 170 hybrid latexes prepared by RAFT-mediated surfactant-free emulsion polymerization

By using organic pigment-based ink-jet inks, the digital ink-jet printing of textiles is one kind of environmentally friendly technology for cleaner dyeing. Due to the shortcomings of easy agglomeration and poor water dispersion stability of organic nanoparticles, however, the encapsulation and dispersion of organic pigment nanoparticles are also hot and difficult research problems. In this work, we report the reversible addition-fragmentation chain transfer (RAFT) polymerization technology was used to synthesize random copolymer of 2-(dimethylamino) ethyl methacrylate (DMAEMA), poly(ethylene glycol) methyl ether methacrylate (PEGA), and methyl methacrylate (MMA) or butyl acrylate (BA) with a trithiocarbonate reactive end-group. These cationic macromolecular RAFT agents (macro-RAFT) with a pH of 5 were subsequently adsorbed at the surface of size-monodisperse colloidal Pigment Red 170 particles. The absorbed macro-RAFT agents were considered to be the living points to mediate the RAFT polymerization of monomers (MMA and BA) by starved feed emulsion polymerization. TEM results shown that the resulting hybrid latexes synthesized in presence of the tri-copolymer macro-RAFT agents resulted in the formation of individually encapsulated pigment particles. In addition, the dynamic light scattering (DLS), zeta potential and stability tests found that the macro-RAFT agent participated in the growing latex stabilization which is the key to obtaining the stable and uniform core-shell hybrid latex. More importantly, the preparation of film-forming copolymer/pigment hybrid latex in this study shown that the high potential of the P(DMAEMA- co -PEGA- co -MMA or BA) macro-RAFT agent for the development of polymer-pigment hybrid latexes which has good application properties. • Cationic and brush-type macro-RAFT agents were synthesized through RAFT polymerization. • Amphiphilic macro-RAFT agent has good adsorption and dispersion properties for the C.I. Pigment Red 170. • The film-forming polymers with lower T g are successfully encapsulated on the surface of pigment. • The encapsulated polymer/pigment hybrid latexes exhibit excellent dispersion stability with freeze-thaw, storage and pH.

Temperature-Induced Coloration and Interface Shell Cross-Linking for the Preparation of Polymer-Based Opal Films.

The formation of colloidal crystals and their use as photonic materials are of high interest for various technologies in the field of sensing applications, as templates, absorber materials, catalysts, and membranes. In this study, core-shell particles consisting of a cross-linked poly(methyl methacrylate) core featuring a (polyacrylonitrile-co-styrene) shell are synthesized by starved-feed emulsion polymerization. The resulting particles are investigated with respect to size and monodispersity, as well as the core-to-shell ratio, by means of dynamic light scattering and transmission electron microscopy. Optimized particle sizes are 218 nm for the cores and 276 nm for the core-shell particles. For the formation of highly ordered and free-standing opal films, the particles are processed by the melt-shear organization technique. The resulting films show angle-dependent reflection colors, while reflected colors can be tailored by the design of the core-shell particles. As a focus of this work, polyacrylonitrile as part of the copolymer particle shell is advantageously used both for particle opal film stabilization and for tailoring the reflection colors of the opal films. It is shown that the cyclization reactions at the interface of the particles and within the matrix material significantly influence the optical properties of the opal films upon thermal treatment at 240 °C and for different heat holding times. For instance, the change of color can be simply set from red to blue upon defined thermal treatment conditions. Via this convenient protocol, brilliant reflection colors can thus be obtained based on the insights into the structure-property relationships of the underlying particle architectures and interface reactions. The scalable opal films will pave the way to functional colored materials as interesting candidates for a manifold of sensing applications and temperature-responsive polymeric materials.

Preceramic core-shell particles for the preparation of hybrid colloidal crystal films by melt-shear organization and conversion into porous ceramics

In this work, the preparation of porous hybrid particle-based films by core-shell particle design and convenient film preparation is reported. Monodisperse core particles consisting of poly(methyl methacrylate‑co‑allyl methacrylate) (P(MMA‑co‑ALMA)) were synthesized by starved-feed emulsion polymerization followed by the introduction of an initiator-containing monomer (inimer) for subsequent atom transfer radical polymerization (ATRP). The inimer shell allowed for the introduction of allylhydrido polycarbosilane (SMP-10) under ATRP conditions by grafting to the core particles. The functionalization of the prepared core-shell particles was investigated by IR spectroscopy (FTIR), scanning transmission electron microscopy (STEM) and solid-state NMR combined with dynamic nuclear polarization (DNP). The obtained hard core/soft preceramic shell particles were subjected to the melt-shear organization technique, enabling a convenient alignment into a colloidal crystal structure in one single step without the presence of a dispersion medium or solvent for the designed particles. Moreover, the hybrid particle-based films were converted into a porous ceramic structure upon thermal treatment. As a result, freestanding ceramic porous films have been obtained after degradation of the organic template core particles. Noteworthy, the conversion of the matrix material consisting of SMP-10 into the ceramic occurred with preservation of the pristine colloidal crystal template structure. Herein, the first example of core-shell particle preparation by combining different polymerization methodologies and application of the convenient melt-shear organization technique is shown, paving a new way to ceramic materials with tailored morphology and porosity.

A quantitative cryoTEM study on crosslinked nanocapsule morphology in RAFT-based vesicle polymerization

The effect of crosslinking on the morphology of nanocapsules synthesized by vesicle-templated reversible addition-fragmentation chain transfer (RAFT) polymerization was investigated and it was found that although crosslinking increases the fraction of protruded capsules, it is not the origin of the protrusions. Starved-feed emulsion polymerization of methyl methacrylate and tert-butyl acrylate with varying amounts of a range of crosslinkers using a seed of cationic vesicles covered by anionic co-oligomers containing a RAFT functional group, results in several different structures, with true spherical capsules and protruded capsules being the main products under the used reaction conditions. Quantitative cryoTEM studies allowed the counting of the different morphologies and it was found that the final fraction of protruded structures strongly depended on the used crosslinker. In the case of using 10 mol% of ethylene glycol dimethacrylate, ∼90% of the observed structures were protruded capsules, whereas this was only ∼4% in the case of 10 mol% ethylene glycol diacrylate. Finally, tomography showed that the protrusions are an integral part of the polymer shell.

Controlling the Morphology of Film-Forming, Nanocomposite Latexes Containing Layered Double Hydroxide by RAFT-Mediated Emulsion Polymerization

Stable nanocomposite latexes with sandwich, encapsulated, or armored morphology were produced by starved-feed emulsion polymerization in the presence of layered double hydroxide (LDH) nanoparticles. Four statistical copolymers of acrylic acid (AA) and n-butyl acrylate (BA) were adsorbed on the LDH surface, and a film-forming methyl acrylate (MA)/BA (8:2 mass/mass) monomer feed was chosen to facilitate subsequent film formation under ambient conditions. P(AA17.5-co-BA17.5)-R (R = RAFT function) produced the sandwich morphology, while P(AA7.5-co-BA7.5)-R gave the encapsulated morphology, which is remarkable given that nonencapsulated morphologies are normally considered to be the preferred equilibrium structures for nanocomposite particles. Adsorption behavior and monomer conversion profiles were very similar for the two systems, and we tentatively ascribe the morphological difference to the higher density of RAFT functions in the P(AA7.5-co-BA7.5)-R system. A RAFT-free analogue produced armored latexes, highlighting the importance of the RAFT function for promoting growth of the polymer shell from the nanoparticle surface.

Design and Preparation of Highly Filled Water‐Borne Polymer–Gibbsite Nanocomposites

AbstractHighly filled, high solids content, water‐borne polymer–Gibbsite nanocomposites are prepared with Gibbsite contents as high as 35 wt%. The polymer–Gibbsite nanocomposites are synthesised via conventional starved feed emulsion polymerization using negatively charged butyl acrylate‐co‐acrylic acid oligomers, which functioned as electrosteric stabilizers for the initial platelets and the subsequently formed latex particles. A simple mathematical model describing the amount of cooligomer required for the colloidal stability of the initial Gibbsite platelets and the subsequently formed particles was derived. This model was used to determine the reaction conditions required for obtaining colloidally stable nanocomposites with a targeted filler content. Cryogenic transmission electron microscopy characterization of the resulting nanocomposites with filler contents up to 20 wt% revealed fully encapsulated Gibbsite platelets and a mixed morphology of “muffin‐like” and encapsulated particles was obtained at higher filler contents.

Single-source macroporous hybrid materials by melt-shear organization of core–shell particles

The preparation of porous materials is an interesting field for a huge variety of potential applications. Herein we report an efficient and convenient strategy for the creation of inverse colloidal crystal structures based on soft core/shell polymer particle templating. This single-source strategy is based on starved-feed emulsion polymerization of hybrid core/shell particles consisting of a poly(methyl methacrylate-co-allyl methacrylate) (P(MMA-co-ALMA)) core and a poly(ethyl acrylate-co-(3-methacryloxypropyl-trimethoxysilane)) (PEA-co-PMEMO) shell. The resulting monodisperse particles are analyzed with respect to their size and distribution by transmission electron microscopy (TEM) and dynamic light scattering (DLS) measurements. The hybrid monodisperse core/shell particles can be aligned to a colloidal crystal by using the convenient melt-shear organization technique. As a result, free-standing and crack-free hybrid polymer colloidal crystal films are accessible without the need of any solvent or dispersion medium. The processing step is investigated regarding different parameters comprising temperature and pressure for the influence on the colloidal crystal film formation. Furthermore, resulting core/shell ratio is tailored by starved-feed emulsion polymerization conditions, since the ratio affects the quality of the porous structure after thermal treatment of colloidal crystal films. The incorporation of alkoxysilane-containing monomers offers a unique crosslinking strategy that yields mechanically robust and thermally stable films. Due to the increased stability, a removal of PMMA cores is possible by thermal treatment of the templating colloidal crystal films leading to almost isoporous free-standing hybrid materials as determined by thermogravimetric analysis (TGA) and scanning electron microscopy (SEM).

Synthesis of Breathing Metallopolymer Hollow Spheres for Redox-Controlled Release.

A convenient synthetic approach for the preparation of uniform metallopolymer-containing hollow spheres based on 2-(methacryloyloxy)ethyl ferrocenecarboxylate (FcMA) as monomer by sequential starved feed emulsion polymerization is described. Core/shell particles consisting of a noncrosslinked poly(methyl methacrylate) core and a slightly crosslinked ferrocene-containing shell allows for the simple dissolution of core material and, thus, monodisperse metallopolymer hollow spheres are obtained. Since PFcMA is incorporated in the particle shell, herein investigated hollow spheres can be addressed by external triggers, i.e., solvent variation and redox chemistry in order to change the particle swelling capability. PFcMA-containing core/shell particles and hollow spheres are characterized by transmission electron microscope (TEM), scanning electron microscopy, cryogenic TEM, thermogravimetric analysis, and dynamic light scattering in terms of size, size distribution, hollow sphere character, redox-responsiveness, and composition. Moreover, the general suitability of prepared stimulus-responsive nanocapsules for the use in catch-release systems is demonstrated by loading the nanocapsules with malachite green as model payload followed by release studies.

Synthesis of Polymer/Silica Hybrid Latexes by Surfactant-Free RAFT-Mediated Emulsion Polymerization

The reversible addition–fragmentation chain transfer (RAFT) polymerization technique was used to synthesize random copolymers of poly(ethylene glycol) methyl ether acrylate) (PEGA) and n-butyl acrylate (BA) and terpolymers of acrylic acid (AA), PEGA and BA with a trithiocarbonate reactive end-group. These macromolecular RAFT agents (macro-RAFTs) were subsequently adsorbed at the surface of size-monodisperse colloidal silica particles with diameters varying between 40 and 450 nm. Adsorption isotherms for both macro-RAFTs could be well fitted to the Langmuir adsorption model, the AA-based macro-RAFT agent showing however a lower maximum adsorption. The adsorbed macro-RAFT agents were subsequently chain extended with a mixture of methyl methacrylate (MMA) and BA by starved feed emulsion polymerization. Cryo-TEM analysis of the resulting hybrid latexes synthesized in the presence of the P(AA-co-PEGA-co-BA) terpolymers resulted in multipod-like particles while the P(PEGA-co-BA) copolymers showed the formation ...

Controlled Synthesis of Polymeric Nanocapsules by RAFT-Based Vesicle Templating

Polymeric nanocapsules were synthesized by encapsulating extruded vesicles of dimethyldioctadecyl ammonium bromide (DODAB) using a reversible addition-fragmentation chain transfer (RAFT)-based encapsulation approach. Random copolymers containing acrylic acid and butyl acrylate units were first synthesized by RAFT in solution using dibenzyl trithiocarbonate (DBTTC) as the RAFT agent. These anionic copolymer chains were subsequently adsorbed onto the surface of cationic DODAB vesicles and then chain extended to form a polymeric shell by starved feed emulsion polymerization. Cryogenic transmission electron microscopy (cryo-TEM) characterizations demonstrate the successful formation of nanocapsules.

Cross-linked latex particles grafted with polyisoprene as model rubber-compatible fillers

Model filler particles were obtained by grafting polyisoprene (PIP) chains onto spherical latex particles of polystyrene cross-linked with 12 mol% divinylbenzene. These particles, with a narrow size distribution and a diameter of ca. 400 nm, were synthesized by emulsifier-free starved-feed emulsion polymerization. Acetyl coupling sites were introduced randomly at either low (5 mol%) or high (30 mol%) target substitution levels on the latex particles by Friedel–Crafts acylation with acetyl chloride and AlCl 3 in nitrobenzene. ‘Living’ polyisoprenyllithium chains, generated from isoprene and sec-butyllithium ( sec-BuLi), were then coupled with the acetylated particles. The PIP side chains had a high 1,4-polyisoprene microstructure content and a number-average molecular weight ( M n) of either 1.5 × 10 3 (1.5 K), 5 × 10 3 (5 K), or 3 × 10 4 (30 K). The PIP content of the grafted particles was determined from the yield of isolated particles and by 1H NMR spectroscopy analysis. The grafted latex particles were blended in solution with linear polyisoprene ( M n = 3.95 × 10 5, 395 K). The influence of the filler–matrix interactions on the rheological behavior of the blends was determined by dynamic mechanical analysis for the different filler blends. Increases in complex viscosity and storage modulus, and decreased damping factors were observed in all cases relatively to the pure matrix polymer. The enhancements, decreasing in the order 30 mol% > 5 mol% acetylation, and with the grafted PIP chain length as 30 K > 5 K ≈ 1.5 K, are deemed to reflect the extent of interactions between the filler particles and the polymer matrix.

Polymer Encapsulated Gibbsite Nanoparticles: Efficient Preparation of Anisotropic Composite Latex Particles by RAFT-Based Starved Feed Emulsion Polymerization

Anisotropic polymer-inorganic composite latex particles were synthesized by using a RAFT-based encapsulation approach on cationic gibbsite platelets. By using the RAFT agent dibenzyl trithiocarbonate, a series of amphipatic living random RAFT copolymers with different combinations of acrylic acid and butyl acrylate units were synthesized. These RAFT copolymers were used as living stabilizers for the gibbsite platelets and chain extended to form a polymeric shell by starved feed emulsion polymerization. Cryo-TEM characterization of the resulting composite latexes demonstrates the formation of anisotropic composite latex particles with mostly one platelet per particle. Monomer feed composition, chain length, and hydrophilic-lipophilic balance of the RAFT copolymer were found to be important factors for the overall efficiency of the encapsulation. Good control over platelet orientation and high encapsulation efficiency were achieved via this route.

Control of Surfactant Level in Starve Fed Emulsion Polymerization: 4. Mathematical Model and Experimental Test

In emulsion polymerization processes it is important to control the surfactant level to avoid secondary nucleation (too much surfactant) and coagulation (too little). Seeded emulsion polymerizations are especially sensitive since the buffering effect of micellar soap is absent and the surfactant concentration is generally low. Surface tension measurements were employed to monitor the instantaneous free surfactant concentration. A previously developed Langmuir site adsorption model was employed to relate surface tension to surfactant concentration from first principles. This model describes the partition of added sodium dodecylbenzenesulfonate (SDBS) and mobilein situsurfactant between the aqueous phase and the particle surface in the presence of anchored sulfate groups. High solids contents in typical synthetic reactions result in significant contributions from thein situsurfactant and anchored groups. In a model MMA/BA latex, the agreement between observed and calculated surface tension was ∼1 dyn/cm, enabling design control of starve fed emulsion polymerization. When the surface tension was maintained at 45–57 dyn/cm, the process successfully generated 500 nm to 3 μm monodisperse particles.

Polymer-supported reagents as aids in controlled degradation of polymers containing ozonides in the main chain to give telechelic oligomers

The work-up of ozonides derived from the ozonolysis of methacrylate copolymers containing main chain unsaturation has been studied. We have used: periodate supported on Amberlyst A26 (SPIR) (a supported oxidizing agent); polystyrene-supported diphenyl phosphine (SPR) (a mild supported reducing agent) and borohydride supported on Amberlyst A26 (BER) (a more powerful supported reducing agent). Poly(butyl methacrylate-cobutadiene)s were synthesized by starve fed emulsion polymerization. These materials, and the homopolymer, poly(butyl methacrylate), were then ozonized at different temperatures and worked up with each of the reagents listed above. The differing work-ups generated telechelic oligomers in good yield (99%+). Changes in molecular weight with ozonization temperature were observed. Aldehyde end-groups were detected by 1H- and 13C-NMR. Hydroxyl end-groups were observed by FTIR and 13C-NMR spectroscopy. The presence of hydroxyl groups was also further confirmed by forming the tosylate. Carboxyl groups were observed by FTIR and 13C-NMR and quantified by titration. SPR-generated oligomers had approximately 80% of the chain-ends Adehyde functional, BER and SPIR gave oligomers with 99+% hydroxyl and carboxyl functionality, respectively.

Control of Surfactant Level in Starve Fed Emulsion Polymerization: 3. Langmuir Site Adsorption Model for Competitive Adsorption of in Situ and Added Surfactants in the Presence of Anchored Groups

In emulsion polymerization processes it is important to control the surfactant level to avoid secondary nucleation (too much surfactant) and coagulation (too little). Persulfate initiators generate two types of surface active sulfate-containing species; anchored sulfate groups (10-20%) and mobile in situ surfactant (ISS; 50-70%). This paper examines the significance of the competition between these two species and an added surfactant, sodium dodecylbenzene sulfonate (SDBS). SDBS soap titrations were performed on five uncleaned methyl methacrylate/butyl acrylate latexes with particle sizes from 500 nm to 3.25 μm at volume fractions from 1 to 30%. Not surprisingly, traditional Langmuir adsorption analyses were unsatisfactory, even after correction for finite volume fraction of solids. We develop a Langmuir site adsorption model to describe the competitive adsorption of ISS and SDBS in the presence of anchored sites and fit the surface tension data from 84 data points to obtain three parameters: the adsorption equilibrium constants for SDBS ( K s = 760 ± 30 liter mol -1) and ISS ( K 1 = 50 ± 12 liter mol -1) and the limiting area per molecule (APM = 0.37 ± 0.01 nm 2). These parameters are quite consistent with literature values determined in noncompetitive situations. The anchored groups were most significant on smaller particles, and the mobile ISS adsorption was most significant on smaller particles at high volume fraction. The relatively weak attraction of the ISS to the particle surface is due to its low molecular weight (∼400 Da per sulfate group) and results in desorption upon latex dilution.

Emulsion polymerization of styrene in the presence of carbohydrate-based amphiphiles

Novel amphiphilic N-alkyl-, N-decenyl-, and N-alkyl-N'-methyl-semicarbazones of maltose and maltotriose with CnH2n+1 alkyl chains and n=8,9,10,11,12,16 were applied as emulsifiers in styrene emulsion polymerization. Surfactant properties, emulsion polymerization, and rheology were examined as a function of amphiphile molecular architectures. Both critical micelle concentration and average polystyrene particle size increased with decreasing alkyl chain length. Using N-methyl-N-[11-(acryloylamino)-undecanoyl]-glucamine comonomer in a starved feed emulsion polymerization process, it was possible to prepare uniform polystyrene latex with glucamide surface.