Dispersion Copolymerization Research Articles

Complexes of Charged-Neutral Block Copolymers and Surfactants: Process-Dependent Features and Long-Term Stability of Their Aqueous Dispersions

Aqueous dispersions of charged-neutral block copolymers (poly(acrylamide)-b-poly(acrylate)) complexed with an oppositely charged surfactant (dodecyltrimethylammonium) have been prepared by different approaches: the simple mixing of two solutions (MS approach) containing the block copolymer and surfactant, with their respective simple counterions, and dispersion of a freeze-dried complex salt prepared in the absence of simple counterions (CS approach). The CS particles were investigated under different conditions: dispersion of a CS in salt-free water and dispersion of a CS in a dilute salt solution, the latter condition yielding dispersions with the same composition as the MS process. Additionally, aged dispersions (up to 6 months) and dispersed complexes of the polyacrylate homopolymer and dodecyltrimethylammonium surfactant were evaluated. By employing different characterization techniques, it was seen that dispersions prepared by the MS approach display nanometric spherical particles with disordered cores, and poor colloidal stability, partially caused by the absence of surface charge (ζ-potential close to zero). Oppositely, anisometric particles were formed in CS dispersions and were large enough to sustain micellar cubic cores. The CS particles presented long-time colloidal stability, partially due to a net negative surface charge, but the stability varied with the length of the neutral block composing the corona. Our results demonstrate that all dispersed particles are metastable structures, with physicochemical properties strongly dependent on the preparation procedure, thus making these particles suitable for fundamental studies and potential applications where accurate control of their properties, including size, shape, internal structure, and stability, is desired.

Block Copolymer Adsorption on the Surface of Multi-Walled Carbon Nanotubes for Dispersion in N,N Dimethyl Formamide

This research aims to characterize the adsorption morphology of block copolymer dispersants of the styrene-block-4-vinylpyridine family (S4VP) on the surface of multi-walled carbon nanotubes (MWCNT) in a polar organic solvent, N,N-dimethyl formamide (DMF). Good, unagglomerated dispersion is important in several applications such as fabricating CNT nanocomposites in a polymer film for electronic or optical devices. Small-angle neutron scattering (SANS) measurements, using the contrast variation (CV) method, are used to evaluate the density and extension of the polymer chains adsorbed on the nanotube surface, which can yield insight into the means of successful dispersion. The results show that the block copolymers adsorb onto the MWCNT surface as a continuous coverage of low polymer concentration. Poly(styrene) (PS) blocks adsorb more tightly, forming a 20 Å layer containing about 6 wt.% PS, whereas poly(4-vinylpyridine) (P4VP) blocks emanate into the solvent, forming a thicker shell (totaling 110 Å in radius) but of very dilute (<1 wt.%) polymer concentration. This indicates strong chain extension. Increasing the PS molecular weight increases the thickness of the adsorbed layer but decreases the overall polymer concentration within it. These results are relevant for the ability of dispersed CNTs to form a strong interface with matrix polymers in composites, due to the extension of the 4VP chains allowing for entanglement with matrix chains. The sparse polymer coverage of the CNT surface may provide sufficient space to form CNT-CNT contacts in processed films and composites, which are important for electrical or thermal conductivity.

One-Step Synthesis of Biphasic, Cavity-forming Polymer Particles via Dispersion Copolymerization of Styrene and Sulfobetaine Methacrylate.

A one-step dispersion copolymerization technique is demonstrated to fabricate biphasic particles as an approach to streamline the production of particles with complex morphology. The model system studies a monomer feed of hydrophobic styrene and hydrophilic, zwitterionic sulfobetaine methacrylate (SBMA) in a water/isopropanol cosolvent mixture. The resulting particles have a core-shell morphology that can be transformed, simply by washing the particles with water, into particles with a single surface opening connected to an interior cavity. Results indicate that particle morphology is dependent on the presence of nanoscopic SBMA-rich aggregates in the initial reaction mixture to act as nucleation sites, forming an SBMA-rich core encased in a styrene-rich shell. Systematic study of the morphology evolution reveals that the difference in monomer solubility profile can be exploited to control compositional drift of the particle composition during copolymerization yielding copolymer with sufficiently different composition to form phase-separated particle morphology. When SBMA is replaced with various ionic comonomers, the cavity-forming morphology is observed when reaction conditions result in low solubility of the comonomer in the cosolvent mixture. Based on these results, design guidelines are developed that may be applied to a variety of systems requiring complex and responsive particles made from chemically distinct comonomer pairings.

Formulation And Evaluation Of Berberine Hydrochloride Film Coated Tablet

The purpose of the present study was to formulate and evaluate Berberine HCl Film coated tablet. Preformulation studies of API were done. The film coated tablets have advantages over conventional oral dosage forms, film coated tablet also influences the release of drug after compression. Film coating also help in making the tablet with good taste masking properties and excellent mechanical strength. It was revealed in the study that cellulosic coating materials were unable to resist the compression forces whereas hydroxypropyl methyl cellulose co-polymers resist the forces. Furthermore, aqueous dispersions of hydroxypropyl methyl cellulose co-polymers showed high flexibility as that of cellulosic materials thereby providing resistance from destructive compressional forces. The Preformulation characteristics were done as per the Pharmacopeial specifications. The drugs and excipients compatibility studies were carried out by FT-IR spectroscopy. Various pre-compressional parameters like bulk density, tapped density, compressibility index and Hausner’s ratio and post-compressional parameters like weight variation, thickness, hardness, friability, disintegration time and drug release were studied. The spectra elucidate that there was no interaction between Drug and excipients. In order to achieve the best optimized product, five different formulations were developed using diluents, binder, glidant, lubricant, and different concentrations of super-disintegrant. The tablets were prepared by using wet granulation method. Optimization was done and it was found that release profile was found to be best with super-disintegrant that is Crospovidone and Enhance DT. Protectab HP-1 coating was done on Berberine HCl tablets. In-vitro release was carried out in medium 6.8 pH Phosphate buffer. The formulation F-5 was showed better drug release and selected as an optimized formulation.

Morphological investigation of SBS modified bitumen by innovative microscopies: AFM and CLSM

Styrene-Butadiene-Styrene (SBS) is one of the most commonly used copolymer in the PMB production. SBS modification results in different material characteristics on the neat bitumen depending on the SBS type and of course the amount of the SBS used in the modification. Within the scope of this study, morphological characterisation of SBS modified samples involving different amount of SBS copolymer (4%, 5% and 6%) were examined by using innovative microscopies as AFM and CLSM. The topographic and phase properties of the PMB samples were obtained by using AFM and the dispersion and interaction of SBS copolymer with the bitumen were interpreted based on the images obtained by CLSM. As a result it was concluded that, the amount of the copolymer used in the modification process directly effects the morphological properties of the final product (PMB).

A Study on Aqueous Dispersing of Carbon Black Nanoparticles Surface-Coated with Styrene Maleic Acid (SMA) Copolymer.

Carbon black (CB) particles tend to aggregate in aqueous solutions, and finding an optimum dispersing condition (e.g., selection of the type of dispersant) is one of the important tasks in related industries. In the present study, three types of styrene maleic acid (SMA) copolymer dispersants were synthesized, labeled respectively 'SMA-1000', 'SMA-2000', and 'SMA-3000', which have 1, 2, and 3 styrene groups in their repeating units. Then, asymmetrical flow field-flow fractionation (AsFlFFF) was employed to measure the particle size distributions of the aqueous CB dispersions. For the particle size analysis of the CB dispersions, dynamic light scattering (DLS) showed relatively lower reproducibility than AsFlFFF. AsFlFFF showed that the use of SMA-3000 yielded a CB dispersion with the most uniform particle size distribution. When the SMA-3000 dispersant was used, the particle size tended to increase after 1 h of milling as the milling time increased, probably due to the re-agglomeration of the particles by excessive milling. The particle size distributions from AsFlFFF were consistent with the colorimetric observations. With the SMA-3000 dispersant, the lowest L∗ value was observed after 1 h of milling. The AsFlFFF and colorimetric analyses suggest that a stable CB dispersion can be obtained by either 3-h of milling with the SMA-2000 or 1-h of milling with the SMA-3000.

Colloidal Aqueous Dispersions of Methyl (meth)Acrylate-Grafted Polyvinyl Alcohol Designed for Thin Film Applications

In this paper, the aqueous copolymer dispersions of methyl (meth)acrylate-grafted poly(vinyl alcohol) are in situ synthesized and studied as a promising platform for the deposition of thin films with advanced applications. A series of dispersions of the varied copolymer structure and composition are obtained at mild reaction conditions by carrying out a redox polymerization at a different monomer-to-PVA ratio and initiator concentration. The obtained colloidal particles are characterized by Fourier transformed infrared spectroscopy, nuclear magnetic resonance, dynamic light scattering, and transmission electron microscopy. The copolymer dispersions are further used for deposition of thin films on silicon substrates. The films are characterized optically through reflectance measurements and non-linear curve fitting. Their suitability for the optical sensing of acetone vapors is confirmed by reflectance measurements before and during their exposure to analyte vapors. The cross sensitivity, sensing repeatability, and recovery of the sensitive films are discussed.

Kinetics of Polymer Network Formation by Nitroxide-Mediated Radical Copolymerization of Styrene/Divinylbenzene in Supercritical Carbon Dioxide

The kinetics of nitroxide-mediated dispersion copolymerization with crosslinking of styrene (STY) and divinylbenzene (DVB) in supercritical carbon dioxide (scCO2) is addressed experimentally. 2,2,6,6-Tetramethylpiperidinyl-1-oxy (TEMPO) and dibenzoyl peroxide (BPO) were used as nitroxide controller and initiator, respectively. A high-pressure cell with lateral sapphire windows at 120 °C and 207 bar was used to carry out the polymerizations. The nitroxide-mediated homopolymerization (NMP) of STY, as well as the conventional radical copolymerization (FRC) of STY/DVB, at the same conditions were also carried out as reference and for comparison purposes. The effect of nitroxide content on polymerization rate, evolution of molecular weight averages, gel fraction, and swelling index was studied.

Design of novel temperature-resistant and salt-tolerant acrylamide-based copolymers by aqueous dispersion polymerization

ABSTRACT Development of polymer-based flooding technology to improve oil recovery efficiency, water dispersion copolymerization of acrylamide, cationic monomer methacryloxyethyltrimethyl ammonium chloride (METAC), and anionic monomer acrylic acid (AA) were carried out in aqueous ammonium sulfate solution with polyvinyl pyrrolidone (PVP) as the stabilizer. The copolymers were characterized by 1H-NMR, FT-IR, TG, and SEM to confirm that they were prepared successfully and exhibited excellent salt-resistant property. Moreover, the effect of the aqueous solution of ammonium sulfate (AS) concentration, stabilizer concentration, and initiator concentration on the viscosity and size were systematically investigated. To further improve the thermal endurance properties of copolymer, hydrophobic monomers with different alkyl chain lengths were added to the above system. The acrylamide-based quadripolymer possessed prominent thermal and salt endurance properties by utilizing the advantages of zwitterionic structure and hydrophobic monomer. With the temperature rising, the viscosity retention could reach 70.2% in the water and 63.8% in the saline. This work had expected to provide a new strategy to design polymers with excellent salinity tolerance and thermal-resistance performances.

Poly(oligoethylene glycol methacrylate) Star‐Shaped Copolymers with Hydroxypropyl Methacrylate Cores

AbstractStar‐shaped copolymers with crosslinked hyperbranched cores, varying in both number and length of the arms, are prepared by the reversible addition‐fragmentation chain transfer (RAFT) polymerization technique. Star synthesis is conducted via a simple, “core‐first” method. Hydroxypropyl methacrylate monomer is used for the formation of the hyperbranched/crosslinked core, with ethylene glycol dimethacrylate used as a bifunctional monomer in the role of the cross‐linker. Two different cross‐linker/chain transfer agent ratios are chosen to manipulate the number of the arms in the final star nanostructure. Oligoethylene glycol methacrylate (OEGMA500) is used as a biocompatible and hydrophilic component for the creation and extension of the arms. Arm length is controlled by the amount of OEGMA monomer used in the second polymerization step. Molecular characterization of the four synthesized stars is achieved via size exclusion chromatography and nuclear magnetic resonance, which provides information regarding the molar mass, dispersity, and composition of each star‐shaped copolymer. Dynamic light scattering (DLS) studies of copolymers in N,N‐dimethyl formamide solutions provide sizes of individual copolymer molecules in the size range of 8–20 nm. Aqueous dispersions of copolymers are investigated by DLS, cryogenic transmission electron microscopy, and atomic force microscopy, which show the formation of spherical aggregates with diameters of 60–350 nm, dependent on the arm number and length of star copolymers. The obtained sizes and size distributions, along with the hydroxyl‐group‐bearing cores, indicate that the star copolymer can be used as potential nanocarriers for drugs or bioimaging agents.

One-pot synthesis of block copolymer dispersant by ICAR ATRP with ppm copper catalyst and the dispersibility on pigment

The controlled / living polymerization mechanisms have advantages on synthesizing the dispersant with defined structures and compositions, while encountering with individual drawbacks in industrial application. Based on the initiators for continuous activator regeneration atom transfer radical polymerization (ICAR ATRP) of oligo(ethylene oxide)methyl ether methacrylate (OEEMA) and glycidyl methacrylate (GMA) monomers, the diblock copolymers POEOMA-b-P(OEOEMA-co-GMA) were prepared. The GMA units were further modified with 3-mercaptopropionic acid (MPA) agent. The polymerization and modification procedure can be readily realized in a one-pot technology with complete monomer conversion (~100%) and high ring-opening efficiency (~100%), as well as low concentration copper catalyst (100 ppm). Using the MPA modified P(OEOEMA-co-GMA) as anchoring block, POEOMA as stabilizing block, the obtained block copolymers can be used as dispersant to disperse and stabilize the pigment yellow 14. The standing experiment, optical microscope (OM) and dynamic light scattering (DLS) measurements reached to a consistent conclusion that the absolute number of carboxyl groups on each chain modulate the dispersibility of the dispersions, rather than the relative content of carboxyl groups. This work provided a feasible one-pot technology to efficient dispersants.

Tuning the Glass Transition Temperature of a Core-Forming Block during Polymerization-Induced Self-Assembly: Statistical Copolymerization of Lauryl Methacrylate with Methyl Methacrylate Provides Access to Spheres, Worms, and Vesicles.

A series of poly(lauryl methacrylate)–poly(methyl methacrylate-stat-lauryl methacrylate) (PLMAx–P(MMA-stat-LMA)y) diblock copolymer nanoparticles were synthesized via RAFT dispersion copolymerization of 90 mol % methyl methacrylate (MMA) with 10 mol % lauryl methacrylate (LMA) in mineral oil by using a poly(lauryl methacrylate) (PLMA) precursor with a mean degree of polymerization (DP) of either 22 or 41. In situ1H NMR studies of the copolymerization kinetics suggested an overall comonomer conversion of 94% within 2.5 h. GPC analysis confirmed a relatively narrow molecular weight distribution (Mw/Mn ≤ 1.35) for each diblock copolymer. Recently, we reported an unexpected morphology constraint when targeting PLMA22–PMMAy nano-objects in mineral oil, with the formation of kinetically trapped spheres being attributed to the relatively high glass transition temperature (Tg) of the PMMA block. Herein we demonstrate that this limitation can be overcome by (i) incorporating 10 mol % LMA into the core-forming block and (ii) performing such syntheses at 115 °C. This new strategy produced well-defined spheres, worms, or vesicles when using the same PLMA22 precursor. Introducing the LMA comonomer not only enhances the mobility of the core-forming copolymer chains by increasing their solvent plasticization but also reduces their effective glass transition temperature to well below the reaction temperature. Copolymer morphologies were initially assigned via transmission electron microscopy (TEM) studies and subsequently confirmed via small-angle X-ray scattering analysis. The thermoresponsive behavior of PLMA22–P(0.9MMA-stat-0.1LMA)113 worms and PLMA22–P(0.9MMA-stat-0.1LMA)228 vesicles was also studied by using dynamic light scattering (DLS) and TEM. The former copolymer underwent a worm-to-sphere transition on heating from 20 to 170 °C while a vesicle-to-worm transition was observed for the latter. Such thermal transitions were irreversible at 0.1% w/w solids but proved to be reversible at 20% w/w solids.

Dispersion polymerization of styrene/acrylonitrile in polyether stabilized by macro-RAFT agents

A series of poly(acrylate polyether)s (RPA) was designed and synthesized by reversible addition-fragmentation chain transfer (RAFT) copolymerization, which were then used as dispersants for the dispersion copolymerization of styrene/acrylonitrile in polyethers in a semicontinuous approach to prepare graft polyether polyol (POP) with high solid content. The effects of structure, dosage, and feed ratio for macro-RAFT agent RPA on the stability, viscosity, and particle size of POP were examined and discussed. The dispersion polymerization process was also characterized by gradient elution polymer chromatography, and the results indicated that RPA was rapidly consumed and block-type stabilizer formed in the initial stage of polymerization. A portion of RPA added with monomer feeding provided better stability for the semicontinuous polymerization process.

Experimental Study on the Rheology and Setting Behavior of Calcium Sulfoaluminate Cement Paste Modified with Styrene-Butadiene Copolymer Dispersion

Experimental Study on the Rheology and Setting Behavior of Calcium Sulfoaluminate Cement Paste Modified with Styrene-Butadiene Copolymer Dispersion

Investigation of the water barrier properties of graft copolymer latex films of acrylate and poly(dimethylsiloxane) macromonomers synthesized by RAFT miniemulsion polymerization

It is challenging to improve the water barrier performance for waterborne protective coating. We synthesized a series of acrylic-polydimethylsiloxane (PDMS) graft copolymer latexes p(MMA-co-BA)-g-PDMS) with high PDMS content of up to 50%, which were considered as bottle-brush polymers using reversible addition-fragmentation chain transfer mediated “macromonomer” miniemulsion copolymerization. We investigated the effect of PDMS side chains on the water barrier performance of graft copolymer latex film derived from these particles and their utilization in anti-corrosion coatings. The water contact angle reaches 117° for films cast from aqueous dispersions of graft copolymers with 50% PDMS, which indicates that their surface is significantly enriched with PDMS. The increase in PDMS content has a highly positive effect on the water barrier performance. Differential scanning calorimeter (DSC) on copolymer films after soaking in water indicates that the high PDMS content (50% PDMS) graft copolymer has only freezing bound water in films. Electrochemical impedance spectra tests showed that the graft copolymer exhibited a significant improvement in corrosion resistance over the control polyacrylate sample without PDMS. Furthermore, transmission electron microscopy observations reveal that the PDMS phase changes from a spherical domain texture to a bicontinuous gyroid texture in the bulk of latex films with the increasing PDMS content, which makes them suitable as waterborne anti-corrosion silicone coatings.

Seeded RAFT Polymerization of Styrene for the Synthesis of Stable Dispersions of Amphiphilic Block Copolymers and Composite Nanoparticles

Seeded RAFT Polymerization of Styrene for the Synthesis of Stable Dispersions of Amphiphilic Block Copolymers and Composite Nanoparticles

Styrene–acrylic acid copolymers as new stabilizers of dispersion RAFT polymerization of butyl acrylate

The RAFT-based copolymers of acrylic acid and styrene may be successfully used as stabilizers of dispersion polymerization of butyl acrylate by providing the formation of stable block copolymer dispersion.

Development and Modeling of a Continuous Dispersion Copolymerization Process in the Presence of a Stabilizing Agent Elaborated in situ

Development and Modeling of a Continuous Dispersion Copolymerization Process in the Presence of a Stabilizing Agent Elaborated in situ

ПОРІВНЯННЯ ПОЛІОЛІВ ЯК КАРБОНІЗУЮЧИХ АГЕНТІВ ВОГНЕЗАХИСНИХ КОМПОЗИЦІЙ ІНТУМЕСЦЕНТНОГО ТИПУ

Purpose. To study the influence of the carbonizing agent structure on the formation of thermal insulating char layer of intumescent system acid donor/polyol and on the fire protection efficiency of the system at high temperatures. Methodology. A fire retardant mixture of an acid donor (phosphates ammonium, urea, melamine)/ polyol was chosen as a model intumescent system. Dispersion of vinyl acetate copolymer with ethylene was used as a polymeric component. The study applied the characteristics of the char layer of the intumescent composition at a certain temperature. The volumetric intumescent coefficient (K, cm3/g), mass of char residue (m, %), structure and density of the char layer are proposed as the main estimated parameters of flame retardant effect. IR spectroscopy was used to identify products of thermolysis of intumescent systems. Determination of fire protection efficiency of intumescent coatings was carried out in a mini-oven under standard fire conditions. Findings. The influence of polyol structure on the formation of thermal insulating char layer of intumescent acid donor/polyol system and the prediction of fire protection efficiency of this system under high temperature conditions has been investigated. It has been shown that under conditions of thermal shock the fire protection efficiency is more dependent on the nucleophilic reactivity of the polyol towards the unsaturated phosphorus atom of the acid donor than on its thermal stability. It has been found that pentaerythritol, dipentaerythritol, starch, dextrin, xylitol and sorbitol are the most effective carbonizing agents, regardless of the structure of the acid donor. It has been proved by infrared spectroscopy that at high temperatures as a result of the decomposition of pentaerythritol one of the reaction products is the aldehydes interacting with pentaerythritol with the formation of oligomeric compounds with a simple ether bond C-O-C. At the same time, pentaerythritol can be considered as a universal source of carbon framework for intumescent flame retardants regardless of the phosphate structure used. Originality. It has been shown that an important factor to increase the fire protection efficiency of intumescent systems is the use of polyols with an increased nucleophilicity in the esterification between polyol and phosphoric acid.Practical value. The optimal polyols as carbonizing agents for formulation of intumescent coatings with enhanced fire protection properties have been determined.

ПОРІВНЯННЯ АМІНІВ ЯК ГАЗОУТВОРЮВАЧІВ ВОГНЕЗАХИСНИХ КОМПОЗИЦІЙ ІНТУМЕСЦЕНТНОГО ТИПУ

Purpose. Study of influence of blowing agents amines structure on the construction processes of thermal insulating char layer of intumescent system ammonium polyphosphate/pentaerythritol/amine and fire protection efficiency of this system at high temperatures. Methodology. A fire retardant mixture of ammonium polyphosphate/pentaerythritol/amine was chosen as a model intumescent system. Dispersion of vinyl acetate copolymer with vinyl ether of versatic acid was used as a polymeric component. A step-by-step study of the characteristics of the char layer of the intumescent composition was applied in the study, consisting in the analysis of the characteristics of the char formed after keeping the intumescent composition samples at a certain temperature between 100 and 800 °C, char residue mass (m, %), structure and density of the formed char layer. The method of infrared spectroscopy was used for identification of products of thermolysis of intumescent systems. Determination of fire protection efficiency of intumescent coatings was carried out in a mini-oven under standard fire conditions. Findings. The influence of the structure of amines blowing agents on the formation of char layer of intumescent system ammonium polyphosphate/pentaerythritol/amine was studied. Physico-chemical parameters of char layer formed during high temperature swelling of intumescent system components with varying amine: urea, melamine, dicyandiamide, guanidine, thiocarbamide, formylthiosemicarbazide, thiosemicarbazide, phenylethylcarbamide have been determined. In the temperature range 200–400 oC for systems with linear amines (urea, thiocarbamide, thiosemicarbazide), there is a rapid formation of insulating layer with intense outgassing (high intumescent coefficients K) and the same rapid its destruction with significant losses of char residue mass (Δm). The presence of melamine, dicyandiamide and guanidine in intumescent system provides constancy of intumescent coefficient at minimal mass loss. Chemical transformations of intumescent systems were studied by the method of infrared spectroscopy when the investigated amines were varied. It was found that linear diamines do not form stable spatially branched phosphamide compounds with phosphates as the basis of a thermostable heat-insulating frame. At the same time in IR spectra of char residue systems with melamine, dicyandiamide and guanidine the absorption bands of P-N-C bonds (1070–1050 cm-1) and P-N (980–950 cm-1) up to 600–700 oC are observed. Fire tests proved that melamine, dicyandiamide and guanidine are blowing agents providing maximum protection of metal against fire and can be used for composition of fire retardants for steel constructions.Originality. It has been proved that amines in intumescent polyphosphate system perform at least two functions: blowing agents by means of thermal destruction to incombustible gases and nucleophilic compound that takes part in char layer formation by aminolysis of electrophilic substrates.Practical value. The optimum amine blowing agents for developing formulations of intumescent coatings with enhanced flame retardant properties have been established.