Aqueous Dispersion Polymerization Research Articles

Stability of Aqueous Polymeric Dispersions for Ultra-Thin Coating of Bi-Axially Oriented Polyethylene Terephthalate Films

The stability of polyacrylate and polyester based aqueous dispersions designed for ultrathin coating of extruded plastic films, especially bi-axially oriented polyethylene terephthalate (BOPET), was studied. Also, the effect of the gemini surfactant based defoaming/wetting agent on the properties of the dispersions was examined. The addition of the defoaming/wetting agent resulted in reducing the surface free tension of the polyacrylate and polyester dispersion by 15% and 20%, respectively and the initial foam height by 60% and 15%, respectively. At the same time, the agent addition did not compromise the temperature and pH stability of the dispersions. Such modified dispersion can be utilized for ultrathin coating of plastic film used for packaging, to improve their processability, printability, and metallization.

Direct Synthesis of Polymer Nanotubes by Aqueous Dispersion Polymerization of a Cyclodextrin/Styrene Complex.

A one-step synthesis of nanotubes by RAFT dispersion polymerization of cyclodextrin/styrene (CD/St) complexes directly in water is presented. The resulted amphiphilic PEG-b-PS diblock copolymers self-assemble in situ into nanoparticles with various morphologies. Spheres, worms, lamellae, and nanotubes were controllably obtained. Because of the complexation, the swelling degree of polystyrene (PS) blocks by free St is limited, resulting in limited mobility of PS chains. Consequently, kinetically trapped lamellae and nanotubes were obtained instead of spherical vesicles. During the formation of nanotubes, small vesicles first formed at the ends of the tape-like lamellae, then grew and fused into nanotubes with a limited chain rearrangement. The introduction of a host-guest interaction based on CDs enables the aqueous dispersion polymerization of water-immiscible monomers, and produces kinetically trapped nanostructures, which could be a powerful technique for nanomaterials synthesis.

Direct Synthesis of Polymer Nanotubes by Aqueous Dispersion Polymerization of a Cyclodextrin/Styrene Complex

AbstractA one‐step synthesis of nanotubes by RAFT dispersion polymerization of cyclodextrin/styrene (CD/St) complexes directly in water is presented. The resulted amphiphilic PEG‐b‐PS diblock copolymers self‐assemble in situ into nanoparticles with various morphologies. Spheres, worms, lamellae, and nanotubes were controllably obtained. Because of the complexation, the swelling degree of polystyrene (PS) blocks by free St is limited, resulting in limited mobility of PS chains. Consequently, kinetically trapped lamellae and nanotubes were obtained instead of spherical vesicles. During the formation of nanotubes, small vesicles first formed at the ends of the tape‐like lamellae, then grew and fused into nanotubes with a limited chain rearrangement. The introduction of a host–guest interaction based on CDs enables the aqueous dispersion polymerization of water‐immiscible monomers, and produces kinetically trapped nanostructures, which could be a powerful technique for nanomaterials synthesis.

Temperature-Induced Morphological Transitions of Poly(dimethylacrylamide)–Poly(diacetone acrylamide) Block Copolymer Lamellae Synthesized via Aqueous Polymerization-Induced Self-Assembly

Aqueous dispersion polymerization of diacetone acrylamide (DAAM) by chain extension from a hydrophilic poly(N,N-dimethylacrylamide) (PDMA30) macromolecular chain transfer agent (macro-CTA) to produce PDMA30–PDAAMx block copolymer nano-objects was investigated in detail by systematically varying solids content and degree of polymerization of the core-forming PDAAM, leading to the formation of pure lamellae, mixed lamellae/vesicles, and pure vesicles as revealed by dynamic light scattering (DLS), transmission electron microscopy (TEM), atomic force microscopy (AFM), and scanning electron microscopy (SEM). PDMA30–PDAAMx lamellae were found to span an unprecedented wide space in the morphology phase diagram. Moreover, in situ cross-linking of lamellae via statistical copolymerization of DAAM with an asymmetric cross-linker allyl acrylamide and the effect of cross-linking density on the colloidal and morphological stabilities were studied, representing the first report on in situ cross-linking of lamellae duri...

Stable aqueous dispersion of polymer functionalized graphene sheets from electrochemical exfoliation for anticorrosion application

A green approach of achieving stable aqueous dispersion of graphene by noncovalent functionalization using hydrolyzed styrene-maleic anhydride copolymer has been successfully accomplished. The alkaline solution of hydrolyzed styrene-maleic anhydride copolymer was used as the electrolyte during the electrochemical exfoliation of graphite and simultaneously functionalized the exfoliated graphene sheets. The formation of single-layer graphene was confirmed by X-ray diffraction, atomic force microscopy, and transmission electron microscopy analyses. Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analyses confirm the existence of hydrolyzed styrene-maleic anhydride copolymer on the surface of graphene via noncovalent interaction. The results of electrochemical measurements performed in 3.5 wt% NaCl solution indicated that the addition of well-dispersed hydrolyzed styrene-maleic anhydride copolymer functionalized graphene (SMA-graphene) into waterborne organic silicone resin system remarkably improved anticorrosion performance compared with pure waterborne organic silicone resin coating. This significantly enhanced corrosion protection is mainly due to the longer and circuitous diffusion pathway of the corrosive medium derived from highly dispersed SMA-graphene sheets in the composite coating.

Aqueous Polymer Dispersion Coating Used for Osmotic Pump Tablets: Membrane Property Investigation and IVIVC Evaluation.

The objective of this study was to investigate the fundamental properties of propranolol hydrochloride osmotic pump tablets coated by aqueous polymer dispersion, simultaneously exploring the in vitro and in vivo correlation of the tablet. The physicochemical properties and parameters of aqueous polymer dispersion membranes (SEM, water uptake, and water vapor transmission coefficient) were investigated. In addition, the release behavior and the in vitro release and in vivo absorption profiles of the tablets coated by aqueous polymer dispersion were investigated by comparing with propranolol hydrochloride osmotic pump tablets coated by an organic solvent. Results showed that the similarity factor (f 2) between cellulose acetate-coated tablet and Eudragit-coated tablet was 78.1, and f 2 between cellulose acetate-coated tablet and Kollicoat-coated tablet was 77.6. The linear IVIVC of Eudragit-coated and Kollicoat-coated osmotic pump tablets was determined, which confirmed excellent correlation between the absorption in vivo and the drug release in vitro. Consequently, the membrane coated by aqueous polymer dispersion or organic solvent has similar in vitro release rates of controlled release. Also, compared with organic solvent coating, aqueous polymer dispersion has numerous advantages, such as reduced toxicity and no environmental damage. Therefore, the aqueous polymer dispersion technology has enormous potential as a replacement of organic solvent coating.

Ex vivo skin permeation and penetration of nonivamide from and in vivo skin tolerability of film-forming formulations containing porous silica

AimThe purpose of this study was to evaluate skin permeation and penetration of nonivamide which has been formulated in novel film-forming formulations (FFFs). These formulations aim to prolong the availability of capsaicinoids which are used in long-term treatment of chronic pruritus. MethodsAn oily solution of nonivamide was loaded into porous silica particles which then were suspended in an aqueous dispersion of a sustained release polymer. Permeation and penetration experiments were performed ex vivo with postauricular porcine skin using modified Franz diffusion cells. The penetrated drug amount was assessed ex vivo by skin surface biopsy followed by cryo-sectioning. Furthermore, in vivo skin irritation experiments were performed to compare the potential skin irritation caused by the FFFs to conventionally used semi-solid formulations. ResultsPermeation rates of nonivamide from FFF through the skin are comparable to that from clinically used immediate release formulations. This elucidates the therapeutic safety profile of the novel FFF. Penetration studies confirmed the prolonged drug availability at the site of action. FFFs were found not to irritate the skin of healthy volunteers. ConclusionFFFs with sustained nonivamide penetration represent safe and easy-to-use formulations. They therefore may improve the treatment of chronic pruritus with capsaicinoids by enhancing patient compliance through a sustained release regime.

Preparation of MRI-visible gadolinium methacrylate nanoparticles with low cytotoxicity and high magnetic relaxivity

A new convenient and easy-scalable one-step synthetic strategy to achieve metal-containing polymer nanoparticles for applications as magnetic resonance imaging contrast agent is reported. In this study, a novel contrast agent based on poly(gadolinium methacrylate) (poly(Gd(MAA)3)) nanoparticles was prepared by one-step aqueous dispersion polymerization of gadolinium methacrylate monomer (Gd(MAA)3), whereby stable particles were obtained due to the association of GdIII with the polymer carboxylate anions, which provided latent crosslinking of the polymer nanoparticles without the addition of further crosslinking reagents. The morphology and final composition of the corresponding nanoparticles was thoroughly characterized and their cytotoxicity as well as their potential use in MRI was evaluated in vitro on HEK 293T cells by using the CCK-8 assay. The presented results demonstrated, that the poly(Gd(MAA)3) nanoparticles had a spherical morphology with mesoporous substructure, a sufficiently low cytotoxicity and an exceptionally high longitudinal relaxivity of r1 = 12.613 mM−1 s−1, making these nanoparticles excellent candidates for in vivo imaging systems. Herein described poly(Gd(MAA)3) nanoparticles can be valuable in a wide range of biomedical applications with simultaneous bioconjugation, drug delivery as well as imaging capabilities for the early detection of lesions of the brain and the central nervous system, for assessing cardiac function, and for detecting tumors.

Micro encapsulation of Naproxen By Complex Coacervation and Aqueous Colloid Dispersion Part ( 1 )

Naproxen is a non steroidal anti inflammatory and antipyretic drug which has local irritation effect on the stomach, and unpleasant taste, besides bad flowability and light sensitivity .The drug was prepared as microcapsules by complex coacervation method using acacia-gelatin coating materials , and aqueous colloid polymer dispersion method ( ACPD ), using ethyl cellulose and sodium alginate coating materials . The results indicated that microcapsules prepared by 2:1 core:wall ratio is the best for both methods, with an average encapsulation efficiency (75%) and avarege yield (90%) .
 Moreover the drug release was affected mainly by core : ratio ,pH enviroment and method of microencapsulation .
 Key words: Naproxen,Microcapsule , Aqueaus colloid polymer dispersion

A Modified Organic Method for Preparation of Ibuprofen Microcapsules As a Sustained Release Solid Dosage Form

ABSTRACT:Microencapsulation is used to modify and retard drug release as well as to overcome the unpleasant effect(gastrointestinal disturbances) which are associated with repeated and overdose of ibuprofen per day.So that, a newly developed method of microencapsulation was utilized (a modified organic method) through amodification of aqueous colloidal polymer dispersion method using ethylcellulose and sodium alginate coating materials toprepare a sustained release ibuprofen microcapsules.The effect of core : wall ratio on the percent yield and encapsulation efficiency of prepared microcapsules was low, whereas, the release of drug from prepared microcapsules was affected by core: wall ratio ,proportion of coating material andpresence of additive(PEG4000). The 2:1 core : wall ratio was compared (in weight equivalent to 300mg and 600mg drug)with Fenbid® spansule capsule 300mg and Balkaprofen® tablet 600mg respectively. It was found that the release of drugfrom selected ratio and Balkaprofen® tablet was more or less similar(P 0.05) .This sustained release ratio wasencapsulated in weight equivalent to 300mg drug to be administered once daily (600mg) as two capsules as the reference.The capsules were stable within 6 months of storage at room temperature.

Preparation and Evaluation of Atenolol Floating Beads as a Controlled Delivery System

This study aims to encapsulate atenolol within floating alginate-ethylcellulose beads as an oral controlled-release delivery system using aqueous colloidal polymer dispersion (ACPD) method.To optimize drug entrapment efficiency and dissolution behavior of the prepared beads, different parameters of drug: polymer ratio, polymer mixture ratio, and gelling agent concentration were involved.The prepared beads were investigated with respect to their buoyancy, encapsulation efficiency, and dissolution behavior in the media: 0.1 N HCl (pH 1.2), acetate buffer (pH 4.6) and phosphate buffer (pH 6.8). The release kinetics and mechanism of the drug from the prepared beads was investigated.All prepared atenolol beads remained floating on 0.1 N HCl (pH 1.2) medium over 24 hours. Besides, high yield beads of 73.07- 84.31% was obtained. Encapsulation efficiencies were in the range of 33.10 % -79.04 %, and were found to increase as a function of increasing drug: polymer mixture ratio and the gelling agent concentrations.Moreover, atenolol release profile from the beads was affected by the pH of the dissolution medium. It was found to be slowest in 0.1 N HCl (pH 1.2) and fastest in phosphate buffer (pH 6.8).The obtained results suggest that atenolol could be formulated as a controlled release beads, using ethylcellulose and alginate as polymers, using ACPD method.
 Keywords: Floating beads, Atenolol, Controlled Delivery System

Star Architecture Promoting Morphological Transitions during Polymerization-Induced Self-Assembly.

Polymerization-induced self-assembly (PISA) via reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization is an effective method to produce block copolymer nano-objects of various morphologies at high solids. However, current PISA formulations have been limited to linear block copolymers. We report the synthesis of AB2 star block copolymers via RAFT aqueous dispersion polymerization of diacetone acrylamide using a poly(ethylene glycol) methyl ether bearing two chain transfer agents as the difunctional macromolecular chain transfer agent (macro-CTA), which was efficiently synthesized using 2,4,6-trichloro-1,3,5-triazine and activated esters to afford a high end functionality (97%). The star polymer architecture can significantly promote morphological transitions to obtain higher-order morphologies at both lower solids and lower degrees of polymerization of the core-forming block in comparison with its linear counterpart. This work demonstrates that polymer architecture is another important parameter that should be considered when conducting PISA synthesis to obtain complex morphologies.

In Situ Cross-Linking as a Platform for the Synthesis of Triblock Copolymer Vesicles with Diverse Surface Chemistry and Enhanced Stability via RAFT Dispersion Polymerization

An intrinsic dilemma exists for block copolymer vesicles—improving the colloidal stability of vesicles using long/charged stabilizing blocks lowers the propensity of morphological transition to vesicles. Moreover, maintaining the vesicular morphology requires effective structure stabilization via cross-linking. We report a strategy to circumvent this problem and simultaneously improve the colloidal and structural stability of vesicles synthesized via polymerization-induced self-assembly (PISA) using dispersion polymerization. More specifically, in situ cross-linked poly(N,N-dimethylacrylamide)-b-poly(diacetone acrylamide-co-allylacrylamide) diblock copolymer vesicles are first synthesized via aqueous dispersion polymerization, which then serve as a robust platform to initiate the growth of a third hydrophilic block of either neutral poly(N,N-dimethylacrylamide), anionic poly(2-acrylamido-2-methyl-1-propanesulfonic acid sodium salt), or cationic poly(3-acrylamidopropyl trimethylammonium chloride) with reta...

Modular Monomers with Tunable Solubility: Synthesis of Highly Incompatible Block Copolymer Nano-Objects via RAFT Aqueous Dispersion Polymerization.

The high incompatibility of block copolymers consisting of a neutral stabilizer block and a polyelectrolyte core-forming block is exploited to drive phase segregation during polymerization-induced self-assembly (PISA). A modular approach to systematically tune the solubility of ionic monomers/polymers is developed to efficiently identify monomers suitable for aqueous dispersion polymerizations. The strong phase segregation ability of the neutral-polyelectrolyte block copolymers favors the formation of worms over a relatively broad composition range and even at very low solids. These findings suggest that the degree of incompatibility between the stabilizer block and the core-forming block should be considered as one of the key parameters when studying morphological transitions in PISA.

Preparation and Cross-Linking of All-Acrylamide Diblock Copolymer Nano-Objects via Polymerization-Induced Self-Assembly in Aqueous Solution.

Various carboxylic acid-functionalized poly(N,N-dimethylacrylamide) (PDMAC) macromolecular chain transfer agents (macro-CTAs) were chain-extended with diacetone acrylamide (DAAM) by reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion polymerization at 70 °C and 20% w/w solids to produce a series of PDMAC–PDAAM diblock copolymer nano-objects via polymerization-induced self-assembly (PISA). TEM studies indicate that a PDMAC macro-CTA with a mean degree of polymerization (DP) of 68 or higher results in the formation of well-defined spherical nanoparticles with mean diameters ranging from 40 to 150 nm. In contrast, either highly anisotropic worms or polydisperse vesicles are formed when relatively short macro-CTAs (DP = 40–58) are used. A phase diagram was constructed to enable accurate targeting of pure copolymer morphologies. Dynamic light scattering (DLS) and aqueous electrophoresis studies indicated that in most cases these PDMAC–PDAAM nano-objects are surprisingly resistant to changes in either solution pH or temperature. However, PDMAC40–PDAAM99 worms do undergo partial dissociation to form a mixture of relatively short worms and spheres on adjusting the solution pH from pH 2–3 to around pH 9 at 20 °C. Moreover, a change in copolymer morphology from worms to a mixture of short worms and vesicles was observed by DLS and TEM on heating this worm dispersion to 50 °C. Postpolymerization cross-linking of concentrated aqueous dispersions of PDMAC–PDAAM spheres, worms, or vesicles was performed at ambient temperature using adipic acid dihydrazide (ADH), which reacts with the hydrophobic ketone-functionalized PDAAM chains. The formation of hydrazone groups was monitored by FT-IR spectroscopy and afforded covalently stabilized nano-objects that remained intact on exposure to methanol, which is a good solvent for both blocks. Rheological studies indicated that the cross-linked worms formed a stronger gel compared to linear precursor worms.

Effect of Monomer Solubility on the Evolution of Copolymer Morphology during Polymerization-Induced Self-Assembly in Aqueous Solution.

Polymerization-induced self-assembly (PISA) has become a widely used technique for the rational design of diblock copolymer nano-objects in concentrated aqueous solution. Depending on the specific PISA formulation, reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion polymerization typically provides straightforward access to either spheres, worms, or vesicles. In contrast, RAFT aqueous emulsion polymerization formulations often lead to just kinetically-trapped spheres. This limitation is currently not understood, and only a few empirical exceptions have been reported in the literature. In the present work, the effect of monomer solubility on copolymer morphology is explored for an aqueous PISA formulation. Using 2-hydroxybutyl methacrylate (aqueous solubility = 20 g dm–3 at 70 °C) instead of benzyl methacrylate (0.40 g dm–3 at 70 °C) for the core-forming block allows access to an unusual “monkey nut” copolymer morphology over a relatively narrow range of target degrees of polymerization when using a poly(methacrylic acid) RAFT agent at pH 5. These new anisotropic nanoparticles have been characterized by transmission electron microscopy, dynamic light scattering, aqueous electrophoresis, shear-induced polarized light imaging (SIPLI), and small-angle X-ray scattering.

Free-Radical Copolymerization Behavior of Plant-Oil-Based Vinyl Monomers and Their Feasibility in Latex Synthesis

Vinyl monomers from soybean, sunflower, linseed, and olive oils were copolymerized with styrene (St), methyl methacrylate (MMA), and vinyl acetate (VAc) to determine the reactivity of biobased monomers in radical copolymerization, as well as their feasibility in emulsion processes for the synthesis of biobased latexes. Radical copolymerization of plant-oil-based monomers is described with the classical Mayo–Lewis equation. Using emulsion (or miniemulsion) polymerization with MMA or VAc, stable aqueous polymer dispersions with latex particles measuring 80–160 nm and containing 3–35 wt % of biobased monomer units were successfully synthesized. The number-average molecular weight of the latex copolymers (20 000–150 000) decreases by increasing the degree of unsaturation in monomers and their content in the reaction feed. The presence of plant-oil-based fragments changes the Tg of resulting copolymers from 105 to 79 °C in copolymerization with MMA and from 30 to 11 °C in copolymerization with Vac. As a result, biobased units provide considerable flexibility (elongation at break of about 250%) and improve the toughness of the normally rigid and brittle poly(MMA). Even a small amount (2–5%) of biobased fragments incorporated into the structure of poly(VAc) significantly improves water resistance and provides hydrophobicity to the resulting polymer latex films. The obtained results clearly indicate that the vinyl monomers from plant oils can be considered as good candidates for internal plasticization of polymeric materials through reducing intermolecular interactions in copolymers.

Synthesis of Hydrogen-Bonded Pore-Switchable Cylindrical Vesicles via Visible-Light-Mediated RAFT Room-Temperature Aqueous Dispersion Polymerization

Analogous to cellulose, polymers whose monomer units possess both hydrogen donators and acceptors are generally insoluble in ambient water because of hydrogen bonding (HB). Herein we present stimuli-responsive long aqueous cylindrical vesicles (nanotubes) synthesized directly using HB-driven polymerization-induced self-assembly (PISA) under visible-light-mediated RAFT aqueous dispersion polymerization at 25 °C. The PISA undergoes an unprecedented film/silk-to-ribbon-to-vesicle transition and films/silks/ribbons formed at low DPs (∼25-85) of core-forming block in free-flowing aqueous solution. Pore-switchable nanotubes are synthesized by electrostatic repulsive perturbation of the HB association in anisotropic vesicular membranes via inserting minor ionized monomer units into the core-forming block. These nanotubes are synthesized at >35% solids, and tubular membranes are more sensitive than spherical counterparts in response to aqueous surroundings. This facile, robust, and general strategy paves a new avenue toward scale-up production of advanced intelligent nanomaterials.

Microstructure, local dynamics, and flow behavior of colloidal suspensions with weak attractive interactions.

We present a comprehensive micro- and macrorheological study of the effect of weak depletion attraction (Ψdep ≈ 1–10 kBT) on dense colloidal suspensions stabilized by short-range repulsive interactions. We used aqueous polymer dispersions as model system and demonstrated the unique capabilities of multiple particle tracking (MPT) to disclose structural changes in such technically important systems exhibiting many characteristic features of hard sphere systems. Below the hard sphere freezing point ϕc, viscosity increases monotonically with increasing Ψdep due to the transition from a fluid to a fluid/crystalline and finally to a gel state. Above ϕc, increasing attraction strength first results in a viscosity reduction corresponding to the formation of large, permeable crystals and then in a viscosity increase when a network of dense, small crystals forms. The fraction of the fluid and crystal phase, particle concentration in each phase as well as the modulus of the micro-crystals are obtained, the latter decreases with Ψdep. Above the colloidal glass transition strong heterogeneities and different local particle mobility in the repulsive and attractive arrested states are found. Particles are trapped in the cage of neighboring particles rather than in an attractive potential well. The intermediate ergodic state exhibits uniform tracer diffusivity.

Crosslinked 1,2,4-triazolium-type poly(ionic liquid) nanoparticles

In this work we studied covalently crosslinked poly(ionic liquid) nanoparticles synthesized via aqueous dispersion polymerization of 1,2,4-triazolium ionic liquid monomers in the presence of a dication crosslinker. Compared to their non-crosslinked counterparts, the nanoparticles showed improved structural integrity in organic media. Assisted by cryogenic electron microscopy, these nanoparticles were analyzed in detail and found to present vastly diverse shapes and highly ordered inner mesostructures. Upon altering the length of the alkyl substituents on the triazolium cation from dodecyl to tetradecyl and hexadecyl, a shape transformation from elongated “nanoworms” to a mixture of “onion-like” and “wasp-like” nanoparticles was observed. Additionally, the size variation of these colloidal nanoparticles was investigated systematically by polymerizations at different concentrations of monomer, external added salt and crosslinking agent. Finally, the crosslinked poly(ionic liquid) nanoparticles were able to readily disperse multi-walled carbon nanotubes in water and organic media.