Polyester synthesis in aqueous miniemulsion

Biodegradable Polyester Synthesis in Renewed Aqueous Polycondensation Media: The Core of the New Greener Polymer-5B Technology

An innovative enzymatic polycondensation of dicarboxylic acids and dialcohols in aqueous polymerization media using free and immobilized lipases was developed. Various parameters (type of lipases, temperature, pH, stirring type and rate, and monomer carbon chain length) of the polycondensation in an oil-in-water (o/w) miniemulsion (>80% in water) were evaluated. The best results for polycondensation were achieved with an equimolar monomer concentration (0.5 M) of octanedioic acid and 1,8-octanediol in the miniemulsion and water, both at initial pH 5.0 with immobilized Pseudozyma antarctica lipase B (PBLI). The synthesized poly(octamethylene suberate) (POS) in the miniemulsion is characterized by a molecular weight of 7800 g mol−1 and a conversion of 98% at 45 °C after 48 h of polycondensation in batch operation mode. A comparative study of polycondensation using different operation modes (batch and fed-batch), stirring type, and biocatalyst reutilization in the miniemulsion, water, and an organic solvent (cyclohexane:tetrahydrofuran 5:1 v/v) was performed. Regarding the polymer molecular weight and conversion (%), batch operation mode was more appropriate for the synthesis of POS in the miniemulsion and water, and fed-batch operation mode showed better results for polycondensation in the organic solvent. The miniemulsion and water used as polymerization media showed promising potential for enzymatic polycondensation since they presented no enzyme inhibition for high monomer concentrations and excellent POS synthesis reproducibility. The PBLI biocatalyst presented high reutilization capability over seven cycles (conversion > 90%) and high stability equivalent to 72 h at 60 °C on polycondensation in the miniemulsion and water. The benefits of polycondensation in aqueous media using an o/w miniemulsion or water are the origin of the new concept strategy of the green process with a green product that constitutes the core of the new greener polymer-5B technology.

Multisegmented polymers via step-growth and RAFT miniemulsion polymerization

We report a method to efficiently prepare multisegmented polymers via a combination of step-growth (SG) and reversible addition-fragmentation chain transfer (RAFT) polymerization.

Fundamentals of Emulsion Polymerization

A comprehensive overview of the fundamentals of emulsion polymerization and related processes is presented with the object of providing theoretical and practical understanding to researchers considering use of these methods for synthesis of polymer colloids across a wide range of applications. Hence, the overview has been written for a general scientific audience with no prior knowledge assumed. Succinct introductions are given to key topics of background science to assist the reader. Importance is placed on ensuring mechanistic understanding of these complex polymerizations and how the processes can be used to create polymer colloids that have particles with well-defined properties and morphology. Mathematical equations and associated theory are given where they enhance understanding and learning and where they are particularly useful for practical application. Practical guidance also is given for new researchers so that they can begin using the various processes effectively and in ways that avoid common mistakes.

Improved malleability of miniemulsion-based vitrimers through in situ generation of carboxylate surfactants

Vitrimer particles with excellent osmotic and hydrolytic stability were synthesized by miniemulsion polymerization thanks to in situ generation of surfactants.

Biodegradable crosslinked polyesters derived from thiomalic acid and S-nitrosothiol analogues for nitric oxide release

Crosslinked polyesters with Young's moduli similar to that of certain soft biological tissues were prepared via bulk polycondensation of thiomalic acid and 1,8-octanediol alone, and with citric or maleic acid. The copolymers were converted to nitric oxide (NO)-releasing S-nitrosothiol (RSNO) analogues by reaction with tert-butyl nitrite. Additional conjugation steps were avoided by inclusion of the thiolated monomer during the polycondensation to permit thiol conversion to RSNOs. NO release at physiological pH and temperature (pH 7.4, 37 °C) was determined by chemiluminescence-based NO detection. The average total NO content for poly(thiomalic-co-maleic acid-co-1,8-octanediol), poly(thiomalic-co-citric acid-co-1,8-octanediol), and poly(thiomalic acid-co-1,8-octanediol) was 130 ± 39 μmol g-1, 200 ± 35 μmol g-1, and 130 ± 11 μmol g-1, respectively. The antibacterial properties of the S-nitrosated analogues were confirmed against Escherichia coli and Staphylococcus aureus. The hydrolytic degradation products were analyzed by time-of-flight mass spectrometry after a 10-week study to investigate their composition. Tensile mechanical tests were performed on the non-nitrosated polymers as well as their S-nitrosated derivatives and suggested that the materials have appropriate Young's moduli and elongation values for biomedical applications.

Formation of Cross-Linked Films from Immiscible Precursors through Sintering of Vitrimer Nanoparticles

Colloidal dispersions of epoxy-acid vitrimers have been synthesized by miniemulsion polymerization. This versatile strategy enables obtaining stable cross-linked particles, even from initially incompatible precursors, while minimizing hydrolysis of the ester bonds formed during the curing. After drying of the latexes, trans-esterification exchanges occurring at high temperatures through interparticle interfaces induces an efficient sintering into homogeneous cross-linked polymer films.

Effect of Cross-Linking on the Structure and Growth of Polymer Films Prepared by Interfacial Polymerization

Interfacial polymerization of tri- and bifunctional monomers (A3B2 polymerization) is investigated by dissipative particle dynamics to reveal an effect of cross-linking on the reaction kinetics and structure of the growing polymer film. Regardless of the comonomer reactivity and miscibility, the kinetics in an initially bilayer melt passes from the reaction to diffusion control. Within the crossover period, branched macromolecules undergo gelation, which drastically changes the scenario of the polymerization process. Comparison with the previously studied linear interfacial polymerization (Berezkin, A. V.; Kudryavtsev, Y. V. Linear Interfacial Polymerization: Theory and Simulations with Dissipative Particle Dynamics J. Chem. Phys. 2014, 141, 194906) shows similar conversion rates but very different product characteristics. Cross-linked polymer films are markedly heterogeneous in density, their average polymerization degree grows with the comonomer miscibility, and end groups are mostly trapped deeply in the film core. Products of linear interfacial polymerization demonstrate opposite trends as they are spontaneously homogenized by a convective flow of macromolecules expelled from the reactive zone to the film periphery, which we call the reactive extrusion effect and which is hampered in branched polymerization. Influence of the comonomer architecture on the polymer film characteristics could be used in various practical applications of interfacial polymerization, such as fabrication of membranes, micro- and nanocapsules and 3D printing.

Thiol-Michael addition miniemulsion polymerizations: functional nanoparticles and reactive latex films

Thiol-Michael addition polymerization is successfully implemented in a miniemulsion polymerization system.

Light-Mediated Thiol-Ene Polymerization in Miniemulsion: A Fast Route to Semicrystalline Polysulfide Nanoparticles

Historically, the synthesis of aqueous polymer dispersions has focused on radical chain-growth polymerization of low-cost acrylate or styrene emulsions. Herein, we demonstrate the potential of UV-initiated thiol-ene step-growth radical polymerization, departing from a nontransparent difunctional monomer miniemulsion based on ethylene glycol dithiol and diallyl adipate. Performed without solvent and at ambient conditions, the photopolymerization process is energy-effective, environmentally friendly, and ultrafast, leading to full monomer consumption in 2 s, upon irradiating a miniemulsion contained in a 1 mm thick quartz cell microreactor. The resultant linear poly(thioether ester) particles have an average diameter of 130 nm. After water evaporation, they yield a clear elastomeric film combining chemical resistance and high degree of crystallinity (55%).

Synthesis of polyester nanoparticles in miniemulsion obtained by radical ring-opening of BMDO and their potential as biodegradable drug carriers

5,6-Benzo-2-methylene-1,3-dioxepane (BMDO) is used to obtain degradable polymeric nanoparticles via a statistical free-radical copolymerization with MMA and styrene in direct miniemulsion. The nanoparticles are analyzed by means of IR, NMR, DLS, SEM, and TEM. They show excellent cellular uptake and drug delivery properties. The cellular uptake into HeLa cells of particles resulting from copolymerization of BMDO with styrene is drastically enhanced compared to pure polystyrene. As a model drug system, paclitaxel is incorporated in PBMDO particles and its release and the effect on HeLa cells is studied and compared to commercial drug formulations. It is found that a drug delivery system based on PBMDO shows an excellent pharmacological effect.

Miniemulsion polymerization as a versatile tool for the synthesis of functionalized polymers

The miniemulsion technique is a particular case in the family of heterophase polymerizations, which allows the formation of functionalized polymers by polymerization or modification of polymers in stable nanodroplets. We present here an overview of the different polymer syntheses within the miniemulsion droplets as reported in the literature, and of the current trends in the field.

Miniemulsion polymerization and the structure of polymer and hybrid nanoparticles

The miniemulsion process allows the formation of complex structured polymeric nanoparticles and the encapsulation of a solid or liquid, an inorganic or organic, or a hydrophobic or hydrophilic material into a polymer shell. Many different materials, ranging from organic and inorganic pigments, magnetite, or other solid nanoparticles, to hydrophobic and hydrophilic liquids, such as fragrances, drugs, or photoinitators, can be encapsulated. Functionalization of the nanoparticles can also be easily obtained. Compared to polymerization processes in organic solvents, polymerization to obtain polymeric nanoparticles can be performed in environmentally friendly solvents, usually water.

Oil-in-oil emulsions: a unique tool for the formation of polymer nanoparticles

Polymer latex particles are nanofunctional materials with widespread applications including electronics, pharmaceuticals, photonics, cosmetics, and coatings. These materials are typically prepared using waterborne heterogeneous systems such as emulsion, miniemulsion, and suspension polymerization. However, all of these processes are limited to water-stable catalysts and monomers mainly polymerizable via radical polymerization. In this Account, we describe a method to overcome this limitation: nonaqueous emulsions can serve as a versatile tool for the synthesis of new types of polymer nanoparticles. To form these emulsions, we first needed to find two nonmiscible nonpolar/polar aprotic organic solvents. We used solvent mixtures of either DMF or acetonitrile in alkanes and carefully designed amphiphilic block and statistical copolymers, such as polyisoprene- b-poly(methyl methacrylate) (PI- b-PMMA), as additives to stabilize these emulsions. Unlike aqueous emulsions, these new emulsion systems allowed the use of water-sensitive monomers and catalysts. Although polyaddition and polycondensation reactions usually lead to a large number of side products and only to oligomers in the aqueous phase, these new conditions resulted in high-molecular-weight, defect-free polymers. Furthermore, conducting nanoparticles were produced by the iron(III)-induced synthesis of poly(ethylenedioxythiophene) (PEDOT) in an emulsion of acetonitrile in cyclohexane. Because metallocenes are sensitive to nitrile and carbonyl groups, the acetonitrile and DMF emulsions were not suitable for carrying out metallocene-catalyzed olefin polymerization. Instead, we developed a second system, which consists of alkanes dispersed in perfluoroalkanes. In this case, we designed a new amphipolar polymeric emulsifier with fluorous and aliphatic side chains to stabilize the emulsions. Such heterogeneous mixtures facilitated the catalytic polymerization of ethylene or propylene to give spherical nanoparticles of high molecular weight polyolefins. These nonaqueous systems also allow for the combination of different polymerization techniques to obtain complex architectures such as core-shell structures. Previously, such structures primarily used vinylic monomers, which greatly limited the number of polymer combinations. We have demonstrated how nonaqueous emulsions allow the use of a broad variety of hydrolyzable monomers and sensitive catalysts to yield polyester, polyurethane, polyamide, conducting polymers, and polyolefin latex particles in one step under ambient reaction conditions. This nonpolar emulsion strategy dramatically increases the chemical palette of polymers that can form nanoparticles via emulsion polymerization.

Nanoparticles and nanocapsules created using the Ouzo effect: spontaneous emulisification as an alternative to ultrasonic and high-shear devices

The preparation of polymeric particles and capsules by means of spontaneous droplet formation and subsequent polymer precipitation or synthesis is well-known. However, spontaneous emulsification is a phenomenon that has often been erroneously interpreted. This Minireview provides new insights into the preparation of metastable liquid dispersions by homogeneous liquid-liquid nucleation, and is based primarily on a recent study by Vitale and Katz (Langmuir, 2003, 19, 4105-4110). This spontaneous emulsification, which they named the Ouzo effect, occurs upon pouring, into water, a mixture of a totally water-miscible solvent and a hydrophobic oil--and optionally some water--thus generating long-lived small droplets, which are formed even though no surfactant is present. Herein, we review and reinterpret the most relevant publications on the synthesis of a variety of dispersions (pseudolatexes, silicone emulsions, biodegradable polymeric nanocapsules, etc.), which we believe have actually been synthesized using the Ouzo effect. The Ouzo effect may also become a substitute for high-shear techniques, which, to date have only been of limited utility on industrial scales.

Polycondensation of Dicarboxylic Acids and Diols in Water Catalyzed by Surfactant-Combined Catalysts and Successive Chain Extension

Direct dehydration polycondensation of dicarboxylic acids and alcohols was carried out by surfactant-combined Brønsted and Lewis acids. This procedure did not require the removal of water, because the esterification was established at the interface of the emulsion in water. Emulsion polycondensations of 1,9-nonanediol (1,9-ND) and dodecanedioic acid (DDA) (the molar ratio of dicarboxylic acid to diol = 1:1) were carried out at 80 degrees C for 48 h in the presence of 16 wt % DBSA. The corresponding polyester (M(w) = 10.1 x 10(3)) was obtained in an excellent yield (99%). Chain extension in the emulsion was carried out using hexamethylene diisocyanate as the chain extender. SEC measurements indicated the expected shift to higher molecular weight region (M(w) = 11.4 x 10(3), M(w)/M(n) = 3.4) compared with parent polyester (M(w) = 4.5 x 10(3), M(w)/M(n) = 2.2).