Showing papers on "Polymerization published in 2010"

Organocatalysis: Opportunities and Challenges for Polymer Synthesis

Abstract: Organocatalysis offers a number of opportunities in polymer synthesis and was among the earliest methods of catalyzing the synthesis of polyesters. In the following Perspective we attempt to highlight the opportunities and challenges in the use of organic molecules as catalysts or initiators for polymerization reactions. The ring-opening polymerization of cyclic monomers is used as a representative polymerization process to illustrate some of the features of organic catalysts and initiators and to compare them to metal-based approaches. The convergence of convenience, functional group tolerance, fast rates, and selectivities will continue to drive innovations in polymerization catalysis, and it is our perspective that organocatalysis will continue to play an important role in these developments.

Stereocontrolled ring-opening polymerization of cyclic esters: synthesis of new polyester microstructures.

Abstract: Synthesis of aliphatic polyesters has been studied intensively due to their biocompatible and biodegradable properties and their potential applications in medical and agricultural fields. There has been particular emphasis over the past decade on the synthesis of discrete, well-characterized complexes that are active polymerization initiators for the ring-opening polymerization (ROP) of lactide (LA) and β-butyrolactone (BBL) to give, respectively, poly(lactide) (PLA) and poly(3-hydroxybutyrate) (PHB). These recent advances in catalyst design have led to a variety of polyester microstructures. This tutorial review focuses on the use of metal-based complexes for the stereoselective ROP of rac-LA and rac-BBL.

Stereocontrolled ring-opening polymerisation of lactide

Abstract: The important advances and current trends in the stereocontrolled ring-opening polymerisation of lactide are discussed in this tutorial review. Microstructures, structural characterisation methods and the properties of stereoregular poly(lactide)s are examined. The application of metal-based catalysts dominates this area although simple anionic polymerisation and organocatalytic routes that demonstrate control of the polymer tacticity are discussed.

Enhanced thermoelectric performance of single-walled carbon nanotubes/polyaniline hybrid nanocomposites.

Abstract: Hybrid nanocomposites containing carbon nanotubes (CNTs) and ordered polyaniline (PANI) have been prepared through an in situ polymerization reaction using a single-walled nanotube (SWNT) as template and aniline as reactant. TEM, SEM, XRD, and Raman analyses show that the polyaniline grew along the surface of CNTs forming an ordered chain structure during the SWNT-directed polymerization process. The SWNT/PANI nanocomposites show both higher electrical conductivity and Seebeck coefficient as compared to pure PANI, which could be attributed to the enhanced carrier mobility in the ordered chain structures of the PANI. The maximum electrical conductivity and Seebeck coefficient of composites reach 1.25 × 104 S m−1 and 40 μV K−1, respectively, and the maximum power factor is up to 2 × 10−5 W m−1 K−2, more than 2 orders of magnitude higher than the pure polyaniline. This study suggests that constructing highly ordered chain structure is a novel and effective way for improving the thermoelectric properties of c...

Hyperbranched Polyglycerols: From the Controlled Synthesis of Biocompatible Polyether Polyols to Multipurpose Applications

Abstract: Dendritic macromolecules with random branch-on-branch topology, termed hyperbranched polymers in the late 1980s, have a decided advantage over symmetrical dendrimers by virtue of typically being accessible in a one-step synthesis. Saving this synthetic effort once had an unfortunate consequence, though: hyperbranching polymerization used to result in a broad distribution of molecular weights (that is, very high polydispersities, often Mw/Mn > 5). By contrast, a typical dendrimer synthesis yields a single molecule (in other words, Mw/Mn = 1.0), albeit by a labor-intensive, multistep process. But 10 years ago, Sunder and colleagues reported the controlled synthesis of well-defined hyperbranched polyglycerol (PG) via ring-opening multibranching polymerization (ROMBP) of glycidol. Since then, hyperbranched and polyfunctional polyethers with controlled molar mass and low polydispersities (Mw/Mn = 1.2−1.9) have been prepared, through various monomer addition protocols, by ROMBP. In this Account, we review the p...

Step-growth polymerization of inorganic nanoparticles.

Abstract: Self-organization of nanoparticles is an efficient strategy for producing nanostructures with complex, hierarchical architectures. The past decade has witnessed great progress in nanoparticle self-assembly, yet the quantitative prediction of the architecture of nanoparticle ensembles and of the kinetics of their formation remains a challenge. We report on the marked similarity between the self-assembly of metal nanoparticles and reaction-controlled step-growth polymerization. The nanoparticles act as multifunctional monomer units, which form reversible, noncovalent bonds at specific bond angles and organize themselves into a colloidal polymer. We show that the kinetics and statistics of step-growth polymerization enable a quantitative prediction of the architecture of linear, branched, and cyclic self-assembled nanostructures; their aggregation numbers and size distribution; and the formation of structural isomers.

Thiol-yne click chemistry: A powerful and versatile methodology for materials synthesis

Abstract: Radical mediated thiol-yne polymerization reactions complement the more well-known thiol-ene radical polymerization processes, with the added advantage of increased functionality. In one system studied, the rate constant for the addition of the thiol to the vinyl sulfide created by the initial reaction of the thiol with the alkyne is three times faster than the initial reaction. When hydrocarbon based dialkynes and dithiols were copolymerized, the resulting thiol-alkyne networks containing only hydrocarbon and sulfide linking groups exhibited refractive index values tunable above 1.65, with the refractive index directly related to the sulfur content. The thiol-yne reaction was also found to be useful in functionalizing thiol-terminated polymer chain ends via sequential Michael thiol-ene addition followed by the thiol-yne reaction: the result is the dual functionalization of the polymer chain end. A thermally responsive polymer hydrogel network was formed when an yne terminated water-soluble homopolymer was polymerized with a tetrafunctional thiol.

Metal-catalyzed immortal ring-opening polymerization of lactones, lactides and cyclic carbonates.

Abstract: This Perspective article summarizes efforts paid in our group to develop efficient metal-based catalysts for the immortal ring-opening polymerization (iROP) of cyclic esters in the presence of large amounts of alcohols (ROH) as chain transfer agents. The catalyst systems reviewed include discrete organometallic complexes based on rare earths, magnesium, calcium and more specifically zinc, as well as simple systems employing metal triflate salts, notably Al(OTf)3, for the (stereo)controlled iROP of lactide (LA), β-butyrolactone (BBL) and trimethylenecarbonate (TMC). Special emphasis is given to systems that allow the use of minute amounts of metal catalysts and large loadings of both monomer and alcohol for the rapid and productive formation of functional polyesters (H–Pol–OR) with controlled molecular features.

Mechanically bonded macromolecules

Abstract: Mechanically bonded macromolecules constitute a class of challenging synthetic targets in polymer science The controllable intramolecular motions of mechanical bonds, in combination with the processability and useful physical and mechanical properties of macromolecules, ultimately ensure their potential for applications in materials science, nanotechnology and medicine This tutorial review describes the syntheses and properties of a library of diverse mechanically bonded macromolecules, which covers (i) main-chain, side-chain, bridged, and pendant oligo/polycatenanes, (ii) main-chain oligo/polyrotaxanes, (iii) poly[c2]daisy chains, and finally (iv) mechanically interlocked dendrimers A variety of highly efficient synthetic protocols—including template-directed assembly, step-growth polymerisation, quantitative conjugation, etc—were employed in the construction of these mechanically interlocked architectures Some of these structures, ie, side-chain polycatenanes and poly[c2]daisy chains, undergo controllable molecular switching in a manner similar to their small molecular counterparts The challenges posed by the syntheses of polycatenanes and polyrotaxanes with high molecular weights are contemplated

Polymer Brushes via Controlled, Surface-Initiated Atom Transfer Radical Polymerization (ATRP) from Graphene Oxide

Abstract: A method for growing polymers directly from the surface of graphene oxide is demonstrated. The technique involves the covalent attachment of an initiator followed by the polymerization of styrene, methyl methacrylate, or butyl acrylate using atom transfer radical polymerization (ATRP). The resulting materials were characterized using a range of techniques and were found to significantly improve the solubility properties of graphene oxide. The surface-grown polymers were saponified from the surface and also characterized. Based on these results, the ATRP reactions were determined to proceed in a controlled manner and were found to leave the structure of the graphene oxide largely intact.

Cyclic polymers: Synthetic strategies and physical properties

Abstract: Syntheses of cyclic polymers including cyclic homo- polymers, cyclic block copolymers, sun-shaped polymers, and tadpole polymers are discussed on the basis of a differentia- tion between synthetic methods and synthetic strategies (e.g., polycondensation, ring-ring equilibration, or ring-expansion polymerization). Furthermore, all synthetic methods are classi- fied as kinetically or thermodynamically controlled reactions. Characteristic properties of cyclic polymers such as smaller hydrodynamic volume, lower melt viscosities, and higher thermostabilities are compared to the properties of their linear counterparts. Furthermore, the nanophase separation of cyclic diblock copolymers is discussed. V C 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 251-284, 2010

Novel polymerization catalysts and hydride clusters from rare-earth metal dialkyls

Abstract: This Review gives an overview on recent progress in the synthesis and chemistry of rare-earth metal dialkyl complexes bearing monoanionic ancillary ligands, with an emphasis on novel polymerization catalysts. These structurally well-defined and highly reactive compounds are prepared either by alkane elimination reactions between trialkyl rare-earth complexes and acidic neutral ligands, or by the metathetical reactions of rare-earth trihalides with the alkali metal salts of the corresponding ligands. On treatment with an appropriate borate compound, the dialkyl complexes are converted into the corresponding cationic monoalkyl species, which serve as excellent catalysts for the polymerization and copolymerization of a variety of olefins to yield a series of new polymer materials that exhibit novel properties. Alternatively, hydrogenation of the dialkyl rare-earth complexes with H(2) affords a new class of rare-earth polyhydride complexes with unique features in terms of both their structure and reactivity.

Compact Biocompatible Quantum Dots via RAFT-Mediated Synthesis of Imidazole-Based Random Copolymer Ligand

Abstract: We present a new class of polymeric ligands for quantum dot (QD) water solubilization to yield biocompatible and derivatizable QDs with compact size (∼10−12 nm diameter), high quantum yields (>50%), excellent stability across a large pH range (pH 5−105), and low nonspecific binding To address the fundamental problem of thiol instability in traditional ligand exchange systems, the polymers here employ a stable multidentate imidazole binding motif to the QD surface The polymers are synthesized via reversible addition−fragmentation chain transfer-mediated polymerization to produce molecular weight controlled monodisperse random copolymers from three types of monomers that feature imidazole groups for QD binding, polyethylene glycol (PEG) groups for water solubilization, and either primary amines or biotin groups for derivatization The polymer architecture can be tuned by the monomer ratios to yield aqueous QDs with targeted surface functionalities By incorporating amino-PEG monomers, we demonstrate cova

Recent advances in ring-opening metathesis polymerization, and application to synthesis of functional materials

Abstract: This article reviews the development of catalysts for ring-opening metathesis polymerization (ROMP), synthesis of polymers bearing amino acids and peptides by ROMP of functionalized norbornenes, formation of aggregates and micelles, and applications of the polymers to medical materials. It also describes the control of monomer unit sequences, that is, living polymerization to synthesize block copolymers, and alternating copolymerization that is achieved on the basis of acid–base interactions.

Synthesis of MWCNTs‐core/thiophene polymer‐sheath composite nanocables by a cationic surfactant‐assisted chemical oxidative polymerization and their structural properties

Abstract: Multi-walled carbon nanotubes (MWCNTs)-core/thiophene polymer-sheath composite nanocables were synthesized by chemical oxidative polymerization of 3,4-ethylenedioxythiophene (EDOT) with oxidant (FeCl3) in the presence of cationic surfactant, deceyltrimethyl ammonium bromide (DTAB). In the polymerization process, DTAB surfactant molecules were adsorbed on the surface of MWCNTs and forms MWCNTs-DTAB soft template. Upon the addition of EDOT and oxidant, the polymerization take place on the surface of MWCNTs and PEDOT is gradually deposited on the surface of MWCNTs. The resulting MWCNTs-PEDOT nanocomposites have the nanocable structure. Nanocomposites were characterized by HRTEM, FE-SEM, XRD, XPS, TGA, FTIR and PL, respectively. The π-π interactions between PEDOT and MWCNTs enhancing the thermal and electrical properties of the nanocomposites with loading of MWCNTs. The temperature dependence conductivity measurements show that the conductivity of the nanocomposite decrease with a decrease of temperature, and conductivity-temperature relationship is well fit by the quasi-one dimensional variable range hopping mode. The mechanism for the formation of composite nanocables was explained on the basis of self- assembly of micelles. The reported self-assembly strategy for the synthesis of PEDOT-coated MWCNTs in micellar medium is a rapid, versatile, potentially scalable, stable, and making it useful for further exploitation in a varies types of applications. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1477–1484, 2010

RAFT synthesis of sterically stabilized methacrylic nanolatexes and vesicles by aqueous dispersion polymerization.

Abstract: Emulsion polymerization is widely used for waterborne coatings. Reducing the latex particle size is known to promote coalescence and hence enhance film formation. However, the synthesis of smaller latexes usually requires additional surfactant, which can compromise the quality of waterborne coatings (e.g. poor adhesion and reduced film quality due to migration of excess surfactant). In principle, reactive surfactants offer a potentially decisive advantage over conventional surfactants in emulsion polymerization because they bind irreversibly to the latex and hence cannot migrate during film formation; this allows defect-free coatings to be produced with reduced moisture sensitivity. Over the last two decades, controlled/living radical polymerization techniques have become powerful tools in polymer synthesis. There are many examples of latex syntheses based on these approaches. For example, nitroxide-mediated living radical polymerization has been used by Charleux, El-Aasser, Okubo, and Georges to mediate the miniemulsion polymerization of n-butyl acrylate and styrene. ATRP has been optimized by Matyjaszewski and Okubo for the (mini)emulsion polymerization of (meth)acrylic and styrene monomers. Reversible addition– fragmentation chain transfer (RAFT) polymerization has been extensively exploited in the context of both emulsion and miniemulsion polymerization by Hawkett, Charleux, El-Aasser, Cunningham, and Zhu. There are also a number of RAFT syntheses conducted under nonaqueous dispersion polymerization conditions. However, as far as we are aware, there are only three examples of the application of controlled/living radical polymerization techniques for latex syntheses by aqueous dispersion polymerization. In each case, a relatively expensive speciality monomer was utilized for the latex core, namely N-isopropylacrylamide or N,N’-diethylacrylamide. This relative lack of research is perhaps surprising, because aqueous dispersion polymerization is conceptually much simpler than aqueous emulsion polymerization since the initial reaction solution is homogeneous in the former case. Presumably, the paucity of experimental data merely reflects the fact that there are relatively few vinyl monomers that are suitable for latex syntheses by aqueous dispersion polymerization. Recently, we reported the use of conventional (nonliving) free radical chemistry for the aqueous dispersion polymerization of a commodity methacrylic monomer, 2hydroxypropyl methacrylate (HPMA). The resulting PHPMA latexes were stabilized by poly(N-vinylpyrrolidone) and the mean particle diameter could be varied from approximately 100 to 1000 nm diameter, with good control over the particle size distribution being achieved in most cases. Herein we explore the RAFT synthesis of sterically stabilized PHPMA nanolatexes of 20 to 100 nm diameter by surfactant-free aqueous dispersion polymerization using a poly(glycerol monomethacrylate)-based chain transfer agent (CTA) as the reactive steric stabilizer. Thus both the latex cores and the steric stabilizer chains of the resulting nanolatexes are highly hydroxylated for this prototype formulation. Moreover, varying the length of the targeted PHPMA chains allows the final size of the sterically stabilized nanolatex particles to be controlled quite precisely (see Scheme 1, Table 1, and the Supporting Information).

Monodisperse Polymer Capsules: Tailoring Size, Shell Thickness, and Hydrophobic Cargo Loading via Emulsion Templating

Abstract: The preparation of monodisperse polymer (polydopamine, PDA) capsules by a one-step interfacial polymerization of dopamine onto dimethyldiethoxysilane (DMDES) emulsion droplets and removal of the DMDES templates with ethanol is reported. The diameters of the PDA capsules can be tailored from 400 nm to 2.4 μm by varying either the DMDES emulsion condensation time or the emulsion concentration used for templating. Further, capsules with defined nanometer-scale shell thicknesses (ranging from ∼10 to 30 nm) can be prepared by adjusting the emulsion concentration. This shell thickness can be increased by repeated interfacial polymerization of dopamine, with three cycles yielding capsules with a shell thickness of up to 140 nm (for a 0.6% v/v suspension). Functional substances, such as organically stabilized magnetic (Fe3O4) nanoparticles, quantum dots (CdSe/CdS), and hydrophobic drugs (thiocoraline), can be preloaded in the emulsion droplets, and following PDA coating and DMDES removal, these materials remain encapsulated in the polymer capsules. All of the unloaded and loaded PDA capsules are monodisperse and do not aggregate. This work provides new avenues for the preparation of polymer capsules with defined size and shell thickness and for the encapsulation of a range of hydrophobic substances. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A Nanocellulose Polypyrrole Composite Based on Microfibrillated Cellulose from Wood

Abstract: It is demonstrated that it is possible to coat the individual fibers of wood-based nanocellulose with polypyrrole using in situ chemical polymerization to obtain an electrically conducting continuous high-surface-area composite. The experimental results indicate that the high surface area of the water dispersed material, to a large extent, is maintained upon normal drying without the use of any solvent exchange. Thus, the employed chemical polymerization of polypyrrole on the microfibrillated cellulose (MFC) nanofibers in the hydrogel gives rise to a composite, the structure of which—unlike that of uncoated MFC paper—does not collapse upon drying. The dry composite has a surface area of ∼90 m2/g and a conductivity of ∼1.5 S/cm, is electrochemically active, and exhibits an ion-exchange capacity for chloride ions of 289 C/g corresponding to a specific capacity of 80 mAh/g. The straightforwardness of the fabrication of the present nanocellulose composites should significantly facilitate industrial manufactur...

Polypropylene/Graphene Oxide Nanocomposites Prepared by In Situ Ziegler−Natta Polymerization

Abstract: This paper reports the first example of preparation of polypropylene/graphene oxide (PP/GO) nanocomposites via in situ Ziegler−Natta polymerization. A Mg/Ti catalyst species was incorporated into GO via surface functional groups including −OH and −COOH, giving a supported catalyst system primarily structured by nanoscale, predominantly single GO sheet. Subsequent propylene polymerization led to the in situ formation of PP matrix, which was accompanied by the nanoscale exfoliation of GO, as well as its gradual dispersion. Morphological examination of the ultimate PP/GO nanocomposites by TEM and SEM techniques revealed effective dispersion in nanoscale of GO in PP matrix. High electrical conductivity was discovered with thus prepared PP/GO nanocomposites; for example, at a GO loading of 4.9 wt %, σc was measured at 0.3 S·m−1.

Method for low temperature bonding and bonded structure

Abstract: A method for bonding at low or room temperature includes steps of surface cleaning and activation by cleaning or etching. The method may also include removing by-products of interface polymerization to prevent a reverse polymerization reaction to allow room temperature chemical bonding of materials such as silicon, silicon nitride and SiO2. The surfaces to be bonded are polished to a high degree of smoothness and planarity. VSE may use reactive ion etching or wet etching to slightly etch the surfaces being bonded. The surface roughness and planarity are not degraded and may be enhanced by the VSE process. The etched surfaces may be rinsed in solutions such as ammonium hydroxide or ammonium fluoride to promote the formation of desired bonding species on the surfaces.