Showing papers on "Copolymer published in 2015"

7.7% Efficient All-Polymer Solar Cells.

Abstract: By controlling the polymer/polymer blend self-organization rate, all-polymer solar cells composed of a high-mobility, crystalline, naphthalene diimide-selenophene copolymer acceptor and a benzodithiophene-thieno[3,4-b]thiophene copolymer donor are achieved with a record 7.7% power conversion efficiency and a record short-circuit current density (18.8 mA cm(-2)).

Photo-PISA: Shedding Light on Polymerization-Induced Self-Assembly

Abstract: Herein we report an aqueous photoinitiated polymerization-induced self-assembly (photo-PISA) for the preparation of a remarkably diverse set of complex polymer nanoparticle morphologies (e.g., spheres, worms, and vesicles) at room temperature. Ultrafast polymerization rates were achieved, with near quantitative monomer conversion within 15 min of visible light irradiation. An important feature of the photo-PISA is that diblock copolymer vesicles can be prepared under mild conditions (room temperature, aqueous medium, visible light), which will be important for the preparation of functional vesicles loaded with biorelated species (e.g., proteins). As a proof of concept, silica nanoparticles and bovine serum albumin (BSA) were encapsulated in situ within vesicles via the photo-PISA process.

Highly Robust Palladium(II) α-Diimine Catalysts for Slow-Chain-Walking Polymerization of Ethylene and Copolymerization with Methyl Acrylate.

Abstract: A series of sterically demanding α-diimine ligands bearing electron-donating and electron-withdrawing substituents were synthesized by an improved synthetic procedure in high yield. Subsequently, the corresponding Pd complexes were prepared and isolated by column chromatography. These Pd complexes demonstrated unique properties in ethylene polymerization, including high thermal stability and high activity, thus generating polyethylene with a high molecular weight and very low branching density. Similar properties were observed for ethylene/methyl acrylate copolymerization. Because of the high molecular weight and low branching density, the generated polyethylene and ethylene/methyl acrylate copolymer were semicrystalline solids. The (co)polymers had unique microstructures originating from the unique slow-chain-walking activity of these Pd complexes.

Polymerization-induced thermal self-assembly (PITSA)

Abstract: Polymerization-induced self-assembly (PISA) is a versatile technique to achieve a wide range of polymeric nanoparticle morphologies. Most previous examples of self-assembled soft nanoparticle synthesis by PISA rely on a growing solvophobic polymer block that leads to changes in nanoparticle architecture during polymerization in a selective solvent. However, synthesis of block copolymers with a growing stimuli-responsive block to form various nanoparticle shapes has yet to be reported. This new concept using thermoresponsive polymers is termed polymerization-induced thermal self-assembly (PITSA). A reversible addition-fragmentation chain transfer (RAFT) polymerization of N-isopropylacrylamide from a hydrophilic chain transfer agent composed of N,N-dimethylacrylamide and acrylic acid was carried out in water above the known lower critical solution temperature (LCST) of poly(N-isopropylacrylamide) (PNIPAm). After reaching a certain chain length, the growing PNIPAm self-assembled, as induced by the LCST, into block copolymer aggregates within which dispersion polymerization continued. To characterize the nanoparticles at ambient temperatures without their dissolution, the particles were crosslinked immediately following polymerization at elevated temperatures via the reaction of the acid groups with a diamine in the presence of a carbodiimide. Size exclusion chromatography was used to evaluate the unimer molecular weight distributions and reaction kinetics. Dynamic light scattering and transmission electron microscopy provided insight into the size and morphologies of the nanoparticles. The resulting block copolymers formed polymeric nanoparticles with a range of morphologies (e.g., micelles, worms, and vesicles), which were a function of the PNIPAm block length.

Guidelines for the Synthesis of Block Copolymer Particles of Various Morphologies by RAFT Dispersion Polymerization

Abstract: This article presents the recent developments of radical dispersion polymerizaton controlled by reversible addition fragmentation chain transfer (RAFT) for the production of block copolymer particles of various morphologies, such as core-shell spheres, worms, or vesicles. It is not meant to be an exhaustive review but it rather provides guidelines for non-specialists. The article is subdivided into eight sections. After a general introduction, the mechanism of polymerization-induced self-assembly (PISA) through RAFT-mediated dispersion polymerization is presented and the different parameters that control the morphology produced are discussed. The next two sections are devoted to the choice of the monomer/solvent pair and the macroRAFT agent. Afterwards, post-polymerization morphological order-to-order transitions (i.e. morphological transitions triggered by extrinsic stimuli) or order-to-disorder transitions (i.e. disassembly of chains) are discussed. Assemblies based on more complex polymer architectures, such as triblock copolymers, are presented next, and finally the possibility to stabilize these structures by crosslinking is reported. The manuscript ends with a short conclusion and an outlook.

Self-assembly concepts for multicompartment nanostructures

Abstract: Compartmentalization is ubiquitous to many biological and artificial systems, be it for the separate storage of incompatible matter or to isolate transport processes. Advancements in the synthesis of sequential block copolymers offer a variety of tools to replicate natural design principles with tailor-made soft matter for the precise spatial separation of functionalities on multiple length scales. Here, we review recent trends in the self-assembly of amphiphilic block copolymers to multicompartment nanostructures (MCNs) under (semi-)dilute conditions, with special emphasis on ABC triblock terpolymers. The intrinsic immiscibility of connected blocks induces short-range repulsion into discrete nano-domains stabilized by a third, soluble block or molecular additive. Polymer blocks can be synthesized from an arsenal of functional monomers directing self-assembly through packing frustration or response to various fields. The mobility in solution further allows the manipulation of self-assembly processes into specific directions by clever choice of environmental conditions. This review focuses on practical concepts that direct self-assembly into predictable nanostructures, while narrowing particle dispersity with respect to size, shape and internal morphology. The growing understanding of underlying self-assembly mechanisms expands the number of experimental concepts providing the means to target and manipulate progressively complex superstructures.

Photoinduced Postsynthetic Polymerization of a Metal–Organic Framework toward a Flexible Stand-Alone Membrane

Abstract: Metal-organic frameworks (MOFs) are a promising class of nanoporous polymeric materials. However, the processing of such fragile crystalline powders into desired shapes for further applications is often difficult. A photoinduced postsynthetic polymerization (PSP) strategy was now employed to covalently link MOF crystals by flexible polymer chains, thus endowing the MOF powders with processability and flexibility. Nanosized UiO-66-NH2 was first functionalized with polymerizable functional groups, and its subsequent copolymerization with monomers was easily induced by UV light under solvent-free and mild conditions. Because of the improved interaction between MOF particles and polymer chains, the resulting stand-alone and elastic MOF-based PSP-derived membranes possess crack-free and uniform structures and outstanding separation capabilities for Cr(VI) ions from water.

Stable Elastomeric Anion Exchange Membranes Based on Quaternary Ammonium-Tethered Polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene Triblock Copolymers

Abstract: A chemically stable and elastomeric triblock copolymer, polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS), was functionalized with various benzyl- and alkyl-substituted quaternary ammonium (QA) groups for anion exchange membrane (AEM) fuel cell applications. Synthetic methods involving transition metal-catalyzed C–H borylation and Suzuki coupling were utilized to incorporate six different QA structures to the polystyrene units of SEBS. Changes in AEM properties as a result of different QA moieties and chemical stability under alkaline conditions were investigated. Anion exchange polymers bearing the trimethylammonium pendants, the smallest QA cation moiety, exhibited the most significant changes in water uptake and block copolymer domain spacing to offer the best ion transport properties. It was demonstrated that incorporating stable cation structures to a polymer backbone comprising solely C–H and C–C bonds resulted in AEM materials with improved long-term alkaline stability. After 4 weeks in...

Photocontrolled Organocatalyzed Living Radical Polymerization Feasible over a Wide Range of Wavelengths

Abstract: Photocontrolled organocatalyzed living radical polymerization was conducted over a wide range of irradiation wavelengths (350–750 nm) The polymerization was induced and controlled at the desired wavelengths by exploiting suitable organic catalysts This system was finely responsive to the irradiation wavelength; the polymerization was instantly switched on and off, and the polymerization rate was sensitively modulated by altering the irradiation wavelength The polymer molecular weight and its distribution (Mw/Mn = 11–14) were well controlled for methacrylate monomers up to fairly high conversions in many cases The monomer scope encompassed various functional methacrylates, and their block copolymers were obtained The feasibility of such a wide range of wavelengths and the fine response to the wavelength are unprecedented features As a unique application of the wavelength-responsive nature of this system, we demonstrated “one-pot” selective regulation of living radical polymerization and another typ

Visible-Light-Controlled Living Radical Polymerization from a Trithiocarbonate Iniferter Mediated by an Organic Photoredox Catalyst

Abstract: Living radical polymerization of acrylates and acrylamides from trithiocarbonate iniferters using a compact fluorescent lamp (CFL) bulb and 10-phenylphenothiazine as an organic photoredox catalyst is reported. With this system, chain growth can be efficiently switched between “on” and “off” in response to visible light. Polymer molar masses increase linearly with conversion, and narrow molar mass distributions are obtained. The excellent fidelity of the trithiocarbonate-iniferter enables the preparation of triblock copolymers from macro-iniferters under the same visible-light mediated protocol, using UV light without a photoredox catalyst or under traditional thermally induced RAFT conditions. We expect that the simplicity and efficiency of this metal-free, visible-light-mediated polymerization will enable the synthesis and modification of a range of materials under mild conditions.

Fluorinated Oligomers and Polymers in Photopolymerization.

Abstract: After an introduction reporting the properties and the applications of fluoropolymers and photopolymerizable derivatives, several basic information on photopolymerization processes are proposed. Then, this review deals with the state of the art on the synthesis of photopolymerizable fluoromonomers and oligomers: most classes of monomers are treated in separate sections (except fluorinated allyl ethers, which are used in copolymerization and are mentioned with the fluoro(meth)acrylics and macromonomers), eventually dividing the descriptions according to the monomer functionality. A short section further is devoted to fluorinated photoinitiators. After the synthesis, this review describes the main issues of the photopolymerization of fluorinated monomers together with the properties and performances obtained. A focus is given on the telechelic monomers and oligomers to insure a suitable crosslinking and on the copolymerization of fluorinated monomers for the surface modification of the obtained materials. Finally, properties and relevant applications (such as coatings and adhesives, optical fibers and flexible displays, polymer Exchange Membrane for Fuel Cell, microfluidic devices, high performance elastomers, and replica moldings) of these fluorinated photopolymerized materials will illustrate this review.

pH‐Responsive Non‐Ionic Diblock Copolymers: Ionization of Carboxylic Acid End‐Groups Induces an Order–Order Morphological Transition

Abstract: A carboxylic acid based reversible additionfragmentation transfer (RAFT) agent is used to prepare gels composed of worm-like diblock copolymers using two non-ionic monomers, glycerol monomethacrylate (GMA) and 2-hydroxypropyl methacrylate (HPMA). Ionization of the carboxylic acid end-group on the PGMA stabilizer block induces a worm-to-sphere transition, which in turn causes immediate degelation. This morphological transition is fully reversible as determined by TEM and rheology studies and occurs because of a subtle change in the packing parameter for the copolymer chains. A control experiment where the methyl ester derivative of the RAFT agent is used to prepare the same diblock copolymer confirms that no pH-responsive behavior occurs in this case. This end-group ionization approach is important for the design of new pH-responsive copolymer nano-objects as, unlike polyacids or polybases, only a minimal amount of added base (or acid) is required to drive the morphological transition.

Development of Lignin Supramolecular Hydrogels with Mechanically Responsive and Self-Healing Properties

Abstract: The development of functional polymers from renewable lignin is attractive due to the depletion of fossil fuel and increasing environmental usage. A series of poly(ethylene glycol) methyl ether methacrylate (PEGMA)-grafted lignin hyperbranched copolymers were prepared by atom transfer radical polymerization (ATRP). The chemical structures, molecular characteristic and thermal properties of these copolymers were evaluated and such copolymers were prepared in a range of molecular weights from 38.7 to 65.0 kDa by adjusting the PEGMA-to-lignin weight ratio. As a result from their hyperbranch architecture, their aqueous solutions were found to form supramolecular hydrogels with a very low critical gelation concentration of 1 wt % copolymers, in the presence of α-cyclodextrin (α-CD). The rheological properties of the supramolecular assemblies were investigated and these hydrogel systems showed tunable mechanical response and excellent self-healing capability. Combined with good biocompatibility, these new types...

Copolymerization of Propylene and Polar Monomers Using Pd/IzQO Catalysts

Abstract: Palladium catalysts bearing imidazo[1,5-a]quinolin-9-olate-1-ylidene (IzQO) ligands polymerize α-olefins while incorporating polar monomers. The steric environment provided by N-heterocyclic-carbene (NHC) enables regioselective insertion of α-olefins and polar monomers, yielding polypropylene, propylene/allyl carboxylate copolymers, and propylene/methyl acrylate copolymer. Known polymerization catalysts bearing NHC-based ligands decompose rapidly, whereas the present catalyst is durable because of structural confinement, wherein the NHC-plane is coplanar to the metal square plane. The present catalyst system enables facile access to a new class of functionalized polyolefins and helps conceive a new fundamental principle for designing NHC-based ligands.

Synthesis and characterization of microcrystalline cellulose‐graft‐poly(methyl methacrylate) copolymers and their application as rubber reinforcements

Abstract: In this study, redox-initiated free radical graft copolymerization of microcrystalline cellulose (MCC) and methyl methacrylate (MMA) has been carried out in aqueous media to develop a novel cellulose-based copolymer. Cerium ammonium nitrate was used as the initiator in the presence of nitric acid. Effects of monomer concentration, initiator concentration, polymerization time, and polymerization temperature on the graft parameters of copolymers were studied. The successful grafting copolymerization between MCC and MMA was validated through attenuated total reflection, wide-angle X-ray diffraction, field-emission scanning electron microscopy, and thermal gravimetric analysis. In comparison to native MCC, the resultant copolymers exhibited enhanced thermal stability and better compatibility with natural rubber, suggesting its potential application as reinforcement material in rubber industry. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42666.

Testing the vesicular morphology to destruction: birth and death of diblock copolymer vesicles prepared via polymerization-induced self-assembly.

Abstract: Small angle X-ray scattering (SAXS), electrospray ionization charge detection mass spectrometry (CD-MS), dynamic light scattering (DLS), and transmission electron microscopy (TEM) are used to characterize poly(glycerol monomethacrylate)55-poly(2-hydroxypropyl methacrylate)x (G55-Hx) vesicles prepared by polymerization-induced self-assembly (PISA) using a reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion polymerization formulation. A G55 chain transfer agent is utilized to prepare a series of G55-Hx diblock copolymers, where the mean degree of polymerization (DP) of the membrane-forming block (x) is varied from 200 to 2000. TEM confirms that vesicles with progressively thicker membranes are produced for x = 200–1000, while SAXS indicates a gradual reduction in mean aggregation number for higher x values, which is consistent with CD-MS studies. Both DLS and SAXS studies indicate minimal change in the overall vesicle diameter between x = 400 and 800. Fitting SAXS patterns to a vesicl...

Hierarchically porous polymers from hyper-cross-linked block polymer precursors

Abstract: We report synthesis of hierarchically porous polymers (HPPs) consisting of micropores and well-defined 3D continuous mesopores by combination of hyper-cross-linking and block polymer self-assembly. Copolymerization of 4-vinylbenzyl chloride (VBzCl) with divinylbenzene (DVB) in the presence of polylactide (PLA) macro-chain-transfer agent produced a cross-linked block polymer precursor PLA-b-P(VBzCl-co-DVB) via reversible addition-fragmentation chain transfer polymerization. A nanoscopic bicontinuous morphology containing PLA and P(VBzCl-co-DVB) microdomains was obtained as a result of polymerization-induced microphase separation. While a basic treatment of the precursor selectively removed PLA to yield a reticulated mesoporous polymer, hyper-cross-linking of the precursor by FeCl3 generated micropores in the P(VBzCl-co-DVB) microdomain via Friedel-Crafts alkylation and simultaneously degraded PLA to produce the HPP containing micropores in the mesoporous framework. The mesopore size of the HPP could be precisely controlled from 6 to 15 nm by controlling the molar mass of PLA. We demonstrate acceleration in adsorption rate in the HPP compared to a hyper-cross-linked microporous polymer.

Living Polymerization of Ethylene and Copolymerization of Ethylene/Methyl Acrylate Using “Sandwich” Diimine Palladium Catalysts

Abstract: Cationic Pd(II) catalysts incorporating bulky 8-p-tolylnaphthyl substituted diimine ligands have been synthesized and investigated for ethylene polymerization and ethylene/methyl acrylate copolymerization. Homopolymerization of ethylene at room temperature resulted in branched polyethylene with narrow Mw/Mn values (ca. 1.1), indicative of a living polymerization. A mechanistic study revealed that the catalyst resting state was an alkyl olefin complex and that the turnover-limiting step was migratory insertion, thus the turnover frequency is independent of ethylene concentration. Copolymerization of ethylene and methyl acrylate (MA) was also achieved. MA incorporation was found to increase linearly with MA concentration, and copolymers with up to 14 mol % MA were prepared. Mechanistic studies revealed that acrylate insertion into a Pd–CH3 bond occurs at −70 °C to yield a four-membered chelate, which isomerizes first to a five-membered chelate and then to a six-membered chelate. Barriers to migratory insert...

Biodegradable and renewable poly(lactide)–lignin composites: synthesis, interface and toughening mechanism

Abstract: Poly(lactide) (PLA)–lignin composites were fabricated by blending lignin-g-rubber-g-poly(D-lactide) copolymer particles and commercial poly(L-lactide) (PLLA) in chloroform. To synthesize the copolymer, a poly(e-caprolactone-co-lactide) (PCLLA) rubbery layer was formed via the lignin-initiated ring opening copolymerization of an e-caprolactone/L-lactide mixture, followed by the formation of poly(D-lactide) (PDLA) outer segments via the polymerization of D-lactide. The PDLA segments may contribute to strong interfacial interactions between lignin-rubber-PDLA and PLLA matrix by stereocomplexation, which was observed using differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR) and wide angle X-ray scattering (WAXS). The quasi-random structure of PCLLA and the formation of the outer PDLA segments were characterized by nuclear magnetic resonance (NMR). A Tg of ∼−36 °C for PCLLA was detected by DSC, which confirms the rubbery character of the synthesized copolymer. The resulting renewable and biodegradable composites exhibited a six-fold increase of elongation at break and a simultaneous improvement in their tensile strength and Young's modulus, though to a lesser extent. Light scattering, WAXS, small angle X-ray scattering (SAXS) and scanning electron microscope (SEM) studies suggested that good lignin dispersion, rubber-initiated crazing and strong filler/matrix interactions due to stereocomplexation are the effective mechanisms behind the excellent mechanical performance of these composites.

Loading of Silica Nanoparticles in Block Copolymer Vesicles during Polymerization-Induced Self-Assembly: Encapsulation Efficiency and Thermally Triggered Release.

Abstract: Poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) diblock copolymer vesicles can be prepared in the form of concentrated aqueous dispersions via polymerization-induced self-assembly (PISA). In the present study, these syntheses are conducted in the presence of varying amounts of silica nanoparticles of approximately 18 nm diameter. This approach leads to encapsulation of up to hundreds of silica nanoparticles per vesicle. Silica has high electron contrast compared to the copolymer which facilitates TEM analysis, and its thermal stability enables quantification of the loading efficiency via thermogravimetric analysis. Encapsulation efficiencies can be calculated using disk centrifuge photosedimentometry, since the vesicle density increases at higher silica loadings while the mean vesicle diameter remains essentially unchanged. Small angle X-ray scattering (SAXS) is used to confirm silica encapsulation, since a structure factor is observed at q ≈ 0.25 nm–1. A new two-population model provid...

Selective Polymerization Catalysis: Controlling the Metal Chain End Group to Prepare Block Copolyesters

Abstract: Selective catalysis is used to prepare block copolyesters by combining ring-opening polymerization of lactones and ring-opening copolymerization of epoxides/anhydrides. By using a dizinc complex with mixtures of up to three different monomers and controlling the chemistry of the Zn–O(polymer chain) it is possible to select for a particular polymerization route and thereby control the composition of block copolyesters.

Alternating Copolymerization of Propylene Oxide with Biorenewable Terpene-Based Cyclic Anhydrides: A Sustainable Route to Aliphatic Polyesters with High Glass Transition Temperatures†

Abstract: The alternating copolymerization of propylene oxide with terpene-based cyclic anhydrides catalyzed by chromium, cobalt, and aluminum salen complexes is reported. The use of the Diels–Alder adduct of α-terpinene and maleic anhydride as the cyclic anhydride comonomer results in amorphous polyesters that exhibit glass transition temperatures (Tg) of up to 109 °C. The polymerization conditions and choice of catalyst have a dramatic impact on the molecular weight distribution, the relative stereochemistry of the diester units along the polymer chain, and ultimately the Tg of the resulting polymer. The aluminum salen complex exhibits exceptional selectivity for copolymerization without transesterification or epimerization side reactions. The resulting polyesters are highly alternating and have high molecular weights and narrow polydispersities.

RAFT Dispersion Polymerization in Nonpolar Media: Polymerization of 3-Phenylpropyl Methacrylate in n-Tetradecane with Poly(stearyl methacrylate) Homopolymers as Macro Chain Transfer Agents

Abstract: Poly(stearyl methacrylate) (PSMA) homopolymers, prepared by RAFT radical polymerization, have been employed in the RAFT dispersion polymerization (RAFTDP) of 3-phenylpropyl methacrylate (PPMA) in n-tetradecane. RAFTDPs yielded block copolymers with narrow molecular weight distributions and tunable compositions and allowed for ready access to different polymorphic nanoparticle phases. Polymerization of PPMA at 20 wt %, for a fixed PSMA average degree of polymerization (Xn) of 19, allowed for the in situ preparation of soft matter nano-objects with spherical, worm, and vesicular morphologies. For a fixed block copolymer composition increasing total solids (from 10 to 40 wt %) favored the formation of nanoparticles with higher ordered morphologies. For block copolymer samples that formed soft physical gels at ambient temperature, a macroscopic thermoreversible degelation–gelation phenomenon was observed. The fundamental reason for this was a worm-to-sphere morphology transition that was facilitated, in part...

(a-Diimine)palladium catalyzed ethylene polymerization and ( co )polymerization with polar comonomers

Abstract: In this review, a recent development of cationic a-diimine palladium(II) complexes for ethylene polymerization and copoly-merization with polar functionalized comonomers was briefly described. First, the polymerization mechanism for this type of catalysts was discussed. Next, recent advances in ligand design were provided with special focus on the influence of ligand structures on the catalytic polymerization properties. Last, the ethylene homopolymerization and copolymerization with various polar comonomers, especially acrylate and vinyl ethers were summarized.

Synthetic Tailoring of Solid-State Order in Diketopyrrolopyrrole-Based Copolymers via Intramolecular Noncovalent Interactions

Abstract: Understanding the microstructures of semiconducting polymers is critical for improving the charge transport properties of polymer field-effect transistors (PFETs). A series of diketopyrrolopyrrole-based copolymers designed by implementing the concept of intramolecular noncovalent conformational locks through the functionalization of polymer backbones with fluorine atoms or methoxy groups were synthesized and compared with their unfunctionalized analogue. In contrast to the bimodal texture of the unfunctionalized polymer, the thin films of the polymer with fluorine atoms exhibit predominantly edge-on texture with much improved crystalline ordering. The thin films of the polymer modified with methoxy groups have a principally face-on texture. These dramatic differences in thin-film texture can be correlated with the polymers’ solubilities. Furthermore, the improved crystalline ordering of these semiconductor polymers enables the fabrication of high-performance PFETs: the hole mobility of the methoxy-modifie...