Showing papers in "Macromolecular Rapid Communications in 2007"

‘Click’ Chemistry in Polymer and Materials Science

Abstract: The modification of polymers after the successful achievement of a polymerization process represents an important task in macromolecular science. Cycloaddition reactions, among them the metal catalyzed azide/alkyne ‘click’ reaction (a variation of the Huisgen 1,3-dipolar cycloaddition reaction between terminal acetylenes and azides) represents an important contribution towards this endeavor. They combine high efficiency (usually above 95%) with a high tolerance of functional groups and solvents, as well as moderate reaction temperatures (25–70 °C). The present review assembles recent literature for applications of this reaction in the field of polymer science (linear polymers, dendrimers, gels) as well as the use of this and related reactions for surface modification on carbon nanotubes, fullerenes, and on solid substrates, and includes the authors own publications in this field. A number of references (>100) are included.

Molecular Engineering of the Band Gap of π-Conjugated Systems: Facing Technological Applications

Abstract: For almost two decades, the search of an intrinsically-conductive organic metal has represented the major driving force for research on control of the band gap of extended π-conjugated systems. However, the emergence of the application of π-conjugated oligomers and polymers in field-effect transistors, light-emitting diodes, electrochromic devices and solar cells has introduced major changes in the chemistry of gap engineering. Besides controlled band gap, active materials for electronic and photonic applications must present appropriate absorption and/or emission properties, highest occupied and lowest unoccupied molecular orbital (HOMO and LUMO) energy levels and charge-transport properties. The aim of this short review is to present an overview of the recent trends in this area in order to identify possible directions for future research.

Microwave‐Assisted Polymer Synthesis: Recent Developments in a Rapidly Expanding Field of Research

Abstract: The use of microwave irradiation has become a common heat source in organic chemistry. Inspired by this enormous success, the use of microwave irradiation is also increasingly studied for polymerization reactions. The present review discusses developments in this rapidly growing field of research. The main areas in which the use of microwave irradiation has been explored in the recent years are step-growth polymerizations, ring- opening polymerizations as well as radical polymerizations. These different areas will be addressed in detail, whereby special attention will be given to observed improvements resulting from the use of microwave irradiation as well as the occurrence of non-thermal effects.

Complex Macromolecular Architectures by Reversible Addition Fragmentation Chain Transfer Chemistry: Theory and Practice

Abstract: Reversible addition-fragmentation chain transfer (RAFT) chemistry can be effectively employed to construct macromolecular architectures of varying topologies. The present article explores the principle design routes to star, block, and comb polymers in the context of theoretical design criteria for the so-called Z- and R-group approaches. The specific advantages and disadvantages of each approach are underpinned by selected examples generated in the CAMD laboratories. In particular, we demonstrate how the modeling of full molecular weight distributions can be employed to guide the synthetic effort. We further explore the theory and practice of generating amphiphilic block copolymer structures and their self-assembly. In addition, the article foreshadows how modern synthetic techniques that combine RAFT chemistry with highly orthogonal click chemistry can be employed as a powerful tool that furthers the enhancement of macromolecular design possibilities to generate block (star) copolymers of monomers with extremely disparate reactivities. Finally, the ability of RAFT chemistry to modify the surface of well-defined nano- and microspheres as devices in biomedical application is detailed.

Living Radical Polymerization as a Tool for the Synthesis of Polymer-Protein/Peptide Bioconjugates

Abstract: Combinations of synthetic and natural macromolecules offer a route to new functional materials. While biological and polymer chemistry may not be natural bedfellows, many researchers are focusing their attention on the benefits of combining these fields. Recent advances in living radical polymerization have provided methods to build tailor-made macromolecular moieties using relatively simple processes. This has led to a plethora of block copolymers, end-functional polymers and polymers with a whole range of biological recognition abilities. This review covers work carried out until late 2006 combining living radical polymerization with proteins and peptides in the rapidly- expanding field of bioconjugation. [GRAPHICS] PHICS] in situ reduction, a large number of metal-based functional materials can be prepared. PVP is alkaline, and thus capable of catalyzing the sol-gel process to generate an inorganic shell. Furthermore, pre-formed nanoparticles can also be absorbed by the shell through specific interactions. The PS core is not infiltrative during synthesis, and hollow rings can be derived after the polymer templates are removed. [GRAPHICS] b

Silole‐Containing Polymers: Chemistry and Optoelectronic Properties

Abstract: In this review, the synthesis and optoelectronic properties of various π-conjugated-, σ-conjugated-, pendanted-, and hyperbranched or dendritic silole-containing polymers (SCPs) are described So far, substituted silole, dibenzosilole, dithienosilole, and bis-silicon-bridged stilbene have been incorporated into SCPs The tunable bandgaps from 40-155 eV, variable fluorescent colors from UV to blue, green, and red (RGB) light, fluorescent chemo-sensors for 2,4,6-trinitrotoluene (TNT)-type explosives, aggregation-induced emission, efficient electroluminescence emissions for RGB lights, phosphorescent hosts with high triplet energy level, efficient solar cells, stable field-effect transistors with high hole mobility in air, and attenuation of strong laser power, are the important features of SCPs

Polymorphism Control of Poly(vinylidene fluoride) through Electrospinning

Abstract: Polymorphism control of PVDF has been realized through electrospinning. PVDF fibrous membranes with fiber diameter in the range of 100 nm to several micrometers were produced by electrospinning and the crystal phase of electrospun PVDF fibers can be adjusted at the same time. Through the control of electrospinning parameters such as the solvent, electrospinning temperature, feeding rate, and tip-to-collector distance, PVDF fibrous membranes containing mainly α- or β- or γ-phase could be fabricated successfully.

Exploring Polymers of Intrinsic Microporosity – Microporous, Soluble Polyamide and Polyimide

Abstract: Polyamides and polyimides featuring a spirobifluorene unit as a structure directing motif in the polymer chain show intrinsic microporosity and consequently high surface areas. Such a spirobifluorene generates a 90° kink per repeating unit and thus prevents space-efficient packing or crystallization of the otherwise stiff polymer chains. Thus, the approach presented here extends the concept of polymers of intrinsic microporosity for ladder type poly(dibenzodioxane)s to more common polymers of high commercial interest. For example, a microporous polyimide with a surface area of ≈550 m 2 . g -1 was produced, which is readily soluble in chloroform.

Effect of the Molecular Weight of Poly(3-hexylthiophene) on the Morphology and Performance of Polymer Bulk Heterojunction Solar Cells

Abstract: The morphology and performance of bulk heterojunction solar cells comprised of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C 61 butyric acid methyl ester (PCBM) have been investigated using P3HT with different molecular weights (MWs). It is concluded that the optimum annealing temperature for the bulk heterojunction material is related to the MW of P3HT. The best performance is obtained by using P3HT with an optimum ratio between high MW and low MW components. The corresponding 'ideal morphology' is comprised of highly ordered crystalline regions formed by low MW P3HT embedded and interconnected by a high MW P3HT matrix.

Microwave‐Assisted Synthesis under Continuous‐Flow Conditions

Abstract: Microwave-assisted chemistry is about to change the art and practice of synthesis performed in many academic and industrial laboratories. One of the major drawbacks of this enabling technology is the difficulty associated with scale-up. Because of the limited penetration depth of microwaves into absorbing media, the solution to scale-up lies in continuous-flow processing. In this review we summarize the current state of the art in this field and present an overview on published examples of microwave-assisted synthesis using continuous-flow and stop-flow processing in custom-built or commercially available microwave reactors.

Exploring Microfluidic Routes to Microgels of Biological Polymers

Abstract: Polymer microgels in the size range from several micrometers to hundreds of micrometers are used in the pharmaceutical, cosmetics, nutrition, pesticide, and food industries, as well as in the encapsulation of cells. To date, a broad range of strategies for the generation of polymer microgels exist, however, these methods involve multistage processes, do not utilize biocompatible components or do not allow precise control of the dimensions and internal structure of the microgels. Recently, microfluidic strategies for the production of polymer particles have offered precise control over the shapes, morphologies, and size distributions of polymer colloids. This paper discusses the most recent results obtained by the authors in the area of the microfluidic production of biopolymer microgels. It provides a brief review of the microfluidic methods for the continuous synthesis and fabrication of microgels, sets the criteria for the successful microfluidic generation of biomicrogels, and describes two methods for the preparation of microgels by microfluidic means. The article concludes with a summary and an outlook.

Self-Assembly of Large Multimolecular Micelles from Hyperbranched Star Copolymers

Abstract: This work focused on the synthesis and aqueous self-assembly of a series of novel hyperbranched star copolymers with a hyperbranched poly[3-ethyl-3-(hydroxymethyl)oxetane] (HBPO) core and many linear poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) arms. The copolymers can synchronously form unimolecular micelles (around 10 nm) and large multimolecular micelles (around 100 nm) in water at room temperature. TEM measurements have provided direct evidence that the large micelles are a kind of multimicelle aggregates (MMAs) with the basic building units of unimolecular micelles. It is the first demonstration of the self-assembly mechanism for the large multimolecular micelles generated from the solution self-assembly of hyperbranched copolymers.

Yttrium Complexes as Catalysts for Living and Immortal Polymerization of Lactide to Highly Heterotactic PLA

Abstract: Amino-alkoxy-bis(phenolate) yttrium complexes act in the presence of an excess of alcohol (up to 50 equiv. vs. Y) as highly active and stereoselective catalysts for rac-lactide and rac-β-butyrolactone polymerizations. These versatile systems enable the production of large quantities of polymer with small amounts of catalyst, optimizing productivity, and also allow the preparation of polymers with functional end groups, which may be employed as intermediates for macromolecular engineering applications.

Microporous Polymers as Potential Hydrogen Storage Materials

Abstract: Microporous organic polymers offer the possibility of storing hydrogen safely at low temperatures and moderate pressures via physisorption. A range of polymers of intrinsic microporosity (PIMs) have been studied. The best PIM to date is based on a triptycene monomer and takes up 2.7% H2 by mass at 10 bar/77 K. Hypercrosslinked polymers (HCPs) also show promising performance, particularly at pressures >10 bar. The form of the H2 isotherm is influenced by the micropore distribution, a higher concentration of ultramicropores (pore size <0.7 nm), as found in PIMs, being associated with enhanced low pressure adsorption. The performance of polymers relative to other microporous materials (carbons and metal-organic frameworks) is compared and promising methods to enhance the hydrogen uptake of microporous polymers are suggested.

Oligomers and Polymers Based on Bridged Phenylenes as Electronic Materials

Abstract: The synthesis, properties, and application in electronic devices of ladder and step-ladder phenylene-based oligomers and polymers are reviewed with an emphasis on control of properties by synthetic design. Bridged polyphenylenes can be prepared with a range of different amounts and types of bridges. Fully bridged polymers suffer the problem of incomplete formation of bridges during polymer analogous reactions. This problem is surmounted by the synthesis of regular stepladder polymers in which the monomers are well-characterized oligo(ladder-phenylene)s. By controlling the degree of bridging and thus the planarity of the polymer, its optical properties can be tuned. The optical and electronic properties can be further controlled by means of the type of bridges used.

Unprecedented Blue Intrinsic Photoluminescence from Hyperbranched and Linear Polyethylenimines: Polymer Architectures and pH-Effects

Abstract: The intrinsic photoluminescence properties of hyperbranched polyethylenimines (PEIs) and their linear counterpart (LPEIs) have been studied in absence of any classical fluorescent probes. The comparison of the inherent fluorescence emission between hyperbranched polyethylenimines and their linear analogues demonstrates that linear polyamines are capable of producing strong intrinsic photoluminescence species having long excited lifetimes without need of having a tridimensional- branched structure. The creation of inherently fluorescent polymeric centers from hyperbranched and linear polyethyleimines can be modulated by specific chemical modification and oxidation of amine groups as well as by adjusting the acidity of the polymer.

Palladium Aryl Sulfonate Phosphine Catalysts for the Copolymerization of Acrylates with Ethene

Abstract: The reaction of 2-[bis(2-methoxy-phenyl)phosphanyl]-4-methyl-benzenesulfonic acid (a) and 2-[bis(2',6'-dimethoxybiphenyl-2-yl)phosphanyl]benzenesulfonic acid (b) with dimethyl(N,N, N',N'-tetramethylethylenediamine)-palladium(II) (PdMe 2 (TMEDA)) leads to the formation of TMEDA bridged palladium based polymerization cat- CO 2 R alysts (la and 1b). Upon reaction with pyridine, two mononuclear catalysts are formed (2a and 2b). These catalysts are able to homopolymerize ethylene and also copolymerize ethylene with acrylates or with norbornenes. With ligand b, high molecular weight polymers are formed in high yields, but higher comonomer incorporations are obtained with ligand a.

A New Poly(2,7‐Dibenzosilole) Derivative in Polymer Solar Cells

Abstract: A new soluble conjugated copolymer based on 2,7-dibenzosilole and 4,7-dithien-2-yl-2,1,3-benzothiadiazole units has been synthesized (PBSDTBT). Bulk heterojunction solar cell devices are fabricated using this material as the donor and [6,6]-phenyl-C 61 butyric acid methyl ester (PCBM) as the acceptor. The power conversion efficiency is 1.6% under AM1.5 illumination. This material also shows a good V oc (0.97 V). The results are quite promising considering the relatively large bandgap (1.9 eV) of this polymer.

Controlled Release of DNA from Self‐Degrading Microcapsules

Abstract: Self-disintegrating microcapsules were prepared by encapsulating a highly active mix of proteases (Pronase®) into biodegradable polyelectrolyte shells. Pronase was captured by micron-sized calcium carbonate particles that were subsequently embedded into onion-like shells of poly(L-arginine) and poly(L-aspartic acid). EDTA treatment was used to extract the calcium carbonate constituents from the resulting core-shell particles. As a consequence, Pronase was released into the capsule interior and started to digest the surrounding polyelectrolyte shell. Lifetimes of such self-disintegrating capsules could be successfully adjusted to seconds, hours or days by varying the amount of encapsulated Pronase. The enzyme-mediated, sustained release of encapsulated DNA is presented as a prospective application in drug delivery.

Interactions of Ionic Liquids with Polysaccharides 1. Unexpected Acetylation of Cellulose with 1‐Ethyl‐3‐methylimidazolium Acetate

Abstract: The homogeneous conversion of cellulose in the ionic liquid 1-ethyl-3-methylimidazolium acetate with 2-furoyl chloride, p-toluenesulfonyl chloride, and triphenylmethyl chloride yields surprisingly pure cellulose acetate samples in any case. From NMR spectroscopic studies, it may be concluded that during the homogeneous functionalization reactive intermediates including furane-2-carboxylic acid/acetic acid anhydride and acetic acid triphenylmethyl ester are formed leading to the cellulose acetates with DS values in the range from 0.55 to 1.86.

Tandem RAFT polymerization and click chemistry : An efficient approach to surface modification

Abstract: PS grafted silica nanoparticles have been prepared by a tandem process that simultaneously employs RAFT polymerization and click chemistry. In a single pot procedure, azide-modified silica, an alkyne functionalized RAFT agent and styrene are combined to produce the desired product. As deduced by thermal gravimetric and elemental analysis, the grafting density of PS on the silica in the tandem process is intermediate between analogous "grafting to" and "grafting from" techniques for preparing PS brushes on silica. Relative rates of RAFT polymerization and click reaction can be altered to control grafting density.

Piezoelectric Ink‐Jet Printing of Horseradish Peroxidase: Effect of Ink Viscosity Modifiers on Activity

Abstract: In this study a bioink containing the horseradish peroxidase (HRP) enzyme was formulated and jetted with a piezoelectric-based ink-jet deposition system. A number of polymers with different molecular weights, functional groups and electric charge were tested as viscosity modifiers. The impact of viscosity modifiers on HRP activity was systematically studied. It was found that viscosity modifiers typically used in commercial ink formulations significantly impaired HRP activity possibly due to limitations in diffusion. In contrast, carboxymethyl cellulose increased viscosity to the desired range for piezoelectric jetting without negatively affecting the HRP activity. Good jettability was obtained for the HRP bioink by adding a suitable surfactant, a viscosity modifier and a humectant.

Nitroxide-Mediated Aqueous Dispersion Polymerization: From Water-Soluble Macroalkoxyamine to Thermosensitive Nanogels

Abstract: Self-stabilized nanoparticles with a temperature-responsive poly[(N,N-diethylacrylamide)-co-(N,N′-methylenebisacrylamide)] microgel core and a covalently attached hairy shell were synthesized via a simple nitroxide-mediated controlled free-radical aqueous dispersion polymerization, using a poly(sodium acrylate) alkoxyamine macroinitiator. With this method, high solid content, surfactant-free particle suspensions were prepared, with diameter ranging from 49 to 118 nm at high temperature, and able to reversibly swell with water at low temperature. The proposed method requires a limited number of reagents in a simple polymerization procedure and thus avoids many drawbacks generally encountered in the synthesis of thermally responsive microgel particles. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.

Polymeric One-Dimensional Photonic Crystals by Continuous Coextrusion

Abstract: It is shown that narrowband one-dimensional photonic crystals can be fabricated from polymeric materials using laboratory scale layer-multiplying coextrusion technology. The tuning of the photonic bandgap is demonstrated with films that selectively filter different regions of the visible electromagnetic spectrum. The layer uniformity of the photonic crystals is evaluated by comparing the measured UV-vis transmission spectra with model simulations, and is independently confirmed with atomic force microscopy. Assemblies of alternating polystyrene and poly(methyl methacrylate) layers exhibit a narrow reflection band with close to 100% reflection in good agreement with the prediction for uniform layers. The flexibility of the process is demonstrated by the fabrication of elastomeric one-dimensional photonic crystals. It is anticipated that this technology will enable the rapid and facile realization of new polymeric optical devices.

Polyelectrolytes Revisited: Reliable Determination of Intrinsic Viscosities

Abstract: The linear extrapolation of (hh0)/(h0c) towards c !0 constitutes the basis of traditional methods to determine intrinsic viscosities (h), where h is the viscosity of polymer solutions of concentration c and h0 is the viscosity of the pure solvent. With uncharged macromolecules this procedure works well; for polyelectrolytes it fails because of the pronounced non-linearity of the above dependence at high dilution resulting from the increasing electrostatic inter- actions. This contribution presents a new method for the determination of (h). It rests upon the application of the laws of phenomenological thermodynamics to the viscosity of polymer solutions and introduces a generalized intrinsic viscosity enabling a comparison of differently charged and uncharged polymers.

How Carbon Nanotube Crushing can Improve Flame Retardant Behaviour in Polymer Nanocomposites

Abstract: Nanocomposites based on an ethylene-vinyl acetate copolymer (27 wt.-% vinyl acetate) and multiwall carbon nanotubes (MWNTs) have been prepared by melt blending and their thermal degradation and flame retardant properties have been evaluated. Special attention has been paid to the influence of the nanotube nature on the flammability properties and more particularly on the time to ignition (TTI) as measured by cone calorimetry. It has been shown that there is a strong influence of the nature of carbon nanotubes on the fire behaviour of the composites, especially previous MWNTs crushing proved to substantially delay the TTI while maintaining much reduced heat release rate (HRR). Such a remarkable behaviour might be explained by the chemical reactivity of radical species present at the surface/extremities of crushed MWNTs during the combustion process.

Conjugated Polymers as Optical Probes for Protein Interactions and Protein Conformations

Abstract: There is a need for highly sensitive, multi-parallel protein sensors within diagnostics and proteomic research. Conjugated polymers (CPs) have been demonstrated as highly sensitive optical probes for protein biosensing. Compared to small molecules, the polymeric probe has the possibility of multiple interactions and a collective response, which enhances the sensor signal. The optical output is colorimetric or, more sensitive, fluorescence based, including Forster energy transfer and changes in the emission wavelengths and/or intensity. Using CPs, many interesting protein detection events have been demonstrated, e.g., protein interactions, enzymatic activity, amyloid fibril formation, and detection by aptamers. CPs have also been successfully used to stain bacterial, cellular, and tissue samples. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.

Isothermal Crystallization of Isotactic Poly(propylene) Studied by Superfast Calorimetry

Abstract: The isothermal crystallization behavior and the structure and morphology of isotactic poly(propylene) (iPP) and iPP/hydrogenated hydrocarbon resin (HR) 90/10 blend were analyzed. To cover the entire temperature range, isothermal crystallizations were studied using superfast calorimetry at a high cooling rate in the range 0 to 110 °C, and by conventional DSC at a low cooling rate in the range 120 to 140 °C. Structural and morphological changes due to the different thermal treatments were also analyzed. The complete crystallization curve ranging from T g to T m showed bimodal crystallization behaviors for both iPP and iPP/HR 90/10 blend. This result is explained by taking into consideration the polymorph properties of iPP. It is in fact assumed that the curve from T g to 60°C referred mainly to the crystallization kinetics of the iPP mesomorphic form by homogeneous nucleation, whereas the curve from 60 °C to T m mainly represented the crystallization kinetic curve for the monoclinic α form by heterogeneous nucleation. This hypothesis is confirmed by the analysis of the structures obtained using wide angle X-ray experiments. Moreover, the addition of HR to iPP causes a drastic reduction in the crystallization rate of iPP in both regions due to the diluent effect of the miscible resin.

Direct Synthesis of Pyridyl Disulfide-Terminated Polymers by RAFT Polymerization

Abstract: A trithiocarbonate RAFT agent was modified with a pyridyl disulfide group and used in the direct synthesis of endgroup pyridyl disulfide-functionalized homo- and amphiphilic 'block copolymers of oligo (ethylene glycol) acrylate (PEG-A) and butyl acrylate (BA). Both the homoand copolymerizations were found to be well controlled via the RAFT mechanism. The NMR analysis indicated that both the homopolymers of PEG-A and the amphiphilic diblock copolymers of PEG-A and BA possessed pyridyl disulfide terminal groups. A UV-Vis absorption test revealed that the pyridyl disulficle endgroup of the polymer could be efficiently used to couple thiol-bearing molecules to the polymer without the need for any post-polymerization modification. This communication presents the first efficient direct synthesis of thiol-reactive endgroup-functionalized well-defined polymers via the RAFT technique.

Cationic Polymerization of Poly(vinyl ether) Bearing a TEMPO Radical: A New Cathode-Active Material for Organic Radical Batteries

Abstract: PTVE was synthesized as a new active material for organic radical batteries. Cationic polymerization of a monomer bearing a TEMPO radical moiety took place. The spin concentration of PTVE was estimated to be 2.75 × 10 21 spins · g -1 (100% spin per repeating unit). The PTVE is extremely stable; there is no decrease in spin concentration when storing PTVE samples for more than a year under aerobic conditions at room temperature. The redox potential of PTVE is 3.55 V (vs. Li/Li + ). A coin-type cell using a PTVE/VGCF composite electrode was also fabricated, and then performed charge/discharge measurements. The discharge capacity of PTVE is 114 mAh ·g -1 (84% of the theoretical value).