Showing papers in "Macromolecular Rapid Communications in 2008"

'Click' Chemistry in Polymer and Material Science: An Update

Abstract: The metal catalyzed azide/alkyne ‘click’ reaction (a variation of the Huisgen 1,3-dipolar cycloaddition reaction between terminal acetylenes and azides) has vastly increased in broadness and application in the field of polymer science. Thus, this reaction represents one of the few universal, highly efficient functionalization reactions, which combines both high efficiency with an enormously high tolerance of functional groups and solvents under highly moderate reaction temperatures (25–70 °C). The present review assembles an update of this reaction in the field of polymer science (linear polymers, surfaces) with a focus on the synthesis of functionalized polymeric architectures and surfaces.

Putting Electrospun Nanofibers to Work for Biomedical Research

Abstract: Electrospinning has been exploited for almost one century to process polymers and related materials into nanofibers with controllable compositions, diameters, porosities, and porous structures for a variety of applications. Owing to its high porosity and large surface area, a non-woven mat of electrospun nanofibers can serve as an ideal scaffold to mimic the extracellular matrix for cell attachment and nutrient transportation. The nanofiber itself can also be functionalized through encapsulation or attachment of bioactive species such as extracellular matrix proteins, enzymes, and growth factors. In addition, the nanofibers can be further assembled into a variety of arrays or architectures by manipulating their alignment, stacking, or folding. All these attributes make electrospinning a powerful tool for generating nanostructured materials for a range of biomedical applications that include controlled release, drug delivery, and tissue engineering.

Polymer “Clicking” by CuAAC Reactions

Abstract: The CuAAC "click" reaction has developed as one of the most useful and widely employed reactions in ligation within polymer chemistry. This is due to the unique properties of the Cu(I) catalysis which renders the reaction quantitative even at low concentrations, orthogonal with other chemistries and extremely robust. The formed triazole on the other hand is of intermediate polarity and chemically and biochemically "invisible", and the CuAAC provides the ideal "click" reaction for stitching together polymer architectures of unprecedended complexity as was it molecular LEGO. The CuAAC "clicking" in polymer chemistry is increasing exponentially and lead to highly defined polymer materials with novel properties.

Construction of Linear Polymers, Dendrimers, Networks, and Other Polymeric Architectures by Copper‐Catalyzed Azide‐Alkyne Cycloaddition “Click” Chemistry

Abstract: The enrichment of materials synthesis with the diverse chemical building blocks and functional groups of small molecule organic chemistry has been greatly accelerated in recent years by the introduction of the copper-catalyzed azide-alkyne cycloaddition (CuAAC). The efficiency and modular nature of this unique reaction enables materials chemists to prepare novel functional materials of unprecedented complexity. This review summarizes the application of CuAAC to the field of materials construction, defined here as the preparation of materials with architectural integrity dependent upon the triazole linkage. Recent examples, including linear polymers, dendrimers, polymer networks, polymeric nanoparticles, and other polymeric architectures, are described.

Self-Cleaning and Next Generation Anti-Fog Surfaces and Coatings

Abstract: Due to their high surface energy, hydrophilic surfaces are susceptible to contaminations which are difficult to remove and often ruin the surface. Traditional anti-fog coatings are especially limited by contaminants, as the prevention of fogging is enhanced as hydrophilicity increases. Thus, advanced solutions to fogging are required which incorporate some degree of self-cleaning ability without significant losses in anti-fog character. Potential next generation anti-fog surfaces are characterized with particular emphasis on extended lifetime stimuli- responsive surfaces. Surfactant-based surfaces exhibited simultaneous hydrophilicity, necessary for anti-fogging, and oleophobicity, necessary for contamination resistance. The combination of these features rendered the surface as self-cleaning.

Click Chemistry: A Powerful Tool to Create Polymer-Based Macromolecular Chimeras

Abstract: The combination of polymeric with biological materials, to create biohybrid macromolecules that merge the properties of both the natural and synthetic components, is a flourishing area in both lifesciences and biotechnology.Theclick chemistry philosophy hasrecentlyprovided a powerful tool in this direction, leading to a plethora of novel, tailor-made biomacromolecules with unprecedented structural characteristics and properties. The different synthetic strategies, using the alkyne‐azide click cycloadditions to bioorthogonally achieve the coupling of synthetic polymers with nucleic acids, peptides, sugars, proteins or even viruses and cells is described. The review covers the latest developments in this very dynamic and rapidly expanding field.

A Novel Strategy to Incorporate Carbon Nanotubes into Thermoplastic Matrices

Abstract: Multiwalled carbon nanotubes (MWNT) are introduced into thermoplastic matrices (polycarbonate and polyamide) by melt blending using polyethylene (PE) based concentrates with high MWNT loadings (24-44 wt.-%). MWNT surfaces were treated with a metallocene-based complex to afford the in-situ polymerization of ethylene directly from the surface. The resulting concentrates showed excellent MWNT pre-dispersion. Due to the high interfacial energy between MWNT and PE, the nanotubes migrate into matrix polymers with lower interfacial energies, like polycarbonate and polyamide, and thereby remain in their excellent dispersion state. Thus, electrical percolation is achieved at lower MWNT contents as compared to direct incorporation. For polycarbonate it is shifted from 0.75 to 0.25 wt.-%.

Responsive Polymer‐Protein Bioconjugates Prepared by RAFT Polymerization and Copper‐Catalyzed Azide‐Alkyne Click Chemistry

Abstract: Responsive polymer-protein conjugates were synthesized by combination of reversible addition-fragmentation chain transfer (RAFT) polymerization and a grafting-to approach by a highly efficient “click chemistry” strategy. A model protein, bovine serum albumin (BSA), was functionalized with an alkyne moiety by reaction of its free cysteine residue with propargyl maleimide. Azido-terminated poly(N-isopropylacrylamide) (PNIPAM-N3) was prepared via RAFT, and polymer-protein coupling was accomplished by copper-catalyzed azide-alkyne cycloaddition. In aqueous solution, the conjugates were observed by dynamic light scattering to be larger than the free polymer or the unmodified protein. Upon heating above the PNIPAM lower critical solution temperature (LCST), the PNIPAM-BSA bioconjugates formed stable nanoparticles composed of dehydrated polymer and hydrophilic protein.

Hybrid Process for Fabricating 3D Hierarchical Scaffolds Combining Rapid Prototyping and Electrospinning

Abstract: An ideal scaffold should have good mechanical properties and provide a biologically functional implant site. A rapid prototyping system has been introduced as a good method of fabricating 3D scaffolds that mimic the structure in the human body. However, the scaffolds have strands that are too smooth and a pore size that is too large relative to the seeded cells and present unfavorable conditions for initial cell attachment. To overcome these problems, we propose a hybrid technology combining a 3D rapid prototyping system and an electrospinning process to produce a hierarchical 3D biomedical scaffold. The resulting structure consists of alternating layers of 3D-structured/microsized polymer strands and nanofiber webs. The results of cell culturing of chondrocytes indicate that this technique is a feasible new method for fabricating high quality 3D polymeric scaffolds.

Aniline Oligomers – Architecture, Function and New Opportunities for Nanostructured Materials

Abstract: In this mini review, we strive to highlight the opportunities that exist for the use of aniline oligomeric species in functional materials by reviewing the current state-of-the-art of the various synthetic strategies, as well as the growing number of publications where more complex block-like architectures have been shown. Areas for further investigation and possible future development are highlighted as well.

Click Assisted One‐Pot Multi‐Step Reactions in Polymer Science: Accelerated Synthetic Protocols

Abstract: Presently, the majority of reports deal with combining chemical reactions, in a stepwise fashion, to obtain well-defined polymers. In the future, chemists need to address new challenges such as increase in the range of available efficient reactions, developing libraries of compatible one-pot reactions, and the application of obtained materials in key industries. Indeed, the rising importance of the click concept has now devised robust synthetic approaches in various fields of research. The unique selectivity of the click reaction is today a new found toolbox for scientists to investigate one-pot multi-step systems. Several accelerated protocols have elegantly been reported to obtain a library of advanced polymers.

Synthesis of Near‐Infrared Responsive Gold Nanorod/PNIPAAm Core/Shell Nanohybrids via Surface Initiated ATRP for Smart Drug Delivery

Abstract: Nanosized near infrared (NIR) responsive nanohybrids are synthesized by surface-initiated atom transfer radical polymerization (SI-ATRP) of N-isopropylacrylamide (NIPAAm) on gold nanorods (Au NRs). Transmission electron microscopy images demonstrate that the nanohybrids have a clear core/shell structure. Temperature-variable 1 H NMR spectroscopy, quasi-elastic light scattering (QELS), UV-vis spectroscopy, and laser irradiation prove that the nanohybrids are both temperature and NIR responsive. Norvancomycin (NVan) loading and release experiments show that the drug release rate can be modulated by NIR irradiation. Such an intelligent drug-delivery system might find applications in non-invasive controlled drug release in future.

Acid-Degradable Core-Crosslinked Micelles Prepared from Thermosensitive Glycopolymers Synthesized via RAFT Polymerization

Abstract: A thermoresponsive block copolymer, namely poly(acryloyl glucosamine)-block-poly(N-isopropylacryamide) (PAGA(180)-b-PNIPAAM(350))was simultaneously self-assembled and cross-linked in aqueous medium via RAFT polymerization at 60 degrees C to afford core-crosslinked micelles exhibiting a glycopolymer corona and a PNIPAAM stimuli-responsive core. An acid-labile crosslinking agent, 3,9-divinyl-2,4,8,10-tetraoxaspiro[5.5]-undecane, was employed to generate thermosensitive and acid-degradable core-shell nanoparticles. Stable against crosslinked micelles readily hydrolyzed block copolymers at lower pH (30 min and 12 h respectively pH = 2 and 4).

Linear High Molecular Weight Ladder Polymer via Fast Polycondensation of 5,5′,6,6′‐Tetrahydroxy‐3,3,3′,3′‐tetramethylspirobisindane with 1,4‐Dicyanotetrafluorobenzene

Abstract: A high molecular weight ladder polymer based on 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-spirobisindane and 1,4-dicyanotetraflurobenzene has been synthesized by polycondensation under high-intensity mixing conditions at about 155 °C and cyclic-free products were obtained in high yield with low molecular weight distribution (1.7-2.3). The reaction could be completed within a few minutes. The polymer properties were characterized by GPC, 1 H NMR, 13 C NMR, F NMR, FT-IR, and MALDI-TOF MS. In addition, the mechanical properties, apparent surface areas and gas permeability are also reported. This procedure can also be used for the synthesis of other ladder polymers by irreversible polycondensations of tetraphenols with activated tetrafluoro aromatics.

Synthesis of High Density Polymer Brushes on Nanoparticles by Combined RAFT Polymerization and Click Chemistry

Abstract: In the present paper, we report the successful preparation of high density, well-defined polymer brushes by RAFT polymerization on silica nanoparticles. Our strategy includes (i) "grafting from" approach for brush formation, (ii) facile click reaction to immobilize RAFT agent, (iii) synthesis of R-supported chain transfer agent (CTA) over Z-supported CTA, and (iv) use of more active trithiocarbonate RAFT agent over conventional dithioester type RAFT agent. With the advantage of the properties of high-density polymer brushes, these diblock copolymer-modified silica nanoparticles open the route to the elaboration of a new family of nanocomposite colloids with potential applications in responsive or smart systems.

Polymerized Lyotropic Liquid Crystal Assemblies for Membrane Applications

Abstract: Cross-linked lyotropic liquid crystal (LLC) assemblies represent a new class of polymer materials for membrane applications. These materials are formed by the phase-segregation and self-assembly of polymerizable amphiphiles in water into condensed ordered ensembles that can be cross-linked in situ with retention of microstructure. The resulting LLC polymer networks have ordered, nanometer-scale aqueous and cross-linked organic domains, which can be used to affect gas solubility and diffusivity through the polymer to help separate molecules via the solution-diffusion mechanism. The open aqueous domains can also be used for pore transport and size exclusion with resolution on the molecular size level. The use and application potential of cross-linked LLC assemblies as gas separation membranes, selective vapor barrier materials, and water nanofiltration and desalination membranes are presented.

Cellular Uptake of DNA Block Copolymer Micelles with Different Shapes

Abstract: The cellular uptake of DNA block copolymer micelles composed of DNA-b-PPO in Caco-2 cells was studied. In particular it was investigated if the shape of micelle aggregates influences the internalization. Rod-like polymeric particles were taken up 12 times more efficiently than their spherical counter parts although they were composed of the same constituents. Furthermore, it was observed that internalization of all the micelle systems was more efficient than the pristine DNA controls. A cytotoxicity assay proved the non-toxic nature of DNA-b-PPO micelle aggregates.

Design of a Linear Poly(3-hexylthiophene)/Fullerene-Based Donor-Acceptor Rod-Coil Block Copolymer

Abstract: Novel fullerene-grafted poly(3-hexylthiophene) (P3HT)-based rod-coil block copolymers have been synthesized. The regioregular P3HT rod block has been synthesized by a modified Grignard metathesis reaction (GRIM). An original in situ end-capping reaction has been developed in order to convert the P3HT block into an efficient macro-initiator for the nitroxide-mediated radical polymerization (NMRP) of the coil block. Controlled radical polymerization of the second poly(butylacrylate-stat-chloromethylstyrene) [P(BA-stat-CMS)] block has been done through various conditions leading to different coil block lengths. The final electron donor-acceptor block copolymer has been obtained after C 60 grafting in soft conditions. Copolymers have been characterized by 1 H NMR and size exclusion chromatography. Optical characterizations, before and after C 60 grafting, are reported.

Responsive Backbones Based on Alternating Triazole-Pyridine/Benzene Copolymers: From Helically Folding Polymers to Metallosupramolecularly Crosslinked Gels

Abstract: Step-growth polymerization using Cu-catalyzed 1,3-dipolar cycloaddition reactions, commonly referred to as "click chemistry," has been used to prepare poly[(1,2,3 -triazol-4-yl-1,3-pyridine)-alt -(1,2,3 -triazol-1-yl-1,3 -phenylene)]s. The recently discovered strong preference of the 2,6-bis(1,2,3 -triazol-4-yl)pyridine (BTP) subunits to adopt an anti-anti conformation enables the extended heteroaromatic polymer strands to adopt a helical conformation, as shown by circular dichroism (CD) spectroscopy. Addition of various transition metal ions leads to coordinative crosslinking and therefore efficient gelation of the polymer solutions. The integration of the BTP scaffold in the main chain of the described polymers illustrates a synthetically inspired approach to readily access new functional macromolecules with potential applications as sensing and magnetic/emissive materials.

Intramolecular Click Cycloaddition: An Efficient Room‐Temperature Route towards Bioconjugable Polymeric Nanoparticles

Abstract: A highly efficient room-temperature synthetic route to bioconjugable polymeric nanoparticles in the 5-20 nm size range based on single-chain intramolecular click cycloaddition is described. It is illustrated by preparing single-chain cross-linked polymeric NPs from poly[MMA-co-(3-azidopropyl methacrylate)-co-(3-trimethylsilyl-propyn-1-yl methacrylate)] terpolymers using a one-pot procedure and a continuous addition technique. For polymeric NPs with an excess of azide groups, aminoacid/PMMA NPs were easily obtained by performing a second click reaction with propargyl glycine. This versatile and general method opens the way to the synthesis of other kinds of polymeric and bioconjugated NPs beyond those reported in this communication.

Efficient Surface Modification of Divinylbenzene Microspheres via a Combination of RAFT and Hetero Diels-Alder Chemistry

Abstract: A combination of reversible addition fragmentation chain transfer (RAFT) polymerization and hetero Diels-Alder (HDA) chemistry has been utilized to successfully generate functional core-shell microspheres. Initially, precipitation polymerization in conjunction with the RAFT technique has been employed to synthesize divinylbenzene (DVB) microspheres with surface expressed RAFT groups. Subsequently, HDA cycloaddition has been performed under mild reaction conditions (50 degrees C, 24 h) with a diene-functionalized poly(epsilon-caprolactone) (PCL). While the successful grafting is immediately evident by optical inspection of the microspheres (color change from purple to white), X-ray photoelectron spectroscopy (XPS), and attenuated total reflectance spectroscopy (ATR) were additionally employed to characterize the chemical composition and surface functionalization of the microspheres. Further, confocal microscopy was used to con-firm the presence of grafted PCL chains after labeling them with rhodamine B.

Control of the Dynamic Motion of a Gel Actuator Driven by the Belousov-Zhabotinsky Reaction

Abstract: A novel self-oscillating gel actuator with gradient structure, which generates a pendulum motion by fixing one edge of the gel without external stimuli was achieved. The gel was synthesized by copolymerizing the ruthenium catalyst for the Belousov-Zhabotinsky reaction with N-isopropylacrylamide and 2-acrylamido- 2-methylpropane sulfonic acid. Furthermore, we clarified that the period and amplitude for the self-oscillating behavior of the gel actuator are controllable by changing the composition, temperature, and size of the gel. The maximum amplitude of the novel gel actuator is about a 100 times larger than that of the conventional self-oscillating gel system.

Macromolecular Engineering of Biodegradable Polyesters by Ring‐Opening Polymerization and ‘Click’ Chemistry

Abstract: Biodegradability makes aliphatic polyesters valuable candidates for biomaterials and environmentally friendly thermoplastics. Nevertheless, their chemical modification, which is mandatory for a series of potential applications, is usually a problem because it must be carried out under very mild conditions in order to prevent degradation by hydrolysis and/or transesterification from occurring. In this review, the copper(I)-catalyzed azide-alkyne cycloaddition, which is a click reaction, is shown to be very efficient to bypass these problems and to tailor the macromolecular architecture and functionality of those polyesters without facing undesired degradation reactions.

Superhydrophobic 3D Microstructures Assembled From 1D Nanofibers of Polyaniline

Abstract: Superhydrophobic dandelion-like 3D microstructures self-assembled from 1D nanofibers of PANI were prepared by a self-assembly process in the presence of perfluorosebacic acid (PFSEA) as a dopant. The dandelion-like microspheres (about 5 μm) are composed of uniform Y-shaped junction nanofibers of about 210 nm average diameter and several micrometers in length, as measured by SEM. The dandelion-like microstructure is coreless with a hollow cavity, and the shell thickness is about one third of the sphere diameter, as measured by TEM. Since PFESA dopant has a low surface energy perfluorinated carbon chain and two hydrophilic -COOH end groups, it has dopant, is a "soft-template" and brings about superhydrophobic functions at the same time. Moreover, it is proposed that the self-assembly of PANI 1D nanofibers, driven by a combined interaction of hydrogen bonding, π-π stacking and hydrophobic interactions, leads to the formation of the 3D microstructures.

Improved PEDOT Conductivity via Suppression of Crystallite Formation in Fe(III) Tosylate During Vapor Phase Polymerization

Abstract: Vapor phase polymerization was used to synthesize high conductivity poly(3,4-ethylenedioxyphenylene) (PEDOT). The monomer is presented to an oxidant-rich substrate in vapor form and even for short polymerization times, 10-30 min, Fe(III) tosylate has a propensity for water absorption leading to crystal formation. Poor oxidant treatment before polymerization or high humidity during polymerization can create holes in the PEDOT film decreasing its conductivity. The addition of an amphiphilic copolymer poly(ethylene glycol)-ran-poly-(propylene glycol) suppresses crystal growth allowing better film formation. The humidity level during synthesis was optimized at 35% relative humidity (RH), producing a conductivity of 761 S cm- 1 . Additionally, the copolymer extends the RH range that is tolerable for polymer synthesis.

Regulation of Micellar Morphology of PCL‐b‐PEO Block Copolymers by Crystallization Temperature

Abstract: The effect of crystallization temperature on the micellar morphology of PCL-b-PEO block copolymers in water has been studied. It is found that the micellar morphology of PCL n PEO 44 and PCL n PEO 113 changes with crystallization temperature in different ways because of two competitive factors: perfection of the PCL crystals in the core and deformation of the soluble PEO block. For PCL n PEO 44 , perfection of the PCL crystals dominates the micellar morphology and lamellar micelles are formed at a higher crystallization temperature. For PCL n PEO 113 the micellar morphology is mainly determined by the tethering density and spherical micelles or cylindrical micelles with a larger length/diameter ratio are formed at a higher crystallization temperature because of the larger tethering density.

New Photocleavable Structures, 4 Acylgermane-Based Photoinitiator for Visible Light Curing

Abstract: As highly reactive acylphosphine oxide-based photoinitiators (PIs) are limited in the application for dental materials by their absorption behavior, we were interested to prepare acylgermane 1. UV-Vis absorption maximum of the important n-π* transition was red shifted about 30 nm compared to monoacylphosphine oxides. Photo-DSC results with a dental LED lamp showed nearly the same reactivity for 1 compared to camphorquinone (CO), while monoacylphosphine oxides are not reactive. In broadband irradiation experiments, significantly higher reactivity compared to CO was found. Application-oriented tests showed sufficient storage stability of the formulation and excellent photobleaching behavior.

Enhanced Mechanical Performance of Self‐Bundled Electrospun Fiber Yarns via Post‐Treatments

Abstract: A new route to high-performance electrospun polymer fibers was developed using a self-bundling electrospinning technique combined with post-treatments such as stretching and annealing under conditions similar to those used for conventional fibers. Self-bundled electrospun PAN fiber yarns were characterized by SEM, mechanical tests, polarized FT-IR spectroscopy and WAXD. The obtained results revealed that the PAN nanofiber yarns possessed enhanced alignment, a higher degree of crystallinity and higher molecular orientation after treatments, resulting in a remarkable improvement in mechanical performance, approaching the strength value of the corresponding conventional fibers.

Degradable Multilayer Films and Hollow Capsules via a 'Click' Strategy

Abstract: Degradable polymeric multilayer films and microcapsules are fabricated by 'click' chemistry using dextran modified with azide and alkyne moieties. Alternating layers of dextran modified with azide and alkyne groups, respectively, are covalently bonded by virtue of the 1,3-dipolar cycloaddition reaction, known as click chemistry, which leads to the formation of stable triazole cross-links between the successive layers. The dextran is modified in such a way that the azide and alkyne moieties are connected to the dextran backbone by a hydrolyzable carbonate ester. Therefore, the obtained multilayered structures can be degraded by simple hydrolysis. This type of multilayer avoids the use of polyelectrolytes, which are potentially cytotoxic, and could, therefore, be interesting for the fields of drug delivery and tissue engineering.