Macromolecular Theory and Simulations
Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Talents, Trends and Highlights
in Macromolecular Chemistry and Physics
Talent Articles highlight outstanding young scientists developing new, original ideas in the field of polymer science, explained by the authors of those new concepts.
Trend Articles are short overview contributions that highlight important contemporary developments in the field of polymer science, including the author's personal opinion on new directions, recent achievements and still open questions in the field.
Highlight Articles are short papers describing recent very important research results in the field of polymer science. They emphasize the importance of the presented research work and instruct readers on its significance.
TREND: "Heavy-Atom" Donor-Acceptor Conjugated PolymersGregory L. Gibson and Dwight S. Seferos*
Donor-acceptor polymers containing "heavy" atoms below the first row of the periodic table are widely studied with an eye to organic electronics. These polymers demonstrate desirable optical and electronic properties, including high charge-carrier mobility. This article elucidates trends in heavy-atom polymer structure–property relationships by examining single atom substitutions in select donor–acceptor architectures.
Macromol. Chem. Phys., DOI: 10.1002/macp.201400042
TALENT: Two Non-covalent Methods to Decorate Nanoparticles with Block CopolymersChristophe Schatz
Two novel approaches of particle functionalization with block copolymers are introduced. The first method is based on the physical adsorption of a charged block copolymer with two adsorbing blocks. The second method consists of self-assembling a bilayer of amphiphilic block copolymer at the particle surface through a change of solvent polarity.
Macromol. Chem. Phys., DOI: 10.1002/macp.201300756
TREND: Polysaccharide Biocatalysis: From Synthesizing Carbohydrate Standards to Establishing Characterization MethodsJelena Ciric, Dejan M. Petrovic and Katja Loos*
In vitro enzymatic synthesis is the future for polysaccharide production. By synthesizing and characterizing various polysaccharides with complicated structures, they are understood better and a much closer understanding of nature is reached. The characterization of widely used natural carbohydrates, such as starch and cellulose, can be improved after a detailed analysis of their enzymatically synthesized analogs. An overview of both enzymatic synthesis and various characterization techniques of polysaccharides is presented in this article.
Macromol. Chem. Phys., DOI: 10.1002/macp.201300801
TALENT: Composing Well-Defined Stimulus-Responsive Materials Through Postpolymerization Modification ReactionsPeter J. Roth
Choosing the right building blocks is the key to designing novel smart materials. This article combines theoretical fundamentals of different types of stimulus-responsiveness, emphasizing lower and upper critical solution temperature (LCST and UCST) behavior, with a range of illustrations of postpolymerization modification reactions in order to provide guidance on how to compose well-defined smart polymers with tailored properties.
Macromol. Chem. Phys., DOI: 10.1002/macp.201400073
TREND: Recent Trends and Future Outlooks in the Field of Clay-Containing Polymer Nanocomposites
Suprakas Sinha Ray
This article highlights recent developments in academic and industrial research in the field of clay-containing polymer nanocomposites, including current commercial successes, providing a short overview on key research challenges, as well as future outlooks and open questions in the field.
Macromol. Chem. Phys., DOI: 10.1002/macp.201400069
TALENT: Facile One-Pot Synthesis of New Functional Polymers through Multicomponent Systems
Shiqi Wang, Changkui Fu, Yen Wei and Lei Tao*
One-pot strategies, which combine in situ monomer synthesis and controlled radical polymerization together, are applied into innovative functional polymer preparation. This methodology is simple, efficient, and versatile. In this talent article, most advances in one-pot synthesis strategies are summarized and their further applications are discussed.
Macromol. Chem. Phys., DOI: 10.1002/macp.201300738
TREND: Mechanism and Kinetics of Dithiobenzoate-Mediated RAFT Polymerization - Status of the Dilemma
Developments in the understanding of the mechanism and kinetics of dithiobenzoate-mediated reversible addition-fragmentation chain-transfer (RAFT) polymerization over the period 2006–2013 are critically assessed with specific reference to choice of reagents and polymerization conditions, reagent and product stability, side reactions and factors that may lead to retardation.
Macromol. Chem. Phys., DOI: 10.1002/macp.201300562
TALENT: Self-Assembly of Globular-Protein-Containing Block CopolymersBradley D. Olsen
The direct self-assembly of globular-protein-containing block copolymers provides an attractive method for the fabrication of biofunctional nanostructures; a variety of different solid state and block copolymer gel nanostructures may be formed. The thermodynamics and processing of these systems are heavily influenced by the folded, biofunctional structure of the protein.
Macromol. Chem. Phys., DOI: 10.1002/macp.201300235
TALENT: Tailoring Cellulose Surfaces by Controlled Polymerization MethodsAnna Carlmark
To expand the utilization of cellulose beyond its traditional uses, it is necessary to modify the surface of the fibers. This paper summarizes the modification of cellulose by controlled polymerization methods such as ATRP, RAFT, ROP, and ROMP. The combination of the excellent properties of cellulose with functional polymers creates new materials of great potential in advanced material applications.
Macromol. Chem. Phys., DOI: 10.1002/macp.201300272
TREND: The Solvent in Physical Gelation: Polymers Versus Organogelators
Debarshi Dasgupta, Jean-Michel Guenet*
A discussion of the gelation mechanisms involved in polymer thermoreversible gels and organogels is presented. The implication of the solvent as an active actor and not only a mere diluent is shown.
Macromol. Chem. Phys., DOI: 10.1002/macp.201300094
TALENT: Non-Natural Amino Acids for Protein Engineering and New Protein ChemistriesInchan Kwon,* Sung In Lim
Two distinct strategies, residue-specific and site-specific incorporation, allow biosynthesis of a protein containing non-natural amino acids. Non-natural amino acids introduced into a protein can be used to manipulate spectral and catalytic properties of a protein and provide new protein chemistries for bioconjugation with versatile molecules.
Macromol. Chem. Phys., DOI: 10.1002/macp.201200710
TREND: MAPLE Deposition of MacromoleculesKimberly B. Shepard, Rodney D. Priestley*
Matrix-assisted pulsed laser evaporation (MAPLE) is used to deposit thin films of a vast range of macromolecules, including polymers, proteins, and composite materials. The numerous advantages of MAPLE are discussed, and recent reports of MAPLE-deposited films for electronic and medical applications are highlighted.
Macromol. Chem. Phys., DOI: 10.1002/macp.201200621
TREND: Recent Trends in the Chemistry of Shape-Memory Polymers
Konstanze K. Julich-Gruner, Candy Löwenberg, Axel T. Neffe, Marc Behl, Andreas Lendlein*
Shape-memory polymers (SMPs) are stimuli-sensitive materials capable of performing complex movements on demand. This trend article highlights current approaches in the chemistry of SMPs (e.g., tailoring segment chemistry to integrate additional functions). It is illustrated that SMPs can be constructed on the molecular level as a modular system of different building blocks and netpoints.
Macromol. Chem. Phys., DOI: 10.1002/macp.201200607
TREND: Can the Structures of Semicrystalline Polymers be Controlled Using Interfacial Crystallographic Interactions?Haixin Zhou, Shouke Yan*
Epitaxy based on crystallographic interaction can govern the crystal structure of overgrowing polymers. It therefore provides a simple and efficient way to fabricate ordered structures of homopolymers with controlled chain orientation, crystal modification, and spatial arrangement of the backbone chain. An expansion of this method to control structures of polymer blends is a trend and challenge in the field of polymer science.
Macromol. Chem. Phys., DOI: 10.1002/macp.201200530
TREND: Microstructure Control: An Underestimated Parameter in Recent Polymer Design
Nezha Badi, Delphine Chan-Seng, Jean-François Lutz*
Macromolecular parameters such as tacticity, regioregularity, and co-monomer sequences determine, in large parts, the properties of polymer materials. However, these crucial aspects are currently overlooked by polymer chemists. The present article emphasizes the extreme importance of these parameters in 21st century polymer research.
Macromol. Chem. Phys., DOI: 10.1002/macp.201200475
TREND: Chemical Vapor Deposition for Solvent-Free Polymerization at SurfacesJose Luis Yagüe, Anna Maria Coclite, Christy Petruczok, Karen K. Gleason*
Initiated chemical vapor deposition (iCVD) polymerization is a very elegant technique for designing new patterns and tuning the chemistry available on any kind of surface. These polymers attract considerable attention in many different fields of application. This trends article highlights the latest achievements in the fabrication of new surfaces and functional materials via iCVD and presents significant insights in its scale-up process.
Macromol. Chem. Phys., DOI: 10.1002/macp.201200600
TALENT: Renewable Polyols for Polyurethane Synthesis via Thiol-ene/yne Couplings of Plant OilsGerard Lligadas
Nowadays, the utilization of chemicals derived from renewable feedstock is in the spotlight of the polymeric industry. Plant oils and derivatives are important platform chemicals due to their amazing chemical versatility. Herein, these materials together with thiol-ene/yne couplings are presented as a perfect ecofriendly combination to prepare hydroxyl building blocks for polyurethane technology.
Macromol. Chem. Phys., DOI: 10.1002/macp.201200582
TREND: Thieno[3,4-c]pyrrole-4,6-dione-Based Polymers for Optoelectronic ApplicationsAgnieszka Pron, Philippe Berrouard, Mario Leclerc*
Recently, push–pull type conjugated polymers consisting of thieno[3,4-c]pyrrole-4,6-dione (TPD) motif as an electron-deficient moiety gained a lot of attention for applications in plastic electronics. For instance, incorporation of TPD-based polymers into bulk heterojunction (BHJ) solar cells resulted in devices with power conversion efficiency (PCE) up to 8.5%. This Trend Article summarizes current research on such TPD-based polymers with special emphasis on structure–property relationships.
Macromol. Chem. Phys., DOI: 10.1002/macp.201200549
TALENT: New Applications of Photolabile Nitrobenzyl Groups in PolymersSamuel W. Thomas III
New approaches to photoresponsive materials with nitrobenzyl esters are described using conjugated polymers and polyelectrolyte multilayer films that respond to UV light. Photocleavage of cations from polyelectrolytes in layer-by-layer (LbL) films disrupts their integrity, while conjugated materials with nitrobenzyl pendants show photochemically controlled fluorescence efficiency and solubility.
Macromol. Chem. Phys., DOI: 10.1002/macp.201200486
TALENT: Polymers as Probes for Multimodal Imaging with MRIKristofer J. Thurecht
Polymeric systems are an ideal platform for developing multimodal molecular imaging agents due to the ability to tailor their chemo-physical properties. Polymers facilitate marrying imaging modalities that provide high resolution such as MRI, with highly sensitive modalities such as positron emission tomography or fluorescence, through manipulation of the chemical structure of the macromolecules.
Macromol. Chem. Phys., DOI: 10.1002/macp.201200420
TREND: Bioinspired Microorigami by Self-Folding Polymer FilmsLeonid Ionov
Recent advances in the development and application of biomimetic self-folding polymer films, which mimic natural mechanisms of movement and form complex 3D structures, are discussed in this manuscript.
Macromol. Chem. Phys., DOI: 10.1002/macp.201200246
TREND: Combinations of Elements: a New Paradigm for Fire Retardancy
Thirumal Mariappan, Charles A. Wilkie*
The presence of a nanodimensional material, together with a conventional fire retardant, leads to increased char formation and better fire retardancy.
Macromol. Chem. Phys., DOI: 10.1002/macp.201200363
TREND: Emergence of Polymer Stereocomplexes for Biomedical ApplicationsAnnabelle Bertin
Stereocomplexes of polylactide and poly(methyl methacrylate) are poised to have a big impact in the biomedical field because they offer improved properties and additional possibilities compared to the individual polymers in terms of tunable drug release and degradation rate as well as mechanical strength, not to mention their potential in terms of engineering of macromolecular constructs and surfaces.
Macromol. Chem. Phys., DOI: 10.1002/macp.201200143
TREND: Chemical Routes Toward Multicompartment ColloidsDaniel Crespy,* Roland Hinrich Staff, Tanja Becker, Katharina Landfester
Complex colloidal structures can be elaborated via a cornucopia of synthetic pathways. The different routes are classified in: assembly of colloids, synthesis with the use of sacrificial templates, and internal phase separation in colloidal droplets. A tentative analogy between the basic arithmetic operations and these routes is proposed.
Macromol. Chem. Phys., DOI: 10.1002/macp.201200124
TREND: Beyond Orientation: The Impact of Electric Fields on Block CopolymersClemens Liedel, Christian W. Pester, Markus Ruppel, Volker S. Urban, Alexander Böker*
Since 1991, electric fields have been shown to strongly affect block copolymer structures. Aside from alignment, morphological distortions, order–order, and order–disorder transitions have been described both in bulk and thin films. Important findings of the last two decades are summarized and perspectives for future progress in the field of block copolymers in electric fields are outlined.
Macromol. Chem. Phys., DOI: 10.1002/macp.201100590
TREND: Current Trends in the Field of Self-Healing MaterialsNathalie K. Guimard, Kim K. Oehlenschlaeger, Jiawen Zhou, Stefan Hilf, Friedrich Georg Schmidt,* Christopher Barner-Kowollik*
The development of self-healing materials has become of increasing interest to material scientists in the last 20 years, given the extraordinary advantages that such systems offer in a wide range of applications. The design of an optimal self-healing material depends on many factors, including material application, stability, and production cost.
Macromol. Chem. Phys., DOI: 10.1002/macp.201100442
TALENT: Novel Controlled Polymerization of Cyclo-olefins, Dienes, and Trienes by Utilizing Reaction Properties of Late Transition MetalsDaisuke Takeuchi
Diimine Pd complexes promote polymerization of cyclopentenes, non-conjugated dienes, and trienes to produce polymers with controlled structure. The polymers show characteristic properties including thermoreversible gelation and liquid crystalline formation. Diimine Ni complexes bring about cyclopolymerization of diallylfluorene to yield polymers containing five- and/or six-membered rings in controlled stereochemistry.
Macromol. Chem. Phys., DOI: 10.1002/macp.201100182
TREND: Externally Induced Thermal Actuation of Polymer NanocompositesYing Hu, Wei Chen*
Thermally active polymers have attracted great attention because of the convenience and effectiveness of the thermal stimulation among the stimuli-responsive polymers. The trend article presents a brief overview of recent progress on externally induced thermal actuation of polymer nanocomposites, with emphasis on the influence of embedded nanomaterials which serve as "nanoantennas" and "nanoheaters" for harvesting and converting the external stimulus into thermal stimulation.
Macromol. Chem. Phys., DOI: 10.1002/macp.201100068
TREND: What Morphologies Do We Want? - TEM Images from Dilute Diblock Copolymer SolutionsHong Zhao, Qianjin Chen, Liangzhi Hong, Lei Zhao, Jianfang Wang, Chi Wu*
Various exotic morphologies of block copolymers in solutions have been reported only based on TEM imaging. Do they really exist in solutions or are they just some kinetically frozen structures formed during the TEM sample preparation? Fairly speaking, more and more people realize that it is necessary to use cryo-TEM to ascertain different morphologies of block copolymers in solutions. However, when a modern cryo-TEM is not accessible, a combination of different methods, such as LLS, freeze-drying, and TEM should be used.
This Trend Article is addtionally featured on MaterialsViews.
Macromol. Chem. Phys., DOI: 10.1002/macp.201000696
TALENT: Polymers for Control FreaksLaura Hartmann
Compared to biological polymers, most synthetic polymers utilized in medicine are often polydisperse in nature, statistically modified, and empirically optimized. Inherent distributions result in disperse structure-property relationships, which renders interpretation of the biological properties for such polymers difficult. Laura Hartmann presents in her Talent Article a novel synthetic strategy towards monodisperse, sequence-defined poly(amidoamine)s. Variations of the chemical structures are used to directly control the ability of such polycations to complex DNA and function as non-viral vectors. Her future work is expected to provide a deeper understanding of the interactions of fully synthetic with biological systems and using these interactions for the design of bioactive polymer-based materials.
This Talent Article is addtionally featured on MaterialsViews.
Macromol. Chem. Phys., DOI: 10.1002/macp.201000479
TREND: Optical Probes of Charge Generation and Recombination in Bulk Heterojunction Organic Solar CellsIan A. Howard, Frédéric Laquai*
Understanding the principles of charge generation and recombination in organic solar cells is a prerequisite for future material development and device optimization. Optical probes, especially transient absorption spectroscopy, are valuable tools to study the dynamics of excited states such as excitons and charges, over a wide-range of timescales. New insights from recent studies may help to guide the future material development without having to rely on entirely empirical strategies for device optimization.
Macromol. Chem. Phys. 2010, DOI: 10.1002/macp.201000353
TREND: Contemporary Mass Spectrometry and the Analysis of Synthetic Polymers: Trends, Techniques and Untapped PotentialGene Hart-Smith, Christopher Barner-Kowollik*
The current Trend article - written in an easily accessible tutorial style fashion - provides an introduction to the fundamental principles of polymer mass spectrometry from the ionisation process itself to the choice of mass analyser. In addition, selected applications are highlighted and commented upon.
Macromol. Chem. Phys. 2010, DOI: 10.1002/macp.201000107
TALENT: Diels-Alder Cycloaddition-Cycloreversion: A Powerful Combo in Materials DesignAmitav Sanyal
Incorporation of the reactive maleimide group into macromolecular structures enables the fabrication of thiol reactive polymeric materials. Until recently, challenge in preserving the maleimide group during synthetic manipulations such as polymerization has hampered the development of such materials. The Diels-Alder/retro Diels-Alder reaction combination offers a viable solution to this problem. Furthermore, the reaction combination also enables the design of thermoreversible materials.
Macromol. Chem. Phys. 2010, DOI: 10.1002/macp.201000108
TREND: Glycopolymers of Various Architectures - More than Mimicking NatureBrigitte Voit,* Dietmar Appelhans
Carbohydrates have a highly important role in biological functions. The increasing understanding of their biological interactions has also triggered a strongly increased interest in the preparation of synthetic glycopolymers of various architectures and well-defined structure which can mimic biological functions in a less complex environment. In the last few years synthetic approaches in polymer science have been refined and newly developed in order to achieve complex carbohydrate architectures and to make use of them in various areas like glycomics, biotechnology, biosensors, and medicine.
Besides the use of especially controlled radical polymerization techniques, highly efficient polymer analogous reactions that can be carried out in aqueous media have been developed and applied to linear and dendritic macromolecules. Self assembly aspects and their effectiveness in biological functions have been assessed.
Macromol. Chem. Phys. 2009, DOI: 10.1002/macp.201000007
TREND: In situ Synthesis of Polymer/Clay Nanocomposites by Living and Controlled/Living PolymerizationMehmet Atilla Tasdelen, Johannes Kreutzer, Yusuf Yagci*
The present trend article reports on the recent progress of the in situ synthesis of polymer/clay nanocomposites with well-defined structures and highly exfoliated morphologies. The methods used for the preparation are classified according to the individual polymerization mechanisms. Other possibilities such as multi-mode polymerization that combines different polymerization methods and click chemistry are also described. A special emphasis is devoted to the structures and morphologies of the obtained nanocomposites rather than their practical properties.
Macromol. Chem. Phys. 2010, DOI: 10.1002/macp.200900590
TREND: Organometallic-Mediated Radical Polymerization: Developing Well-Defined Complexes for Reversible Transition Metal-Alkyl Bond HomolysisKevin M. Smith, W. Stephen McNeil, Alaa S. Abd-El-Aziz*
Organometallic-mediated radical polymerization (OMRP) has emerged as a powerful new class of living controlled radical polymerization. In order to fulfill its potential in the polymerization of vinyl acetate (VOAc) and other challenging monomers, the effects of ancillary ligands on the metal-alkyl bond dissociation energy in OMRP reagents must be thoroughly explored. Recent results investigating structure-activity relationships in well-defined cobalt, iron and chromium complexes will be discussed. The involvement of radical intermediates in oxidative addition of secondary alkyls for catalytic cross-coupling reactions catalyzed by first row transition metals will also be examined for relevant design concepts.
Macromol. Chem. Phys. 2010, DOI: 10.1002/macp.200900581
TALENT: Plant Oils as Renewable Resources in Polymer ScienceMichael A. R. Meier
Due to depleting fossil resources, the ever increasing emission of greenhouse gases and toxic waste, as well as the inefficient utilization of our available resources, we have to implement the principles of green chemistry whenever and wherever possible. Plant oils are already the most important renewable resource for the chemical industry. Due to their inherent doublebond functionality, they offer the possibility of being transformed via several very efficient catalytic processes. Especially, new developments in olefin metathesis allow the chemist to directly polymerize or introduce a variety of functional groups to these renewable resources in an efficient manner.
Therefore, olefin metathesis with plant-oil-derived fatty acids and their derivatives can contribute to a sustainable development of our future, since this approach has great potential for the substitution of currently used petrochemicals and a variety of value-added chemical intermediates, especially for the polymer industry, can be derived from these resources in a straightforward fashion. This contribution will address and discuss the most recent developments in this field of research.
Macromol. Chem. Phys. 2009, DOI: 10.1002/macp.200900168
TREND: Has Click Chemistry Lead to a Paradigm Shift in Polymer Material Design?Christopher Barner-Kowollik,* Andrew J. Inglis
Has the introduction of the click chemistry concept by Sharpless and colleagues in 2001 lead to a paradigm shift in how we approach the design of macromolecular materials; or is it simply a relatively inconsequential re-branding exercise of already existing and slightly optimized but well-tried and tested reactions as some critics would have it?
The current Trend Article analyses the situation by examining a series of select macromolecular research fields to shed light on this question, providing an unambiguous answer: The focusing of polymer chemists through the click concept on what constitutes a powerful modular chemical transformation to generate a specific polymeric material is a defining element in contemporary synthetic polymer chemistry, transcending a specific reaction. Without the introduction of the click philosophy several classes of innovative materials and polymer designs would not have been realized.
Macromol. Chem. Phys. 2009, DOI: 10.1002/macp.200900139
TALENT: Electrostatic Self-Assembly as Route to Supramolecular StructuresFranziska Gröhn
We introduce and discuss the recently developed concept of electrostatic self-assembly for the formation of nanoscale assemblies in solution. As opposed to many approaches to self-assembly relying on amphiphilicity, the driving force here is electrostatics plus secondary interaction such as stacking of aromatic molecule parts: Polyelectrolyte dendrimers can be linked with multiply charged aromatic dye molecules as structural counterions yielding 100 nm scale aggregates of narrow size distribution and different shapes. We discuss competing interaction forces and the potential of this approach to lead to versatile and functional supramolecular structures.
Macromol. Chem. Phys. 2008, DOI: 10.1002/macp.200800290
TALENT: Challenges in Glassy Dynamics of PolymersAnatoli Serghei
This work is focused on the glassy dynamics of polymers under conditions of one-dimensional confinement (in thin films). Several important topics are addressed: (a) preparative factors with large impact on the molecular dynamics of thin polymer films (oxidative degradation, plasticizing effects, residual stresses leading to metastable states); (b) it is emphasized the necessity to characterize the glass transition by measuring relaxation time distribution functions; (c) it is shown that different experimental techniques do not necessarily deliver converging results when applied to characterise the dynamics of confined polymers; (d) a novel approach is demonstrated which grants a direct experimental access to interfacial polymer dynamics; (e) measurements on nearly isolated polymer chains are presented.
Macromol. Chem. Phys. 2008, DOI: 10.1002/macp.200800197
TREND: Trends in Polyolefin ChemistryWalter Kaminsky
Polyolefins have grown faster in recent years than many other polymers. The production of poly(propylene) increased rapidly when it was possible to optimize the isotacticity of the polymer chain. New fields for future polymer sciences are the defined short and long chain branched polyolefins, block copolymers by chain shuttling, living and emulsion polymerization, and polyolefin nanocomposite materials. These research fields will create polymers with new and specific properties and applications in the near future. Compared to the formation of polymers in nature, the possibilities are today very limited for the synthetic chemistry. Especially, there are great deficits in tailoring the microstructure of copolymers with two or more monomers in a well defined way. It will be a great challenge to solve this problem but then it opens up exciting advantages.
Macromol. Chem. Phys. 2008, DOI: 10.1002/macp.200700575
TREND: Microstructured Reactors for Polymer Synthesis: A Renaissance of Continuous Flow Processes for Tailor-Made Macromolecules?Daniel Wilms, Johannes Klos, Holger Frey*
Organic synthesis in microfluidic devices has attracted increasing interest in recent years. However, little efforts had been undertaken to exploit this novel technology for polymer chemistry until several recent studies demonstrated the interesting potential of microreactors for the synthesis and modification of polymers. In fact, anionic polymerizations in continuous capillary flow-tube systems were established already in 1962 in pioneering work by Szwarc. Subsequent work focused on detailed kinetic analyses in such reactors. The present article explores different current strategies developed by several research groups to realize bulk and solution polymerizations using continuous flow microreactors. Inherent benefits and limitations of these systems compared to traditional laboratory set-ups are discussed. We present a variety of recent pioneering and advanced approaches to realize free radical, controlled radical, cationic and anionic polymerizations in microtechnological reaction devices. In some cases, surprisingly narrow molecular weight distributions have been obtained, demonstrating the promising potential of this approach for the tailoring of polymer structures.
Macromol. Chem. Phys. 2008, DOI: 10.1002/macp.200700588
TREND: Combinatorial and High-Throughput Methods in Macromolecular Materials Research and DevelopmentDean C. Webster
Combinatorial and high-throughput experimentation is used to accelerate the rate of experimentation in macromolecular science. Combinatorial and high-throughput methods are used in macromolecular science to discover and optimize catalysts for polymerization reactions, discover compositions that have specific desired properties, and systematically explore polymer structure-property relationships. The use of high-throughput methods can enable the discovery of complex catalyst systems or polymer compositions that would not be feasible using conventional experimental methods. In addition, combinatorial data can be used as inputs into computer models to enable the accurate prediction of material properties as a function of composition.
Macromol. Chem. Phys. 2008, DOI: 10.1002/macp.200700558
TALENT: Metallopolyyne Polymers as New Functional Materials for Photovoltaic and Solar Cell ApplicationsWai-Yeung Wong
The need to develop inexpensive renewable energy sources has stimulated intensive scientific research for efficient, low-cost, lightweight, photovoltaic devices. Organic polymer-based photovoltaic elements have offered the potential to obtain cheap and fabrication-easy methods to harvest energy from sunlight as compared to inorganic semiconductors. Encouraging progress has been made over the past few years in the field of photovoltaic solar cells using organic polymers. One attractive alternative discussed in this Talent Article is the development of photovoltaic and solar cells that are based on the exploitation of strongly absorbing metallopolyynes of platinum as the electron donors in bulk heterojunction devices. Power conversion efficiencies of over 4% have been achieved by blending polyplatinynes with electron-accepting methanofullerene. We predict that these conjugated organometallic congeners will make important contributions to identify environmentally friendly hi-tech solutions to the energy problem. This review includes a short summary of the recent achievements of the author in this field and relevant work by others. The ongoing challenges and future prospects of this research area are also discussed.
Macromol. Chem. Phys. 2008, DOI: 10.1002/macp.200700563
TREND: Polymer Synthesis and Modification by Use of MicrowavesMareike Bardts, Nina Gonsior, Helmut Ritter*
Nowadays, microwave-assisted polymer chemistry is a rapidly growing field of research. In the last few years, various examples of reaction accelerations, selectivities, and higher yields have been reported. In this contribution, the current state of the art is summarized and an overview on microwave-assisted polymerizations is presented, whereby special attention is given to advantages and promising future trends in this intriguing field of research.
Macromol. Chem. Phys. 2008, DOI: 10.1002/macp.200700443
TALENT: Synthetic Models of Weak Attractive Ligand-Polymer Interactions in Olefin Polymerization CatalystsMichael C. W. Chan
The subject of extremely weak hydrogen bonds such as CH...FC remains a contentious and topical area of research. The design and synthesis of a family of Group-4 post-metallocene catalysts supported by F-functionalized tridentate ligands that impose the fluorine substituent(s) in close proximity to the metal center is described, and for the first time, the elusive CH...FC interaction is characterized by a neutron diffraction study. The nature of the weak intramolecular CH...FC contacts in these complexes in solution and in the solid state is probed using multinuclear NMR spectroscopy in tandem with neutron and X-ray crystallography. These CH...FC interactions are important with regards to design implications and potential applications in olefin polymerization catalysts because they corroborate the proposed ortho-F...H() ligand-polymer contacts derived from density functional theory calculations for the Group 4 fluorinated phenoxyimine catalysts. Compared with the established agostic and cocatalyst-metal contacts, weak attractive non-covalent interactions between a non-innocent ligand and the polymer chain is a novel concept in polyolefin catalysis.
Macromol. Chem. Phys. 2008, DOI: 10.1002/macp.200700322
TALENT: Recent Gelation Studies on Irreversible and Reversible Systems with Dynamic Light Scattering and Rheology - A Concise SummarySven Richter
This contribution is a short summary of the recent achievements of the author in the field of gelation research on irreversible gelling systems based on N-vinylcaprolactam and on thermoreversible systems (xanthan gum/locust bean gum, and gelatin) mainly based on dynamic light scattering and oscillatory shear rheology. These investigations are discussed in the framework of studies of other authors. It will be pointed out that both methods are well suited to detect the sol-gel transition, but some expectations that the two different methods can lead to different results will be given, which may be of importance to other systems. In the main focus is the comparison of dynamical critical exponents yielded from the two methods at the sol-gel transition.
Macromol. Chem. Phys. 2008, DOI: 10.1002/macp.200700285
TREND: Charged Polymers via Controlled Radical Polymerization and their Implications for Gene DeliveryWilliam H. Heath, Askim F. Senyurt, John Layman, Timothy E. Long*
Non-viral gene delivery agents are notorious for their poor nucleic acid transfection efficiency and relatively high cell cytotoxicity. Thus, many investigators are exploring the important parameters involved in charged polymer-mediated gene delivery, such as chemical composition, molecular weight, structural architecture, surface charge, etc. It is important to develop clear structure-property relationships in order to design successful nucleic acid delivery agents for gene therapy. To elucidate these relationships, well-defined materials are necessary. Controlled radical polymerization methods offer a facile route to systematically produce well-defined, structurally distinct gene delivery agents. The use of charged polymers prepared via controlled radical polymerizations to elucidate transfection mechanisms or develop new delivery vectors will be reviewed herein.
Macromol. Chem. Phys. 2008, DOI: 10.1002/macp.200700216
TREND: Hierarchical Organization of Colloidal Particles: From Colloidal Crystallization to Supraparticle ChemistryErik W. Edwards, Dayang Wang,* Helmuth Möhwald
Recent developments in the hierarchical organization of micro- and nanoparticles suggest a categorical shift in which the focus has changed from colloidal crystallization based on van der Waals forces to the assembly of clusters of a well-controlled number of particles through various covalent and non-covalent interactions, referred to here as supraparticle chemistry. This article highlights some of the advances that have been made during this transition and discusses some of the promising future directions that should be realized.
Macromol. Chem. Phys. 2008, DOI: 10.1002/macp.200600655
TALENT: Functional Polymer-Bioconjugates as Molecular LEGO(R) BricksHans G. Börner
The controlled integration of sequence-defined oligopeptides into synthetic polymers leads to peptide-polymer conjugates with precisely defined, multifunctional peptide segments. These bioconjugates allow for the direct realization of bio-inspired polymer science. Peptides combine self-assembly properties with the potential to actively interact with biological systems. Hence conjugates can be exploited to program microstructure formation processes in polymeric materials by controlling secondary interactions between the peptide segments. Moreover, the programmable functionalities of the peptides can be used to tune specific interactions, e.g., between drugs and polymeric drug carriers or between inorganic crystal surfaces and polymeric crystal-growth modifiers.
Macromol. Chem. Phys. 2008, DOI: 10.1002/macp.200600559
TALENT: Poly(2-oxazoline)s: Alive and KickingRichard Hoogenboom
The development of various living/controlled polymerization techniques has allowed the synthesis of a large variety of well-defined (co)polymers with varied polymer length, composition, and architecture, for example. Screening this large possible parameter space for a polymer with certain properties can be a very demanding process. Therefore, we aim to rapidly synthesize and systematically screen libraries of copolymers to determine structure-property relationships that might allow the future design of novel (co)polymers with predictable properties. The cationic ring-opening polymerization of 2-oxazolines has been adapted for the synthesis of libraries of well-defined (co)polymers. In this contribution, the optimization of the polymerization procedure using both high-throughput experimentation and microwave irradiation is discussed. Subsequently, the microwave-assisted synthesis of well-defined libraries of (co)poly(2-oxazoline)s and the determination of structure-property relationships for these polymers is described. Moreover, the polymerization of a soy-based 2-oxazoline monomer will be illustrated as a green approach to replace current oil-based feedstock by renewable resources.
Macromol. Chem. Phys. 2008, DOI: 10.1002/macp.200600558
HIGHLIGHT: Catalytic Olefin Polymerization is a Mature Field. Isn't it?
We often hear that there is nothing left to discover in Ziegler-Natta chemistry, and that polyolefins have no more secrets to reveal. In reality, scientific research in the area has never been so much alive. Just as an example, a recent paper in Science (2006, 312, 714-719) introduces altogether a novel class of post-metallocene catalysts (see figure) and a revolutionary concept of polyolefin chain growth leading to materials with unprecedented microstructure and properties already bound for industrial production. This highlight aims at guiding the reader to the new challenging frontiers of Ziegler-Natta catalyst and material design.
HIGHLIGHT: New Methods for Anionic Polymerizations at Elevated Temperatures: "Retarded Anionic Polymerizations"
N. B. Bowden
Critical new advances in living anionic polymerizations, in particular retarded anionic polymerizations (RAP), which uses new reagents to initiate and control the polymerization, are highlighted here. The emergent area of RAP allows anionic polymerizations to be carried out under conditions that are more amenable to industrial synthesis (i.e., at elevated temperatures) and to synthesize new polymer architectures.
HIGHLIGHT: DNA-Synthetic Polymer Conjugates
The development of methods to prepare conjugated polymers in which functional moieties of DNA are connected to artificial polymers is a promising strategy to generate novel functional materials that combine the functions of both. Recent studies in the field are reviewed here with particular attention to the synthesis of a thymine-poly(thiophene) conjugated polymer, an example of a DNA function bound to a stable polymer backbone, which proved highly selective in the detection of Hg+ ions.
HIGHLIGHT: Styrene/Maleic Anhydride Macro-RAFT-Mediated Encapsulation
The encapsulation of a liquid by RAFT-mediated miniemulsion polymerization seems like a robust method. The use of a styreneûmaleic anhydride copolymer as a macro-RAFTagent offers potential for the further construction of nanostructured latex particles.
HIGHLIGHT: Towards Powering Nanometer-Scale Devices with Molecular Motors: Single Molecule Engines
Future nanodevices will require molecular motors to generate mechanical work. Single polymer chains for which an external stimulus changes the flexibility are possible candidates. The figure shows a possible working cycle of such a polymeric motor. The stimulus can be an electrochemical potential. As a proof of principle poly(ferrocenyldimethylsilane) was reversibly oxidized and reduced and its flexibility was shown to change accordingly.
HIGHLIGHT: Photodeformable Polymers - A New Kind of Promising Smart Material for Micro- and Nano-Applications
Y. Yu,* T. Ikeda*
The direct conversion of light energy into mechanical power (photomechanical effect) is achieved by deformations of photodeformable polymers. Recent developments in the field are presented, including the concept of using photo-crosslinking to prepare deformable polymers with various pre-determined shapes. The Figure shows a polymer film doped with SCAA molecules in its permanent shape (a), its temporary shape (b), and the recovered shape (c).
HIGHLIGHT: New Materials for Rapid Prototyping Applications
J. Stampfl,* R. Liska*
Rapid prototyping (RP) is a widely used manufacturing tool in the product development cycle. This Highlight gives a brief overview of the currently available RP techniques with special emphasis on three-dimensional (3D) printing. By using polymer ionomers some of the drawbacks of 3D printing can be eliminated. The article describes the chemical background of polymer ionomers and the relevance of these materials for future developments in RP.
HIGHLIGHT: Multicompartment Micelles: Has the Long-Standing Dream Become a Reality?
J.-F. Lutz,* A. Laschewsky*
The question as to whether the dream of realizing multicompartment micelles has been achieved is comprehensively answered here with the most recent advancements in this exciting field being highlighted. Multicompartment micelles are complex nanosized systems that possess a water-soluble shell and a hydrophobic core, which subsequently contains microdomains. Very recently, the morphology of such a multicompartment micelle was visualized for the first time by cryo-TEM. The future awaiting this exciting field is also discussed.
HIGHLIGHT: Multiblock Copolymers: PEO Stuck in the Middle
Robert B. Grubbs
A rare example of ABC triblock copolymer with poly(ethylene oxide) as the central block was recently reported. The copolymer was effectively prepared through the combination of living anionic polymerization, atom transfer radical polymerization, and polymer modification. This method will prove to have a great deal of versatility in allowing the incorporation of PEO blocks in interior positions of block copolymers.