Biomass-derived materials possess vast potential for material science and industry in the next decades. Dwindling fossil resources and an increasing environmental awareness increase the demand for ...sustainable feedstock-based alternatives. In addition to natural rubber (cis-1,4-polyisoprene), the class of terpenes offers a large variety of renewable monomers, like the 1,3-diene monomers β-myrcene and β-farnesene. Living anionic polymerization of bio-based 1,3-diene monomers enables the synthesis of well-defined, high molecular weight block- and statistical copolymers with unique control over molecular weights, polymer architecture, and polydiene microstructure. The resulting materials can be used for a variety of applications. For instance, polyfarnesene has been introduced as an additive in tire mixtures and replaces fossil resource-based rubbery building blocks in styrenic thermoplastic elastomers. In addition, the unsaturated nature of polymyrcene and polyfarnesene renders them accessible for functionalization by a variety of postmodification reactions, which results, for example, in improved interaction with functional fillers. (End-)functionalized polyterpenes are promising candidates as precursors for the synthesis of fully bio-based thermoplastic elastomers. In this Perspective we provide an overview of recent developments regarding the anionic polymerization of terpenes and the considerable potential the resulting polymer architectures offer for material science and a more sustainable future.
Concurrent with the rapid development of both dendrimers and hyperbranched polymers, a novel class of block copolymer architectures has emerged from the combination of these dendritic architectures ...with linear chains, the “
linear–
dendritic block copolymers” (LDBCs). This review gives a comprehensive summary of the state of the art in this rapidly developing field from pioneering early work to promising recent approaches.The different strategies leading to these hybrid architectures with either perfect dendrimer/dendron building blocks or imperfect, yet more conveniently accessible hyperbranched segments, are reviewed and compared. The consequences of the unusual polymer topology for supramolecular structures both in solution and in the solid state are summarized, and important differences in comparison with classical linear block copolymer structures are highlighted. Current challenges in the area of block copolymers, nanotechnology and potential applications of linear–dendritic block copolymers are also considered.
Dendritic macromolecules with random branch-on-branch topology, termed hyperbranched polymers in the late 1980s, have a decided advantage over symmetrical dendrimers by virtue of typically being ...accessible in a one-step synthesis. Saving this synthetic effort once had an unfortunate consequence, though: hyperbranching polymerization used to result in a broad distribution of molecular weights (that is, very high polydispersities, often M w/M n > 5). By contrast, a typical dendrimer synthesis yields a single molecule (in other words, M w/M n = 1.0), albeit by a labor-intensive, multistep process. But 10 years ago, Sunder and colleagues reported the controlled synthesis of well-defined hyperbranched polyglycerol (PG) via ring-opening multibranching polymerization (ROMBP) of glycidol. Since then, hyperbranched and polyfunctional polyethers with controlled molar mass and low polydispersities (M w/M n = 1.2−1.9) have been prepared, through various monomer addition protocols, by ROMBP. In this Account, we review the progress in the preparation and application of these uniquely versatile polyether polyols over the past decade. Hyperbranched PGs combine several remarkable features, including a highly flexible aliphatic polyether backbone, multiple hydrophilic groups, and excellent biocompatibility. Within the past decade, intense efforts have been directed at the optimization of synthetic procedures affording PG homo- and copolymers with different molecular weight characteristics and topology. Fundamental parameters of hyperbranched polymers include molar mass, polydispersity, degree of branching, and end-group functionality. Selected approaches for optimizing and tailoring these characteristics are presented and classified with respect to their application potential. Specific functionalization in the core and at the periphery of hyperbranched PG has been pursued to meet the growing demand for novel specialty materials in academia and industry. A variety of fascinating synthetic approaches now provide access to well-defined, complex macromolecular architectures based on polyether polyols with low polydispersity. For instance, a variety of linear−hyperbranched block copolymers has been reported. The inherent attributes of PG-based materials are useful for a number of individual implementation concepts, such as drug encapsulation or surface modification. The excellent biocompatibility of PG has also led to rapidly growing significance in biomedical applications, for example, bioconjugation with peptides, as well as surface attachment for the creation of protein-resistant surfaces.
The review summarizes current trends and developments in the polymerization of alkylene oxides in the last two decades since 1995, with a particular focus on the most important epoxide monomers ...ethylene oxide (EO), propylene oxide (PO), and butylene oxide (BO). Classical synthetic pathways, i.e., anionic polymerization, coordination polymerization, and cationic polymerization of epoxides (oxiranes), are briefly reviewed. The main focus of the review lies on more recent and in some cases metal-free methods for epoxide polymerization, i.e., the activated monomer strategy, the use of organocatalysts, such as N-heterocyclic carbenes (NHCs) and N-heterocyclic olefins (NHOs) as well as phosphazene bases. In addition, the commercially relevant double-metal cyanide (DMC) catalyst systems are discussed. Besides the synthetic progress, new types of multifunctional linear PEG (mf-PEG) and PPO structures accessible by copolymerization of EO or PO with functional epoxide comonomers are presented as well as complex branched, hyperbranched, and dendrimer like polyethers. Amphiphilic block copolymers based on PEO and PPO (Poloxamers and Pluronics) and advances in the area of PEGylation as the most important bioconjugation strategy are also summarized. With the ever growing toolbox for epoxide polymerization, a “polyether universe” may be envisaged that in its structural diversity parallels the immense variety of structural options available for polymers based on vinyl monomers with a purely carbon-based backbone.
The functional, aliphatic poly(1,2-glycerol carbonate) as a fundamental, simple polymer structure based on glycerol and CO2 was prepared by combination of glycidyl ether monomers with carbon dioxide ...via two different approaches. The material was obtained by two-step procedures either via copolymerization of (i) ethoxy ethyl glycidyl ether (EEGE) or (ii) benzyl glycidyl ether (BGE) with CO2, followed by removal of the respective protecting groups via acidic cleavage for (i) and hydrogenation for (ii). The resulting protected polycarbonate structures and the targeted poly(1,2-glycerol carbonate) were investigated with 1H NMR and 13C NMR spectroscopy as well as 2D-NMR methods. Removal of both protecting groups was possible without significant backbone degradation; however, the hydrogenation route for (ii) turned out to be advantageous. All new poly(carbonate)s have been characterized with respect to their thermal behavior. Protected and deprotected poly(1,2-glycerol carbonate)s were obtained with molecular weights in the range of 5000–25 200 g/mol and a PDI from 1.24 to 2.33. The degradation kinetics of poly(1,2-glycerol carbonate) in DMF has also been studied, demonstrating rather rapid degradation within several days to oligomers and cyclic carbonates.
Celebrating the 100th anniversary of Staudinger's “macromolecular concept”, polymer scientists critically evaluate the past developments and future challenges of polymer science, asking: Quo vadis, ...Macromolecular Science? The main focus in Polymer Science has been on linear polymers or crosslinked systems (elastomers and thermosets) until the late 1980ies. The advent of dendritic polymers, i.e. dendrimers and hyperbranched polymers (HBPs) attracted wide-spread attention in the polymer community. This article gives a brief overview of the developments in the area of hyperbranched polymers and demonstrates that they have since become a novel class of polymer materials.
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•Paul Flory created the foundation of hyperbranched polymers in 1952.•Multifunctional AB(f-1) polycondensation leads to hyperbranched materials.•Modern concepts permit impressive structural control of Mn and moderate dispersity.•Increasing control of degree of polymerization (DP) and degree of branching (DB).•Hyperbranched polymers with manifold chemistries established.
Due to their sensitive reaction to changes in climatic conditions, glaciers have been selected as an essential climate variable (ECV). Although a large amount of ice is located in the Himalayas, this ...region is yet only sparsely represented in global glacier databases. Accordingly, a sound and comprehensive change assessment or determination of water resources was not yet possible. In this study, we present a new glacier inventory for the western Himalayas, compiled from Landsat ETM+ scenes acquired between 2000 and 2002, coherence images from ALOS PALSAR image pairs, the SRTM digital elevation model (DEM) and the ASTER Global DEM (GDEM). Several specific challenges for glacier mapping were found in this region and addressed. They are related to debris cover, orographic clouds, locally variable snow conditions, and creeping permafrost features in cold-dry regions. Additional to seven topographic parameters that are obtained from the ASTER GDEM for each glacier, we also determined the relative amount of debris cover on the glacier surface. The inventory contains 11,400 glaciers larger than 0.02km2, which cover a total area of 9,310km2. Analysis of the inventory data revealed characteristic patterns of mean glacier elevation and relative debris cover amounts that might be related to the governing climatic conditions. The full dataset will be freely available in the GLIMS glacier database to foster further analyses and modeling of the glaciers in this region.
► A glacier inventory for the W-Himalayas was compiled using 7 Landsat ETM+ scenes. ► Challenging conditions for glacier mapping were encountered and addressed. ► ALOS PALSAR coherence images were used to delineate debris-covered glacier parts. ► The inventory consists of 11,550 glaciers (9,370km2) with 7 topographic parameters. ► Dataset is submitted to the GLIMS database and provides a basis for future analyses.
Polyglycerols (sometimes also called “polyglycidols”) represent a class of highly biocompatible and multihydroxy-functional polymers that may be considered as a multifunctional analogue of ...poly(ethylene glycol) (PEG). Various architectures based on a polyglycerol scaffold are feasible depending on the monomer employed. While polymerization of glycidol leads to hyperbranched polyglycerols, the precisely defined linear analogue is obtained by using suitably protected glycidol as a monomer, followed by removal of the protective group in a postpolymerization step. This review summarizes the properties and synthetic approaches toward linear polyglycerols (linPG), which are at present mainly based on the application of ethoxyethyl glycidyl ether (EEGE) as an acetal-protected glycidol derivative. Particular emphasis is placed on the manifold functionalization strategies including, e.g., the synthesis of end-functional linPGs or multiheterofunctional modifications at the polyether backbone. Potential applications like bioconjugation and utilization as a component in degradable biomaterials or for diagnostics, in which polyglycerol acts as a promising PEG substitute are discussed. In the last section, the important role of linear polyglycerol as a macroinitiator or as a highly hydrophilic segment in block co- or terpolymers is highlighted.
Photo‐induced reversibility as a tool for self‐healing: a reversible photo‐induced dendritic macromonomer was synthesized and proven to form networks with different features depending on the ...crosslinking conditions. While networks formed from aqueous systems exhibited a reversible change in their crosslinking degree, networks generated in bulk underwent fully reversibility. The latter was then exploited for generating self‐healing materials by means of a photo‐induced treatment.
Reversible photo‐chemistry was exploited as a very powerful tool to generate not only a novel reversible photo‐active dendritic macromonomer, but also light tunable and self‐healing materials. The macromonomer was photo‐crosslinked under different conditions. Networks produced in aqueous systems showed reversibility in their crosslinking degree whereas networks generated in bulk were fully reversible, which allowed their use to formulate photo‐induced self‐healing materials
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