Getting the Terms Right: Green, Sustainable, or Circular Chemistry?

Green chemistry, sustainable chemistry, and circular chemistry are important concepts for the modern lifestyle, current research directions, and worldwide industries. These three concepts are closely related and interconnected but cannot be used synonymously. In addition, they are addressing two different economic models, i.e., linear economy and circular economy. The current contribution focuses on the importance of these decisive chemistries for the development of a sustainable future and their role in the realm of circular economy and the planetary boundaries framework—especially for the planetary boundary of “novel entities.” Researchers active in the field of polymer chemistry play an important role as plastic pollution and resource in addition to environmental depletion, caused by the still increasing production of polymers and plastics, become more and more pronounced. It is also reported that multi- and interdisciplinary approaches are needed to develop solutions for a sustainable future

Investigation of the Porosity of Poly(sodium methacrylate) Hydrogels by ¹H‐NMR T₂‐Relaxation and Inverse Size‐Exclusion Chromatography

A series of poly(sodium methacrylate) hydrogels, also called superabsorbents, having a theoretical degree of neutralization of 100 mol%, and degree of crosslinking varying from 0.6 to 20 mol%, are synthesized via conventional free radical polymerization. The networks are characterized in detail by inverse size-exclusion chromatography and 1H-NMR relaxometry in order to place particular emphasis on the investigation of the pore size distribution (PSD) and the chain mobility, respectively. The two previously mentioned parameters are compared to understand the correlation between the elastic chain mobilities and the average pore size of the hydrogel. From the resulting data, a new empirical equation is proposed, which is valid under the given experimental conditions and permits a rough estimation of the average PSD from the relaxation data. Thus, the equation permits to reduce the number of analytical techniques needed for the characterization of complex systems such as polymer networks.</p

Synthesis of microspheres as versatile functional scaffolds for materials science applications

Functional polymeric microspheres are of great interest as they have high potential as functional scaffolds in material science applications. Highly cross-linked poly(divinyl benzene) (pDVB) microspheres can be synthesized via the precipitation polymerization technique. Recently, various methods of controlled polymerization techniques (e.g., atom transfer radical polymerization (ATRP), reversible addition fragmentation chain transfer (RAFT), and anionic ring-opening polymerization (AROP)) and highly orthogonal conjugation methods (e.g., copper-catalyzed Huisgen 1,3-dipolar cycloaddition of azides and terminal alkynes (CuAAc), thiol-ene addition and RAFT hetero Diels-Alder cycloaddition (RAFT-HDA)) have been applied to functionalize microspheres via the “grafting from” and “grafting to” approaches. The synthesis of pDVB microspheres, their susbsequent modification via grafting of polymer strands to the surface, and the characterization of the obtained functional particles are reviewed

Surface grafting via the reversible addition–fragmentation chain-transfer (RAFT) process: From polypropylene beads to core–shell microspheres

Leonie Barner studied chemistry at the Universities of Kassel and Gottingen ( Germany). She joined Michael Buback's group and received her Ph. D. in 1998. From 1998 to 2001 she held a senior research position at Sartorius ( Gottingen), developing microfiltration membranes for biotechnology applications. She then joined the Centre for Advanced Macromolecular Design, where she currently holds a senior research associate position. Her prime research interests are controlled/ living radical polymerization methods and the development of novel polymeric surfaces for biotechnology and combinatorial chemistry applications

Polymer on top: Current limits and future perspectives of quantitatively evaluating surface grafting

Well‐defined polymer strands covalently tethered onto solid substrates determine the properties of the resulting functional interface. Herein, the current approaches to determine quantitative grafting densities are assessed. Based on a brief introduction into the key theories describing polymer brush regimes, a user's guide is provided to estimating maximum chain coverage and—importantly—examine the most frequently employed approaches for determining grafting densities, i.e., dry thickness measurements, gravimetric assessment, and swelling experiments. An estimation of the reliability of these determination methods is provided via carefully evaluating their assumptions and assessing the stability of the underpinning equations. A practical access guide for comparatively and quantitatively evaluating the reliability of a given approach is thus provided, enabling the field to critically judge experimentally determined grafting densities and to avoid the reporting of grafting densities that fall outside the physically realistic parameter space. The assessment is concluded with a perspective on the development of advanced approaches for determination of grafting density, in particular, on single‐chain methodologies

Counting the Clicks in Fluorescent Polymer Networks

We introduce a fluorescence‐based methodology enabling the quantification of ligation points in photochemically prepared polymer networks. Well‐defined α,ω‐tetrazole‐capped polymer strands prepared via RAFT polymerization are crosslinked under UV irradiation by a trimaleimide via nitrile imine mediated tetrazole–ene cycloaddition. Thus, for each linkage point a fluorescent pyrazoline ring is formed, resulting in fluorescent networks, which are degradable by aminolysis of the trithiocarbonate functionalities, leading to soluble fragments. The fluorescence emission of the soluble network fragments correlates directly with the number of pyrazoline moieties originally present in the network, thus providing a direct measure of the number of ligation points constituting the network. The herein introduced strategy based on a fluorescence readout is a powerful yet simple approach to quantify network formation processes applicable to a wide class of polymers accessible via RAFT

Counting the clicks in fluorescent polymer networks

We introduce a fluorescence‐based methodology enabling the quantification of ligation points in photochemically prepared polymer networks. Well‐defined α,ω‐tetrazole‐capped polymer strands prepared via RAFT polymerization are crosslinked under UV irradiation by a trimaleimide via nitrile imine mediated tetrazole–ene cycloaddition. Thus, for each linkage point a fluorescent pyrazoline ring is formed, resulting in fluorescent networks, which are degradable by aminolysis of the trithiocarbonate functionalities, leading to soluble fragments. The fluorescence emission of the soluble network fragments correlates directly with the number of pyrazoline moieties originally present in the network, thus providing a direct measure of the number of ligation points constituting the network. The herein introduced strategy based on a fluorescence readout is a powerful yet simple approach to quantify network formation processes applicable to a wide class of polymers accessible via RAFT

Polymers with well-defined end groups via RAFT - synthesis, applications and postmodification

The control over the chain-end functionality of a polymeric chain produced by\ud controlled/‘living’ radical polymerization is inherent to the mechanism of the re- action. Indeed, \ud the final product contains a majority of polymeric chains showing an ω-functional end group which is \ud used to control the molecular weight growth. The growth of the molecular weight can be mediated \ud either via the reversible homolytic cleavage of the covalent bond between the terminal carbon and \ud the chain-end group (e.g. halogen for transition-metal-mediated living radical poly- \ud merization/atom transfer radical polymerization (ATRP), nitroxide for nitroxide- mediated \ud polymerization (NMP)) or via the degenerative transfer of chain-end groups between propagating \ud radicals and dormant species (e.g. thiocarbonylthio groups for reversible addition–fragmentation \ud chain transfer (RAFT)). Furthermore, α-functional end groups can also be introduced via the \ud initiator/mediator of the polymerization, for example, halogen alkyls (ATRP), alkyl nitroxides \ud (NMP) or\ud dithioesters (RAFT)..

The para-fluoro-thiol reaction as an efficient tool in polymer chemistry

In the current contribution, we discuss the application and potential of the versatile para-fluoro-thiol reaction in the context of synthesis and modification of polymers and materials made thereof. General reaction parameters such as solvent, temperature, and activator are reviewed. In addition, orthogonality towards some important ligation methods is examined. A brief description of the applications in which the PFTR was employed is finally provided. We postulate that the PFTR will come to be increasingly considered as a powerful complement to well-established coupling methodologies, due to the generally high selectivity of pentafluorophenyl moieties towards thiols under mild, metal-free conditions