Low weight, low price, and excellent long-term stability are the main advantages of vinyl-based polymers. Such polymers are obtained by chain-growth processes leading to all-carbon backbones, which are non(bio)degradable and nonchemically recyclable. Unfortunately, this chemical stability manifests as postuse persistence; coupled with poor waste management practices, polymers including vinyl derivatives pose major environmental problems today. Given that it is very difficult and costly to design entirely new materials that have both desired properties (mechanical, thermal, solvent resistance, etc.) and recyclability and/or biodegradability at the end of their life cycle, it seems worthwhile to transform already known materials into (bio)degradable/chemically recyclable equivalents. One approach is based on the introduction of cleavable bonds into the polymer backbone, so that degradation (by hydrolysis, for example) produces oligomers which can then be further recycled and/or bioassimilated by micro-organisms. An effective method for incorporating weak bonds randomly into the C-C backbone of a vinyl polymer is the copolymerization of vinyl monomers with cyclic monomers by radical ring-opening polymerization (rROP). This method combines the advantages of ring-opening and radical polymerization, i.e., the production of polymers with heteroatoms and/or functional groups in the main chain, with the robustness, ease of use, and mild polymerization conditions of a radical process. The aim of this tutorial review is to provide polymer chemists with guidelines to use rROP to prepare vinyl-based materials with predictable degradation. This review thus presents the rROP principle, the main families of cyclic monomers copolymerizable with vinyl monomers, and the main applications of the resulting (bio)degradable/chemically recyclable materials (polymers for packaging, latexes and degradable surfaces, 3D printing, biomaterials and water-soluble polymers).
Large wood (used interchangeably with the term "instream wood"), which refers to trees, logs and other wood within a channel, is beneficial to river ecosystems and is being used more frequently as a component of river restoration projects. We identified metrics to evaluate the effectiveness of large wood to promote ecological and geomorphic complexity within channels, which are frequent restoration goals, and employed them at several sites in New England with naturally recruited or placed large wood. Results from our signed-rank tests for the hypotheses we quantitatively evaluated revealed no significant differences in depth variability, velocity variability, velocity magnitude, or depth magnitude between reaches with and without large wood across all sites. Large wood structures did not cause the geomorphic and hydraulic changes we expected to see at either our restoration or natural recruitment sites. Wood additions were not effective at creating pools or other habitat features in erosion-resistant channels with cobble and gravel beds, but did create pools in channels with sufficient quantities of sand bedload to mobilize. We suggest that in watersheds previously occupied by continental glaciers, river restoration projects that use large wood may have limited success at generating desired hydraulic or geomorphic responses due to the relative insensitivity of the landscape to disturbance over management timescales.
Li-rich sulfides are promising alternatives to Li-rich oxides as intercalation materials, the latter suffering from limited cycling reversibility and copious voltage fade, all associated with the redox activity of oxygen ligands upon cycling. Although moving from oxygen to sulfur ligands alleviates some of these drawbacks, sulfides suffer from their lower redox potential, which limits the energy density. Here, we partially replace divalent sulfur ligands with monovalent chlorine and synthesize transition metal sulfochlorides Li2M1-x Mn x S2Cl (with M = Ti4+ and Nb5+) crystallizing in a cation-disordered rock salt (DRX) structure. Owing to the greater electronegativity of chlorine compared to sulfur, we demonstrate an increase in the average redox potential for DRX sulfochlorides. Combining ex situ X-ray absorption spectroscopy measurements at various edges and density functional theory calculations, we demonstrate that chlorine ligands preferentially form Mn-Cl and Li-Cl bonds, while sulfur ligands preferentially coordinate the high valence d0 metals. While sulfur ligands are redox active throughout the charge (and discharge), Mn2+ redox activity depends on the chemical composition, with Li2Ti0.5Mn0.5S2Cl showing cationic redox activity only at the end of the charge and beginning of the discharge. More dramatically, our experimental and computational results demonstrate that the S-S bond formation induces sizable changes in local coordination and partial material dissolution into the electrolyte, triggering cell corrosion and/or short formation as early as the second cycle. Through an electrolyte engineering approach, combining a Cl-scavenger molecule with a cathode electrolyte interphase former, we demonstrate that corrosion and/or shorts formation can be suppressed, and intrinsic cycling properties of sulfochloride DRX materials are investigated. Our work extends the chemical space for designing better intercalation materials, showing the unique opportunities brought by mixed anion compounds.
This article compares two paradigms used to describe, explain, and optimize human development, the Cartesian split, essentialist, and reductionist paradigm and the process-relational one, and the metatheories associated with them, the reductionist metamodel and the dynamic, relational developmental systems (RDS) metamodel, respectively. We provide an RDS-based rationale for rejecting the splitting of quantitative and qualitative changes in depicting human development, discuss past attempts to address issues surrounding quantitative versus qualitative changes, argue that these approaches have failed to adequately provide a theory of the x-axis (time) and, as such, obscure the dynamic integration of quantitative fluctuations and qualitative transformation across the life span. We present a dynamic, RDS-based means to conceptualize and identify ontogenetic tipping points between quantitative fluctuations and qualitative transformations in intraindividual change. Using RDS-based concepts, we recommend methodological means to design, measure, and analyze the integration of quantitative and qualitative change across the human life span.
This paper examines whether the home-market effect (HME)-a foundational prediction of trade theory-applies to the global arms trade. Using bilateral weapons trade data from 1950 to 2007 and building on the framework of Costinot et al. (2019), we construct a country-year-specific composite demand proxy to test for the presence of HME in the weapons industry. Our baseline and robustness results consistently show no evidence of a home-market effect, either in its weak or strong form. Additional analyzes using alternative proxies, estimation methods, and data sources confirm this finding. However, we identify a weak HME during the Cold War period, suggesting structural differences before and after the dissolution of the Soviet Union. Further gravity estimations reveal that arms trade flows are shaped more by geopolitical factors-such as sanctions and alliances-than by domestic demand. Our findings highlight the unique nature of the global arms market compared to conventional industries.
