Effects of polycaprolactone degradation products on the water flea, Daphnia magna: Carbodiimide additives have acute and chronic toxicity.

Plastics have benefited our lives in many ways, but their long persistence in the environment causes serious problems. Rapid decomposition and detoxification of plastics after use are significant challenges. As a possible solution, biodegradable plastics have attracted attention, and for environmental risk assessment research on polymer toxicity, use of indicator organisms, like water fleas and fish, has increased globally. However, such research often focuses on standardized substances without considering changes in toxicity due to plastic degradation products. Additionally, tests generally focus on acute toxicity, while long-term effects on organismal reproduction and lifespan are largely unknown. Understanding the impact of degraded polymers on biological activities is crucial for accurate risk assessment. In this study, we investigated the biological toxicity of substances generated during degradation of polycaprolactone (PCL), a common biodegradable plastic, using the indicator organism, Daphnia magna. We examined PCL, oligocaprolactones (OCLs), and monomers resulting from polymer cleavage, as well as carbodiimides, added during polyester synthesis. As a result, PCL, which is insoluble in water, reduced individual survival and total number of offspring at an exposure concentration of 100 mg/L, while no toxicity was observed for water-soluble degradation products, OCLs, and monomers. Furthermore, carbodiimides, which are expected to be released during PCL degradation, showed strong toxicity, significantly reducing individual survival and total number of offspring at 0.1-10 mg/L. These findings suggest that changes in physical properties due to polymer degradation and release of additives can significantly alter their toxicity.

Effect of Oligomers Derived from Biodegradable Polyesters on Eco- and Neurotoxicity.

Biodegradable polymers are eco-friendly materials and have attracted attention for use in a sustainable society because they are not accumulated in the environment. Although the characteristics of biodegradable polymers have been assessed well, the effects of their degradation products have not. Herein, we comprehensively evaluated the chemical toxicities of biodegradable polyester, polycaprolactone (PCL), and synthetic oligocaprolactones (OCLs) with different degrees of polymerization. While the PCL did not show any adverse effects on various organisms, high levels of shorter OCLs and the monomer (1 µg/mL for freshwater microorganisms and 1 mg/mL for marine algae and mammalian cells) damaged the tested organisms, including freshwater microorganisms, marine algae, and mammalian cells, which indicated the toxicities of the degradation products under unnaturally high concentrations. These results highlight the need for a further understanding of the effects of the degradation products resulting from biodegradable polyesters to ensure a genuinely sustainable society.

Precise characterization of a corridor-shaped structure in Khufu's Pyramid by observation of cosmic-ray muons.

Khufu's Pyramid is one of the largest archaeological monument all over the world, which still holds many mysteries. In 2016 and 2017, the ScanPyramids team reported on several discoveries of previously unknown voids by cosmic-ray muon radiography that is a non-destructive technique ideal for the investigation of large-scale structures. Among these discoveries, a corridor-shaped structure has been observed behind the so-called Chevron zone on the North face, with a length of at least 5 meters. A dedicated study of this structure was thus necessary to better understand its function in relation with the enigmatic architectural role of this Chevron. Here we report on new measurements of excellent sensitivity obtained with nuclear emulsion films from Nagoya University and gaseous detectors from CEA, revealing a structure of about 9 m length with a transverse section of about 2.0 m by 2.0 m.

Synthesis and Degradation of Vinyl Polymers with Evenly Distributed Thioacetal Bonds in Main Chains: Cationic DT Copolymerization of Vinyl Ethers and Cyclic Thioacetals.

We report a novel method to synthesize degradable poly(vinyl ether)s with cleavable thioacetal bonds periodically arranged in the main chains using controlled cationic copolymerization of vinyl ethers with a 7-membered cyclic thioacetal (7-CTA) via degenerative chain transfer (DT) to the internal thioacetal bonds. The thioacetal bonds, which are introduced into the main chain by cationic ring-opening copolymerization of 7-CTA with vinyl ethers, serve as in-chain dormant species to allow homogeneous propagation of vinyl ethers for all internal segments to afford copolymers with controlled overall and segmental molecular weights. The obtained polymers can be degraded into low- and controlled-molecular-weight polymers with narrow molecular weight distributions via hydrolysis. Various vinyl ethers with hydrophobic, hydrophilic, and functional pendants are available. Finally, one-pot synthesis of multiblock copolymers and their degradation into diblock copolymers are also achieved.

Addition-Fragmentation Ring-Opening Polymerization of Bio-Based Thiocarbonyl l-Lactide for Dual Degradable Vinyl Copolymers.

This study is designed to synthesize novel degradable polymers by radical addition-fragmentation ring-opening copolymerization of bio-based thiocarbonyl compounds with various vinyl monomers. Thiocarbonyl l-lactide is capable of radical copolymerization with acrylates and styrene via radical addition to the carbon-sulfur double bonds followed by ring-opening as well as controlled copolymerization in conjunction with the reversible addition-fragmentation chain transfer (RAFT) process. The obtained polymers possess ring-opened thioester and ring-retained thioacetal functionalities in the backbone, both of which could be cleaved under appropriate conditions with different chemical stimuli.

Sulfur-Free Radical RAFT Polymerization of Methacrylates in Homogeneous Solution: Design of exo-Olefin Chain-Transfer Agents (R-CH2 C(=CH2 )Z).

In this work, the development of exo-olefin compounds (R-CH2 C(=CH2 )Z) as chain-transfer agents for the sulfur-free reversible addition-fragmentation chain transfer (RAFT) radical polymerization of methacrylates in homogeneous solution is described. A series of exo-olefin compounds with a methyl methacrylate (MMA) dimer structure as the R group and a substituted α-methylstyrene unit as the -CH2 C(=CH2 )Z (Z: Ph-Y) group were synthesized and used for the radical polymerization of MMA in toluene and PhC(CF3 )2 OH. These compounds underwent transfer of the CH2 C(=CH2 )Z group via addition-fragmentation of the propagating methacryloyl radical. More electron-donating (Y) substituents, such as methoxy and dimethylamino groups, produced polymers with narrower molecular weight distributions. A continuous monomer addition method further improved molecular weight control and enabled the synthesis of colorless, sulfur-free, multiblock copolymers of methacrylates in homogeneous solutions.

Hydrophilic bio-based polymers by radical copolymerization of cyclic vinyl ethers derived from glycerol.

In this study, novel functional polymers were obtained by using glycerol as a bio-based precursor, which is abundant and inexpensive renewable feedstock with a polyol skeleton. Cyclic vinyl ethers with acetal linkage were derived from glycerol to yield well-defined copolymers by reversible addition-fragmentation chain transfer (RAFT) radical copolymerization with common vinyl monomers. The resulting acetal-containing copolymers could be hydrolyzed under acidic conditions to afford water-soluble functional polymers with pendent diols.

Asymmetric Cationic Polymerization of Benzofuran through a Reversible Chain-Transfer Mechanism: Optically Active Polybenzofuran with Controlled Molecular Weights.

Benzofuran (BzF) is a prochiral, 1,2-disubstituted, unsymmetric cyclic olefin that can afford optically active polymers by asymmetric polymerization, unlike common acyclic vinyl monomers. Although asymmetric cationic polymerization of BzF was reported by Natta et al. in the 1960s, the polymer structure has not been clarified, and there are no reports on molecular weight control. Herein, we report dual control of the optical activity and molecular weight of poly(BzF) using thioether-based reversible chain-transfer agents for asymmetric cationic polymerization with ß-amino acid derivatives as chiral additives and aluminum chloride as a catalyst. This asymmetric moderately living cationic polymerization leads to an increase in molecular weight and specific optical rotation with monomer conversion. In addition, asymmetric block polymers consisting of opposite absolute configurational segments were synthesized using both enantiomers sequentially as chiral additives. Finally, a comprehensive analysis of the polymerization products and the model reaction revealed that the optical activity of poly(BzF) originates from the threo-diisotactic structure, which occurs by regio-, trans-, and enantioselective propagation.

Hybridization of Step-/Chain-Growth and Radical/Cationic Polymerizations Using Thioacetals as Key Components for Triblock, Periodic and Random Multiblock Copolymers with Thermoresponsiveness.

A novel strategy for synthesizing a series of multiblock copolymers is developed by combining radical/cationic step-growth polymerizations of dithiols and divinyl ethers and chain-growth cationic degenerative chain-transfer (DT) polymerizations of vinyl ethers using thioacetals as key components. The combination of radical step-growth polymerization and a cationic thiol-ene reaction or cationic step-growth polymerization enables the synthesis of a series of macro chain-transfer agents (CTAs) composed of poly(thioether) and thioacetal groups at different positions. The resulting products are 1) bifunctional macro CTAs with thioacetal groups at both chain ends, 2) periodic macro CTAs periodically having thioacetal groups in the main chain, and 3) random macro CTAs randomly having thioacetal groups in the main chain. Subsequently, the obtained macro CTAs are used for chain-growth cationic DT polymerization of methoxyethyl vinyl ether (MOVE) to result in 1) triblock, 2) periodic, and 3) random multiblock copolymers consisting of poly(thioether) and poly(MOVE) segments. All these triblock and multiblock copolymers composed of hydrophobic poly(thioether) and hydrophilic poly(MOVE) segments show an amphiphilic tendency to form characteristic micelles in aqueous solutions. In addition, due to the thermoresponsive poly(MOVE) segments, the obtained copolymers exhibit lower critical solution temperatures that depend on the segment sequences and lengths.

Biobased Polymers via Radical Homopolymerization and Copolymerization of a Series of Terpenoid-Derived Conjugated Dienes with exo-Methylene and 6-Membered Ring.

A series of exo-methylene 6-membered ring conjugated dienes, which are directly or indirectly obtained from terpenoids, such as ß-phellandrene, carvone, piperitone, and verbenone, were radically polymerized. Although their radical homopolymerizations were very slow, radical copolymerizations proceeded well with various common vinyl monomers, such as methyl acrylate (MA), acrylonitrile (AN), methyl methacrylate (MMA), and styrene (St), resulting in copolymers with comparable incorporation ratios of bio-based cyclic conjugated monomer units ranging from 40 to 60 mol% at a 1:1 feed ratio. The monomer reactivity ratios when using AN as a comonomer were close to 0, whereas those with St were approximately 0.5 to 1, indicating that these diene monomers can be considered electron-rich monomers. Reversible addition fragmentation chain-transfer (RAFT) copolymerizations with MA, AN, MMA, and St were all successful when using S-cumyl-S'-butyl trithiocarbonate (CBTC) as the RAFT agent resulting in copolymers with controlled molecular weights. The copolymers obtained with AN, MMA, or St showed glass transition temperatures (Tg) similar to those of common vinyl polymers (Tg ~ 100 °C), indicating that biobased cyclic structures were successfully incorporated into commodity polymers without losing good thermal properties.

Multifactor Control of Vinyl Monomer Sequence, Molecular Weight, and Tacticity via Iterative Radical Additions and Olefin Metathesis Reactions.

Monomer sequence control in terms of a single monomer unit, particularly in vinyl polymers, is one of the largest challenges in polymer chemistry. Furthermore, multifactor control of monomer sequence, molecular weight, and stereoregularity is an ultimate goal. In this work, we propose a strategy to prepare C-C main-chain sequence-regulated polymers with controlled molecular weights from vinyl monomers via a combination of iterative atom transfer radical additions and olefin metathesis reactions. This strategy enabled the synthesis of sequence-regulated polymers with exact styrene-acrylate-styrene sequences in the C-C main chains, controlled molecular weights of up to 104, and stereoregularities varying with syndiotacticity, isotacticity, and heterotacticity. The utility of this strategy is further demonstrated by formation of block copolymers consisting of sequence-regulated vinyl polymer segments by combining living ROMP of norbornene derivatives.

Thiol-Ene Cationic and Radical Reactions: Cyclization, Step-Growth, and Concurrent Polymerizations for Thioacetal and Thioether Units.

Thiol-ene cationic and radical reactions were conducted for 1:1 addition between a thiol and vinyl ether, and also for cyclization and step-growth polymerization between a dithiol and divinyl ether. p-Toluenesulfonic acid (PTSA) induced a cationic thiol-ene reaction to generate a thioacetal in high yield, whereas 2,2'-azobisisobutyronitrile resulted in a radical thiol-ene reaction to give a thioether, also in high yield. The cationic and radical addition reactions between a dithiol and divinyl ether with oxyethylene units yielded amorphous poly(thioacetal)s and crystalline poly(thioether)s, respectively. Under high-dilution conditions, the cationic and radical reactions resulted in 16- and 18-membered cyclic thioacetal and thioether products, respectively. Furthermore, concurrent cationic and radical step-growth polymerizations were realized using PTSA under UV irradiation to produce polymers having both thioacetal and thioether linkages in the main chain.

Biobased Cycloolefin Polymers: Carvone-Derived Cyclic Conjugated Diene with Reactive exo-Methylene Group for Regioselective and Stereospecific Living Cationic Polymerization.

Carvone, a naturally abundant chiral cyclic α,ß-unsaturated carbonyl compound, was chemically transformed into cyclic exo-methylene conjugated dienes. The exo-methylene group had high reactivity in cationic polymerization and was efficiently polymerized in a controlled manner via regioselective 1,4-conjugated additions using initiating systems effective for living cationic polymerization of vinyl ethers. The obtained polymers with 1,3-cyclohexenyl units and tetra-substituted olefins in the main chain showed high glass transition temperatures over 110 °C. The chiral monomer underwent stereospecific polymerization to result in polymers with low solubility and weak packing of the rigid main chain in the lamellar layers. The racemic mixture resulted in soluble amorphous polymers, which were subsequently hydrogenated into cycloolefin polymers with enhanced thermal properties.

Cooperative reduction of various RAFT polymer terminals using hydrosilane and thiol via polarity reversal catalysis.

Cooperative reduction of thiocarbonylthio terminals of polymers obtained by RAFT polymerization was investigated using a catalytic amount of thiol as a polarity reversal catalyst in conjunction with hydrosilane as a reducing agent. A combination of C12H25SH and Ph3SiH enabled the complete removal of xanthate, dithiobenzoate, and trithiocarbonate groups from poly(vinyl acetate), polystyrene, and poly(methyl acrylate) under the radical conditions.

Controlled Radical Copolymerization of Cinnamic Derivatives as Renewable Vinyl Monomers with Both Acrylic and Styrenic Substituents: Reactivity, Regioselectivity, Properties, and Functions.

A series of cinnamic monomers, which can be derived from naturally occurring phenylpropanoids, were radically copolymerized with vinyl monomers such as methyl acrylate (MA) and styrene (St). Although the monomer reactivity ratios were close to zero for all the cinnamic monomers, such as methyl cinnamate (CAMe), cinnamic acid (CA), N-isopropyl cinnamide (CNIPAm), cinnamaldehyde (CAld), and cinnamonitrile (CN), they were incorporated into the copolymers and significantly increased the glass transition temperatures despite the relatively low incorporation rates of up to 40 mol % due to their rigid 1,2-disubstituted structures. The regioselectivity of the radical copolymerization of CAMe was evaluated on the basis of the results of ruthenium-catalyzed atom transfer radical additions as model reactions. The obtained products suggest that the radicals of MA and St predominantly attack the vinyl carbon of the carbonyl side of CAMe and that the propagation of CAMe mainly occurs via the styrenic radical. The ruthenium-catalyzed living radical polymerization, nitroxide-mediated polymerization (NMP), and reversible addition-fragmentation chain transfer (RAFT) polymerization provided the copolymers with controlled molecular weights, narrow molecular weight distributions, and controlled comonomer compositions. The copolymers of N-isopropylacrylamide (NIPAM) and CNIPAm prepared via RAFT copolymerization showed thermoresponsivity with a lower critical solution temperature (LCST) that could be tuned by altering the comonomer incorporation and a higher LCST than the copolymers of NIPAM and St, which possessed similar molecular weights and similar NIPAM contents, due to the additional N-isopropylamide groups in the CNIPAm units compared to the St units.

Discrete and Stereospecific Oligomers Prepared by Sequential and Alternating Single Unit Monomer Insertion.

Natural biopolymers, such as DNA and proteins, have uniform microstructures with defined molecular weight, precise monomer sequence, and stereoregularity along the polymer main chain that affords them unique biological functions. To reproduce such structurally perfect polymers and understand the mechanism of specific functions through chemical approaches, researchers have proposed using synthetic polymers as an alternative due to their broad chemical diversity and relatively simple manipulation. Herein, we report a new methodology to prepare sequence-controlled and stereospecific oligomers using alternating radical chain growth and sequential photoinduced RAFT single unit monomer insertion (photo-RAFT SUMI). Two families of cyclic monomers, the indenes and the N-substituted maleimides, can be alternatively inserted into RAFT agents, one unit at a time, allowing the monomer sequence to be controlled through sequential and alternating monomer addition. Importantly, the stereochemistry of cyclic monomer insertion into the RAFT agents is found to be trans-selective along the main chains due to steric hindrance from the repeating monomer units. All investigated cyclic monomers provide such trans-selectivity, but analogous acyclic monomers give a mixed cis- and trans-insertion.

Naturally-Derived Amphiphilic Polystyrenes Prepared by Aqueous Controlled/Living Cationic Polymerization and Copolymerization of Vinylguaiacol with R⁻OH/BF3·OEt2.

In this study, we investigated direct-controlled/living cationic polymerization and copolymerization of 4-vinylguaiacol (4VG), i.e., 4-hydroxy-3-methoxystyrene, which can be derived from naturally-occurring ferulic acid, to develop novel bio-based amphiphilic polystyrenes with phenol functions. The controlled/living cationic polymerization of 4VG was achieved using the R⁻OH/BF3·OEt2 initiating system, which is effective for the controlled/living polymerization of petroleum-derived 4-vinylphenol in the presence of a large amount of water via reversible activation of terminal C⁻OH bond catalyzed by BF3·OEt2, to result in the polymers with controlled molecular weights and narrow molecular weight distributions. The random or block copolymerization of 4VG was also examined using p-methoxystyrene (pMOS) as a comonomer with an aqueous initiating system to tune the amphiphilic nature of the 4VG-derived phenolic polymers. The obtained polymer can be expected not only to be used as a novel styrenic bio-based polymer but also as a material with amphiphilic nature for some applications.

Discovery of a big void in Khufu's Pyramid by observation of cosmic-ray muons.

The Great Pyramid, or Khufu's Pyramid, was built on the Giza plateau in Egypt during the fourth dynasty by the pharaoh Khufu (Cheops), who reigned from 2509 bc to 2483 bc. Despite being one of the oldest and largest monuments on Earth, there is no consensus about how it was built. To understand its internal structure better, we imaged the pyramid using muons, which are by-products of cosmic rays that are only partially absorbed by stone. The resulting cosmic-ray muon radiography allows us to visualize the known and any unknown voids in the pyramid in a non-invasive way. Here we report the discovery of a large void (with a cross-section similar to that of the Grand Gallery and a minimum length of 30 metres) situated above the Grand Gallery. This constitutes the first major inner structure found in the Great Pyramid since the nineteenth century. The void, named ScanPyramids' Big Void, was first observed with nuclear emulsion films installed in the Queen's chamber, then confirmed with scintillator hodoscopes set up in the same chamber and finally re-confirmed with gas detectors outside the pyramid. This large void has therefore been detected with high confidence by three different muon detection technologies and three independent analyses. These results constitute a breakthrough for the understanding of the internal structure of Khufu's Pyramid. Although there is currently no information about the intended purpose of this void, these findings show how modern particle physics can shed new light on the world's archaeological heritage.

BAB-random-C Monomer Sequence via Radical Terpolymerization of Limonene†(A), Maleimide†(B), and Methacrylate†(C): Terpene Polymers with Randomly Distributed Periodic Sequences.

A naturally abundant terpene, limonene (A), was radically polymerized with a maleimide derivative (B) and methacrylate (C) in a fluorinated alcohol to give terpolymers with unprecedented BAB-random-C sequences in which the BAB monomer sequence was randomly copolymerized with a C unit. In each binary system, limonene was hardly copolymerized with methacrylate while it was efficiently copolymerized with maleimide to result in a 1:2-alternating BAB periodic sequence, in part due to the penultimate effects and hydrogen-bonding interactions with fluoroalcohol. Methacrylate and maleimide were randomly copolymerized to give copolymers rich in methacrylate units with minimal amounts of maleimide-maleimide sequences. Their terpolymerization resulted in a BAB-r-C sequence as a consequence of the selective BAB polymerization between limonene and maleimide, the random copolymerization between methacrylate and maleimide, and the lack of copolymerization between limonene and methacrylate.

Combination of Cationic and Radical RAFT Polymerizations: A Versatile Route to Well-Defined Poly(ethyl vinyl ether)-block-poly(vinylidene fluoride) Block Copolymers.

Poly(vinylidene fluoride)-containing block copolymers are difficult to prepare and still very rare in spite of their potential use in high added value applications. This communication describes in detail the synthesis of unprecedented poly(ethyl vinyl ether)-block-poly(vinylidene fluoride) (PEVE-b-PVDF) block copolymers (BCP) via the sequential combination of cationic RAFT polymerization of vinyl ethers and radical RAFT polymerization of vinylidene fluoride (VDF). Dithiocarbamate chain transfer agents were found to efficiently control the radical RAFT polymerization of VDF and to be suitable for the preparation of PEVE-b-PVDF BCP. These new block copolymers composed of incompatible polymer segments may find applications owing to their phase segregation and self-assembly behavior.