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Polymers produced by ring-opening metathesis polymerization (ROMP) of strained cyclic olefin monomers, such as norbornene and cyclobutene, are challenging to depolymerize back to their constituent monomers due to their favorable polymerization thermodynamics. Current strategies for creating depolymerizable ROMP polymers focus on designing low-strain monomers with small enthalpic driving forces, which facilitate depolymerization by reducing the monomer polymerizability. Because polymerization thermodynamics is governed by both enthalpic and entropic contributions, we reason that depolymerizable polymers could be achieved from highly strained cyclic olefin monomers if the entropic penalty of polymerization is sufficiently large. Here, we present a depolymerizable polymer system based on a series of strained bicyclo[3.2.1] monomers, which combine a substantial enthalpic driving force (−6 to −11 kcal/mol) with a significant entropic penalty of polymerization (−15 to −24 cal/mol/K). The large entropic penalty, arising from the rigid polymer backbone, lowers the ceiling temperature and imparts depolymerizability to the polymer system, leading to monomer recovery (74–99%) under standard ring-closing metathesis conditions. Moreover, the enthalpic driving force remains sufficient to enable efficient ring-opening metathesis polymerization and block copolymer synthesis. This entropy-driven strategy thus unlocks access to depolymerizable polymers from strained cyclic olefin monomers that are not traditionally considered building blocks for such materials, offering a new direction for the design of chemically recyclable polymers with an expanded monomer scope. 

Degradable polymers are promising materials for use to reduce plastic waste and advance biomedical applications. However, to meet the demands of specific applications, tailoring the properties of degradable polymers through precise modification of their chemical structures is critical. Herein, we present a new class of degradable and functionalizable polyacetals synthesized by the ring-opening metathesis copolymerization (ROMP) of two commercially available monomers: dimethyl oxanorbornadiene-2,3-dicarboxylate (OND) and 4,7-dihydro-1,3-dioxepin (DXP). The resulting polyacetals are not only acid-degradable but also readily and efficiently functionalizable via thia–Michael addition, yielding degradable polymer materials with various functional groups and tunable thermal properties. 

Ring-opening metathesis polymerization (ROMP) has been widely used for the synthesis of functional polymers. However, most ROMP-derived polymers are nondepolymerizable, limiting their sustainability and eco-friendiness. While recent advances in designing low-strain cyclic olefin monomers have enabled the ROMP synthesis of depolymerizable polyolefins, the scope of these monomers remains limited due to the narrow range of ring strain energies (RSEs = 4.7–5.4 kcal/mol) required to allow both polymerization and depolymerization in a closed-loop recycling process. Herein, we present a new class of chemically recyclable polyolefins based on cycloheptene derivatives with RSEs ranging from 3.8 to 7.2 kcal/mol. The wide range of RSEs enabled the establishment of a structure–polymerizability–depolymerizability relationship, shedding light on the role of RSE in both polymerization and depolymerization. A functional group transformation (FGT) strategy, harnessing reversible ketone-to-acetal chemistry, was developed to overcome the low polymerizability of low-strain monomers and the moderate depolymerizability of polymers made from moderate-strain monomers. This FGT approach not only enhanced the chemical recycling of moderately depolymerizable polyolefins but also provided access to highly depolymerizable polyolefins that are challenging to synthesize through direct ROMP of ultralow strain monomers. Moreover, the thermal properties of the chemically recyclable polyolefins developed in this study are highly tunable, with a broad range of glass transition temperatures (−7 to 104 °C), highlighting their potential for various applications. 

Here we report the design and synthesis of acid-degradable and functionalizable polymers via alternating ring-opening metathesis copolymerization of oxanorbornadiene dicarboxylate and 2,3-dihydrofuran. The resulting polymers can undergo post-polymerization modification through... 

Under the $\mathrm{AdS}/\mathrm{CFT}$correspondence, asymptotically anti–de Sitter geometries with backreaction can be viewed as conformal field theory states subject to a renormalization group (RG) flow from an ultraviolet (UV) description toward an infrared (IR) sector. For black holes, however, the IR point is the horizon, so one way to interpret the interior is as an analytic continuation to a “trans-IR” imaginary-energy regime. In this paper, we demonstrate that this analytic continuation preserves some imprints of the UV physics, particularly near its “end point” at the classical singularity. We focus on holographic phase transitions of geometric objects in round black holes. We first assert the consistency of interpreting such black holes, including their interiors, as RG flows by constructing a monotonic $a$function. We then explore how UV phase transitions of entanglement entropy and scalar two-point functions, each of which are encoded by bulk geometry under the holographic mapping, are related to the structure of the near-singularity geometry, which is quantified by Kasner exponents. Using 2D holographic flows triggered by relevant scalar deformations as test beds, we find that the 3D bulk’s near-singularity Kasner exponents can be viewed as functions of the UV physics precisely when the deformation is nonzero. Published by the American Physical Society2024 

Biomass-derived polymer materials are emerging as sustainable and low-carbon footprint alternatives to the current petroleum-based commodity plastics. In the past decade, the ring-opening metathesis polymerization (ROMP) technique has been widely used for the polymerization of cyclic olefin monomers derived from biorenewable resources, giving rise to a diverse set of biobased polymer materials. However, most synthetic biobased polymers made by ROMP are nondegradable because of their all-carbon backbones. Herein, we present a modular synthetic strategy to acid-degradable poly(enol ether)s via ring-opening metathesis copolymerization of biorenewable oxanorbornenes and 3,4-dihydropyran (DHP). 1H NMR analysis reveals that the percentage of DHP units in the resulting copolymers gradually increases as the feed ratio of DHP to oxanorbornene increases. The composition of the copolymers plays a pivotal role in governing their thermal properties. Thermogravimetric analysis shows that an increasing percentage of DHP results in a decrease in the decomposition temperatures, suggesting that the incorporation of enol ether groups in the polymer backbone reduces the thermal stability of the copolymers. Moreover, a wide range of glass transition temperatures (16–165 °C) can be achieved by tuning the copolymer composition and the oxanorbornene structure. Critically, all of the poly(enol ether)s developed in this study are degradable under mildly acidic conditions. A higher incorporation of DHP in the copolymer leads to enhanced degradability, as evidenced by smaller final degradation products. Altogether, this study provides a facile approach for synthesizing biorenewable and degradable polymer materials with highly tunable thermal properties desired for their potential industrial applications. 

Low‐strain cyclic olefin monomers, including five‐membered, six‐membered, eight‐membered, and macrocyclic rings, have been recently exploited for the synthesis of depolymerizable polyolefins via ring‐opening metathesis polymerization (ROMP). Such polyolefins can undergo ring‐closing metathesis depolymerization (RCMD) to regenerate their original monomers. Nevertheless, the depolymerization behavior of polyolefins prepared by ROMP of seven‐membered cyclic olefins, an important class of low‐strain rings, still remains unexplored. In this study, we demonstrate the chemical recycling of polyheptenamers to cycloheptene under standard RCMD conditions. Highly efficient depolymerization of polyheptenamer was enabled by Grubbs' second‐generation catalyst in toluene. It was observed that the monomer yields increased when the depolymerization temperature increased and the starting polymer concentration was reduced. A near‐quantitative monomer regeneration (>96%) was achieved within 1 h under dilute conditions (20 mM of olefins) at 60°C. Moreover, polyheptenamer exhibited a decomposition temperature above 430°C, highlighting its potential as a new class of thermally stable and chemically recyclable polymer materials. 

Abstract Clustering analysis of sequence data continues to address many applications in engineering design, aided with the rapid growth of machine learning in applied science. This paper presents an unsupervised machine learning algorithm to extract defining characteristics of earthquake ground‐motion spectra, also called latent features, to aid in ground‐motion selection (GMS). In this context, a latent feature is a low‐dimensional machine‐discovered spectral characteristic learned through nonlinear relationships of a neural network autoencoder. Machine discovered latent features can be combined with traditionally defined intensity measures and clustering can be performed to select a representative subgroup from a large ground‐motion suite. The objective of efficient GMS is to choose characteristic records representative of what the structure will probabilistically experience in its lifetime. Three examples are presented to validate this approach, including the use of synthetic and field recorded ground‐motion datasets. The presented deep embedding clustering of ground‐motion spectra has three main advantages: (1) defining characteristics that represent the sparse spectral content of ground motions are discovered efficiently through training of the autoencoder, (2) domain knowledge is incorporated into the machine learning framework with conditional variables in the deep embedding scheme, and (3) the method results in a ground‐motion subgroup that is more representative of the original ground‐motion suite compared to traditional GMS techniques. 

Degradable polymers made via ring-opening metathesis polymerization (ROMP) hold tremendous promise as eco-friendly materials. However, most of the ROMP monomers are derived from petroleum resources, which are typically considered less sustainable compared to biomass. Herein, we present a synthetic strategy to degradable polymers by harnessing alternating ROMP of biomass-based cyclic olefin monomers including exo-oxanorbornenes and cyclic enol ethers. A library of well-defined poly(enol ether)s with modular structures, tunable glass transition temperatures, and controlled molecular weights was achieved, demonstrating the versatility of this approach. Most importantly, the resulting copolymers exhibit high degrees of alternation, rendering their backbones fully degradable under acidic conditions.