Pub Date : 2024-10-23DOI: 10.1021/acs.chemrev.3c0064310.1021/acs.chemrev.3c00643
Jonathan D. Schultz*, Jonathon L. Yuly*, Eric A. Arsenault, Kelsey Parker, Sutirtha N. Chowdhury, Reshmi Dani, Sohang Kundu, Hanggai Nuomin, Zhendian Zhang, Jesús Valdiviezo, Peng Zhang, Kaydren Orcutt, Seogjoo J. Jang, Graham R. Fleming, Nancy Makri, Jennifer P. Ogilvie, Michael J. Therien, Michael R. Wasielewski and David N. Beratan*,
Coherence refers to correlations in waves. Because matter has a wave-particle nature, it is unsurprising that coherence has deep connections with the most contemporary issues in chemistry research (e.g., energy harvesting, femtosecond spectroscopy, molecular qubits and more). But what does the word “coherence” really mean in the context of molecules and other quantum systems? We provide a review of key concepts, definitions, and methodologies, surrounding coherence phenomena in chemistry, and we describe how the terms “coherence” and “quantum coherence” refer to many different phenomena in chemistry. Moreover, we show how these notions are related to the concept of an interference pattern. Coherence phenomena are indeed complex, and ambiguous definitions may spawn confusion. By describing the many definitions and contexts for coherence in the molecular sciences, we aim to enhance understanding and communication in this broad and active area of chemistry.
{"title":"Coherence in Chemistry: Foundations and Frontiers","authors":"Jonathan D. Schultz*, Jonathon L. Yuly*, Eric A. Arsenault, Kelsey Parker, Sutirtha N. Chowdhury, Reshmi Dani, Sohang Kundu, Hanggai Nuomin, Zhendian Zhang, Jesús Valdiviezo, Peng Zhang, Kaydren Orcutt, Seogjoo J. Jang, Graham R. Fleming, Nancy Makri, Jennifer P. Ogilvie, Michael J. Therien, Michael R. Wasielewski and David N. Beratan*, ","doi":"10.1021/acs.chemrev.3c0064310.1021/acs.chemrev.3c00643","DOIUrl":"https://doi.org/10.1021/acs.chemrev.3c00643https://doi.org/10.1021/acs.chemrev.3c00643","url":null,"abstract":"<p >Coherence refers to correlations in waves. Because matter has a wave-particle nature, it is unsurprising that coherence has deep connections with the most contemporary issues in chemistry research (e.g., energy harvesting, femtosecond spectroscopy, molecular qubits and more). But what does the word “coherence” really mean in the context of molecules and other quantum systems? We provide a review of key concepts, definitions, and methodologies, surrounding coherence phenomena in chemistry, and we describe how the terms “coherence” and “quantum coherence” refer to many different phenomena in chemistry. Moreover, we show how these notions are related to the concept of an interference pattern. Coherence phenomena are indeed complex, and ambiguous definitions may spawn confusion. By describing the many definitions and contexts for coherence in the molecular sciences, we aim to enhance understanding and communication in this broad and active area of chemistry.</p>","PeriodicalId":51,"journal":{"name":"Macromolecules","volume":"124 21","pages":"11641–11766 11641–11766"},"PeriodicalIF":51.4,"publicationDate":"2024-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142609060","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Oxidative cracking of polyolefins into functionalized molecules or oligomers promises the chemical upcycling of plastic wastes. In this work, we develop a novel approach to polyolefin waste upcycling that utilizes low-temperature oxidative cracking combined with dynamic cross-linking to produce recyclable elastomers. High-density polyethylene is oxidized into functionalized oligomers with end carboxyl groups at 110 °C, achieving tunable number-average molecular weights (Mn) ranging from 1500 to 5500 Da at distributions (D̵) between 2.91 and 3.33. These oligomers with high crystallinity directly react with amorphous cis-polybutadiene containing pendant epoxy groups (an oxidized product of cis-polybutadiene) through esterification, forming a dynamically cross-linked elastomer. The elastomer displays a low glass transition temperature (Tg) of approximately −100 °C while maintaining a melting point (Tm) above 80 °C; it showcases a Young′s modulus (E) of 12.0 ± 0.4 MPa, elongation at break (ε) of 600 ± 28%, tensile strength (σ) of 16.4 ± 0.8 MPa, tensile toughness (UT) of 46.0 ± 3.5 MJ·m–3, and a good elasticity with 81.8% elastic recovery in a 10-cycle tensile test, even higher than that of commercial POEs such as POE-8150 of Dow Company. The dynamic ester-bond-based cross-linking enables the elastomer to be reprocessed. Our study introduces an efficient chemical upcycling process for polyolefin wastes, eliminating the need for tedious separation steps of cracking products.
{"title":"Oxidative Upcycling of Polyolefin Wastes into the Dynamically Cross-Linked Elastomer","authors":"Yinlong Chang, Yangke Xiao, Minghao Sun, Weiqiang Gao, Liqian Zhu, Qingyue Wang, Wen-Jun Wang, Bo-Geng Li, Pingwei Liu","doi":"10.1021/acs.macromol.4c01869","DOIUrl":"https://doi.org/10.1021/acs.macromol.4c01869","url":null,"abstract":"Oxidative cracking of polyolefins into functionalized molecules or oligomers promises the chemical upcycling of plastic wastes. In this work, we develop a novel approach to polyolefin waste upcycling that utilizes low-temperature oxidative cracking combined with dynamic cross-linking to produce recyclable elastomers. High-density polyethylene is oxidized into functionalized oligomers with end carboxyl groups at 110 °C, achieving tunable number-average molecular weights (<i>M</i><sub>n</sub>) ranging from 1500 to 5500 Da at distributions (<i>D̵</i>) between 2.91 and 3.33. These oligomers with high crystallinity directly react with amorphous <i>cis</i>-polybutadiene containing pendant epoxy groups (an oxidized product of <i>cis</i>-polybutadiene) through esterification, forming a dynamically cross-linked elastomer. The elastomer displays a low glass transition temperature (<i>T</i><sub>g</sub>) of approximately −100 °C while maintaining a melting point (<i>T</i><sub>m</sub>) above 80 °C; it showcases a Young′s modulus (<i>E</i>) of 12.0 ± 0.4 MPa, elongation at break (ε) of 600 ± 28%, tensile strength (σ) of 16.4 ± 0.8 MPa, tensile toughness (<i>U</i><sub>T</sub>) of 46.0 ± 3.5 MJ·m<sup>–3</sup>, and a good elasticity with 81.8% elastic recovery in a 10-cycle tensile test, even higher than that of commercial POEs such as POE-8150 of Dow Company. The dynamic ester-bond-based cross-linking enables the elastomer to be reprocessed. Our study introduces an efficient chemical upcycling process for polyolefin wastes, eliminating the need for tedious separation steps of cracking products.","PeriodicalId":51,"journal":{"name":"Macromolecules","volume":"25 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142488015","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-23DOI: 10.1021/acs.macromol.4c01540
Jooyoung Chang, Narayanan Menon, Thomas P. Russell
Wrinkling patterns were used to investigate the mechanical properties of thin poly(styrene) (PS)/poly(methyl methacrylate) (PMMA) and PS/gold (Au) bilayer films. Films were floated on water with a water drop on the surface to induce wrinkling. The thicknesses and thickness ratios of the films were varied over a broad range. The PS/PMMA bilayer was chosen to provide a contrast in wetting properties, with equilibrium contact angles of θPMMA = 68° and θPS = 88° with water. The PS/Au bilayer was chosen to provide a large contrast in Young’s moduli, EAu = 72 GPa and EPS = 3.4 GPa. The stretching (Y) and bending (B) moduli of the bilayer films were obtained from measurements of the length and number of wrinkles in the wrinkle patterns. The experimentally derived values of Y and B were in reasonable agreement with the values computed from the bulk Young’s moduli and the thicknesses of the two components in the bilayer. The values of Y and B did not depend on which face of the film was exposed to the water droplet or bath when the capillary stresses were considered. Thus, finite size effects from the film thicknesses were unimportant over the range of thicknesses studied, and no relative displacement of the films was found, with the films remaining well-bonded even with deformation associated with wrinkling.
皱纹图案用于研究聚苯乙烯（PS）/聚甲基丙烯酸甲酯（PMMA）和聚苯乙烯/金（Au）双层薄膜的机械特性。薄膜漂浮在水面上，表面上有水滴诱发起皱。薄膜的厚度和厚度比在很大范围内变化。选择 PS/PMMA 双层膜是为了提供润湿性能的对比，其与水的平衡接触角分别为 θPMMA = 68° 和 θPS = 88°。选择 PS/Au 双层膜是为了提供较大的杨氏模量对比：EAu = 72 GPa 和 EPS = 3.4 GPa。双层薄膜的拉伸（Y）和弯曲（B）模量是通过测量皱纹图案中皱纹的长度和数量获得的。实验得出的 Y 值和 B 值与根据双层膜中两种成分的体杨氏模量和厚度计算得出的值基本一致。在考虑毛细应力时，Y 和 B 的值并不取决于薄膜的哪一面暴露在水滴或水浴中。因此，在所研究的薄膜厚度范围内，薄膜厚度的有限尺寸效应并不重要，也没有发现薄膜的相对位移，即使发生与起皱有关的变形，薄膜也能保持良好的粘结性。
{"title":"Stretching and Bending Moduli of Bilayer Films Inferred from Wrinkle Patterns","authors":"Jooyoung Chang, Narayanan Menon, Thomas P. Russell","doi":"10.1021/acs.macromol.4c01540","DOIUrl":"https://doi.org/10.1021/acs.macromol.4c01540","url":null,"abstract":"Wrinkling patterns were used to investigate the mechanical properties of thin poly(styrene) (PS)/poly(methyl methacrylate) (PMMA) and PS/gold (Au) bilayer films. Films were floated on water with a water drop on the surface to induce wrinkling. The thicknesses and thickness ratios of the films were varied over a broad range. The PS/PMMA bilayer was chosen to provide a contrast in wetting properties, with equilibrium contact angles of θ<sub>PMMA</sub> = 68° and θ<sub>PS</sub> = 88° with water. The PS/Au bilayer was chosen to provide a large contrast in Young’s moduli, <i>E</i><sub>Au</sub> = 72 GPa and <i>E</i><sub>PS</sub> = 3.4 GPa. The stretching (<i>Y</i>) and bending (<i>B</i>) moduli of the bilayer films were obtained from measurements of the length and number of wrinkles in the wrinkle patterns. The experimentally derived values of <i>Y</i> and <i>B</i> were in reasonable agreement with the values computed from the bulk Young’s moduli and the thicknesses of the two components in the bilayer. The values of <i>Y</i> and <i>B</i> did not depend on which face of the film was exposed to the water droplet or bath when the capillary stresses were considered. Thus, finite size effects from the film thicknesses were unimportant over the range of thicknesses studied, and no relative displacement of the films was found, with the films remaining well-bonded even with deformation associated with wrinkling.","PeriodicalId":51,"journal":{"name":"Macromolecules","volume":"67 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142488039","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-23DOI: 10.1021/acs.macromol.4c01849
Qionghai Chen, Wanhui Huang, Liqun Zhang, Venkat Ganesan, Jun Liu
Tailoring mechanical properties through bond exchange reactions (BERs) demands precise topological manipulation, yet accurately correlating structures and properties to complex topologies remains a challenge. This investigation delves into matrix-free polymer grafted nanoparticles (PGNPs) with dynamic covalent bonds and examines how topological control can modulate material properties. Through coarse–grained molecular dynamics simulations, the alterations in the grafted polymer uniformity (α) induced by BERs triggered by terminals of grafted polymers are examined. Innovative α-kinetics theoretical model is proposed to capture the temporal evolution of topologies and elucidate the significant influence of BER kinetics and initial topology. Additionally, the α-equilibrium theoretical model characterizes equilibrium topologies, revealing the geometric distribution of grafted polymers. The theoretical models are further extended to include scenarios beyond terminal-triggered BERs, affirming their comprehensive applicability. Subsequently, it is elucidated how specific topological configurations can significantly enhance toughness and reveal the intrinsic mechanisms, which enable the construction of structure–property relationships. In summary, this study not only addresses the experimental challenges in the topological characterization of PGNPs, but also underscores the importance of strategic topological design in determining material properties and advancing material science.
通过键交换反应（BERs）定制机械性能需要精确的拓扑操作，但将结构和性能与复杂的拓扑结构准确关联起来仍是一项挑战。本研究深入研究了具有动态共价键的无基质聚合物接枝纳米粒子（PGNPs），并探讨了拓扑控制如何调节材料特性。通过粗粒度分子动力学模拟，研究了由接枝聚合物终端引发的误码分解所引起的接枝聚合物均匀性（α）的变化。提出了创新的 α 动力学理论模型，以捕捉拓扑结构的时间演化，并阐明 BER 动力学和初始拓扑结构的重要影响。此外，α 平衡理论模型还描述了平衡拓扑结构，揭示了接枝聚合物的几何分布。这些理论模型进一步扩展到终端触发的误码率以外的情况，从而肯定了它们的全面适用性。随后，研究阐明了特定拓扑结构如何显著提高韧性，并揭示了其内在机制，从而构建了结构-性能关系。总之，这项研究不仅解决了 PGNPs 拓扑表征中的实验难题，还强调了战略性拓扑设计在确定材料特性和推动材料科学发展方面的重要性。
{"title":"Topological Design and Mechanical Manipulation of Matrix-Free Polymer Grafted Nanoparticles Driven by Bond Exchanging","authors":"Qionghai Chen, Wanhui Huang, Liqun Zhang, Venkat Ganesan, Jun Liu","doi":"10.1021/acs.macromol.4c01849","DOIUrl":"https://doi.org/10.1021/acs.macromol.4c01849","url":null,"abstract":"Tailoring mechanical properties through bond exchange reactions (BERs) demands precise topological manipulation, yet accurately correlating structures and properties to complex topologies remains a challenge. This investigation delves into matrix-free polymer grafted nanoparticles (PGNPs) with dynamic covalent bonds and examines how topological control can modulate material properties. Through coarse–grained molecular dynamics simulations, the alterations in the grafted polymer uniformity (α) induced by BERs triggered by terminals of grafted polymers are examined. Innovative α-kinetics theoretical model is proposed to capture the temporal evolution of topologies and elucidate the significant influence of BER kinetics and initial topology. Additionally, the α-equilibrium theoretical model characterizes equilibrium topologies, revealing the geometric distribution of grafted polymers. The theoretical models are further extended to include scenarios beyond terminal-triggered BERs, affirming their comprehensive applicability. Subsequently, it is elucidated how specific topological configurations can significantly enhance toughness and reveal the intrinsic mechanisms, which enable the construction of structure–property relationships. In summary, this study not only addresses the experimental challenges in the topological characterization of PGNPs, but also underscores the importance of strategic topological design in determining material properties and advancing material science.","PeriodicalId":51,"journal":{"name":"Macromolecules","volume":"93 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142488016","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-23DOI: 10.1021/acs.macromol.4c02047
Binghui Liu, Qian Liu, Yang Pang, Tong Mu, Chengji Zhao
Polybenzimidazole (PBI) exhibits considerable advantages as a leading membrane material for high-temperature proton exchange membrane fuel cells (HT-PEMFCs). However, their harsh synthesis conditions and high processing costs have greatly restricted the large-scale commercialization of HT-PEMFCs. Therefore, developing high-performance and durable membrane materials as alternatives to PBI has been recognized as the key technical challenge for the advancement of HT-PEMFC technology. In this study, a series of novel multiblock copolymers QPSBI-b-xTMA, consisting of acidophobic pentafluorophenyl, acidophilic quaternary ammonium groups, and high free-volume spirobisindane, were synthesized by a straightforward polymerization process involving two kinds of low-molecular-weight oligomers with different structures. The resulting multiblock membranes QPSBI-b-xTMA demonstrate well-defined microporous properties, and the PA-doped membranes exhibit a microphase separation structure, which effectively facilitates proton conduction (75.45 mS cm–1@200 °C). The HT-PEMFCs based on the QPSBI-b-xTMA/PA membrane can operate efficiently within the temperature range of 160–220 °C, achieving a high peak power density of 0.84 W cm–2 without external pressure and humidity. Notably, owing to the siphoning effect of the micropores and the strong quaternary ammonium-biphosphate ion pairs, the fuel cell exhibits a stable performance at a high current density of 0.5 A cm–2 at 160 °C, with a minimal voltage degradation rate of merely 4.7 μV h–1. Thus, the newly developed QPSBI-b-xTMA/PA materials present a promising avenue for HT-PEMFC applications.
作为高温质子交换膜燃料电池（HT-PEMFCs）的主要膜材料，聚苯并咪唑（PBI）具有相当大的优势。然而，其苛刻的合成条件和高昂的加工成本极大地限制了高温质子交换膜燃料电池的大规模商业化。因此，开发高性能、耐用的膜材料作为 PBI 的替代品已被认为是 HT-PEMFC 技术发展的关键技术挑战。本研究通过两种不同结构的低分子量低聚物的直接聚合过程，合成了一系列新型多嵌段共聚物 QPSBI-b-xTMA，它们由疏酸性五氟苯基、亲酸性季铵基团和高自由体积螺双茚满组成。得到的多嵌段膜 QPSBI-b-xTMA 具有明确的微孔特性，掺杂 PA 的膜呈现出微相分离结构，可有效促进质子传导（75.45 mS cm-1@200 °C）。基于 QPSBI-b-xTMA/PA 膜的 HT-PEMFC 可在 160-220 °C 的温度范围内高效运行，在无外部压力和湿度的情况下达到 0.84 W cm-2 的峰值功率密度。值得注意的是，由于微孔的虹吸效应和强季铵-双磷酸离子对，该燃料电池在 160 ℃ 的高电流密度（0.5 A cm-2）下表现出稳定的性能，电压衰减率极低，仅为 4.7 μV h-1。因此，新开发的 QPSBI-b-xTMA/PA 材料为 HT-PEMFC 的应用提供了一条前景广阔的途径。
{"title":"New Multiblock Copolymers Containing Quaternary Ammonium Groups with Ultramicroporous Structure for High-Temperature Proton Exchange Membrane Fuel Cells","authors":"Binghui Liu, Qian Liu, Yang Pang, Tong Mu, Chengji Zhao","doi":"10.1021/acs.macromol.4c02047","DOIUrl":"https://doi.org/10.1021/acs.macromol.4c02047","url":null,"abstract":"Polybenzimidazole (PBI) exhibits considerable advantages as a leading membrane material for high-temperature proton exchange membrane fuel cells (HT-PEMFCs). However, their harsh synthesis conditions and high processing costs have greatly restricted the large-scale commercialization of HT-PEMFCs. Therefore, developing high-performance and durable membrane materials as alternatives to PBI has been recognized as the key technical challenge for the advancement of HT-PEMFC technology. In this study, a series of novel multiblock copolymers QPSBI-<i>b</i>-xTMA, consisting of acidophobic pentafluorophenyl, acidophilic quaternary ammonium groups, and high free-volume spirobisindane, were synthesized by a straightforward polymerization process involving two kinds of low-molecular-weight oligomers with different structures. The resulting multiblock membranes QPSBI-<i>b</i>-xTMA demonstrate well-defined microporous properties, and the PA-doped membranes exhibit a microphase separation structure, which effectively facilitates proton conduction (75.45 mS cm<sup>–1</sup>@200 °C). The HT-PEMFCs based on the QPSBI-<i>b</i>-xTMA/PA membrane can operate efficiently within the temperature range of 160–220 °C, achieving a high peak power density of 0.84 W cm<sup>–2</sup> without external pressure and humidity. Notably, owing to the siphoning effect of the micropores and the strong quaternary ammonium-biphosphate ion pairs, the fuel cell exhibits a stable performance at a high current density of 0.5 A cm<sup>–2</sup> at 160 °C, with a minimal voltage degradation rate of merely 4.7 μV h<sup>–1</sup>. Thus, the newly developed QPSBI-<i>b</i>-<i>x</i>TMA/PA materials present a promising avenue for HT-PEMFC applications.","PeriodicalId":51,"journal":{"name":"Macromolecules","volume":"93 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142488173","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-23DOI: 10.1021/acs.chemrev.4c0046410.1021/acs.chemrev.4c00464
Matthew C. Lamb, Keri A. Steiniger, Leslie K. Trigoura, Jason Wu, Gourab Kundu, He Huang* and Tristan H. Lambert*,
Electrocatalysis and photocatalysis have been the focus of extensive research efforts in organic synthesis in recent decades, and these powerful strategies have provided a wealth of new methods to construct complex molecules. Despite these intense efforts, only recently has there been a significant focus on the combined use of these two modalities. Nevertheless, the past five years have witnessed rapidly growing interest in the area of electrophotocatalysis. This hybrid strategy capitalizes on the enormous benefits of using photons as reagents while also employing an electric potential as a convenient and tunable source or sink of electrons. Research on this topic has led to a number of methods for C–H functionalization, reductive cross-coupling, and olefin addition among others. This field has also seen the use of a broad range of catalyst types, including both metal and organocatalysts. Of particular note has been work with open-shell photocatalysts, which tend to have comparatively large redox potentials. Electrochemistry provides a convenient means to generate such species, making electrophotocatalysis particularly amenable to this intriguing class of redox catalyst. This review surveys methods in the area of electrophotocatalysis as applied to organic synthesis, organized broadly into oxidative, reductive, and redox neutral transformations.
{"title":"Electrophotocatalysis for Organic Synthesis","authors":"Matthew C. Lamb, Keri A. Steiniger, Leslie K. Trigoura, Jason Wu, Gourab Kundu, He Huang* and Tristan H. Lambert*, ","doi":"10.1021/acs.chemrev.4c0046410.1021/acs.chemrev.4c00464","DOIUrl":"https://doi.org/10.1021/acs.chemrev.4c00464https://doi.org/10.1021/acs.chemrev.4c00464","url":null,"abstract":"<p >Electrocatalysis and photocatalysis have been the focus of extensive research efforts in organic synthesis in recent decades, and these powerful strategies have provided a wealth of new methods to construct complex molecules. Despite these intense efforts, only recently has there been a significant focus on the combined use of these two modalities. Nevertheless, the past five years have witnessed rapidly growing interest in the area of electrophotocatalysis. This hybrid strategy capitalizes on the enormous benefits of using photons as reagents while also employing an electric potential as a convenient and tunable source or sink of electrons. Research on this topic has led to a number of methods for C–H functionalization, reductive cross-coupling, and olefin addition among others. This field has also seen the use of a broad range of catalyst types, including both metal and organocatalysts. Of particular note has been work with open-shell photocatalysts, which tend to have comparatively large redox potentials. Electrochemistry provides a convenient means to generate such species, making electrophotocatalysis particularly amenable to this intriguing class of redox catalyst. This review surveys methods in the area of electrophotocatalysis as applied to organic synthesis, organized broadly into oxidative, reductive, and redox neutral transformations.</p>","PeriodicalId":51,"journal":{"name":"Macromolecules","volume":"124 21","pages":"12264–12304 12264–12304"},"PeriodicalIF":51.4,"publicationDate":"2024-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142609002","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Because of the lack of constraints for crystallization, disentangled ultrahigh molecular weight polyethylene (UHMWPE) materials prepared by solution crystallization or low-temperature polymerization can exhibit ultrahigh drawability, making them ideal materials for producing fibers or tapes with ultrahigh modulus and strength. However, their ultrahigh drawability could vanish after a short annealing time applied above their melting temperature (Tm), hampering the aspiration of obtaining high-performance fibers using melt-spinning methods. The mechanism behind this loss of drawability has yet to be fully understood, and the time scale for reconstructing the entanglement networks is a controversial problem. In this work, we present a detailed comparison study of the structure formation of disentangled UHMWPE samples via solution-cast and low-temperature polymerization methods. All disentangled UHMWPE samples exhibit a relatively high crystallinity (above 70%) and similar lamellar stack morphologies. Constraints for forming UHMWPE crystals could be generated within a short time of melting, leading to lamellar stack structures made of widely distributed crystalline and amorphous layers. We revisit the high-temperature annealing effect (using thermal protocols proposed by Rastogi et al. Macromolecules2016, 49 (19), 7497–7509) on disentangled UHMWPE crystals via differential scanning calorimetry (DSC). The melting enthalpies in the final heating runs remain constant and are independent of the annealing time. Combining self-nucleation and flash DSC measurements, we found that the regeneration of entanglement networks occurs in an ultrashort time scale simultaneously accompanied by partial melting. The associated times are so small that they cannot be accurately determined. Our results reveal that the recovery time of entanglements does not follow the scaling law of τ ∼ M3 proposed by the classical reptation model.
{"title":"Structure Formation and Unexpected Ultrafast Re-entanglement Dynamics of Disentangled Ultrahigh Molecular Weight Polyethylene","authors":"Zefan Wang, Biying Li, Fotis Christakopoulos, Kefeng Xie, Caizhen Zhu, Jian Xu, Alejandro J. Müller","doi":"10.1021/acs.macromol.4c01733","DOIUrl":"https://doi.org/10.1021/acs.macromol.4c01733","url":null,"abstract":"Because of the lack of constraints for crystallization, disentangled ultrahigh molecular weight polyethylene (UHMWPE) materials prepared by solution crystallization or low-temperature polymerization can exhibit ultrahigh drawability, making them ideal materials for producing fibers or tapes with ultrahigh modulus and strength. However, their ultrahigh drawability could vanish after a short annealing time applied above their melting temperature (<i>T</i><sub>m</sub>), hampering the aspiration of obtaining high-performance fibers using melt-spinning methods. The mechanism behind this loss of drawability has yet to be fully understood, and the time scale for reconstructing the entanglement networks is a controversial problem. In this work, we present a detailed comparison study of the structure formation of disentangled UHMWPE samples via solution-cast and low-temperature polymerization methods. All disentangled UHMWPE samples exhibit a relatively high crystallinity (above 70%) and similar lamellar stack morphologies. Constraints for forming UHMWPE crystals could be generated within a short time of melting, leading to lamellar stack structures made of widely distributed crystalline and amorphous layers. We revisit the high-temperature annealing effect (using thermal protocols proposed by Rastogi et al. <i>Macromolecules</i> <b>2016</b>, 49 (19), 7497–7509) on disentangled UHMWPE crystals via differential scanning calorimetry (DSC). The melting enthalpies in the final heating runs remain constant and are independent of the annealing time. Combining self-nucleation and flash DSC measurements, we found that the regeneration of entanglement networks occurs in an ultrashort time scale simultaneously accompanied by partial melting. The associated times are so small that they cannot be accurately determined. Our results reveal that the recovery time of entanglements does not follow the scaling law of τ ∼ <i>M</i><sup>3</sup> proposed by the classical reptation model.","PeriodicalId":51,"journal":{"name":"Macromolecules","volume":"28 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142488013","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-23DOI: 10.1021/acs.macromol.4c01687
Taehyoung Kim, En Wang, Joanna M. White, Frank S. Bates, Timothy P. Lodge
The effect of corona block asymmetry on chain exchange kinetics has been investigated using time-resolved small-angle neutron scattering (TR-SANS) with a series of AB di- and ABA′ triblock micelles composed of poly(ethylene-alt-propylene) (A) and polystyrene (B) block copolymers in squalane. The four copolymers maintain constant molecular weight and total block composition, but have different asymmetry ratios of the end blocks, denoted as SEP, EPSEP′-1, EPSEP′-2, and EPSEP. The TR-SANS results reveal a 10-fold acceleration in the chain exchange rate for asymmetric triblock copolymer micelles (EPSEP′-1 and EPSEP′-2) and a hundred-fold acceleration for symmetric triblock copolymers (EPSEP), compared to the SEP diblock copolymer. This enhanced exchange rate is primarily attributed to differences in the micelle structure associated with corona chain entropy during extraction, supported by calculations of grafting chain density and stretching of corona chains. Thus, this study demonstrates an interesting and significant role of block copolymer asymmetry in molecular exchange dynamics.
{"title":"Kinetics of Chain Exchange in Asymmetric ABA′ Triblock Polymer Micelles by Time-Resolved Small-Angle Neutron Scattering","authors":"Taehyoung Kim, En Wang, Joanna M. White, Frank S. Bates, Timothy P. Lodge","doi":"10.1021/acs.macromol.4c01687","DOIUrl":"https://doi.org/10.1021/acs.macromol.4c01687","url":null,"abstract":"The effect of corona block asymmetry on chain exchange kinetics has been investigated using time-resolved small-angle neutron scattering (TR-SANS) with a series of AB di- and ABA′ triblock micelles composed of poly(ethylene-<i>alt</i>-propylene) (A) and polystyrene (B) block copolymers in squalane. The four copolymers maintain constant molecular weight and total block composition, but have different asymmetry ratios of the end blocks, denoted as SEP, EPSEP′-1, EPSEP′-2, and EPSEP. The TR-SANS results reveal a 10-fold acceleration in the chain exchange rate for asymmetric triblock copolymer micelles (EPSEP′-1 and EPSEP′-2) and a hundred-fold acceleration for symmetric triblock copolymers (EPSEP), compared to the SEP diblock copolymer. This enhanced exchange rate is primarily attributed to differences in the micelle structure associated with corona chain entropy during extraction, supported by calculations of grafting chain density and stretching of corona chains. Thus, this study demonstrates an interesting and significant role of block copolymer asymmetry in molecular exchange dynamics.","PeriodicalId":51,"journal":{"name":"Macromolecules","volume":"30 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142487976","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-23DOI: 10.1021/acs.macromol.4c01478
Artem M. Rumyantsev
Coil–globule transition in a single-chain polymer is the cornerstone of polymer physics. Although completely understood for homopolymers, it turns out to be much more sophisticated for copolymers of mere two nonionic monomers because the position and especially sharpness (cooperativity) of the conformational change in them are highly sequence-dependent. In this work, the statistical theory of coil–globule transition in neutral AB copolymers with regular sequences is developed. To describe the role of the primary structure, we go beyond the mean-field approximation and calculate the Gaussian fluctuation correction due to chemical differences (incompatibility) between A and B monomers. Local compositional fluctuations reduce the second and third virial coefficients of monomer interactions; these corrections are found in the general form, and closed-form expressions are provided for block-alternating chains with the block length m. For nonperiodic sequences, the found corrections are annealed averages. Increasing the monomer blockiness is shown to (i) make the globule denser, (ii) shift the conformational transition to higher temperatures, and, most importantly, (iii) narrow the transition region. The collapse sharpens strongly when accompanied or shortly followed by intraglobular microphase separation. The developed theory contributes to a comprehensive understanding of the sequence-tunable conformational behavior of macromolecules, including Khokhlov–Khalatur protein-like copolymers forming globules with the core–shell microstructure.
单链聚合物中的线圈-球体转变是聚合物物理学的基石。尽管人们对均聚物的理解已经非常透彻，但对于仅由两种非离子单体组成的共聚物来说，这一过程却要复杂得多，因为它们构象变化的位置，尤其是锐度（合作性），与序列高度相关。在这项研究中，我们提出了具有规则序列的中性 AB 共聚物中线圈-球状转变的统计理论。为了描述初级结构的作用，我们超越了平均场近似，计算了由于 A 和 B 单体之间的化学差异（不相容性）而产生的高斯波动修正。局部成分波动降低了单体相互作用的第二和第三维里系数；这些修正是以一般形式发现的，并为嵌段长度为 m 的嵌段交替链提供了闭式表达式。结果表明，增加单体嵌段度会：(i) 使球体更致密；(ii) 使构象转变转移到更高温度；最重要的是：(iii) 缩小转变区域。当球内微相分离伴随或紧随球内微相分离时，塌缩现象会强烈加剧。所提出的理论有助于全面理解高分子的序列可调构象行为，包括霍赫洛夫-哈拉特蛋白共聚物形成的具有核壳微结构的球状物。
{"title":"Why Sequence Blockiness Sharpens Coil–Globule Transition in Heteropolymers","authors":"Artem M. Rumyantsev","doi":"10.1021/acs.macromol.4c01478","DOIUrl":"https://doi.org/10.1021/acs.macromol.4c01478","url":null,"abstract":"Coil–globule transition in a single-chain polymer is the cornerstone of polymer physics. Although completely understood for homopolymers, it turns out to be much more sophisticated for copolymers of mere two nonionic monomers because the position and especially sharpness (cooperativity) of the conformational change in them are highly sequence-dependent. In this work, the statistical theory of coil–globule transition in neutral AB copolymers with regular sequences is developed. To describe the role of the primary structure, we go beyond the mean-field approximation and calculate the Gaussian fluctuation correction due to chemical differences (incompatibility) between A and B monomers. Local compositional fluctuations reduce the second and third virial coefficients of monomer interactions; these corrections are found in the general form, and closed-form expressions are provided for block-alternating chains with the block length <i>m</i>. For nonperiodic sequences, the found corrections are annealed averages. Increasing the monomer blockiness is shown to (i) make the globule denser, (ii) shift the conformational transition to higher temperatures, and, most importantly, (iii) narrow the transition region. The collapse sharpens strongly when accompanied or shortly followed by intraglobular microphase separation. The developed theory contributes to a comprehensive understanding of the sequence-tunable conformational behavior of macromolecules, including Khokhlov–Khalatur protein-like copolymers forming globules with the core–shell microstructure.","PeriodicalId":51,"journal":{"name":"Macromolecules","volume":"93 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142488033","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-23DOI: 10.1021/acs.macromol.4c01274
Tingyu Xu, Yunhan Zhang, Fan Peng, Renkuan Cao, Ziwei Liu, Hao Sun, Liangbin Li
Mechanical deformation is known to affect the stability of glassy systems. Some studies report that small-amplitude loading leads to overaging, while large-amplitude loading rejuvenates the system. Recent experiments, however, have shown no overaging effect in lightly cross-linked poly(methyl methacrylate) (PMMA) glasses, raising concerns about previous simulation results. Given the importance of understanding physical aging, this work uses coarse-grained molecular dynamics simulations to examine the impact of cyclic loading/unloading on glassy polymers. The results indicate that overaging occurs in glassy polymer systems only below the Vogel–Fulcher–Tammann temperature (TVFT). Above TVFT, mechanical perturbations with amplitudes below the critical strain significantly accelerate the structural relaxation. Counterintuitively, these perturbations have minimal effect on inherent energy and all examined structural parameters, while particle mobility shows a clear proportional enhancement and increased spatial correlation.
{"title":"Overaging in Glassy Polymers within a Wide Range of Temperature","authors":"Tingyu Xu, Yunhan Zhang, Fan Peng, Renkuan Cao, Ziwei Liu, Hao Sun, Liangbin Li","doi":"10.1021/acs.macromol.4c01274","DOIUrl":"https://doi.org/10.1021/acs.macromol.4c01274","url":null,"abstract":"Mechanical deformation is known to affect the stability of glassy systems. Some studies report that small-amplitude loading leads to overaging, while large-amplitude loading rejuvenates the system. Recent experiments, however, have shown no overaging effect in lightly cross-linked poly(methyl methacrylate) (PMMA) glasses, raising concerns about previous simulation results. Given the importance of understanding physical aging, this work uses coarse-grained molecular dynamics simulations to examine the impact of cyclic loading/unloading on glassy polymers. The results indicate that overaging occurs in glassy polymer systems only below the Vogel–Fulcher–Tammann temperature (<i>T</i><sub>VFT</sub>). Above <i>T</i><sub>VFT</sub>, mechanical perturbations with amplitudes below the critical strain significantly accelerate the structural relaxation. Counterintuitively, these perturbations have minimal effect on inherent energy and all examined structural parameters, while particle mobility shows a clear proportional enhancement and increased spatial correlation.","PeriodicalId":51,"journal":{"name":"Macromolecules","volume":"46 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142487980","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
扫码关注我们
求助内容：
应助结果提醒方式：
京公网安备 11010802042870号