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1.
J Am Chem Soc ; 2024 Jul 17.
Artigo em Inglês | MEDLINE | ID: mdl-39018375

RESUMO

Introducing functionality onto PE surfaces is a longstanding challenge in polymer science, driven by the need for polymer materials with improved adhesion and antifouling properties. Herein, we report surface-initiated hydrogen atom transfer-reversible addition-fragmentation chain transfer (SI HAT-RAFT) as a robust method to grow high-density brush polymers from PE surfaces. We demonstrate that, under mild conditions, direct initiation from the C-H bonds of PE surfaces allows for the graft polymerization of a variety of (meth)acrylate monomers. The resulting polymer brushes reached several hundred nanometers in thickness with densities of ca. 0.62 chains/nm2, compared to the current standard of ∼0.28 chains/nm2. Finally, we show that our method is capable of dramatically improving the adhesive properties of PE surfaces. This work enables the preparation of PE with diverse surface functionalities for potential use in biomedical, industrial, and battery applications.

2.
Science ; 384(6692): 156-157, 2024 Apr 12.
Artigo em Inglês | MEDLINE | ID: mdl-38603514

RESUMO

A bio-based plastic advances recycling.

3.
ACS Appl Energy Mater ; 7(4): 1517-1526, 2024 Feb 26.
Artigo em Inglês | MEDLINE | ID: mdl-38425379

RESUMO

Herein, we systematically examined how composition influenced the properties of vinyl addition polynorbornene anion exchange membranes (AEMs) prepared from 5-n-hexyl-2-norbornene and 5-(4-bromobutyl)-2-norbornene. Copolymerization kinetics revealed that 5-n-hexyl-2-norbornene is consumed faster than 5-(4-bromobutyl)-2-norbornene, leading to a portion of the chain being richer in bromoalkyl groups. The alkyl halide pendants can then be converted to either trimethylammonium or tetrakis(dialkylamino)phosphonium cations through straightforward substitution with trimethylamine or a tris(dialkylamino)phosphazene. A series of cationic ammonium polymers were synthesized first, where conductivity and water uptake increased as a function of increasing ionic content in the polymer. The optimized copolymer had a hydroxide conductivity of 95 ± 6 mS/cm at 80 °C. The living polymerization of the two monomers catalyzed by a cationic tert-butylphosphine palladium catalyst also enabled precise changes in the molecular weight while keeping the functional group concentration constant. Molecular weight did not have a significant impact on hydroxide conductivity over the range of ∼60-190 kg/mol (Mn). The optimized tetraaminophosphonium AEM had the highest conductivity for any tetraaminophosphonium polymer to date (70 ± 3 mS/cm at 80 °C). Clear phase separation and larger domains were observed for the phosphonium-based AEM compared to the ammonium at an identical composition, which is attributed to the larger occupied volume of the phosphorus cation. Fuel cell studies with the two membranes resulted in peak power densities of 1.59 and 0.79 W/cm2 for the ammonium and tetraaminophosphonium membrane electrode assemblies, respectively. The ammonium-based membrane was more water permeable as evidenced by water limiting current studies, which likely contributed to the improved performance.

4.
Angew Chem Int Ed Engl ; 63(3): e202316578, 2024 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-38032347

RESUMO

Leveraging electrochemistry to degrade robust polymeric materials has the potential to impact society's growing issue of plastic waste. Herein, we develop an electrocatalytic oxidative degradation of polyethers and poly(vinyl ethers) via electrochemically mediated hydrogen atom transfer (HAT) followed by oxidative polymer degradation promoted by molecular oxygen. We investigated the selectivity and efficiency of this method, finding our conditions to be highly selective for polymers with hydridic, electron-rich C-H bonds. We leveraged this reactivity to degrade polyethers and poly(vinyl ethers) in the presence of polymethacrylates and polyacrylates with complete selectivity. Furthermore, this method made polyacrylates degradable by incorporation of ether units into the polymer backbone. We quantified degradation products, identifying up to 36 mol % of defined oxidation products, including acetic acid, formic acid, and acetaldehyde, and we extended this method to degrade a polyether-based polyurethane in a green solvent. This work demonstrates a facile, electrochemically-driven route to degrade polymers containing ether functionalities.

6.
J Am Chem Soc ; 145(20): 11151-11160, 2023 May 24.
Artigo em Inglês | MEDLINE | ID: mdl-37167410

RESUMO

Epoxy thermosets are high-volume materials that play a central role in a wide range of engineering applications; however, technologies to recycle these polymers remain rare. Here, we present a catalytic, light-driven method that enables chemical recycling of industrially relevant thiol epoxy thermosets to their original monomer at ambient temperature. This strategy relies on the proton-coupled electron transfer (PCET) activation of hydroxy groups within the polymer network to generate key alkoxy radicals that promote the fragmentation of the polymer through C-C bond ß-scission. The method fully depolymerizes insoluble thiol epoxy thermosets into well-defined mixtures of small-molecule products, which can collectively be converted into the original monomer via a one-step dealkylation process. Notably, this process is selective and efficient even in the presence of other commodity plastics and additives commonly found in commercial applications. These results constitute an important step toward making epoxy thermosets recyclable and more generally exemplify the potential of PCET to offer a more sustainable end-of-life for a diverse array of commercial plastics.

7.
Angew Chem Int Ed Engl ; 62(30): e202304778, 2023 Jul 24.
Artigo em Inglês | MEDLINE | ID: mdl-37141462

RESUMO

The limited number of methods to directly polymerize ionic monomers currently hinders rapid diversification and production of ionic polymeric materials, namely anion exchange membranes (AEMs) which are essential components in emerging alkaline fuel cell and electrolyzer technologies. Herein, we report a direct coordination-insertion polymerization of cationic monomers, providing the first direct synthesis of aliphatic polymers with high ion incorporations and allowing facile access to a broad range of materials. We demonstrate the utility of this method by rapidly generating a library of solution processable ionic polymers for use as AEMs. We investigate these materials to study the influence of cation identity on hydroxide conductivity and stability. We found that AEMs with piperidinium cations exhibited the highest performance, with high alkaline stability, hydroxide conductivity of 87 mS cm-1 at 80 °C, and a peak power density of 730 mW cm-2 when integrated into a fuel cell device.

8.
Angew Chem Int Ed Engl ; 62(20): e202218062, 2023 May 08.
Artigo em Inglês | MEDLINE | ID: mdl-36637901

RESUMO

Polyurethanes (PUs) are a class of materials usually synthesized from isocyanates, diols, and water. Water is essential for producing carbon dioxide (CO2 ) which is used for the self-blowing of the foams. Due to safety concerns with the production of isocyanates, alternative chemistries have been evaluated and cyclic carbonate systems have shown great promise. In a recent advancement by Bourguignon, Grignard, and Detrembleur, a cyclic carbonate and diamine system is capable of generating CO2 for self-blowing through hydrolysis of the carbonate-based monomer. The authors demonstrate that with a simple variation of the diamine monomer a wide range of physical and thermo-mechanical properties were achievable. This work represents a significant step towards safer and more environmentally friendly PUs.

9.
J Am Chem Soc ; 144(34): 15727-15734, 2022 08 31.
Artigo em Inglês | MEDLINE | ID: mdl-35981404

RESUMO

Creation of strong and tough plastics from sustainable and biorenewable resources is a significant challenge in polymer science. This challenge is further complicated when attempting to make these materials using an economically viable process, which is often hindered by the production and availability of chemical feedstocks and the efficiency of the monomer synthesis. Herein, we report the synthesis and characterization of a strong thermoplastic made from 2,3-dihydrofuran (DHF), a monomer made in one step from 1,4-butanediol, a bioalcohol already produced on the plant scale. We developed a green, metal-free cationic polymerization to enable the production of poly(2,3-dihydrofuran) (PDHF) with molecular weights of up to 256 kg/mol at room temperature. Characterization of these polymers showed that PDHF possesses high tensile strength and toughness (70 and 14 MPa, respectively) comparable to commercial polycarbonate, high optical clarity, and good barrier properties to oxygen, carbon dioxide, and water. These properties make this material amenable to a variety of applications, from food packaging to high strength windows. Importantly, we have also developed a facile oxidative degradation process of PDHF, providing an end-of-life solution for PDHF materials.


Assuntos
Furanos , Polímeros , Cátions , Plásticos , Polimerização , Polímeros/química , Temperatura
10.
Acc Chem Res ; 55(14): 1960-1971, 2022 07 19.
Artigo em Inglês | MEDLINE | ID: mdl-35771008

RESUMO

Advances in photocontrolled polymerizations have expanded the scope of polymer architectures and structures that can be synthesized for various applications. The majority of these polymerizations have been developed for radical processes, which limits the diversity of monomers that can be used in macromolecular design. More recent developments of photocontrolled cationic polymerizations have taken a step toward addressing this limitation and have expanded the palette of monomers that can be used in stimuli-regulated polymerizations, enabling the synthesis of previously inaccessible polymeric structures. This Account will detail our group's studies on cationic polymerization processes where chain growth is regulated by light and highlight how these methods can be combined with other stimuli-controlled polymerizations to precisely dictate macromolecular structure.Photoinitiated cationic polymerizations are well-studied and important processes that have control over initiation. However, we wanted to develop systems where we had spatiotemporal control over both polymer initiation and chain growth. This additional command over the reaction provides the ability to manipulate the growing polymer with an external stimulus during a polymerization, which can be used to control structure. To achieve this goal, we set out to develop a method to photoreversibly generate a cation at a growing chain end that could participate in a controlled polymerization process. We took inspiration from previous work on cationic degenerate chain transfer polymerizations of vinyl ethers that used thiocarbonylthio chain transfer agents. These polymerizations were initiated by a strong acid and gave well-defined poly(vinyl ether)s. We posited that we could remove the acid initiator in these systems and reversibly oxidize the thiocarbonylthio chain ends in these reactions with a photocatalyst to give a photocontrolled cationic polymerization of vinyl ethers. This Account will focus on our journey to discover cationic photocontrolled polymerizations. We will summarize our initial developments and detail our mechanistic understanding of these reactions using both organic and inorganic based photocatalysts, and we will outline more recent efforts to expand cationic degenerate chain transfer polymerizations to other thioacetal initiators. Finally, we will detail how these photocontrolled cationic polymerizations can be used to switch monomer selectivity in situ using light to control polymer structure. At the end of the Account, we will discuss our vision for future potential applications of these photocontrolled cationic polymerizations in the synthesis of novel block copolymers and next generation cross-linked networks.


Assuntos
Éteres , Polímeros , Catálise , Cátions/química , Polimerização , Polímeros/química , Compostos de Vinila
11.
Angew Chem Int Ed Engl ; 61(24): e202203344, 2022 Jun 13.
Artigo em Inglês | MEDLINE | ID: mdl-35302707

RESUMO

The ring-opening metathesis polymerization (ROMP) of cyclopropenes using hydrazonium initiators is described. The initiators, which are formed by the condensation of 2,3-diazabicyclo[2.2.2]octane and an aldehyde, polymerize cyclopropene monomers by a sequence of [3+2] cycloaddition and cycloreversion reactions. This process generates short chain polyolefins (Mn ≤9.4 kg mol-1 ) with relatively low dispersities (D≤1.4). The optimized conditions showed efficiency comparable to that achieved with Grubbs' 2nd generation catalyst for the polymerization of 3-methyl-3-phenylcyclopropene. A positive correlation between monomer to initiator ratio and degree of polymerization was revealed through NMR spectroscopy.

12.
J Chem Educ ; 99(10): 3461-3470, 2022 Oct 11.
Artigo em Inglês | MEDLINE | ID: mdl-37552542

RESUMO

Over the past two and a half years, the COVID-19 pandemic severely disrupted almost all aspects of life as people throughout the world were instructed to work-from-home. Scientific researchers, whose work is reliant on access to laboratory equipment, have been acutely impacted by these global changes. In this study, we surveyed graduate students and postdocs in the chemical sciences at a selected number of academic institutions in the United States. We found that many survey participants, especially women, experienced severely diminished research progress and increased anxiety levels during the COVID-19 pandemic. Through factor analysis and multiple regression modeling, we found that during this challenging time participants who reported greater levels of professional support also reported greater research progress and lower levels of anxiety. We also found that, although advisors and departments provide some forms of professional support, there are other types of support that students and postdocs still desire. This phenomenon is magnified for female and underrepresented minority participants, as they need greater levels of professional support and place immense value on the quality of their work environments. Based on these results, we have identified some ways in which departments and advisors can provide the needed support for their graduate students and postdocs, thereby providing timeless advice that is applicable to improving academic work conditions not only during a global pandemic but also in a postpandemic world.

13.
J Am Chem Soc ; 143(50): 21200-21205, 2021 12 22.
Artigo em Inglês | MEDLINE | ID: mdl-34878283

RESUMO

The ability to fabricate polymeric materials with spatially controlled physical properties has been a challenge in thermoset manufacturing. To address this challenge, this work takes advantage of a photoswitchable polymerization that selectively incorporates different monomers at a growing chain by converting from cationic to radical polymerizations through modulation of the wavelength of irradiation. By regulating the dosage and wavelength of light applied to the system, the mechanical properties of the crosslinked material can be temporally and spatially tuned. Furthermore, photopatterning can be achieved both on the macroscale and the microscale, enabling precise spatial control of crosslink density that results in high-resolution control over mechanical properties.

14.
Inorg Chem ; 60(24): 18662-18673, 2021 Dec 20.
Artigo em Inglês | MEDLINE | ID: mdl-34889590

RESUMO

The exploration of pyridine-imine (PI) iron complexes that exhibit redox noninnocence (RNI) led to several interesting discoveries. The reduction of (PI)FeX2 species afforded disproportionation products such as (dmpPI)2FeX (dmp = 2,6-Me2-C6H3, X = Cl, Br; 8-X) and (dippPI)2FeX (dipp = 2,6-iPr2-C6H3, X = Cl, Br; 9-X), which were independently prepared by reductions of (PI)FeX2 in the presence of PI. The crystal structure of 8-Br possessed an asymmetric unit with two distinct electromers, species with different electronic GSs: a low-spin (S = 1/2) configuration derived from an intermediate-spin S = 1 core antiferromagnetically (AF) coupled to an S = 1/2 PI ligand, and an S = 3/2 center resulting from a high-spin S = 2 core AF-coupled to an S = 1/2 PI ligand. Calculations were used to energetically compare plausible ground states. Polydentate diazepane-PI (DHPI) ligands were applied to the synthesis of monomeric dihalides (DHPI)FeX2 (X = Cl, 1-Cl2; X = Br, 1-Br2); reduction generated the highly distorted bioctahedral dimers (DHPA)2Fe2X2 ((3-X)2) containing a C-C bond formed from imine coupling; the monomers 1-X2 could be regenerated upon Ph3CX oxidation. Dihalides and their reduced counterparts were subjected to various alkyl halides and methyl methacrylate (MMA), generating polymers with little to no molecular weight control, indicative of simple radical-initiated polymerization.

15.
J Am Chem Soc ; 143(31): 12268-12277, 2021 08 11.
Artigo em Inglês | MEDLINE | ID: mdl-34333967

RESUMO

The accumulation of persistent plastic waste in the environment is widely recognized as an ecological crisis. New chemical technologies are necessary both to recycle existing plastic waste streams into high-value chemical feedstocks and to develop next-generation materials that are degradable by design. Here, we report a catalytic methodology for the depolymerization of a commercial phenoxy resin and high molecular weight hydroxylated polyolefin derivatives upon visible light irradiation near ambient temperature. Proton-coupled electron transfer (PCET) activation of hydroxyl groups periodically spaced along the polymer backbone furnishes reactive alkoxy radicals that promote chain fragmentation through C-C bond ß-scission. The depolymerization produces well-defined and isolable product mixtures that are readily diversified to polycondensation monomers. In addition to controlling depolymerization, the hydroxyl group modulates the thermomechanical properties of these polyolefin derivatives, yielding materials with diverse properties. These results demonstrate a new approach to polymer recycling based on light-driven C-C bond cleavage that has the potential to establish new links within a circular polymer economy and influence the development of new degradable-by-design polyolefin materials.

16.
Chem Sci ; 12(31): 10544-10549, 2021 Aug 11.
Artigo em Inglês | MEDLINE | ID: mdl-34447548

RESUMO

Advancements in externally controlled polymerization methodologies have enabled the synthesis of novel polymeric structures and architectures, and they have been pivotal to the development of new photocontrolled lithographic and 3D printing technologies. In particular, the development of externally controlled ring-opening polymerization (ROP) methodologies is of great interest, as these methods provide access to novel biocompatible and biodegradable block polymer structures. Although ROPs mediated by photoacid generators have made significant contributions to the fields of lithography and microelectronics development, these methodologies rely upon catalysts with poor stability and thus poor temporal control. Herein, we report a class of ferrocene-derived acid catalysts whose acidity can be altered through reversible oxidation and reduction of the ferrocenyl moiety to chemically and electrochemically control the ROP of cyclic esters.

18.
ACS Appl Mater Interfaces ; 13(6): 7135-7141, 2021 Feb 17.
Artigo em Inglês | MEDLINE | ID: mdl-33543926

RESUMO

Understanding the properties that govern the kinetics of charge storage will enable informed design strategies and improve the rate performance of future battery materials. Herein, we study the effects of structural ordering in organic electrode materials on their charge storage mechanisms. A redox active unit, N,N'-diphenyl-phenazine, was incorporated into three materials which exhibited varying degrees of ordering. From cyclic voltammetry analysis, the crystalline small molecule exhibited diffusion-limited behavior, likely arising from structural rearrangements that occur during charge/discharge. Conversely, a branched polymer network displayed surface-controlled kinetics, attributed to the amorphous structure which enabled fast ionic transport throughout charge/discharge, unimpeded by sluggish structural rearrangements. These results suggest a method for designing new materials for battery electrodes with battery-like energy densities and pseudocapacitor-like rate capabilities.

19.
Angew Chem Int Ed Engl ; 60(9): 4535-4539, 2021 Feb 23.
Artigo em Inglês | MEDLINE | ID: mdl-33137229

RESUMO

The synthesis of high-molecular-weight poly(vinyl ethers) under mild conditions is a significant challenge, since cationic polymerization reactions are highly sensitive to chain-transfer and termination events. We identified a novel and highly effective hydrogen bond donor (HBD)-organic acid pair that can facilitate controlled cationic polymerization of vinyl ethers under ambient conditions with excellent monomer compatibility. Poly(vinyl ethers) of molar masses exceeding 50 kg mol-1 can be produced within 1 h without elaborate reagent purification. Modification of the HBD structure allowed tuning of the polymerization rate, while DFT calculations helped elucidate crucial intermolecular interactions between the HBD, organic acid, and polymer chain end.

20.
J Am Chem Soc ; 142(10): 4581-4585, 2020 03 11.
Artigo em Inglês | MEDLINE | ID: mdl-32046481

RESUMO

Given the ubiquity of carbon-hydrogen bonds in biomolecules and polymer backbones, the development of a photocontrolled polymerization selectively grafting from a C-H bond represents a powerful strategy for polymer conjugation. This approach would circumvent the need for complex synthetic pathways currently used to introduce functionality at a polymer chain end. On this basis, we developed a hydrogen-atom abstraction strategy that allows for a controlled polymerization selectively from a hydridic C-H bond using a benzophenone photocatalyst, a trithiocarbonate-derived disulfide, and visible light. We performed the polymerization from a variety of ethers, alkanes, unactivated C-H bonds, and alcohols. Our method lends itself to photocontrol which has important implications for building advanced macromolecular architectures. Finally, we demonstrate that we can graft polymer chains controllably from poly(ethylene glycol) showcasing the potential application of this method for controlled grafting from C-H bonds of commodity polymers.

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