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Article ; Online: Catalytic Control of Crystallization in Dynamic Networks.

Kuenstler, Alexa S / Bowman, Christopher N

ACS macro letters

2023 Volume 12, Issue 2, Page(s) 133–139

Abstract: The effect of catalysts with varying nucleophilic strength on thiol-thioester bond exchange dynamics and concomitant crystallization was studied in a model semicrystalline polymer network. It was found that the characteristic time scale of covalent bond ... ...

Abstract	The effect of catalysts with varying nucleophilic strength on thiol-thioester bond exchange dynamics and concomitant crystallization was studied in a model semicrystalline polymer network. It was found that the characteristic time scale of covalent bond exchange, τ, could be tuned over a ∼10
Language	English
Publishing date	2023-01-12
Publishing country	United States
Document type	Journal Article
ISSN	2161-1653
ISSN (online)	2161-1653
DOI	10.1021/acsmacrolett.2c00703
Database	MEDical Literature Analysis and Retrieval System OnLINE

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Article ; Online: Leaping liquid crystal elastomers.

Hebner, Tayler S / Korner, Kevin / Bowman, Christopher N / Bhattacharya, Kaushik / White, Timothy J

Science advances

2023 Volume 9, Issue 3, Page(s) eade1320

Abstract: Snap-through mechanisms are pervasive in everyday life in biological systems, engineered devices, and consumer products. Snap-through transitions can be realized in responsive materials via stimuli-induced mechanical instability. Here, we demonstrate a ... ...

Abstract	Snap-through mechanisms are pervasive in everyday life in biological systems, engineered devices, and consumer products. Snap-through transitions can be realized in responsive materials via stimuli-induced mechanical instability. Here, we demonstrate a rapid and powerful snap-through response in liquid crystalline elastomers (LCEs). While LCEs have been extensively examined as material actuators, their deformation rate is limited by the second-order character of their phase transition. In this work, we locally pattern the director orientation of LCEs and fabricate mechanical elements with through-thickness (functionally graded) modulus gradients to realize stimuli-induced responses as fast as 6 ms. The rapid acceleration and associated force output of the LCE elements cause the elements to leap to heights over 200 times the material thickness. The experimental examination in functionally graded LCE elements is complemented with computational evaluation of the underlying mechanics. The experimentally validated model is then exercised as a design tool to guide functional implementation, visualized as directional leaping.
Language	English
Publishing date	2023-01-18
Publishing country	United States
Document type	Journal Article
ZDB-ID	2810933-8
ISSN	2375-2548 ; 2375-2548
ISSN (online)	2375-2548
ISSN	2375-2548
DOI	10.1126/sciadv.ade1320
Database	MEDical Literature Analysis and Retrieval System OnLINE

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Article ; Online: Vat Photopolymerization Additive Manufacturing of Tough, Fully Recyclable Thermosets.

Kuenstler, Alexa S / Hernandez, Juan J / Trujillo-Lemon, Marianela / Osterbaan, Alexander / Bowman, Christopher N

ACS applied materials & interfaces

2023 Volume 15, Issue 8, Page(s) 11111–11121

Abstract: To advance the capabilities of additive manufacturing, novel resin formulations are needed that produce high-fidelity parts with desired mechanical properties that are also amenable to recycling. In this work, a thiol-ene-based system incorporating ... ...

Abstract	To advance the capabilities of additive manufacturing, novel resin formulations are needed that produce high-fidelity parts with desired mechanical properties that are also amenable to recycling. In this work, a thiol-ene-based system incorporating semicrystallinity and dynamic thioester bonds within polymer networks is presented. It is shown that these materials have ultimate toughness values >16 MJ cm
Language	English
Publishing date	2023-02-16
Publishing country	United States
Document type	Journal Article
ISSN	1944-8252
ISSN (online)	1944-8252
DOI	10.1021/acsami.2c22081
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Article ; Online: Radical-Mediated Degradation of Thiol-Maleimide Hydrogels.

Hebner, Tayler S / Kirkpatrick, Bruce E / Fairbanks, Benjamin D / Bowman, Christopher N / Anseth, Kristi S / Benoit, Danielle S W

Advanced science (Weinheim, Baden-Wurttemberg, Germany)

2024 , Page(s) e2402191

Abstract: Michael addition between thiol- and maleimide-functionalized molecules is a long-standing approach used for bioconjugation, hydrogel crosslinking, and the functionalization of other advanced materials. While the simplicity of this chemistry enables ... ...

Abstract	Michael addition between thiol- and maleimide-functionalized molecules is a long-standing approach used for bioconjugation, hydrogel crosslinking, and the functionalization of other advanced materials. While the simplicity of this chemistry enables facile synthesis of hydrogels, network degradation is also desirable in many instances. Here, the susceptibility of thiol-maleimide bonds to radical-mediated degradation is reported. Irreversible degradation in crosslinked materials is demonstrated using photoinitiated and chemically initiated radicals in hydrogels and linear polymers. The extent of degradation is shown to be dependent on initiator concentration. Using a model linear polymer system, the radical-mediated mechanism of degradation is elucidated, in which the thiosuccinimide crosslink is converted to a succinimide and a new thioether formed with an initiator fragment. Using laser stereolithography, high-fidelity spatiotemporal control over degradation in crosslinked gels is demonstrated. Ultimately, this work establishes a platform for controllable, radical-mediated degradation in thiol-maleimide hydrogels, further expanding their versatility as functional materials.
Language	English
Publishing date	2024-04-06
Publishing country	Germany
Document type	Journal Article
ZDB-ID	2808093-2
ISSN	2198-3844 ; 2198-3844
ISSN (online)	2198-3844
ISSN	2198-3844
DOI	10.1002/advs.202402191
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Article: Enamine Organocatalysts for the Thiol-Michael Addition Reaction and Cross-Linking Polymerizations

Sinha, Jasmine / Soars, Shafer / Bowman, Christopher N

Macromolecules. 2021 Feb. 02, v. 54, no. 4

2021

Abstract: This article describes an efficient enamine organocatalyzed thiol-Michael click reaction and its broad application in cross-linking polymerizations. A series of enamines was shown to catalyze the thiol-Michael reaction via a nucleophilic pathway. By ... ...

Abstract	This article describes an efficient enamine organocatalyzed thiol-Michael click reaction and its broad application in cross-linking polymerizations. A series of enamines was shown to catalyze the thiol-Michael reaction via a nucleophilic pathway. By varying the amines as well as the ring size of the ketones, enamines were designed with broad ranges of nucleophilic character ranging from 11 to 17 on the Mayr nucleophilicity scale. Upon evaluating the enamines’ organocatalytic effect on the kinetics of reactions involving a thiol and Michael acceptor, wherein butyl 3-mercaptopropionate and 1-hexyl acrylate were used as model reactants, enamines were shown to outperform their base analogs. The efficiency and overall reaction yields, ranging from 11 to 92% based on the thiol conversion, were highly dependent upon the nucleophilicity of the enamines employed. Interestingly, in situ formation of an enamine via photo-deprotection of an amine in the presence of cyclic ketones facilitated the thiol-Michael reaction efficiently while simultaneously enabling higher functional group conversion. This efficiency in the reaction kinetics and conversion was extended to multifunctional derivatives, which resulted in the formation of highly cross-linked polymers.
Keywords	Lewis bases ; catalytic activity ; crosslinking ; enamines ; organocatalysts ; reaction kinetics ; thiols
Language	English
Dates of publication	2021-0202
Size	p. 1693-1701.
Publishing place	American Chemical Society
Document type	Article
Note	NAL-AP-2-clean
ZDB-ID	1491942-4
ISSN	1520-5835 ; 0024-9297
ISSN (online)	1520-5835
ISSN	0024-9297
DOI	10.1021/acs.macromol.0c02128
Database	NAL-Catalogue (AGRICOLA)

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Article: Flory–Huggins Parameters for Thiol-ene Networks Using Hansen Solubility Parameters

Bongiardina, Nicholas J. / Sinha, Jasmine / Bowman, Christopher N.

Macromolecules. 2021 Dec. 14, v. 54, no. 24

2021

Abstract: Thiol-ene networks based on polar and nonpolar monomers at various crosslinking densities were subjected to swelling in organic solvents to measure the Flory–Huggins interaction parameter. To the best of our knowledge, this is the first example of Flory– ... ...

Abstract	Thiol-ene networks based on polar and nonpolar monomers at various crosslinking densities were subjected to swelling in organic solvents to measure the Flory–Huggins interaction parameter. To the best of our knowledge, this is the first example of Flory–Huggins measurements for thiol-ene networks in organic media. Experimentally determined values were compared to those predicted using the Hansen solubility parameter approach with the assistance of the HSPiP software, which is used industrially to determine the miscibility. It was shown that the polymer suite in this software does not adequately account for thioether bonds by underpredicting the dispersive Hansen parameter by roughly 5 MPa⁰.⁵ when corrected to experimental thiol-ene swelling data. Even with corrections for thioether bonds, HSPiP and Hansen solubility parameters, in general, lack the ability to account for structural factors that impact polymer–solvent interaction parameters, especially for crosslinked polymer networks.
Keywords	computer software ; crosslinking ; polymers ; solubility
Language	English
Dates of publication	2021-1214
Size	p. 11439-11448.
Publishing place	American Chemical Society
Document type	Article
ZDB-ID	1491942-4
ISSN	1520-5835 ; 0024-9297
ISSN (online)	1520-5835
ISSN	0024-9297
DOI	10.1021/acs.macromol.1c01957
Database	NAL-Catalogue (AGRICOLA)

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Article: Tunable Surfaces and Films from Thioester Containing Microparticles

Martinez, Alina M. / Cox, Lewis M. / Darabi, Amir / Bongiardina, Nicholas J. / Bowman, Christopher N.

ACS applied materials & interfaces. 2022 June 06, v. 14, no. 23

2022

Abstract: Reported here, thioester containing microparticles were designed with 40% excess thiol to enable thiol–thioester exchange to facilitate the formation of cohesive films from the particles. A thiol-Michael dispersion polymerization was used to generate ... ...

Abstract	Reported here, thioester containing microparticles were designed with 40% excess thiol to enable thiol–thioester exchange to facilitate the formation of cohesive films from the particles. A thiol-Michael dispersion polymerization was used to generate thioester containing microparticles with a diameter of 4.0 ± 0.4 μm. The particles were then swollen with a base at varying concentrations to activate the thiol–thioester exchange and subsequently compressed between two glass slides. Resultant films were characterized over time with profilometry and atomic force microscopy (AFM) to infer particle coalescence at different catalyst loadings and times. Tensile tests were performed confirming the structural integrity of the particle-based films. Furthermore, microparticles were welded to a nondynamic network demonstrating feasibility in potential applications to generate materials containing differing mechanical properties. Being able to control the functionality of particles, and thus mechanical properties of the resultant films, is also important for applications in coatings, adhesives, and 3D printing where spatial patterning or selective material property control is needed.
Keywords	atomic force microscopy ; catalysts ; glass ; polymerization ; thioesters ; thiols
Language	English
Dates of publication	2022-0606
Size	p. 27177-27186.
Publishing place	American Chemical Society
Document type	Article
ISSN	1944-8252
DOI	10.1021/acsami.2c05113
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Article: Kinetic Analysis of Degradation in Thioester Cross-linked Hydrogels as a Function of Thiol Concentration, pKₐ, and Presentation

Carberry, Benjamin J. / Hernandez, Juan J. / Dobson, Adam / Bowman, Christopher N. / Anseth, Kristi S.

Macromolecules. 2022 Mar. 02, v. 55, no. 6

2022

Abstract: Stimuli-responsive degradation of hydrogels has established and emerging utilities ranging from controlled release of biological products to sacrificial molding. Although covalent adaptable networks are particularly amenable for these applications, their ...

Abstract	Stimuli-responsive degradation of hydrogels has established and emerging utilities ranging from controlled release of biological products to sacrificial molding. Although covalent adaptable networks are particularly amenable for these applications, their degradation kinetics have yet to be clearly elucidated in these swollen material systems. In this work, the thiol–thioester exchange reaction in cross-linked poly(ethylene glycol) (PEG) hydrogels is characterized to determine the relative effects of thiol concentration, pKₐ, and pH on network mass loss and mechanical properties. From these measurements, we identify that network thiols liberated from exchanged thioester cross-links play a significant role in hydrogel degradation, resulting in predictable changes in the storage modulus but nonideal mass loss profiles. These findings highlight how the mechanism of thioester exchange degradation can give rise to useful deviations from ideal degradation behavior, such as amplified degradation rates and linear mass loss profiles. Furthermore, this work empowers the design of on-demand degradable hydrogels with uniquely tunable degradation and mass loss.
Keywords	crosslinking ; hydrogels ; kinetics ; pH ; storage modulus ; thioesters ; thiols
Language	English
Dates of publication	2022-0302
Size	p. 2123-2129.
Publishing place	American Chemical Society
Document type	Article
ZDB-ID	1491942-4
ISSN	1520-5835 ; 0024-9297
ISSN (online)	1520-5835
ISSN	0024-9297
DOI	10.1021/acs.macromol.1c02396
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Article: Spatial and Temporal Control of Photomediated Disulfide–Ene and Thiol–Ene Chemistries for Two-Stage Polymerizations

Soars, Shafer M. / Bongiardina, Nicholas J. / Fairbanks, Benjamin D. / Podgórski, Maciej / Bowman, Christopher N.

Macromolecules. 2022 Feb. 14, v. 55, no. 5

2022

Abstract: A new strategy is reported for the design and synthesis of high sulfur-containing materials for potential use in covalent adaptable networks and optical materials by combining photomediated thiol–ene- and disulfide–ene-based polymerization reactions. ... ...

Abstract	A new strategy is reported for the design and synthesis of high sulfur-containing materials for potential use in covalent adaptable networks and optical materials by combining photomediated thiol–ene- and disulfide–ene-based polymerization reactions. Taking advantage of the relative reaction rates to differentiate sequentially between the thiol–ene and disulfide–ene conjugations, these reactions were performed semiorthogonally to produce polymer networks of controlled architecture. Kinetic analysis demonstrates that the thiol–ene reaction is approximately 30 times faster than the disulfide–ene reaction, enabling spatial and temporal manipulation of material properties via dual-cure networks and photopatterning. A two-stage polymerization approach was implemented with increases in modulus in the second stage of 2–3 orders of magnitude accompanied by increases in the glass-transition temperature of more than 15 °C. Additionally, the thiol–ene reaction in the presence of a disulfide yields materials capable of simultaneous network development and stress relaxation through dynamic bond exchange during in situ polymerization.
Keywords	disulfides ; glass transition temperature ; kinetics ; polymerization ; polymers ; stress relaxation
Language	English
Dates of publication	2022-0214
Size	p. 1811-1821.
Publishing place	American Chemical Society
Document type	Article
ZDB-ID	1491942-4
ISSN	1520-5835 ; 0024-9297
ISSN (online)	1520-5835
ISSN	0024-9297
DOI	10.1021/acs.macromol.1c02464
Database	NAL-Catalogue (AGRICOLA)

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Article ; Online: Additive Manufacture of Dynamic Thiol-ene Networks Incorporating Anhydride-Derived Reversible Thioester Links.

Podgórski, Maciej / Huang, Sijia / Bowman, Christopher N

ACS applied materials & interfaces

2020 Volume 13, Issue 11, Page(s) 12789–12796

Abstract: A photoprintable dynamic thiol-ene resin was developed based on commercially available anhydride, thiol, and ene monomers. The dynamic chemistry chosen for this study relied on the thermal reversibility of the in situ generated thioester-anhydride links. ...

Abstract	A photoprintable dynamic thiol-ene resin was developed based on commercially available anhydride, thiol, and ene monomers. The dynamic chemistry chosen for this study relied on the thermal reversibility of the in situ generated thioester-anhydride links. The resin's rheological and curing properties were optimized to enable 3D printing using the masked stereolithography (MSLA) technique. To achieve a desirable depth of cure of 200 μm, a combination of radical photoinitiator (BAPO) and inhibitor (pyrogallol) were used at a weight ratio of 0.5 to 0.05, resulting in more than 90% thiol-ene conversion within 12 s curing time. In a series of stress relaxation and creep experiments, the dynamic reversible exchange was characterized and yielded rapid exchange rates ranging from minutes to seconds at temperatures of 80-140 °C. Little to no exchange was observed at temperatures below 60 °C. Various 3D geometries were 3D printed, and the printed objects were shown to be reconfigurable above 80 °C and depolymerizable at or above 120 °C. By deactivation of the exchange catalyst (DMAP), the stimuli responsiveness was demonstrated to be erasable, allowing for a significant shift in the actuation threshold. These highly enabling features of the dynamic chemistry open up new possibilities in the field of shape memory and 4D printable functional materials.
Language	English
Publishing date	2020-12-23
Publishing country	United States
Document type	Journal Article
ISSN	1944-8252
ISSN (online)	1944-8252
DOI	10.1021/acsami.0c18979
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