Marshall J. Allen’s research while affiliated with University of Texas at Austin and other places

What is this page?


This page lists works of an author who doesn't have a ResearchGate profile or hasn't added the works to their profile yet. It is automatically generated from public (personal) data to further our legitimate goal of comprehensive and accurate scientific recordkeeping. If you are this author and want this page removed, please let us know.

Publications (8)


Overview of thermoplastic elastomers (TPEs) from contemporary ABA triblock copolymers in conjunction with the present norbornene‐based derivatives. A) Illustration showing monomeric chemical structures, ABA triblock copolymerization strategies, and processing to furnish TPEs with disparate thermomechanical properties. B) Comparing the wide range in stiffness (elastic modulus) values for the present TPEs to biological tissues.
Polymer synthesis and characterization, and thin film preparation. A) Representative DSC traces for A (red) and B (blue) homopolymers, showing disparate Tg values. B) General schematic for block copolymerization. C) Representative GPC traces for each block in the synthesis of 15‐100. Table inset provides number average molecular weight (Mn) in kg mol⁻¹ and dispersity (Đ) relative to polystyrene standards. D) Illustration of polymer synthesis, purification, and film processing. Conditions: i) G3′, 3–5 min; ii) exo‐EH‐NBdE, 7–20 min; iii) exo‐Ad‐NBI, 10‐30 min; iv) ethyl vinyl ether.
Correlating morphology to initial tensile modulus. A) Representative small angle X‐ray scattering (SAXS) data for x‐100 series where x = 5, 10, 15, 30, and 50 wt% A‐block. B) Initial modulus, E0, versus A‐block wt% for 100 and 300 kg mol⁻¹ series. Dashed lines represent linear connections between symbols as a guide. Symbols represent averages of >3 samples and error bars represent ±1 standard deviation from the mean.
Uniaxial tensile testing of representative NB‐TPEs and commercial TPEs. A) Stress–strain plots. B) Plot of tensile strength versus modulus at 100% strain. Symbols represent averages of >3 samples and error bars represent ±1 standard deviation from the mean. C/D) Modulus versus strain plots with supersoft region highlighted (gray). Instantaneous modulus values were obtained from a rolling average of the slope in stress–strain plots over increments of ≈12.5% strain.
Characterizing entanglements, toughness, and elasticity. A) Rheological data for homopolymers of the B‐block, poly(exo‐2‐ethylhexyl‐NBdE) to determine entanglement molecular weight, Me. B) Plot of critical energy release rate versus modulus at 100% strain to quantify toughness in the presence of a crack defect. Symbols represent averages of >3 samples and error bars are ±1 standard deviation from the mean. C) Cyclic loading and unloading with increasing strain (Strobl test) to quantify elasticity for sample 15‐100 as a representative. D) Bar chart of elastic recovery at 100% strain (black) and at the penultimate cycle prior to fracture (white).

+2

Supersoft Norbornene‐Based Thermoplastic Elastomers with High Strength and Upper Service Temperature
  • Article
  • Publisher preview available

May 2024

·

111 Reads

·

3 Citations

Henry L. Cater

·

Marshall J. Allen

·

Mark I. Linnell

·

[...]

·

With over 6 million tons produced annually, thermoplastic elastomers (TPEs) have become ubiquitous in modern society, due to their unique combination of elasticity, toughness, and reprocessability. Nevertheless, industrial TPEs display a tradeoff between softness and strength, along with low upper service temperatures, typically ≤100 °C. This limits their utility, such as in bio‐interfacial applications where supersoft deformation is required in tandem with strength, in addition to applications that require thermal stability (e.g., encapsulation of electronics, seals/joints for aeronautics, protective clothing for firefighting, and biomedical devices that can be subjected to steam sterilization). Thus, combining softness, strength, and high thermal resistance into a single versatile TPE has remained an unmet opportunity. Through de novo design and synthesis of novel norbornene‐based ABA triblock copolymers, this gap is filled. Ring‐opening metathesis polymerization is employed to prepare TPEs with an unprecedented combination of properties, including skin‐like moduli (<100 kPa), strength competitive with commercial TPEs (>5 MPa), and upper service temperatures akin to high‐performance plastics (≈260 °C). Furthermore, the materials are elastic, tough, reprocessable, and shelf stable (≥2 months) without incorporation of plasticizer. Structure–property relationships identified herein inform development of next‐generation TPEs that are both biologically soft yet thermomechanically durable.

View access options

Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Hybrid Epoxy-Acrylate Resins for Wavelength-Selective Multimaterial 3D Printing

April 2024

·

279 Reads

Structures in nature have evolved to combine hard and soft materials in precise 3D arrangements, which imbues bulk properties and functionality that remain elusive to mimic synthetically. However, the potential for biomimetic analogs to seamlessly interface hard materials with soft surfaces for applications ranging from soft robotics and sealants to medical devices (e.g., prosthetics and wearable health monitors) has driven the demand for innovative chemistries and manufacturing approaches. Herein, we unveil a liquid resin for rapid, high resolution digital light processing (DLP) 3D printing of multimaterial objects with an unprecedented combination of strength, elasticity, and stability. Two enabling discoveries are the use of a covalently bound (hybrid) epoxy-acrylate monomer that precludes plasticization of soft domains and a wavelength-selective photosensitizer that greatly accelerates cationic curing for hard domains. Using dual projection for multicolor (UV and violet light) DLP 3D printing, several bioinspired metamaterial structures are produced, including those with a brick-and-mortar architecture to tune toughness, hard springs in a soft cylinder to tune compressive behavior, and a detailed knee joint with “bones” and “ligaments” to provide smooth motion.


Multimorphic Materials: Spatially Tailoring Mechanical Properties via Selective Initiation of Interpenetrating Polymer Networks

December 2022

·

209 Reads

·

22 Citations

Access to multimaterial polymers with spatially localized properties and robust interfaces is anticipated to enable new capabilities in soft robotics, such as smooth actuation for advanced medical and manufacturing technologies. Here, orthogonal initiation is used to create interpenetrating polymer networks (IPNs) with spatial control over morphology and mechanical properties. Base catalyzes the formation of a stiff and strong polyurethane, while blue LEDs initiate the formation of a soft and elastic polyacrylate. IPN morphology is controlled by when the LED is turned “on”, with large phase separation occurring for short time delays (∼1-2 minutes) and a mixed morphology for longer time delays (>5 minutes), which was supported by dynamic mechanical analysis, small angle X-ray scattering, and atomic force microscopy. Through tailoring morphology, tensile moduli and fracture toughness can be tuned across ∼1-2 orders of magnitude. Moreover, a simple spring model is used to explain the observed mechanical behavior. Photopatterning produces “multimorphic” materials, where morphology is spatially localized with fine precision (<100 μm), while maintaining a uniform chemical composition throughout to mitigate interfacial failure. The fabrication of hinges represents a possible use-case for multimorphic materials in soft robotics. This article is protected by copyright. All rights reserved


Polymeric multimaterials by photochemical patterning of crystallinity

October 2022

·

74 Reads

·

41 Citations

Science

An organized combination of stiff and elastic domains within a single material can synergistically tailor bulk mechanical properties. However, synthetic methods to achieve such sophisticated architectures remain elusive. We report a rapid, facile, and environmentally benign method to pattern strong and stiff semicrystalline phases within soft and elastic matrices using stereo-controlled ring-opening metathesis polymerization of an industrial monomer, cis-cyclooctene. Dual polymerization catalysis dictates polyolefin backbone chemistry, which enables patterning of compositionally uniform materials with seamless stiff and elastic interfaces. Visible light-induced activation of a metathesis catalyst results in the formation of semicrystalline trans polyoctenamer rubber, outcompeting the formation of cis polyoctenamer rubber, which occurs at room temperature. This bottom-up approach provides a method for manufacturing polymeric materials with promising applications in soft optoelectronics and robotics.




Mechanically robust hydrophobized double network hydrogels and their fundamental salt transport properties

July 2021

·

24 Reads

·

1 Citation

Water swollen polymer networks are attractive for applications ranging from tissue regeneration to water purification. For water purification, charged polymers provide excellent ion separation properties. However, many ion exchange membranes (IEMs) are brittle, necessitating the use of thick support materials that ultimately decrease throughput. To this end, novel double network hydrogels (DNHs) with variable water content are prepared and characterized in terms of mechanical and ion transport properties to evaluate their potential utility as tough membrane materials. The first network contains fixed anionic charges, while the other is comprised of a copolymer with varied ratios of hydrophobic ethyl acrylate (EA) and hydrophilic dimethyl acrylamide (DMA) repeat units. Characterization of freestanding DNH films reveals a reduction in water content from 88 to 53 wt% and a simultaneous increase in ultimate stress and strain by ~3.5× and ~4.5×, respectively, for 95%/5% EA/DMA, relative to 100% DMA. Fundamental salt transport properties relevant to water purification, including permeability, solubility, and diffusivity, are measured and systematically compared with conventional membrane materials to inform the development of DNHs for membrane applications. The ability to simultaneously reduce water content and increase mechanical integrity highlights the potential of DNHs as a synthetic platform for future membrane applications. Abstract


Mechanically Robust Hydrophobized Double Network Hydrogels for Water Purification

April 2021

·

7 Reads

Water swollen polymer networks are attractive for applications ranging from tissue regeneration to water purification. For water purification, charged polymers provide excellent ion separation properties. However, many ion exchange membranes (IEMs) are brittle, necessitating the use of thick support materials that ultimately decrease throughput. To this end, a series of double network hydrogels (DNHs), synthesized with varied composition to decrease water content, are examined as robust membrane materials for water purification. One network contains fixed anionic charges, while the other comprises a copolymer with different ratios of hydrophobic ethyl acrylate (EA) and hydrophilic dimethyl acrylamide (DMA) repeat units. Characterizing water content and mechanical performance in free standing DNH films reveals a ~5× decrease in water content, while increasing ultimate stress and strain by ~3.5× and ~4.5× for 90:5 EA:DMA relative to pure DMA. Salt transport properties relevant to water purification, including permeability, solubility, and diffusivity, are measured and show improved performance upon reducing water content. Overall, the ability to simultaneously reduce water content, increase mechanical integrity, and decrease salt transport rates highlights the potential of DNHs for membrane applications.

Citations (4)


... The Page group demonstrated a photoredox strategy for the synthesis of interpenetrating polyurethane and acrylate networks. 87 It is easy to envision extending this principle to ROMP. For example, a system in which a photobase generator and ROMP initiator are both present and activated orthogonally. ...

Reference:

PhotoROMP: The Future Is Bright
Multimorphic Materials: Spatially Tailoring Mechanical Properties via Selective Initiation of Interpenetrating Polymer Networks

... Thus, the dosage of light can spatially control the amount of poly(c-DHF) and crosslinking in the thermoset. Critically, these multimaterials are created from a single monomeric functional group by means of spatial control over orthogonal polymerization reactions 36 . ...

Polymeric multimaterials by photochemical patterning of crystallinity
  • Citing Article
  • October 2022

Science

... Therefore, metathesis represents a significant developmental challenge in both academia and the chemical industry. In particular, this process has been intensively utilized for the synthesis of macromolecular materials and functional polymers by ring-opening metathesis polymerization (ROMP) [9][10][11][12][13][14][15][16][17][18][19] and proved to be an effective tool in catalytic depolymerization of plastics as well [20][21][22][23][24][25], constituting a major challenge in the development of new applications. ...

User Guide to Ring-Opening Metathesis Polymerization of endo -Norbornene Monomers with Chelated Initiators
  • Citing Article
  • July 2022

Macromolecules

... Later, ion-pair receptors concurrently encoded with cation binding motifs and anion binding motifs were developed [19][20][21]. Typical examples include strapped crown ether and calix [4] pyrrole-based macrocycles, which have been demonstrated to selectively separate lithium from other alkali cations via solvent extraction [22][23][24][25]. It is noted that ion-pair receptors mostly rely on sophisticated chemical synthesis, thus limiting their real applications. ...

Selective Separation of Lithium Chloride by Organogels Containing Strapped Calix[4]pyrroles
  • Citing Article
  • November 2021

Journal of the American Chemical Society