Dynamic polymer networks: from electronic skin, morphing electronics, biodegradable electronics to stable lithium metal batteries

Abstract: In this talk, I will discuss our recent work on design dynamic polymer networks for a variety of applications that takes advantage of the unique dynamic nature of such polymers. With such materials, we explore new applications for electronic skin, implantable electronics and energy storage.

Conjugated Polymers Inspired by Crystalline Silicon

Abstract: The semiconductor silicon underlies technologies including computers, solar cells, and many more. Yet silicon synthesis relies on top-down, high-temperature approaches that yield only the most thermodynamically stable forms of silicon. Uncovering new structure-function space demands a different synthetic vision. This talk will describe the synthesis of molecular and polymeric silanes inspired by the complexity, selectivity, and elegance of target-oriented organic synthesis. Topics include the chemo selective polymerization of novel bifunctional silane monomers, selective preparation of linear and cyclic polycyclosilanes, optical tuning by copolymerization, and the stereocontrolled synthesis of cis- and trans-siladecalin. Approaches to the structural characterization of novel silane architectures will also be discussed.

Title: Semicrystalline Photopolymer Networks for Additive Manufacturing

Abstract: Photopolymerizable semicrystalline thiol-ene thermoplastics capable of achieving fast polymerization rates and excellent mechanical properties were recently shown to produce useful materials desirable for additive manufacturing (3D printing) and numerous other applications of semicrystalline polymers. These photopolymer systems, composed of commercially available, non-purified monomers, yielded complex printed structures with well-resolved features. The reprocessability of structures printed with non-crosslinked thiol-enes was observed and thus demonstrated its potential applicability for investment casting and recyclable printing. Structurally varied thiol-ene monomers were explored to expand the accessible property space of photopolymer systems implemented as alternative printing systems. Additionally, lightly crosslinked semicrystalline thiol-enes demonstrated improved final mechanical properties. The onset and extent of was controlled by varying the crosslinker and its concentration as well as via the incorporation of various additives to the printing formulation. Thermal conditioning above the melting temperature greatly improved the mechanical performance of the print and in some cases resulted in mechanical properties superior to those obtainable with commercial resins. Finally, complete shape and mechanical recovery of the original printed structure was thermally achieved in a matter of seconds after severe plastic deformation

Making and Unmaking Polymers by RAFT Polymerization

Abstract: RAFT polymerization is one of the most versatile and robust controlled radical polymerization (CRP) techniques and is widely used to prepare a broad range of polymeric materials for diverse applications in various fields. One of the most important properties of RAFT polymers is the ability to maintain high end-group fidelity throughout the polymerization. However, a common misconception in the field is that high end-group fidelity and high dispersity are typically mutually exclusive characteristics. This is a significant limitation as both high and low dispersity polymers exhibit unique properties and functions and as such dispersity is a key parameter in material design.[1] In this talk I will present a straightforward and versatile batch method based on reversible addition-fragmentation chain transfer (RAFT) polymerization to tailor molecular weight distributions for a wide range of monomer classes.[2] Control over dispersity is achieved by mixing two RAFT agents with sufficiently different chain-transfer activities in various ratios, affording polymers with monomodal molecular weight distributions over a broad dispersity range. Notably, high end-group fidelity was demonstrated through the preparation of well-defined block copolymers regardless of the initial homopolymer dispersity. Although high end-group fidelity is crucial to facilitate the synthesis of well-defined block copolymers, it has rarely been exploited to reverse RAFT polymerization and regenerate the monomer. This would be highly beneficial for both fundamental research and applications yet has remained very challenging to achieve. In the second part of the talk, I will discuss a near-quantitative and catalyst-free depolymerization of various linear, bulky, crosslinked, and functional polymethacrylates made by RAFT polymerization.[3] Key to our approach is to exploit the high end-group fidelity of RAFT polymers to generate chain-end radicals at 120 °C. These radicals trigger a rapid unzipping of both conventional (e.g. poly(methyl methacrylate)) and bulky polymers (e.g. poly (oligo(ethylene glycol) methyl ether methacrylate) (POEGMA)). Importantly, the depolymerization product can be utilized to either reconstruct the linear polymer or create an entirely new insoluble gel that can also be subjected to depolymerization. References [1] R. Whitfield, N. P. Truong, D. Messmer, K. Parkatzidis, M. Rolland, A. Anastasaki Chem. Sci., 2019, 10 8724-8734 [2] R. Whitfield, K. Parkatzidis, T. Junkers, N. P. Truong, A. Anastasaki Chem 2020, 6, 1340-1352 [3] H. S. Wang, N. P. Truong, Z. Pei, M. L. Coote, A. Anastasaki J. Am. Chem. Soc 2022, Articles ASAP, DOI: 10.1021/jacs.2c00963

Macromolecular Engineering by Atom Transfer Radical Polymerization

Abstract: Macromolecular Engineering (ME) is a process comprising rational design of (co)polymers with specific architecture and functionality, followed by precise and efficient polymer synthesis and processing to prepare advanced materials with target properties. Many advanced nanostructured functional materials were recently designed and prepared by reversible deactivation radical polymerization. Copper-based ATRP (atom transfer radical polymerization) catalytic systems with polydentate nitrogen ligands are among most efficient reversible deactivation radical polymerization systems. Recently, by applying new initiating/catalytic systems, Cu level in ATRP was reduced to a few ppm. ATRP of acrylates, methacrylates, styrenes, acrylamides, acrylonitrile and other vinyl monomers was controlled by various external stimuli, including electrical current, light, mechanical forces and ultrasound, also in the presence of air. Various copolymers, molecular brushes, hybrid materials and bioconjugates were prepared with high precision. Special emphasis will be on nanostructured multifunctional hybrid materials for application related to biology, environment, and energy.

High Transference Number Polymer Electrolytes Derived from Lithium Bis(malonato)borate: From Solutions to Gels

Abstract: Advances in next-generation, high power Li-ion batteries require the development of new electrolytes that are stable over wide voltage windows. The thermodynamic efficiencies of such cells will further benefit from high lithium-ion transference number (tLi+) electrolytes, in which the ionic current is carried primarily by mobile Li+ ions with minimal anion motion. We describe the scalable synthesis of new classes of linear polymer electrolytes derived from acyclic diene metathesis (ADMET) polymerizations of lithium bis(alkenylmalonato)borate (LiBAMB), and complementary gel electrolytes derived from its thiol-ene step-growth polymerizations. Solution electrochemical characterization of poly(LiBAMB) with Mn = 2.7–55 kg/mol in carbonate solvents reveals their electrochemical stabilities up to 5.2 V (v. Li/Li+) with ionic conductivities s ≈ 0.35 mS/cm when [Li+] ≈ 0.10 M. 1H and 7Li DOSY NMR measurements establish that these solutions exhibit tLi+ = 0.77–0.98, in agreement with direct potentiostatic polarization measurements. On the other hand, thiol-ene polymers of LiBAMB form physically-crosslinked gels when [Li+] ≥ 1.0 M that exhibit high tLi+ ≈ 1 through ionic aggregation. These two studies suggest new and general molecular design principles for high transference number electrolytes for numerous applications.

Design of Polymer Electrolytes with Superionic Ion Transport

Abstract: Progress toward durable, high-energy density lithium-ion batteries has been hindered by instabilities at electrolyte-electrode interfaces leading to poor cycling stability, and by safety concerns associated with energy-dense lithium metal anodes. Solid polymeric electrolytes (SPEs) can help mitigate these issues, however SPE conductivity is limited by sluggish polymer segmental dynamics. Transport through the free volume of ordered, supersonically conductive domains results in decoupling of ion motion and polymer segmental dynamics. Although crystalline domains are conventionally detrimental to ion conduction in SPEs, we demonstrate that semicrystalline polymer electrolytes with labile ion-ion interactions and tailored ion sizes exhibit excellent lithium conductivity (1.6 mS/cm) and selectivity (t+~0.6-0.8). This allows for simultaneous optimization of typically orthogonal properties including conductivity, Li-selectivity, mechanics, and processability.

Control of polymer electrolytes organization and functions

Abstract: Molecular electrolytes are ubiquitous components of life and physical sciences that also control the organization and properties of materials with important technological applications. Many models have been developed over the years to explain the organization and discover new functions of polyelectrolytes. In this talk, I will describe the organization and key functions of polyelectrolytes in bulk and confinement including the co-assembly of polyelectrolytes with enzymes into catalytic membranes and the actuation of hydrogels.

Protein-based bioplastics for sustainable additive manufacturing

Abstract: Bio-sourced and biodegradable polymers for additive manufacturing could enable the rapid fabrication of parts for a broad spectrum of applications ranging from healthcare to aerospace. However, a limited number of these materials are suitable for vat photopolymerization processes. Herein, we report a process to fabricate protein-based constructs using commercially available vat photopolymerization printers. Bovine serum albumin (BSA) is a single-chain nanoparticle that can be chemically derivatized with acrylate and methacrylate functionalities. Aqueous resins were formulated from these materials to produce complex 3D geometrical constructs with a resolution comparable to commercial resins. While BSA is often used in cell culture protocols and diagnostic assays, we demonstrate that BSA can serve as junctions within polymer networks to afford stiff hydrogels and bioplastics with unique physical properties. Protein-based shape-memory objects and engineered living materials were 3D printed and will be highlighted as opportunities for future applications.

Advancing Materials Sustainability: Small Molecules and Polymers from Biomass and Plastics Waste

Abstract: From a materials standpoint, advancing polymer sustainability involves the sourcing of materials from renewable feedstocks, along with the harnessing of polymer/plastics waste in the creation of closed-loop frameworks that valorize traditional waste. For the renewables case, lignin is the largest natural source of aromatic carbon on the planet, and thus, lignin-derived products have emerged as critical elements in the next generation of polymers. However, the valorization of lignin to high-performance and cost-competitive materials remains a challenge due to lignin’s perceived recalcitrance, inherent structural variability, and complexity of deconstructed lignin bio-oil mixtures. Recently, we have demonstrated that materials with reproducible thermal and mechanical characteristics can be synthesized in a controlled and predictable manner from batches of monomers with complex and somewhat variable compositions, such as minimally processed bio-oils obtained from deconstructed lignin. As one example, we have combined polymer science and catalysis to generate new, high-performance, pressure-sensitive adhesives from compounds obtained directly from raw biomass (poplar wood) deconstruction with properties, cost, and processing methods that were competitive and compatible with commercial tapes. Additionally, we have developed structure-activity relationships for lignin-derived compounds that were used to design new systems that had drop-in potential in both synthesis and materials properties (relative to petroleum-based analogues), yet most importantly, demonstrated reduced environmental impacts when screened by several common toxicity assays. Finally, we have leveraged these activities to design new catalytic processes that enable scalability towards continuous processes, along with the translation of these lignin deconstruction concepts to the recovery and valorization of macromolecules from polymer/plastics waste.

A Circular Economy for Plastics

Abstract: One of the goals of a circular economy is to design-out waste and pollution by re-orienting industry around materials that can be re-used and recycled. For polymeric materials used in plastics, elastomers, and thermosets, those in use today were never designed to be recycled. As a result, they have accumulated in both terrestrial and aquatic ecosystems throughout the world in such alarming quantities that their influence can no longer be ignored. If circularity is to be realized broadly, new polymer chemistries are needed for deconstructing both simple and complex products such that monomers, additives, fillers, and other materials to be reused in manufacturing without loss in performance or aesthetics. In this seminar, I will describe our efforts to address these challenges using polydiketoenamine resins (PDK), which undergo reversible polymerization using atom- and energy-efficient processes. PDK resins lay the groundwork for how to commodify polymers as highly valuable, renewable resources for a circular economy. PDK resins also bring to the forefront intriguing new concepts in polymer chemistry and physics, particularly the reconfigurability of soft matter exhibiting dynamic bonds.

Polymer Self-Assembly in the Presence of Liquid Crystals

Abstract: The presence of mesogens attached to block copolymers (BCPs) or blended with BPCs can result in a rich interplay of self-assembly on multiple length scales, and provides new opportunities to control nanostructure development. This talk explores the self-assembly and directed self-assembly of a variety of mesophase forming systems – liquid crystalline (LC) BCPs, block co-oligomers and BCP-analogous macromolecules containing mesogens. These systems display rich phase behavior, including the formation of highly persistent domains, gyroid morphologies and strongly asymmetric phase diagrams, and we encounter systems with structural periodicities as small as ~6 nm. The stimuli responsiveness of LC mesophases represents a useful handle via which to control ordering processes, and we examine this in the context of a photoresponsive system in which cis-trans isomerization can be used to stimulate rapid ordering transitions under ambient conditions. We address the phase behavior and magnetic field alignment of LC BCPs in the presence of labile mesogens. The surface anchoring of the mesogens provides control over the orientation of the BCP structures, and volumetric swelling by the labile mesogens leads to order-order transitions. In particular, we observe a transition from hexagonal cylinders to FCC spheres beyond a critical mesogen concentration. Despite the isometric nature of the cubic lattice, this system aligns with its [100] axis parallel to an applied magnetic field, resulting in a degenerate, fiber-like texture. This response originates from symmetry breaking due to the action of the field, and shares features in common with magnetic metallic systems that undergo structural phase transformations associated with magnetic ordering.

Seeded Growth of Crystallizable Polymeric Amphiphiles: Recent Advances and Applications

Abstract: The ability to prepare materials in the 10 nm – 100 micron size regime with controlled shape, dimensions, tailored functionality, and structural hierarchy is still in its relative infancy and currently remains the virtually exclusive domain of biology. In this talk recent developments concerning a promising “seeded growth” route to well-defined 1D, 2D, and more complex hierarchical materials on these length-scales termed “living” crystallization-driven self-assembly (CDSA), will be described. Living CDSA can be regarded as a type of “living supramolecular polymerization” that is analogous to well-known “living” covalent (e.g., anion initiated) polymerizations of molecular monomers, but on a much longer length scale (typically, 20 nm – 5 microns). Living CDSA also shows analogies to biological “nucleation-elongation” processes such as amyloid fiber growth. The building blocks or “monomers” used for living CDSA consist of a rapidly expanding range of crystallizable amphiphiles such as block copolymers, homopolymers with charged termini, or planar-stacking molecules with a wide variety of chemistries. The seeds used as “initiators” for living CDSA are usually prepared from preformed polydisperse 1D or 2D assemblies by sonication. This talk will focus on the creation of functional architectures via living CDSA with emphasis on applications in catalysis, optoelectronics, nanomedicine, and surface modification. Successful scale-up will be discussed.

The Role of Liquid-Liquid Phase Separation and Non-equilibrium Chemistry in the Self-assembly of Amphiphilic Block Copolymers

Abstract: The self-assembly of amphiphilic block copolymers into 1D, 2D, and 3D nanostructures is of great interest in the areas of drug delivery, medical imaging, catalysis, and templated synthesis. The properties of these materials are intrinsically linked to both their molecular and hierarchical structure. Consequently, research in this area has been focused on providing a fundamental understanding of how the molecular structure and assembly environment can be tailored to control the hierarchical assembly process. As most block copolymer assembly processes are kinetically controlled, I believe it necessitates and understanding of the self-assembly mechanism. In this talk I show how the self-assembly mechanisms of amphiphilic block copolymers can be studied using Liquid Phase and Cryogenic Transmission Electron Microscopy. I will also discuss how liquid-liquid phase separation can plays a role in solvent switch processes, and how non-equilibrium chemistry can play a role in polymerization induced self-assembly processes.

Proteomimetic Polymers for Expanding the Druggable Proteome”

Abstract: In this presentation, we will describe the development of a new class of peptide polymer conjugate accessed via graft-through polymerization of peptidyl-monomers. The resulting dense array of peptides gives rise to key emergent properties that we exploit for the development of these materials as therapeutics: 1) Multivalency, 2) High molecular weight and tunable length scales, 3) Proteolytic/chemical stability and 4) Efficient intracellular penetration. We will highlight examples of the utility of this approach for engaging critical intracellular protein-protein interactions driving neurodegenerative disease and cancer.

Guided by Biology: Defined hyaluronan click-crosslinked hydrogels for in vitro 3D cell culture

Abstract: With the goal of screening cells in an environment that mimics that of native tissue, we designed a hydrogel for 3D cell culture. With 3D cell culture, we gain an understanding of both cell invasion and cell viability, thereby providing insight that is inherently unavailable with traditional 2D cell culture. To achieve a suitable environment, we synthesized hyaluronan-based hydrogels because hyaluronan is often over-expressed in invasive tumours including those in the breast, brain and lung [1]. To facilitate cell invasion and remodelling of the matrix, the hydrogels are crosslinked with peptides that can be degraded by matrix metalloproteinases (MMPs) secreted by the cells. To enhance cell adhesion, the hydrogels are modified with proteins and/or peptides; to facilitate cell invasion, the hydrogels are modified with growth factor concentration gradients [2]. Using well-defined hyaluronan-based hydrogels, we investigate both breast cancer [3,4], brain cancer and lung cell [5] invasion and their response to different therapeutic treatments. Acknowledgments: We are grateful to NSERC and CIHR for funding. References: [1] Fisher, S.; Anandakumaran P.; Owen, S.C.; Shoichet, M.S. 2015 “Tuning the microenvironment: click-crosslinked hyaluronic acid based hydrogels provide a platform for studying breast cancer cell invasion”, Advanced Functional Materials, 25: 7163-72; doi: 10.1002/adfm.201502778 [2] Fisher, S.A.; Tam, R.Y.; Fokina, A.; Mahmoodi, M.M.; Distefano, M.D.; Shoichet, M.S. 2018 “Photo-immobilized EGF chemical gradients differentially impact breast cancer cell invasion and drug response in defined 3D hydrogels” Biomaterials, 178: 751-66; doi: 10.1016/j.biomaterials.2018.01.032 [3] Baker, A.E.G.; Bahlmann, L.C.; Tam, R.Y.; Liu, J.C.; Ganesh, A.N.; Mitrousis, N.; Marcellus, R.; Spears, M.; Bartlett, M.S.; Cescon, D.W.; Bader, G.D.; Shoichet, M.S. 2019 “Benchmarking to the gold standard: hyaluronan-oxime hydrogels recapitulate xenograft models with in vitro breast cancer spheroid culture”, Advanced Materials, 31: e1901166; doi: 10.1002/adma.201901166 [4] Baker, A.E.G.; Bahlmann, L.C.; Xue, C.; Lu, Y.H.; Chin, A.A.; Cruickshank, J.; Cescon, D.W.; Shoichet, M.S. 2022 “Chemically and mechanically defined hyaluronan hydrogels emulate the extracellular matrix for unbiased in vivo and in vitro organoid formation and drug testing in cancer”, Materials Today, in press xx1-x18; doi: 10.1016/j.mattod.2022.01.023 [5] Tam, R.Y.; Yockell-Lelievre, J.; Smith, L.J.; Julian, L.M.; Choey, C.; Baker, A.E.G.; Hasim, M.S.; Dimitroulakos, J.; Stanford, W.L.; Shoichet, M.S. 2018“Rationally designed 3D hydrogels model invasive lung diseases enabling high-content drug screening”, Advanced Materials, 1806214: 1-9; doi: 10.1002/adma.201806214

Exploring How Chirality Impacts the Biological Properties of Synthetic Macromolecules

Abstract: Chirality and molecular conformation are central components of biopolymers, giving rise to the functions of living systems. While synthetic polymers are often designed to interact with biopolymers, the potential impacts of their absolute stereochemistry remain largely unexplored. This talk will describe our efforts to synthesize chiral polymers and then explore how handedness and other molecular descriptors can be leveraged to tune their biological properties. New iterative exponential growth (IEG) methods for the synthesis of enantiomeric pairs of norbornene-terminated macromonomers that differ by their conformational flexibility will be introduced. Ring-opening metathesis polymerization (ROMP) of these macromonomers to produce water-soluble, chiral bottlebrush copolymers (CBPs) will be described. In vitro and in vivo studies reveal that conformationally flexible, enantiomeric CBPs show several-fold differences in cytotoxicity, cell uptake, blood pharmacokinetics, and liver clearance. Comparably rigid enantiomeric CBPs showed no differences in these same assays. A simple model that correlates greater conformational freedom with enhanced chiral recognition will be presented that is consistent with these results, and that may guide the design of future chiral synthetic polymers for biomedical applications.

Polymer Capsule Shells bearing Hindered Urea Bonds: Thermally Induced Shell Fusion and Destruction

Abstract: This presentation will focus on the preparation of temperature-responsive capsule shells containing hindered urea bonds in the polymer backbone, templated by interfacial polymerization in a water-free Pickering emulsion stabilized by alkylated graphene oxide (GO) nanosheets. Under gentle heating, the dynamic covalent bonds allow the capsule shells to either fuse into monolith, when compacted, or undergo destruction in the presence of a primary amine. We explored the impact of monomer identity on the formation of capsule shells and confirmed that the temperature at which the polymers undergo reaction is controlled by the hindrance of the secondary diamine monomer, supported by variable temperature FTIR spectroscopy measurements. In addition, we found that the identity of the liquid core also impacts the temperature-responsivity, with more polar liquids requiring lower temperatures. This tailored polymer chemistry can be generalized to various emulsion systems and chemical reagents to produce tailored structures, with potential in energy storage, molecular separation, controlled release, and so on.

Simpler, Faster and Better – Pushing the Limits of Polymer Synthesis

Abstract: The orthogonal functionalization of polymeric materials is a critical design strategy for the “bottom-up” fabrication of nanostructured systems. In synthesizing these nanostructures, functional group interconversion and efficient organic transformations are key to obtaining materials with exceptional properties. The design of multi-functional building blocks for common polymeric materials and their extension to commercial products will be demonstrated. In addition, a novel methodology for printing 3D objects with spatially resolved mechanical and chemical properties is reported. The power of this approach is showcased through the one-step fabrication of bioinspired soft joints and mechanically reinforced “brick-and-mortar” structures using tailored photochromic dyes.