Polymer-protein conjugates significantly improve the bioavailability of therapeutic proteins; however, systematic evaluations of how distinct structural parameters of polymers effect the bioactivities of the conjugated proteins remain challenging due to the formation of a heterogeneous mixture of final conjugates using polymers with dispersity (e.g., PEG, etc.). To solve this long-standing problem, we developed a new class of discrete polymer-protein conjugates with full control over the conjugation site on proteins and structural parameters of the conjugated polymers, which were synthesized via an efficient, scalable, and convergent strategy–iterative exponential growth (IEG)–for obtaining polymers with defined stereochemistry, length, rigidity, and functionality. The uniform construction of our discrete polymer-protein conjugates enabled systematic evaluation of the structural impact on protein bioactivities and provided a new approach of controlling biomaterial properties. Therefore, it could potentially serve as a guidance for future protein conjugates drug design to achieve high therapeutic efficacy and excellent long-term stability.
Amphiphilic homo polycaprolactones (PCLs) having di-, tri-, tetra(ethylene glycol) (ME2, ME3, ME4) mono functional groups and a tri(ethylene glycol)/dodecyl (ME3DD) di functional group were synthesized by ring opening polymerization (ROP) of the corresponding γ-functionalized ε-caprolactone (CL) monomers. All the homopolymers formed spherical micelles in aqueous media with variable sizes between 73.2 nm-152.0 nm. The critical micelle concentration (CMC) for PME2CL, PME3CL, PME4CL, and PME3DDCL were 2.2 × 10−1, 2.4 × 10−1, 3.7 × 10−1 gL−1, and 1.8 × 10−2 gL−1, respectively. With the increasing of hydrophilic oligo(ethylene glyco) chain length, the polymeric micelles became less stable and their cloud point tempeature increased from 58.6 oC–85.8 oC. PME3DDCL micelles were more stable due to the increased hydrophobicity from the additonal dodecyl functional group and had the highest loading capacity of 4.8%. However, it significantly affected the cloud point tempeature (Tcp) of PME3DDCL which was not detected even lowing temperature to 4 oC. Compared with homopolymers, amphiphilic blcok copolymers tend to have higher thermodynamic stability. Therefore, a new amphiphilic diblcok copolymer polycaprolatone-block-poly(triethylene glyco/propyl-di-substituted caprolacotne) (PCL44-b-P(ME3PyCL)56) with a mocelular weight of 5,300 g/mol and a PDI of 1.69 was preparared by sequential polymerization. The self-assembly was achieved in aqueous media and the CMC was 2.41 × 10−3 gL−1. It is comparable to that (1.54 × 10−3 gL−1) of polycaprolactone-block-poly(triethylene glycol) (PCL48-b-P(ME3)52) diblock copolymer with a molecular weight of 6,000 g/mol and a PDI of 1.38.
Ice growth is a major problem in cell storage, infrastructure maintenance and in food industry. Chemical tools to modulate ice formation/growth have great (bio)technological value. Existing solutions to control ice growth have focussed on using antifreeze/ice-binding proteins from extremophile organisms, while recently polymeric inhibitors have emerged. Previous reports of nanomaterial architectures containing ice recrystallisation-active macromolecules did not show enhancements in activity. In contrast, native antifreeze proteins show size and aggregation state-dependent activity. In this work, the concept of using polymerization-induced self-assembly (PISA) to generate unique nanomaterials that are capable of inhibiting ice growth is shown for the first time. We introduce polymer nanomaterials that are potent inhibitors of ice recrystallization, employing steric stabilizing polymers known to inhibit ice growth such as poly(vinyl alcohol) (PVA) and others, with not any known activity such as poly(ethylene glycol) (PEG), and poly(vinyl pyrrolidone) (PVP). Crucially, engineering the core-forming block with poly(diacetone acrylamide) enabled PISA to be conducted in saline media. In the first case, a PVA graft macroinitiator was developed to perform PISA and the most active particles inhibited ice growth as low as 0.5 mg.mL-1 and were more active than the PVA stabilizing block alone, showing that the dense packing of this nanoparticle format enhanced activity. PEG and PVP coronas were also active when assembled into nanoparticle formulations, whereas the core-block composition had no impact. This challenges the hypothesis that specific ice-binding domains are essential for activity. Larger nanoparticles demonstrated higher activity than smaller ones, but ice-nucleation activity was not observed in this case. This approach offers a platform towards ice-controlling soft materials using a broad range of polymers that are synthetically accessible and tuneable.
Cationic polymer vehicles have emerged as promising platforms for nucleic acid delivery because of their scalability, biocompatibility, and chemical versatility. Advancements in synthetic polymer chemistry allow us to precisely tune chemical functionality with various macromolecular architectures to increase the efficacy of nonviral-based gene delivery. As various macromolecular architectures continue to be explored, this work demonstrates cationic bottlebrush polymer-mediated transgene expression and compare four unimolecular defined bottlebrush polymers to their linear analog. Poly n-dimethylamino ethylmethacrylate bottlebrushes were synthesized while, keeping the side chain degree of polymerization constant. Characterization of the physical and chemical properties were measured, while evaluating the toxicity and delivery efficiency of pDNA in vitro. Bottleplexes not only displayed vast increases in %EGFP+ cells in comparison to linear polymers, but also bottlebrushes increase transgene expression with respect to increasing molecular weight. Bottleplexes and polyplexes both displayed high pDNA internalization however, quantitative confocal analysis revealed higher levels of nuclear colocalization of pDNA payloads when delivered with bottleplexes compared to linear vehicles. This work was advanced to explore how bottlebrush end-group modification can alter the bottleplex stability, binding, and ultimately delivery of both pDNA and Cas9 protein therapeutics. A cationic bottlebrush polymer was altered to include a range of hydrophobicity/philicity as end-groups to explore the effect while binding pDNA and Cas9 protein. Overall, this work displays that macromolecular design of bottlebrush polymers serve as efficient polymer-based gene delivery vectors.
While HIV treatments have improved, there is still not an effective HIV vaccine available to prevent the spread of the virus. Broadly neutralizing antibodies (bNAbs) against HIV have been developed, but passively-transferred immunity only lasts for as long as the bNAbs persist in the body, which is typically on the order of weeks to a few months. To address this challenge, we have developed an injectable, supramolecular polymer-nanoparticle (PNP) hydrogel to serve as a subcutaneous antibody delivery depot to extend antibody pharmacokinetics (PK). In order to tailor this platform to deliver antibodies with different PK profiles, it is critical to understand how the underlying supramolecular network structure and dynamics affect the rate of release of cargo encapsulated in the hydrogel network. We report the measured rheological properties of various PNP hydrogel formulations as well as the diffusion of both the polymeric hydrogel components and encapsulated antibodies measured using fluorescence recovery after photobleaching (FRAP). A combination of X-ray and neutron small angle scattering experiments provides further insight into the structure of our system. Furthermore, we have conducted preliminary in vivo studies and applied compartment modeling to quantify the contribution of the depot to the overall PK profile of an antibody drug. The robust structural and dynamic understanding of the PNP hydrogels developed from our results will allow us to design next-generation biomaterials to effectively extend the delivery of antibodies against HIV as well as other viruses and infectious diseases.
This work reveals the influence of pendant hydrogen bonding strength and distribution on self-assembly and the resulting thermomechanical properties of A-AB-A triblock copolymers. Inspired by complementary hydrogen bonding interactions between nucleobase pairs in DNA, we prepared cytosine acrylate (CyA) and ureidocytosine acrylate (UCyA)-functionalized A-AB-A triblock copolymers using reversible addition-fragmentation chain transfer (RAFT) polymerization. Thermal, thermomechanical, and morphological analysis revealed the microphase-separated structures of the triblock copolymers. CyA triblock copolymers exhibited a cylindrical microphase-separated morphology according to small-angle X-ray scattering. UCyA triblock copolymers bearing highly oriented quadruple hydrogen bonds promoted the central-external block interactions resulting in a more phase mixed structure than the CyA copolymers. Stronger physical crosslinks within UCyA copolymers extend the plateau modulus nearly 150 °C. Controlled microstructures resulted in A-AB-A UCyA triblock copolymers with superior tensile strength, extensibility, and toughness compared to the AB random copolymer and ABA triblock copolymer analogs. These experiments provided fundamental structure-property-processing relationships of the A-AB-A triblock copolymer tailoring of the self-association constants of the A unit and concentration of A unit in the central block. Balancing the design parameters as mentioned above offers a strategy of tuning thermomechanical and morphological properties of block copolymers.
Lignin is the most abundant natural source of aromatics, and although its recovery/isolation from biorefineries is increasing, current commercial extraction is primarily through Kraft pulping. Only 2% of the separated Kraft lignin (~160 kt/y) is recovered, and the lack of isolation infrastructure hinders the potential utility of existing lignin feedstocks. Additionally, structural heterogeneity, broad molecular weight distribution, dark color, and unpleasant odor generally limit lignin to low-value applications. Deconstruction to aromatic compounds is a promising strategy for the generation of high-value bioproducts from lignin, and in this work, two catalytic processes were examined for the valorization of technical lignin samples from numerous sources (e.g., Kraft, soda, organosolv, and thermomechanical pulping). First, the technical lignins were deconstructed via a conventional reductive catalytic fractionation (RCF) process, and a correlation between lignin thermal stability and phenolic product yield was developed. This relationship enabled the development of a facile screening method for the ‘deconstructability’ of technical lignins. Second, a novel, reactive distillation-reductive catalytic deconstruction (RD-RCD) process was leveraged to simultaneously deconstruct lignin to its constituent phenolic building blocks and purify those compounds. RD-RCD was similar to conventional RCF with respect to phenolic yields and product distributions but operated at significantly lower pressure, resulting in a safer, less-costly process that may be more scalable than existing valorization approaches. Finally, to demonstrate the utility of the RD-RCD bio oils, a biobased stereolithography resin was prepared and successfully printed with a commercial stereolithography (SLA) 3D printer.
Rare Earth Elements (REEs: La–Lu, Y, and Sc) are critical components for innovations in green energy and technology, therefore more effective technologies for the domestic extraction and purification of REEs are in ever-increasing demand. Metal-chelating polymers have great potential in these applications due to their relatively low cost and high affinity for target elements. However, while much research has focused on specific ligands attached to polymers, little is known about the effect of polymer architecture itself on metal chelation. We will report on our most recent progress in the design, synthesis, and application of polymers for the selective chelation of various REEs. In addition to synthesizing a series of metal-chelating polymers, we elucidated the thermodynamics of binding using isothermal titration calorimetry (ITC) to gain insight into the specific structure-metal binding relationships of these materials. ITC enables the direct measurement of the binding affinity (Ka), enthalpy changes (ΔH), and stoichiometry of the interactions between macromolecules and metal ions in solution. By elucidating the thermodynamic profile of each chelating material, we have gained insight into each materials’ properties as a metal chelator.
This paper will serve as a brief introduction to Prof. Tim Long’s symposium in honor of his receiving the 2022 Paul Flory Polymer Chemistry Education Award. Tim has effectively integrated research leadership with teaching excellence spanning a diverse set of communities, from dedication to the undergraduate researcher to training the next generation polymer innovators to ACS short courses for life-long learning for the industrial scientist. Influencing multidisciplinary education, he has led two polymer science-based institutes: Macromolecules Innovation Institute at Virginia Tech and Sustainable Macromolecular Materials and Manufacturing at Arizona State University. His exemplary and multifaceted approach to polymer science education makes him a worthy recipient of the ACS Paul J. Flory Polymer Education Award.
Pressure sensitive adhesives are designed to create a bond under applied pressure and provide a balance between shear holding ability, tack, and peel adhesion. Crosslinking of PSAs can lead to improved shear strength.A variety of chemical and UV crosslinkers have been employed in acrylic systems to obtain balanced PSA properties. One frequently employed approach has been to use diacrylates, which crosslink acrylic PSAs with free radical chemistry. However, a free-radical mechanism is also typically used for the polymerization of the PSA, which means that crosslinking and polymerization occur simultaneously. In order to trigger physical properties on demand orthogonal chemistries are frequently utilized. This approach spans application areas from photolithography to biophysics to pressure sensitive adhesives. The breadth of chemistries developed for this type of triggered reaction or staged reaction is tremendous with many different strategies. Hot-melt PSAs are becoming more widely used due to their elimination of solvent and cost benefits. However, creating high performance PSAs from hot-melt coated adhesives requires a carefully designed, effective crosslinking strategy providing an easily processable adhesive with balanced properties. The crosslinking agent precursor should be stable and unreactive during hot-melt processing to avoid gelation and/or poor coating. The precursor should also effectively crosslink the adhesive once activated after the coating process is completed. This talk will address a variety of approaches to enable hot-melt pressure sensitive adhesives.
Consumers increasingly expect and demand sustainable products without trade-offs in performance, convenience, and/or cost. Concerned companies, like P&G, have established sustainability goals that include the use of large percentages of recycled raw materials in their products and packaging. To satisfy consumers’ expectations and achieve companies’ goals, P&G has embarked on a multipronged strategy to create and sustain a circular economy for polymers. The scope of these efforts is comprehensive and includes polymers used across P&G’s entire portfolio of brands and product applications. Delivering a circular economy requires redefining what has been historically considered to be “waste” and instead reclassifying these materials as valuable raw materials that can transformed into products. New technologies and breakthrough innovation will be required solve the challenges that lie ahead. Towards this end, we will most certainly depend on the expertise, ingenuity, and executional excellence of the entire polymer science community. We must educate and empower both current and next generation of polymer scientist and engineers to reinvent our polymer economy. This work is being presented in honor of Professor Timothy Long, who has been a passionate educator, research leader, and friend to many in the polymer community.
This talk will provide an overview the circular economy of polymers and touch on the research and innovation underway to deliver it.
In honor of Prof. Timothy Long’s reception of the Paul J. Flory Award, it’s my privilege to share my experiences as a student in the Macromolecules Innovation Institute during his directorship and our work during my time as graduate researcher in his group at Virginia Tech. Elastomers remain an enticing and elusive material class for additive manufacturing platforms due to the traditional paradoxes involved in the optimization of their structure-property-processing relationships. While optimal performance typically originates from high molecular weight linear precursors crosslinked at low levels, viscosity limitations in most leading printer platforms typically restrict photopolymer molecular weights to oligomeric ranges and below. Further, additive manufacturing (AM) platforms such as vat photopolymerization (VP, SLA, DLP) and UV-Assisted Direct Ink Writing (UV-DIW) rely on rapid fluid-solid transitions induced by light and relatively low shear forces to template fluids into load-bearing shapes, which are unamenable to the curing chemistry and rheology developed for traditional elastomer manufacturing methods. Our work investigates the use of polymer colloids (latex, dispersions, etc.), a polymer processing medium prevalent throughout nature and industry, as a uniquely suited candidate for multiple AM platforms through the introduction of novel photo-reactivity and colloidal rheology tailored to each platform. The resulting printable colloids prove an effective strategy to circumvent traditional photopolymer obstacles and combine high elastomeric performance with the complex geometries unique to AM fabrication.
Polymer compounding is the process of making a formulation based on mixing polymers and additives that yield targeted properties and functionality. In 2018 the authors, who both received graduate educations from Professor Timothy Long, launched a specialty polymer compounding business focused on polymer compound development and production using twin-screw extrusion. The fundamentals of polymer science learned from our time in Professor Long's group (chemistry, structure-property relationships, and characterization) form the foundation of what we do on a dailly basis to differentiate and grow the business and deliver innovative solutions and quality products to our customers.
At DuPont, our company’s purpose is to empower the world with the essential innovations to thrive. Our innovations are focused on some of the world’s most complex challenges. To enable success, one must work collaboratively, applying cutting-edge science and engineering to bring extraordinary business impact. But it’s not just the science and technology that enables success. It’s also the people, agile strategies for innovation, sustainability, digital advancements, and customer co-development that create impact. It’s also about portfolio management: the risk management balancing act of targeting high value challenges that push the boundaries of the market while continuing to deliver innovative solutions that meet customer expectations. In this symposium honoring Tim Long, I’ll share my story beyond the science and the lessons he taught that laid the foundation for a non-laboratory career in science with a focus on portfolio management.
Instead of having devices that take us away from the people around us, the next computing platform will help us be more present with each other and move the device out of the way. The desire for faster, lighter, more energy efficient devices presents great opportunities in the development of new specialty materials that meet challenging requirements. Understanding of structure-property-processing relationships enables quick design and testing cycle of new materials. Rapid on demand material innovation is critical for fast iteration of device design and fabrication cycles. Robust materials for electronic device fabrication must be designed with multiple constraints in mind. For example, a typical photoresist polymer for semiconductor manufacturing needs to meet photolithographic requirements, have good etch resistance, meet surface energy criteria, and integrate well with the whole film stack. Linking these functional performance metrics to fundamental polymer structural characteristics and processing parameters are essential to meeting application requirements. This talk will highlight how in-depth understanding of polymer fundamentals guides the development of novel functional materials for next generation electronic devices. This talk is also dedicated to Dr. Tim Long for his contribution in spreading the knowledge of polymer fundamentals and empowering his students to push the frontier of material innovation.
Structural resins have historically found ubiquitous use across various industries as lightweight adhesives. As the automotive, aerospace and electronics industries continue to look to increase performance to weight ratios, the need for improved resin designs becomes apparent. One main focus here is the improvement of ductility in glassy materials. In particular, highly crosslinked networks, such as epoxy-amines, provide an encouraging platform for solvent and creep resistance, high strength, and environmental stability, however they suffer from brittle-like behavior well below the Tg. Over the last decade, several efforts have systematically probed the influence of the ‘static’ network structure on the performance of crosslinked glasses. However, responsive, or adaptive, glasses provide a relatively unexplored avenue for an on-demand mechanical response. While three response mechanisms are outlined to provide a range of mechanical behaviors on demand: (i) shape-changing functionalities which locally yield or soften the material to stimulate chain mobility; (ii) bond forming (or breaking) chemistries which increase (or decrease) the stiffness of the material; and (iii) energy absorbing groups which convert the incoming stimuli into a spatially controlled heating and result in a designed softening of the material, many challenges still remain in achieving controlled responses deep in the glassy state.
Scholars estimate that over 7,000 languages are spoken across the world today, and in the words of Nelson Mandela, "If you talk to a man in a language he understands, that goes to his head. If you talk to him in his language, that goes to his heart." The languages of science and engineering are equally diverse, but at the heart of many discoveries, we find a researcher who masters a multilingual vocabulary, fluent in their native scientific language yet also conversational with other disciplines. A mechanical engineer may define a fiber manufacturing process as stochastic while the synthetic chemist describes the randomness of the same nonwoven fabric. Speaking multiple scientific languages will facilitate innovation and catalyze our search for rapidly emerging interactions of science and engineering. This lecture will highlight an evolution of structure-property-processing relationships that guide both research discovery and interdisciplinary education of our next generation workforce. Moreover, this lecture will be a celebration of a teamed approach to discovery with a vibrant thread of fundamental science and engineering that connects many amazing graduate students from the Long research group. Our students are now challenged to sustain their passion for the science of sustainability due to many factors, including variable economics, uncertainty in energy calculations, diversity in civil infrastructure, regionally inspired sustainable feed stocks, and the often missing yet essential industry-university partnership. “Benign by design” remains a critical perspective for our future material sustainability leaders.
An interdisciplinary approach to education in sustainable macromolecular materials and manufacturing
Radical ring-opening polymerization (rROP) can be used to introduce labile ester groups into the backbone of otherwise rigid radical polymers, improving their chemical responsivity and degradability. However, this technique has been characterized as having poor reactivity with more activated monomer species like acrylates and styrene. In recent reports, thionolactone platforms have been introduced to overcome common issues seen with typical rRO monomers and facilitate targeted degradation. While a 7-membered thionolactone has been successful for copolymerization of acrylates, new monomers must be synthesized and studied to achieve different incorporation profiles with acrylamide monomers, facilitate reactivity with styrene, and advance mechanistic understanding of this new monomer family. To further this aim, a new 6-membered cyclic xanthate (6RCX) monomer has been identified that copolymerizes relatively evenly with acrylamide-based monomers. Further investigations have also revealed topochemical polymerizations in the solid-state that leads to regioregular homopolymers with high molecular weights. Both the co- and homopolymerizations of the 6RCX will be discussed in this presentation, along the development of analogs to improve long-term stability in the solid-state.
Organocatalyzed atom transfer radical polymerization (O-ATRP) is a method for synthesizing well-defined polymers under mild conditions using organic photocatalysts (PCs). In O-ATRP, the PC is photoexcited by light, generating an excited state PC that is responsible for activating an alkyl halide and beginning polymer propagation. The PC radical cation that forms during this process is then responsible for deactivation of the polymer, which limits undesirable side reactions known as termination. Although PCs in O-ATRP are typically present in low concentrations, they still add undesired color to the product polymers and may have negative health effects since their toxicity is often unknown. Currently, precipitation of the polymers is the most common purification method employed to address these concerns, but a more efficient and effective purification method is needed. To address this issue[DC1] , a range of purification methods were tested for their effectiveness in removing PCs and their impact on the polymer. Polymers were evaluated before and after purification to understand if molecular weight, dispersity, or chain-end groups changed as a result of purification. The most effective purification method was then tested on a variety of O-ATRP PCs to determine the scope of PCs with which this method can be used.
Isocyanurates are commonly used in the polymer industry because their high degree of crosslinking gives rise to superior mechanical properties. Due to their high degree of stability, isocyanurate bonds are not recyclable by any current industrial recycling methods. Dynamic covalent bonding has been used successfully to promote recyclability in similar polymer systems, including polyurethanes. We hypothesized that isocyanurates may be recycled using similar methods without sacrificing their mechanical properties. Isocyanurate dynamic bonding was investigated using small-molecule organic compounds, which allowed the reaction to be monitored via gas chromatography/mass spectrometry. Recycling industrial isocyanurate waste into new consumer products would reduce their environmental impact.
Crosslinked polyethylene (XLPE) has high water absorption resistance and thermal resistance due to the closed-cell structure. In addition, it shows good buoyancy characteristics due to its low density. These features make the material attractive to many industries and applications, such as a submarine power cable. However, XLPE is a thermoset polymer that reaches its degradation point readily without the melt phase, leading to carbon dioxide (CO2) emissions. For example, 540 tons of XLPE wastes per year end up on landfill sites from electrical cables in Arizona state. Therefore, this research aims to investigate sustainable manufacturing and possible physical and chemical methods to recycle XLPE. One protocol disperses XLPE into a few polymer matrices (e.g., rigid polyurethane foam (RPU) or PE foam) after several processing steps from the XLPE chunks. The investigation includes testing and analyzing thermal, mechanical, and structural characterization to design sustainable methods for upcycling XLPE and use this as a demonstration for recycling general thermoset materials.
Thermally-responsive materials have been prepared in a multitude of ways for a wide variety of applications. One aspect not previously exploited is the ability to induce changes in polymer architecture to induce changes in polymer solubility. Diels-Alder (DA) chemistry and light-activated ATRP was utilized to incorporate DA linkages at various locations within the polymer backbone and side chain. Upon the application of a thermal stimulus, polymer topology was altered as measured by changes in solution-state structures.[figure1]
Polylactide (PLA) is a bio-derived and industrially compostable polymer, and is one of the most commonly used sustainable plastics in industry. One of the limitations on expanding the commercial use of neat PLA is its poor melt strength (i.e., extensional viscosity), which makes it difficult to use in processing methods that require uniaxial extension, such as foaming and film blowing. In the work reported here, we tuned the melt strain hardening of poly (+/- lactide) using the backbone degree of polymerization (Nbb) in a graft architecture to improve its melt strength. To accomplish this, we synthesized graft-poly(D,L-lactide) samples of differing Nbb using a graft-through ring-opening metathesis polymerization. The samples were tested on an ARES-G2 rheometer with an extensional viscosity fixture. The data indicates a critical value of the backbone degree of polymerization above which a graft polymer will begin to melt strain harden. We attribute this to a star-to-bottlebrush transition, in which the behavior of the graft polymer changes from star-like at small values of Nbb to bottlebrush-like as Nbb increases. This work provides important information regarding the design of graft polymers, which should be considered when using this architecture to improve the processability of sustainable plastics, like PLA.
Polyvinylidene fluoride (PVDF) is a thermoplastic polymer that is well known for its piezoelectric and pyroelectric properties, and its applications include smart sensing, actuation, and energy harvesting. The piezoelectric response of PVDF is influenced by the amount of all-trans β-crystalline polymorph. PVDF blends with polymethylmethacrylate (PMMA) have shown increased overall crystallinity as well as higher β-phase content. Polyhedral oligomeric silsesquioxane (POSS) has also been shown to increase crystallinity in semi-crystalline polymers and to improve processability through viscosity modification. This study explores the effects of PMMA-POSS copolymers and POSS additives on α-phase and β-phase crystallinity and rheological response in PVDF polymer blends using melt rheology, DMA, DSC, and surface analysis.
The green chemistry revolution drives the interest for monomers with reduced toxicity and broader applications. As synthetic chemistries continue to develop, the desire to infuse sustainability into research catalyzes the development of new pathways for polymer synthesis. One such example is the utilization of carbonyldiimidazole (CDI) to drive the isocyanate-free synthesis of polyurethane foams and thermoplastics in a solvent-free, catalyst-free process. The versatile reactivity of CDI enables new families of bis-carbonylimidazole (BCI) monomers, which readily react with amines to form linear and crosslinked polyurethanes. Aliphatic and aromatic diols react with CDI to form these BCI monomers at high yields. Reacting these BCI monomers with triamines in the melt results in foaming caused by the thermal degradation of the BCI monomer to produce CO2. Working times are readily tuned with either organic or organometallic catalysts to allow for sufficient mold filling and final part encapsulation. This new CDI chemistry presents the potential for new structure-property relationships for high performance applications and safer engineering platforms for manufacturing while simultaneously implementing green chemistry. The elimination of petroleum-derived solvent, while simultaneously increasing the versatility of the final polyurethane harmonizes BCI monomers with green chemistry. Current research focuses on understanding the fundamental structure-property relationships in the isocyanate-free CDI system, with an overarching goal of creating a more circular use for polyurethanes globally.
Group-transfer polymerization of Michael-type monomers (GTP) and ring-opening polymerization of lactones (ROP) are polymerization types benefiting from catalysis mediated by homogeneous metal complexes. Applying polymerization catalysts gives advantages like tunable molecular weight with low polydispersity, stereoregularity, block copolymerization or chain-end functionalization. With emphasis on GTP and ROP, some of the most applied polymerization complexes share the same metal (e.g. yttrium or zirconium) and use similar ligand motifs such as cyclopentadienyl derivatives or bisphenolates. Yet, only little is known about combining those polymerization techniques, possibly yielding GTP-b-ROP block copolymers. Beside the pioneering work from Yasuda et al., so far this research is limited to few examples combining methyl methacrylate and some lactones. However, transferring this principle to functional Michael-type monomers such as 2-vinylpyridine (2VP) or dimethyl acrylamide and different lactones such as (-)-menthide ((-)-M) or ε-caprolactone (CL) is highly challenging as catalyst structure, choice of monomer pairs and reaction conditions are crucial parameters for obtaining controlled block copolymers. By utilizing yttrium bisphenolates, combinations of 2VP as Michael-type monomer with CL or (-)-M as lactones to AB- and BAB-type copolymers could be generated, establishing a pathway towards precisely tunable GTP-b-ROP block copolymers. While the living-type propagation of the polymerization is maintained in both steps, kinetic investigation and chain end-capping revealed a catalytic copolymerization with two different mechanisms. Due to the differences in chemical nature of the two building blocks those new materials can form pH-responsive micelles and undergo microphase-separation. These results act as detailed proof of principle of pioneering work by Yasuda et al. and further research focuses on finding novel combinations of monomers.
The synthesis of metal-organic frameworks (MOFs) from multitopic ligands connected through a flexible polymer backbone has previously relied on polymer ligands with broad dispersities and poor control over molecular weight. Utilizing such polymers leads to integrated polymer-MOF hybrid materials with indeterminate composition, thereby precluding a fundamental understanding of the role of polymer composition, and limited scope. By using a reversible addition fragmentation chain transfer (RAFT) polymerization, we have developed low dispersity homopolymers and diblock copolymers bearing MOF-forming benzenedicarboxylic acid (H2bdc) linkers on the sidechains. Using these macromolecular ligands in combination with metal salts and free H2bdc allowed for the synthesis of crystalline polymer-MOF hybrids, which exhibited tunable stabilities and surfaces areas and represent the first example of an integrated polymer-MOF material from a chain-growth polymerization to exhibit permanent porosity. Furthermore, these results highlight the fundamental role that polymer dispersity plays in the formation of these integrated polymer-MOF hybrids.
Levoglucosenone (LGO) is a biomass-derived molecule that is prepared through the acid-catalyzed pyrolysis of cellulosic waste on a multi-ton/year scale.1,2 Special considerations were recently given to the synthesis of renewable monomers and polymers from LGO, a versatile platform but also as a highly tunable molecule thanks to the presence of readily reactive functional moieties such as α,β-conjugated C=C.3 Herein, we introduce the one-pot two-step synthesis of a new citronellol-containing five-membered lactone (HBO-citro) from LGO. Two kinds of monomers having either three or two reactive hydoxy groups (Triol-citro and Lactol-citro) were then prepared from HBO-citro. The novel monomers were then engaged in solvent-free polycondensations involving diacyl chlorides or diethyl esters with different chain lengths. Branched citronellol-containing renewable polyesters with low Tg ranging from -20 to -42 °C were prepared. To assess the biodegradability of the obtained polymers a commercial lipase was used. An impact of the polymer structure as well as of the co-monomer chain length on the enzyme accessibility and degradation profile was observed. Indeed, a higher degradation profile was found for the polyesters prepared using co-monomers having longer chain lengths, likely due to the decreased steric hindrance around the ester bonds which allowed enhanced accessibility of the enzyme. Other renewable polymers, such as hydroxy-functionalized polycarbonates, were also prepared from Triol-citro. These functional LGO-derived polymers are not only fully biobased with a branched structure, but also bear citronellol side chains that were successfully crosslinked via ultraviolet irradiation to further control the polymer properties.
Transition metal-catalyzed carbonylative polymerization (COPs) takes advantages of low-cost, low-carbon-footprint monomers to produce a variety of degradable polymers with high atomic efficiency. We have developed a zwitterionic principle of designing catalyst for the COP of cyclic ethers (eq 1). The same-type Ni(II) catalysts can be an interesting platform for generating copolymer of CO and ethylene as well. This presentation will discuss the carbonylative copolymerization of ethylene and cyclic ethers (eq 2) catalyzed by the zwitterionic Ni(II) catalysts, the mechanism of the polymerization, and the materials properties of the poly(ketone-co-ester-co-ether) products.
The development of superior scaffold materials for tissue engineering applications by utilising the electroactivity properties of conductive polymers was previously proven to support cell attachment and proliferation. This phenomenon happens via an electrical conduction mechanism that enables cellular signalling and function in tissues to replicate normal electrophysiology. However, the poor biodegradability of conductive scaffolds significantly barred the realisation of their true potential. Moreover, the presence of toxic residues at a molecular level and scaffolds’ biodegradation rate from the degradation process can agitate the immunogenicity response, hence causing complications for one’s health. There remains a challenge to obtain scaffolds with integrated high performance and stability. In the present work, electrically conductive, porous hydrogel scaffolds at different vol. % of PEDOT: PSS addition (0, 0.5, 1.0, 1.5, 2.0 vol.%) were fabricated by using a reversed casting method. SEM, attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR), Xray Diffraction (XRD), and electrochemical impedance spectroscopy (EIS) were used to characterise the porous hydrogels. The in vitro biodegradation test was conducted to reveal the porous hydrogel’s swelling behaviour, together with its chemical and electrical stability performances against the experienced biodegradation behaviour. Considering easy preparation and critical discussions on the biodegradability properties, our findings warrant further investigations in terms of the scaffolds’ immunogenicity to provide a well rounded approach for the development of electrically conductive biomaterials.
Treatment of a disease is effective when a drug can reach the correct location in the body and at the ideal rate. Instead of investigating new drugs, drug delivery systems are developed in an effort to decrease side effects and improve the drug efficacy. Drugs can be encapsulated in nanocarriers such as micelles, vesicles, or hydrogels. The nanocarrier protects the therapeutic agent and releases the drug once the drug reaches its needed destination. Smart materials are developed to respond to changes in the environment such as pH, temperature, presence of small molecules, or redox conditions. Here, we present our progress towards developing a hybrid drug delivery system that combines a vesicle nanocarrier into a hydrogel. Due to our interest in self-assembly and supramolecular chemistry we have developed a supramolecular amphiphile that is capable of self-assembly into a vesicle nanocarrier. We have demonstrated triggered degradation and release of a fluorescent dye as a model drug in the presence of the naturally abundant antioxidant glutathione. The vesicles have been crosslinked into hydrogel via a thiol-disulfide exchange on the vesicle surfaces and shows promise as a dual triggered drug delivery system.
This lecture follows the course of research that elaborates synthetic structures with concave surfaces into container compounds. These containers are deep, open-ended cavitands that largely surround their target molecules and confine their motions. The selectivity of the recognition event and the forces involved are presented. Progress on the development of water-soluble cavitands and their application to difficult separations are reported. The structure and vase-like shape of a deepened cavitand is shown below.
In a league of its own, fluorine has the potential to enable us to engineer biopolymers with highly desirable properties. In one of our current projects we work to establish fluorous interactions as an orthogonal tool in peptide and protein engineering. The incorporation of fluorine substituents in otherwise hydrophobic amino acid side chains induces sometimes drastic changes of biophysical properties of peptides with regard to hydrophobicity, lipophilicity and solubility that cannot be produced in this form by any other functionality known for natural amino acids. The combination of fluorine substituents, which lead to the much-described and widely used omniphobic properties in organic polymers, with the water-soluble properties of peptides (depending on their sequence and folding) promises extremely interesting results. Surprisingly, peptides build up exclusively by fluorinated amino acids (fluoropeptides) are still largely unexplored. Thus, we break new scientific ground. We have established a chemical synthesis approach that enables access to various side chain fluorinated, aliphatic amino acids in gram-scale. This made possible the synthesis of a library of the first fluoropeptides which are fluorinated foldamers of α peptides consisting of differently fluorinated variants of α aminobutyric acid (Fig. 1). Our library design allows a systematic study on the impact of the fluorination degree of the individual amino acid on peptide properties such as hydrophobicity and conformation. The fluoropeptide library was studied in the presence of different liposomes by CD and IR spectroscopy as well as in fluorescence based leakage assays and HPLC based hydrophobicity assays.
Figure 1: Rational design of fluoropeptide library
The conversion of polyolefins to higher value materials could contribute to our ability to reuse plastic waste and to use polyolefins with well-defined microstructures as the starting point for the creation of materials with new properties and functions. Our group has developed reactions that functionalize polyethylene and polyisobutylene at typically inert C-H bonds by a series of catalytic reactions that install hydroxyl, oxo, amino, and boryl groups. The development of these reactions, the mechanisms of these reactions, and the new properties created by the installation of this functionality will be presented in this seminar.
Although the word polymer was already coined by Jöns Jakob Berzelius in 1833, it was through the pioneering work of Hermann Staudinger in 1920, that it was recognized that the macroscopic properties of polymers both in solution and solid state are the result of the macromolecular nature of the molecules. The impressive progress in supramolecular chemistry, however, paved the way to design polymers and materials that lack the macromolecular structure. Instead, highly directional secondary interactions are used to assemble many small organic molecules into a polymer array. Especially ordered arrays of molecules are highly interesting due to the cooperative nature of their supramolecular assembly processes and the chirality of the polymers formed. In the lecture, the concept of supramolecular polymers will be illustrated with a special focus on multicomponent assembly and the use of chirality to understand these assembly processes and to use the chirality due to its unprecedented functionalities.
Today polyolefin materials created by rationally designed early transition metal catalysis are produced on a vast commodity scale and for a myriad of societally relevant applications. Furthermore, careful mechanism-based catalyst design has enabled the production of commercial macromolecules with equisite control of architecture, rheology, and numerous other desirable chemical and physical properties. Nevertheless, two challenges have proven difficult for conventional polyolefin catalytic processes to surmount and are the subject of this lecture: 1) The introduction of polar functional groups into polyolefins which would enhance polymer surface adhesion, rheology, mixing, and other functional properties needed for advanced, value-added products. While metal catalyst-mediated copolymerization of non-polar olefins with polar comonomers would seem to be the most straightforward, atom- and energy-efficient approach, the Lewis basicity of polar co-monomers introduces a severe impediments. Here we report new groups 3 and 4 catalytic systems and successful strategies for copolymerizing non-polar olefins with polar comonomers. This includes advances in the mechnistic understanding of polar monomer enchainment mechanism, focusing on barriers and strategies to mitigate them, as well as the properties of the resulting materials. The approach is both experimental and theoretical. 2) The efficient deconstruction of diverse polyolefin homopolymers and copolymers to reduce molecular mass with significant rates and selectivity, without co-production of other undesirable carbonaceous materials. Here we report the synthesis and physiocochemical characerization of new families of highlly electrophilic organo-early transition metal catalysts which mediate the rapid hydogenlysis of polyethylene homo- and co-polymers as well as isotactic polypropylene under mild conditions. Detailed experimental and theoretical studies of the mechanism(s) by which the C-C cleaving hydrogenolysis processes proceed and their implications are discussed.