Distinguished Polymer Lecturer Series

3D PRINTING NEEDS NEW POLYMERS: FROM PRINTED SATELLITES TO PRINTED PHARMACEUTICALS

Additive manufacturing, or 3D printing, revolutionizes the fabrication of unique and complex architectures in a layer-by-layer approach. In concert with engineering innovation, design and synthesis of novel polymers is crucial for the development of these technologies beyond their current limitations. A unique synthetic strategy involving simultaneous photo-polymerization and crosslinking of acrylate systems during vat photo-polymerization printing overcomes traditional material challenges associated with the technique. This novel approach combines processing advantages of low molecular weight systems with tunable (thermo) mechanical performance similar to high molecular weight polymer networks. Additionally, unrivaled fabrication of polyimide structures with micron-scale resolution is possible through solvent-based vat-photopolymerization printing. Synthesis of poly(amic diethyl acrylate ester) as novel photo-crosslinkable precursors enables printing of novel 3D organogels. After thermal treatment, these objects isotropically shrink and imidize to produce high-resolution thermoplastic polyimide objects. Finally, Ion-containing polymers introduce unique functionality and processing advantages to 3D printing. Targeted material design provides novel poly(ether ester) ionomers suitable for fused deposition modeling (FDM) additive manufacturing. Standard synthesis through melt polymerization of poly(ethylene glycol) and sulfonated isophthalate produces a printable, water-soluble ionomer. Ion exchange to divalent counter-ions such as calcium, magnesium, and zinc provides a high degree of tunability in melt viscosity. Poly(ether esters) ionomers with calcium counterions yielded flexible filament for subsequent processing and printing. Increased processability from ion interactions and tuned viscosity enables unprecedented FDM printing below 80 °C.

Dr. Long is in the Department of Chemistry, and Macromolecules Innovation Institute at Virginia Tech in Blacksburg, Virginia. He can be contacted at telong@vt.edu; http://www.chem.vt.edu/general.php?page=tlong.

THE GREENING OF SILICONES: EXPLOITING NATURAL MATERIALS

Silicones are widely used in developed economies, in applications from sealants in your bathroom to breast implants. They have many attractive features. However, they are completely synthetic – there are no compelling reports of organic silicon-carbon bonds being produced in nature. The high energetic (upstream) process required for silane preparation prevents silicones from being considered green materials. One strategy to mitigate the environmental burden of silicones and, at the same time, broaden the range of properties they can attain, would involve the incorporation of natural materials (Scheme). The synthesis of composite materials requires control over the hydrophobic/hydrophilic interface. We have approached this challenge by utilizing both physical and covalent modification of the natural materials. Permanent chemical anchoring using click chemistry leads to surface-active silicones. An attractive alternative utilizes temporary grafting via a transesterification with boronic acids; the resulting silicones are also water dispersible. However, the Piers-Rubinsztajn (PR) reaction proved particularly amenable to phenolic natural materials. Thus, random modification of lignin, or its derivative eugenol led to either silicones foams or elastomers. The benefits and detriments of these and related synthetic strategies will be explored.

Michael A. Brook, Scott E. Laengert, Ben Macphail, Robert Bui, Sijia Zheng, Alyssa F. Schneider, Mengchen Liao, Yang Chen and Jianfeng Zhang are at the Department of Chemistry and Chemical Biology at McMaster University in Ontario, Canada. Dr. Brook can be contacted at mabrook@mcmaster.ca; http://www.chemistry.mcmaster.ca/silicone.

FUNCTIONAL POLYMER MATERIALS DESIGNED FOR ADVANCED APPLICATIONS AND SUSTAINABILITY

With advances in the translation of nanoscience to nanotechnology comes a need to consider sustainable sourcing of the building blocks used to create the nanotechnological devices at the same time that the functional performance application is defined. This presentation will highlight contributions that polymer chemistry can make toward nanotechnology that is capable of impacting global needs, such as water-food-energy-health, and the grand challenges that must be solved in the coming decade. The focus will include an integration of current approaches to construct nanoscopic systems from natural products with the design of hybrid nanoscopic systems that are capable of pollutant sequestration and magnetic recovery toward environmental remediation, or for drug delivery with selective therapeutic outcomes, among other applications.

 

Dr. Wooley is a professor in the Department of Chemistry, Chemical Engineering and Material Science and Engineering at Texas A&M University in College Station, Texas. She can be contacted at wooley@chem.tamu.edu; http://www.chem.tamu.edu/faculty/karen-wooley/

F - CATALYTIC REARRANGEMENTS OF SILSESEQUIOXANES (SQS) AND ANALOGS: New Cage Sizes and Unusual Reactive Properties

We have been exploring the use of tBu4NF as a means to transform either polymeric T resins or single functional group T8 cages into mixed functional T10 and T12 SQs as illustrated in the two following reactions.1-3
To this end, we have now developed simple, multigram routes to pure PhT8, PhT10¬ and PhT12. The PhT8 system offers cubic symmetry whereas the PhT10 system offers fivefold symmetry and is therefore a very unusual molecule. In contrast, the PhT12 compound has no symmetry. We have also been able to identify and isolate still larger cages as will be discussed. The various cage sizes allow us to explore the effects of symmetry and size on a wide variety of properties. For example, the PhT8 cage brominates almost exclusively in the ortho position. The PhT10 also brominates preferentially in the same position whereas the PhT12 is less selective. Modeling studies seem to explain the observed behavior. We have also used Heck catalytic cross coupling to functionalize the ortho-bromo derivatives of the cages and explored their photophysical properties.

 

Dr. Laine is in the Departments of 1Materials Science and Engineering, 2Macromolecular Science and Engineering, and 3Chemistry at the University of Michigan in Ann Arbor, Michigan. He can be contacted at talsdad@umich.edu; http://www.mse.engin.umich.edu/people/talsdad

J. Furgal,3 M. Bahrami,1 H. Hashemi,2 J. Kieffer,2 X. Mao,2 T. Goodson III3

DEVELOPMENT OF ELECTROCATALYTIC MODELS FOR TESTING THEORY

One approach for designing improved nanoparticle catalysts involves the use of first-principles calculations, such as density functional theory (DFT), to predict the structural properties of efficient, new materials. As these types of calculations have begun to emerge, however, it has become increasingly clear that there are few really good experimental models available to test their predictions.

Dendrimer-encapsulated nanoparticles (DENs) provide an opportunity to meet this need, because their size, composition, and structure can be controlled and because they have a size that is compatible with DFT calculations (<300 atoms). DENs are synthesized by complexing metal ions with interior tertiary amines of poly(amido amine) (PAMAM) dendrimers, followed by chemical reduction. In this talk, I will discuss the basic approach for synthesizing DENs, provide two examples of the interplay of theory and experiment that leads to a better understanding of electrocatalysis, and then discuss some very recent work focused on more complex (and hence more realistic) electrocatalytic structures comprised of DENs and metal oxide surfaces.

Dr. Crooks is in the Department of Chemistry at The University of Texas in Austin, TX. He can be contacted at crooks@cm.utexas.edu; http://rcrooks.cm.utexas.edu/research/; http://tmi.utexas.edu/tmi-people/richard-crooks/.

TERNARY LAYERED CHALCOGENIDES FOR SUPERCAPACITOR APPLICATIONS

Ever growing need for energy generation and storage applications demands development of materials with high performance and long term stability. Layer-structured materials are advantageous for supercapacitor applications owing to their ability to host a variety of atoms or ions, large ionic conductivity and high surface area. In particular, ternary or higher-order layered materials provide a unique opportunity to develop stable supercapacitor devices with high specific capacitance values by offering additional redox sites combined with the flexibility of tuning the interlayer distance by substitution. CuSbE2 (E = S or Se) are ternary layered semiconductor materials that are composed of sustainable and less-toxic elements. We have used solution-based approaches for the synthesis of mono-, few- and multiple layers of CuSbE2 (E = S or Se) and their systematic study for use as supercapacitors, along with the effect of ionic size of electrolyte ions on the specific capacitance and long-term cycling performance behavior.

Electronic structure calculations based on density functional theory predict that very high specific capacitance values are achievable using CuSbS2, making it a very attractive layer-structured material for supercapacitor applications. Quasi-solid-state flexible supercapacitor devices fabricated using CuSbS2 nanoplates exhibit an aerial capacitance value of 40 mF/cm2 with excellent cyclic stability and no loss of specific capacitance at various bending angles. Moreover, the supercapacitors are operable over a wide temperature range.

Dr. Gupta is in the Department of Chemistry and Chemical and Biological Engineering at the Center for Materials for Information Technology, University of Alabama. He can be contacted at Department of Chemistry and Chemical and Biological Engineering, Center for Materials for Information Technology, University of Alabama, AL 35487. He can be contacted at http://www.bama.ua.edu/~agupta/about.html.

POLYMERS: More Than Meets the Eye

Polymers are more than just academically interesting materials. Often referred to as plastics, polymers are present in almost all areas of everyday life. For example, in the kitchen we use plastic utensils and storage containers. In the grocery store you see arrays of plastic bottles and wraps.

Many of your personal technology items are encased to some degree in polymeric material. When thinking about the types of polymers around us, it is clear that polymers exhibit a wide range of properties. Some are soft and elastic, whereas others can be quite hard and stiff. What gives polymers their properties? It turns out that the physical properties of polymers depend largely on the polymer structure at the atomic and molecular level.

The types of atoms and bonds in the structure play a large role in determining polymer properties. Chemists have developed methods to control the structure of polymers at the molecular level, enabling the production of polymers with desirable properties for specific applications. In this lecture, we will examine the relationship between molecular structure and macroscopic properties of polymers, taking a look at specific examples to illustrate these principles in action.

Dr. David Y. Son is in the Department of Chemistry at Southern Methodist University, Dallas, Texas. He can be contacted at Southern Methodist University, Department of Chemistry, Dallas, Texas, 75275-0314. He can be contacted at dson@mail.smu.edu; http://faculty.smu.edu/dson.

NEW VIEWS OF WETTING

In the first decade of the current century, a revolution in the field of wetting took place and the McCarthy group at UMass was central to initiating this event. Two papers are referenced below; one that has the pejorative and provocative title, "How Wenzel and Cassie were Wrong", that disproved two classic theories of wetting and one that is a summary of our papers that were published during 2006-2009 on the topics of fundamental wetting and superhydrophobicity.

A pedagogic introduction to the new views of wetting will be presented. Fundamental issues of interfacial interactions between liquids and solids will be discussed.

Following an introduction to contact angle and contact angle hysteresis, the “Lotus Effect” will be explained from kinetic and thermodynamic points of view. In one section of the talk, it will be shown that perfectly hydrophobic surfaces can be prepared using solution or vapor phase reactions.

Dr. McCarthy is in the Polymer Science and Engineering at the University of Massachusetts, Amherst, MA 01003. He can be contacted at ctmcc@umass.edu; https://www.pse.umass.edu/faculty/researchgroup/mccarthy

NANOSTRUCTURED FUNCTIONAL MATERIALS BY TAMING FREE RADICALS

Many advanced nanostructured functional materials were recently designed and prepared by controlled/ living radical polymerization (CRP). More than 100 million tons of polymers are produced annually world-wide by conventional radical polymerization. However, macromolecular engineering is impossible in this process. Copper-based ATRP (atom transfer radical polymerization) catalytic systems with polydentate nitrogen ligands are among most efficient controlled/living 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 employed for macromolecular engineering of polymers with precisely controlled molecular weights, low dispersities, designed shape, composition and functionality.

Examples of block, graft, star, hyperbranched, gradient and periodic copolymers, molecular brushes and various hybrid materials and bioconjugates prepared with high precision will be presented. These polymers can be used as components of various advanced materials such as health and beauty products, biomedical and electronic materials, coatings, elastomers, adhesives, surfactants, dispersants, lubricants, additives, or sealants. Special emphasis will be on nanostructured multifunctional hybrid materials for application related to environment, energy and catalysis.

Dr. Matyjaszewski is in the Center for Macromolecular Engineering at Carnegie Mellon University, Pittsburg, PA. He can be contacted at matyjaszewski@cmu.edu; https://www.cmu.edu/maty/matyjaszewski/; https://www.cmu.edu/maty/

GREEN POLYMER CHEMISTRY AND BIOCATALYSIS

This presentation will provide examples of how enzyme-catalysis is creating important new opportunities in polymer chemistry, material science and surfactants.

One example is the use of lipases in polymerization reactions. Lipases, due to the mild temperatures at which they work, and their extraordinary selectivity, provide numerous benefits when synthesizing polyesters, polycarbonates and polyamides.

A key benefit is how steric hindrance at the active site results in a high activation energy for crosslinking reactions enabling polymerization of multifunctional monomers while avoiding crosslinking without protection-deprotection steps. The first example of a lipase-catalyzed reactive extrusion ring-opening polymerization will be discussed as an example demonstrating biocatalyst robustness. Whole cell biocatalysis is providing important new routes to biobased monomers from renewable feedstocks. Our laboratory has developed an engineered yeast strain that provides the first efficient bio-technological route to convert fatty acids to w-hydroxyfatty acids (w-HOFAs). In one example, an engineered Candida tropicalis strain used methyl tetradecanoic acid (methyl myristic acid, Me-C14:0) as a feedstock to produce 112 g/L w-hydroxyC14 (w-HOC14) in 55 hours (productivity 2 g/L·h). Examples of how w-HOFAs are being used to develop new bioplastics such as thermoplastic polyurethane elastomers will be discussed.

Professor Gross is in the Department of Chemistry and Biology; Constellation Chair: Biocatalysis and Metabolic Engineering; Center for Biotechnology and Interdisciplinary Studies at Rensselaer Polytechnic Institute, Troy, New York. He can be contact at Resselaer Polytechnic
Institute, 4005B BioTechnology Bldg., 110 8th Street, Troy, N.Y. 12180. He can be contacted at grossr@rpi.edu; http://homepages.rpi.edu/~grossr/index.htm.

THE REVERSIBLE LITHIUM CAPACITY OF PARTIALLY-OXIDIZED GRAPHENE NANOSTRUCTURES

Graphene oxide (GO) was synthesized from expanded graphite (EG) and multi-walled carbon nanotubes (MWCNTs) by a modified Hummer’s method, and was post-reduced under different temperatures and hydrazine conditions.

GOs and partially/fully reduced GOs were characterized by a variety of techniques such as FT-IR, Raman spectroscopy, TGA, SEM, XRD, XPS, and elemental analysis. These characterization methods showed that temperature had a much more significant effect on the performance of reduced-GOs as anode materials than the choice of the environment.

The electrochemical performance of reduced-GOs was greatest when the temperature of reduction was 250 °C regardless of the chemical environment. Within this temperature range, reduced-GOs show a high first-cycle specific capacity over 2000 mAh/g and 1000 mAh/g reversible and irreversible, respectively at a relatively large current density of 500 mA/g. For reduced-GOs at 250 °C and under vacuum, the reversible capacity was maintained at 500 mAh/g during 100 cycles. This performance points to reduced GOs as an attractive alternative to graphite; we will further delineate the effect of surface functionalization on the Li capacity in these materials. Overall, these nanomaterials are capable of further improving the capacity and lifetime of Li-ion batteries, without increasing the costs associated with anode production - a distinct benefit relative to more expensive nanostructural anode options such as carbon nanotubes and graphene nanosheets.

Professor Fahlman is in the Department of Chemistry and Science of Advanced Materials Program, Central Michigan University Mount Pleasant, Michigan. He can be contacted at Dow Science Complex 357, Mount Pleasant, MI 48859. He can be contacted at fahlm1b@cmich.edu; https://www.cmich.edu/colleges/cst/chemistry/Pages/Bradley-Fahlman.aspx.

UNUSUAL PROPERTIES OF POLYMERS AT INTERFACES

Structure and dynamics of interfacial species are very important in the physical properties of polymer systems, such as composites and surface coatings, but the latter is seldom studied. We have focused our research efforts on the molecular motion of polymers at or near solid surfaces. These studies have used nuclear magnetic resonance (NMR), modulated differential scanning calorimetry (MDSC) and Fourier transform infra-red (FTIR) spectroscopy to probe the mobility (and structure) of polymers near solid surfaces. We found that on surfaces, several polymers have properties that are different, often opposite to that of their bulk counterparts.

Polymers from acrylate, methacrylate and related families, are particularly well suited for interfacial studies. These polymers have been adsorbed on large surface-area substrates (nanoparticles) and studied at the interface. For specifically labeled polymers, such as poly(methyl acrylate)-d3 (PMA-d3), we found that the segmental dynamics of the bulk polymer could be classified as "homogeneous", while the surface-adsorbed polymer could be characterized as "heterogeneous" with respect to different regions of the sample. Segments at the polymer-air interface were more mobile and those at the polymer-solid interface were less mobile than those in bulk. The more-mobile segments could be eliminated through over-layering with an unlabeled polymer compression molded on top of the surface polymer. Changes in molecular dynamics with molecular mass of bulk and adsorbed polymers were different. Calorimetry showed increases in the temperatures and breadth of the glass transition region for the surface polymer compared with bulk. The reasons for these differences will be
explored.

Professor Blum is in the Department of Chemistry at Oklahoma State University, Stillwater, Oklahoma. He can be contacted at blum.okstate.edu; http://blum.okstate.edu/.

POLYMERS IN NANOTECHNOLOGY: Making Structures the Length Scale of Molecules

Lithography, the workhorse technology enabling microelectronics manufacture, has reached astonishing success in producing nanoscale features. Despite this, even higher resolution is needed if plans for next generation electronics are to be achieved.

This presentation summarizes approaches to the design of new photoresists that abandon the traditional polymer based strategy and explore the use of several alternative approaches. These materials include block copolymers, molecular glasses and nanoparticle imaging materials with dimensions on the order of 5 nm and less.

In a recent development, metal oxide nanoparticles based on hafnia or zirconia with ligands of organic acids, are shown to be extremely sensitive to EUV radiation (less than 10 mJ/cm2) and produce high-resolution patterns. It is postulated that these photoresists which incorporate photoactive compounds function via a ligand exchange mechanism that gives the materials their very high sensitivity. Also discussed are new photoresists designed to work with organic semiconductors that depend on their immiscibility with other polymers for success.

Dr. Ober is in the Department of Materials Science Engineering at Cornell University, Ithaca, New York. He can be contacted at Cornell University, 310 Bard Hall, Ithaca, New York 14853. He can be contacted at christopher.ober@cornell.edu; http://people.ccmr.cornell.edu/~cober/people.html.