(3eb) Initiation of Methylidene Malonates from Polymers to Promote Mechanical Properties and Polymer Compatibility

Chemical compatibility between polymers is a complex phenomenon, leading to phase separation and mechanical failure for blends of chemically similar polymers (e.g. poly(ethylene) and poly(propylene)) and delamination of multilayered polymer artifacts. In extrusion technologies, a tie-layer is added between dissimilar polymer layers to promote adhesion; primers are used in common paints to prepare surfaces for subsequent polymer-based coatings. Attaching hydrogels to polyolefins and elastomers is particularly challenging due to dissimilar physiochemical properties. My research focuses on a novel polymer that can improve the compatibility and performance of dissimilar polymers to solve application challenges in diverse fields from biomedical devices to recycling. Methylidene malonates are a class of reactive molecules capable of anionic polymerization under facile conditions. Due to their highly reactive structure, polymerization can be initiated by common nucleophiles (e.g. carboxylate salts), and polymerization occurs at room temperature, even in the presence of air and water. I am studying the conditions that govern methylidene malonate polymerization from small amounts of functional groups in the backbone and chain ends of other bulk polymers. The chemistry of the methylidene malonates (mono- vs multifunctional reactive groups, reactive vs. unreactive backbone chemistry) affects the ability of the monomer to undergo chain transfer and termination, in addition to the available initiators and the local environment provided by the bulk polymers, solvents and impurities. Chain growth, in turn, affects polymer physical properties. I am working to understand the dynamics between polymer synthesis and material properties. My goal is to use this understanding of fundamental polymer properties to increase polymer adhesion in biomedical devices and improve mechanical properties of recycled polymers.

To increase polymer adhesion between hydrogel coatings and polymer substrates, I am studying the initiation of methylidene malonate polymerization from a polyolefin or elastomer. We hypothesize that poly(methylidene malonate) architecture and functionality will affect adhesion of the subsequent hydrogel layer. Specifically, bulk poly(ethylene) is combined with an additive containing carboxylic acid and is activated by a base treatment to produce a tethered carboxylate salt. The carboxylate salt initiates polymerization of diethyl methylidene malonate from the surface of the poly(ethylene). Spectroscopic surface characterization techniques, such as attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), are used to determine the effect of initiator concentration and environmental conditions on polymerization. Further studies will determine the effect of the polymerization and functionality on hydrogel adhesion. Technologies which increase the adhesion of hydrogels to polymers typically used in biomedical devices can improve patient health, for instance, in procedures using catheters where hydrogel coatings are not durable and cause embolisms.

In a second project, I hypothesize that multifunctional methylidene malonates can be used to extend the molecular chains of post-consumer recycled (PCR) plastic to increase mechanical properties. Typically, PCR polymers undergo mechanical recycling to transform used items to processed flake or pellets. During the mechanical recycling process, the polymers degrade, forming lower molecular weight species that have decreased mechanical properties, such as tensile strength. Worse mechanical properties translate into poor performance, making it difficult for companies to incorporate recycled polymer into new consumer items and deterring the economics of recycling. By adding a chain extension additive into the mechanical recycling process, the molecular weight of the polymers can be increased, providing mechanical properties amenable or better than virgin polymer. To overcome this limitation, I combine multifunctional oligomers with a model low molecular weight polyester in the polymer melt and study the ability of multifunctional methylidene malonates to chain extend the polyester. Processing conditions such as temperature, initiator activation, and chain extender concentration, are evaluated to determine their efficacy in promoting chain extension. Mechanical properties of polymers before and after chain extension reactions are measured, characterizing potential benefits of different processing conditions. Preliminary work will be used to evaluate the feasibility of using methylidene malonate chemistry to improve recycled polymers, enabling a circular economy.

Research Interests

Before my graduate work, I worked at the DuPont Experimental Station as an associate scientist in Core Research and Development and in a scale-up laboratory for a customer-facing business unit. In this work, I characterized thermomechanical properties of new or improved polymers and polymer coating attributes for treating seeds. I enjoyed studying how fundamental polymer properties affected performance in a wide variety of applications. In my graduate work, I have been able to probe deeper into polymer characterization and measuring polymer performance, in addition to expanding my skills in polymer synthesis and reaction engineering. I have learned more about how chemical functionality and polymer reactivity affect thermomechanical and other physical polymer properties. The combination of skills has given me a deeper appreciation for materials design, and during my post-doctoral studies, I want to continue to explore the complexity of design in pursuit of sustainable materials.

My future goals entail becoming a professor of engineering and an expert in designing material systems to meet application needs. I enjoy learning characterization techniques and exploiting that knowledge to deduce the chemical and physical phenomena of polymers. I am interested in delving deeper into polymer synthesis, but I have a great appreciation for polymer physics and thermodynamics. While working in DuPont’s Thermal Analysis lab, I learned many techniques to probe temperature-dependent polymer interactions; in my graduate studies, I was able to leverage these skills for my own research and offer training to new differential scanning calorimetry users. I enjoy being a resource for researchers new to thermal analysis techniques and thinking about how temperature affects what occurs on a molecular level. I have used rheology to study polymers to varying degrees in all my research positions since my undergraduate work, and I appreciate the many solutions provided by tackling a challenge through a rheology lens. I would love to complement my understanding of polymer physics with scattering experiments, such as x-ray diffraction and neutron scattering.

I am excited to work collaboratively and mentor graduate and undergraduate students in my post-doctoral studies, and hopefully as a future professor. I have worked closely in the lab with an undergraduate student for the past 2 years, starting from the end of the student's freshman year. In my third year, I wrote an original proposal to address student learning in the chemical engineering fundamentals class and was awarded the Douglass Fellowship to develop those ideas. As one of the first students in the Klier lab, I have collaborated extensively with professors and students to learn new techniques and instrumentation, in both my department and other STEM departments who I met through my NSF Soft Materials for Life Sciences fellowship. I have also built relationships to promote a safe lab culture, by collaborating with our chemical safety officer and Environmental Health and Safety experts to build engineering controls and evaluate standard operating procedures.