1. Applications of Diels-Alder Chemistry in Polymer Synthesis
Joshua C. Stambaugh, Sierra E. Gosting, and Philip J. Costanzo
Department of Chemistry and Biochemistry, California Polytechnic State University, CA 93407
Overview
Past Applications
Future Applications
Autonomous Self-Healing Materials
The ability to heal structural materials from impact damage is desired for many applications. This work details the modification of a surface to control delivery of a healing agent. This is accomplished by attaching a diene to a surface and adding a dienophile alter surface functionality under specific temperatures. This project developed a simple and efficient method to functionalize surfaces.
Diels-Alder chemistry is utilized for a myriad of commercial applications during polymer synthesis, ranging from self-healing materials to heat responsive materials to emulsion coatings. In particular, the ability to regulate and control the amount and type of functional group linkages is key component for polymer applications. A common strategy that is employed is the use of phenolic maleimide as a dienophile during Diels-Alder synthesis to control the linkages on a polymer, which determines its properties and functionality.
Moving forward, we are partnering with an industrial sponsor to prepare a waterborne emulsion for rehealable floor coatings and polishes. The first step in this project is to stockpile phenolic maleimide because of its importance as a reagent in many Diels-Alder reactions. This summer, we made 8 batches of phenolic maleimide producing over 300g. The synthesis of phenolic Maleimide will continue throughout the current project.
Hydrophilic
Hydrophobic
Healing agent
Repaired crack
Synthetic Plan
We propose to synthesize a dynamic material whose solution properties can be controlled by various parameters. This project employs Diels-Alder chemistry as a platform for preparing a reversible linkage (Figure 1). Briefly, a diene is attacked by a dienophile to form a ring structure. The formation of the ring structure is temperature dependent and reversible.
Scheme 1. Synthesis of phenolic maleimide
Figure 5. Joshua Stambaugh vacuum filtering the final product.
Figure 1. Reversible Diels-Alder adduct whose formation is temperature dependent.
Red - Diene, Furan. Blue - Dienophile, Maleimide.
Figure 3. TOP : diagram of self-healing material working autonomously to heal a deformity (crack); BOTTOM : Surface functionalization
Conclusions
In the above reaction, cooling the diene and dienophile will create the Diels-Alder adduct, while heating the adduct will return it to its starting components. In our experiments, we used phenolic maleimide (figure 2), which uses a phenol group (ring of carbons with an alcohol group attached) where R2 is located in figure 1. Phenolic Maleimide is an important reagent in many Diels-Alder reactions and is synthesized in a three step process.
Thermally Responsive Automotive Topcoats
Utilizing Diels-Alder chemistry, thermo-responsive surfaces were prepared. Healing agents were able to be delivered by controlling wettability. A thermally responsive, soybean oil based automotive top coat was prepared. Phenolic maleimide was produced on a large scale in 40g batches and was repeatedly successful.
Acknowledgements
This project successfully functionalized soybean oil with Diels-Alder linkages with simple and efficient chemistry. This soybean oil was turned into a coating based on polyurethane that can return to its original shape when heated after deformation.
The 2018 STEM Teacher and Researcher Program and this project have been made possible through support from Chevron ( the National Marine Sanctuary Foundation ( the National Science Foundation through the Robert Noyce Program under Grant # and , the California State University Office of the Chancellor, and California Polytechnic State University. The Costanzo would like to acknowledge the National Science Foundation (NSF: CHE and CHE – ).
Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the funders.
Figure 2. LEFT : The chemical structure of Phenolic Maleimide; RIGHT : Step two of synthesizing phenolic maleimide using P2O5 and fuming sulfuric acid.
Figure 4. TOP : Reversible reaction between diene and dienophile that returns to original shape with heat; BOTTOM : Analysis showing Control coating did not reheal but DA containing coatings did reheal.