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Modifying Chain Transfer Agent Structure for Polymer Synthesis - Rachael Mends
- 1. Modifying Chain Transfer Agent Structure for Polymer Synthesis Rachael Mends Fors Lab
- 2. Polymers are Everywhere • A chemical compound formed by polymerization and consisting essentially of repeating structural units, monomers. • They are a main constituent of our food (starch, protein, etc.), our clothes (polyester, nylons, etc.), our houses (wood cellulose, alkyd paints, etc.), and our bodies (poly(nucleic acids), proteins, etc.). Nylon Nylon 6,6 Nylon 6
- 3. From Plastic Bottles … Polyethylene Terephthalate
- 5. RAFT (Reversible Addition Fragmentation Chain Transfer) Polymerization Optimal control in RAFT polymerization requires choosing an appropriate chain transfer agent (CTA) for the monomer(s) to be polymerized.
- 6. Chain Transfer Agent Structure is Important to the Polymerization Z S S R O The Z group determines the rate of the polymerization The R group influences the rate the polymerization begins
- 7. Chain Transfer Agent Structure Affects Cation Stability O Me Me OS Me Me EtS S SEtS S [Redox]
- 8. Chain Transfer Agent Synthesis: Deriving the Acetal OS Me Me EtS S O O Me MeSEtS S O Me Me Cl Me Me +
- 9. Chain Transfer Agent Synthesis: Acetal Synthesis + H O O O [Acid]Me Me OH Me Me Me Me 4A sieves excess Me s O OH O Acids: H Cl Al Cl Cl Cl Δ , 4A sieves
- 10. Chain Transfer Agent Synthesis: New Additive to Improve the Reaction + H O O O [Acid]Me Me OH Me Me Me Me 4A sieves excess + H O O O [Acid]Me Me OH Me Me Me Me 4A sieves excess OMeMeO OMe Δ , 4A sieves Δ , 4A sieves
- 11. Chain Transfer Agent Synthesis: Acetal Synthesis + H O O O [Acid]Me Me OH Me Me Me Me 4A sieves excess OMeMeO OMe Acids Al Cl Cl Cl H Cl S O O OF3C Sc 3 Δ , 4A sieves
- 12. Chain Transfer Agent Synthesis: Final Working Conditions OMeMeO OMe + H O O O Me Me OH Me Me Me Me 4A sieves excess HCl Theoretical yield: 2.36 g Actual yield: 0.8594 g Percent yield: 36% 1 eq 1.2 eq 0.01 eq 2M HCl Δ , 4A sieves
- 13. Chain Transfer Agent Synthesis: Chlorination and Substitution 1) BCl3 2) S EtS SNa O O Me Me Me Me OS Me Me EtS S
- 14. Future Work MeO OMe OMe + O O Me Me OH Me Me 4A sieves excess HCl O Me Me + Me O Me O Me Me Me OH Me Me 4A sieves excess HCl Me O Me Me Δ , 4A sieves Δ , 4A sieves
- 15. Acknowledgements Fors Group Members Advisor: Brett Fors Michael Supej Veronika Kottisch Brian Peterson Stephanie Rosenbloom Renee Sifri Dillon Gentekos Jacob Trotta Scott Spring Erin Stache Quentin Michaudel Luis Melecio-Zambrano Yuting Ma CHAMPS Program Stephen Lee Brian Crane Rebecca Brome Tom Rutledge Organic Chem TAs
Editor's Notes
- Hello, My name is Rachael Mends and I will be presenting my research involving modifying a chain transfer agent structure for polymer synthesis
- Polymers are everywhere! A polymer is a chemical compound consisting of monomers, theses monomers structurally repeat to form a polymer and the process is called polymerization. Polymers are an integral components of everyday living, they are found in our clothes, food, bodies and so much more. A very well known polymer is nylon, as pictured above – this image is of tent fabric. Some common forms of nylon is nylon 6,6 which has two repeating monomers in its polymer and nylon 6 which has one repeating monomer. Due to the difference in chemical structure, Nylon 6,6 has a higher melting point (difference in melting points), higher stiffness, lower water absorption rate, and a greater resistant to acids in comparison to Nylon 6
- Another example is polyethylene terephthalate, which is most commonly found in plastic bottles. Compared to nylon, it is much more rigid due to the aromatic ring in its chemical structure
- Lastly, polystyrene is another common commercial polymer, it is found in solo cups and other materials. Compared to nylon, polystyrenes' chemical structure – the aromatic ring - allows it to be much more sturdy than nylon however, it is not as rigid as polyethylene terephthalate due to the lack of additional pi bonds. Transition: There are many methods in making polymerization, however this summer with the FORS group I focused on RAFT Polymerization
- RAFT Polymerization, also known as Reversible Addition Fragmentation Chain Transfer Polymerization, requires a chain transfer agent to initiate polymerizations. Transition: A CTA looks like this
- Aforementioned, the Fors group studies RAFT polymerizations, more specifically Cationic RAFT. The CTA’s structure has been studied greatly for Radical RAFT, however, the effects of the CTA in Cationic RAFT is undergoing current exploration. For Radical RAFT, the CTA structure is greatly influenced by the R and Z groups. The Z group determines the rate of the polymerization where as the R group influences how fast the polymerization begins. My research with the Fors group is focused on the effects of the R group in CATIONIC RAFT - The Z group has been studied before, chainge in R group affects polymerizations
- The CTA we are trying to create is (point). In a polymerization, the CTA splits into a cation and a radical. The CTA oxidizes into its respective cation and this ion initiates polymerizations. Ultimately, the stability of the cation determines how fast the polymerization begins. If the cation is too stable, it may potentially led to an unreactive polymerization. Since the cation we are utilizing is a carbocation, we are testing cation stability with resonance structures and various powers of carbocations (and electron desnity and e- withdrawing groups destablizes)
- In order to create our desired CTA, we decided to split the carbon sulfur bond. The two halves of the bond could be created from trithiocarbonate anion and a chloroether. The chloroether would be derived from the corresponding di-isobutyl acetal. Therefore, our first step in achieving our desired CTA was creating the di-isobutyl acetal.
- In trying to create the di-isobutyl acetal, excess isobutanol and benzaldehyde were allowed to react alongside an acid and 4 Armstrong sieves; the entire reaction was heated up. The three acids we decided to use was para-toluene sulfonic acid, hydrochloric acid, and aluminum trichloride. However, the majority of our reaction mixture consisted of our starting material, benzaldehyde; therefore signaling a failed reaction.
- Since all previous tried experiments failed, water is a byproduct which makes the reaction reversible, we decided to introduce trimethyl orthoformate as a reagent because it creates a low boiling point byproduct, methyl formate, as it reacts with water in the reaction. By LeChatlier’s principle, trimethyl orthoformate will boil away and push the reaction forward as a result.
- With a new reagent, we hoped the reaction would occur. However with the acids aluminum trichloride and scandium triflate, the reaction still proved to be ineffective. However, upon the addition of HCl to the reaction, we were finally able to achieve a better yield than previously before.
- With our final working conditions, we were able to achieve a 36% yield. We utilized excess isobutanol, 1 equivalent of benzaldehyde, 0.01 eq of 2M HCl, 1g of 4A sieves and 1.2 eq trimethyl orthoformate, all heated up to create our di isobutyl acetal.
- Our successful acetal is then chlorinated with boron trichloride and then substituted with the trithiocarbonate ion with the trithiocarbonate salt. This reaction occurred at -78 C and thus created our desired CTA.
- Since our desired acetal was created, we decided to try different aldehydes and ketones to create acetals for different CTA cation stability. The first change was using benzophenone in place of benzaldehyde, however, the reaction remained with mostly starting material in the reaction mixture. We are currently looking at the effects of acetone in place of benzaldehyde.
- I'd like to thank my advisor Brett Fors and my mentor Michael Supej for allowing me to have such an amazing research experience this summer. Also, I would like to thank the CHAMPS program for funding my research experience.