Single-Chain - PowerPoint Presentation

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Single-Chain Nanoparticle Fabrication via Photodimerization of Pendant Anthracene ROMP PolymerMark F. Cashman, Peter G. Frank*, Erik B. Berda*Department of Chemistry, University of New Hampshire, Durham, NH12/10/14

Introduction:Biomacromolecules are naturally occurring phenomena—formed by the folding of single-chain polymers—that have had inherent applications in nature, due to the unique properties of their architecturally defined nano-structures. Much research on the architecture of these three-dimensional nano-structures has been conducted, in hopes of discovering areas of application in which implementing the ideals and capabilities of these macromolecular structures would prove advantageous, beneficial, and constructive.Single-Chain Nanoparticles (SCNPs)—similar to the synthetic route of biomacromolecules—are formed via the initiated folding of single-chain polymers, and show promising applications in drug delivery systems, sensing, and diagnostics; these polymers can be formed and functionalized as desired, through various synthetics polymerization methods such as RAFT and ROMP. This experiment was designed to develop a synthetic method that utilizes simplest single-chain polymers possible, that easily and readily polymerize and efficiently undergo intra-chain cross-linking under readily attainable conditions.Since a relatively effective synthesis route for this polymer has already been attained via RAFT polymerization. A ROMP-modified synthesis route was designed in order to further investigate the best possible method. How the ROMP route fares in comparison to its RAFT synthesis counterpart, will help to determine the most efficient method of synthesizing HIN-co-AIO ROMP polymer.

Results and Discussion:The ROMP polymer (8) was synthesized via a one-step ring opening metathesis polymerization (Scheme 1): Monomers hexylimide-modified norbornene (HIN) (3) and anthracene-9-methylimide modified oxabicyclo (AIO) (7) were polymerized, forming ROMP polymer (8), using Grubbs’ Catalyst. Scheme 1: The hexylimide-modified norbornene (3) was synthesized via a two-step reaction (Scheme 2): First, endo-norbornene anhydride (1) was heated under reflux allowing it to reconfigure into exo-norbornene anhydride (2), via a retro Diels Alder. Second, the imide-oxygen is replaced by hexylamine via a dean stark reaction.Scheme 2: The anthracene-9-methylimide modified oxabicyclo (7) was synthesized via a two-step reaction (Scheme 3): First, Maleimide (4) and furan (5) were reacted, via microwave heating, in water, forming a dicarboximide-modified oxabicyclo (6). Second, this dicarboximide-modified oxabicyclo (6) was reacted, via an SN2 type mechanism, with 9-chloro-anthracene.Scheme 3:

Conclusions:Though the polymer synthesis was not achieved in the allotted time, the synthesis of the two monomers were successful with high purity. NMR of both monomers, along with the intermediate-step dicarboximide-modified oxabicyclo molecule, were taken and analyzed. The following NMR of hexylimide-modified norbornene exhibits high purity and reaction completion:With an efficient synthetic route for the polymerization of pendant anthracene polymers discovered, focus can be turned to the effects of rigidity of backbone and functionalization of backbone, on photodimerized intra-chain cross-linking SCNP formation.Future Work:With this polymer (8), new insight into the fabrication of single-chain polymer collapses can be uncovered (Scheme 4): Converting half of this rigid, double-bonded-backbone polymer (8) into a more flexible, single-bonded-backbone polymer (9), and subsequently collapsing both under identical conditions, will allow a comparison to be made to test how the rigidity of a double-bonded backbone influences single-chain polymer collapses.Scheme 4:  

Acknowledgements:Special acknowledgements to Peter Frank and the rest of the Berda Group, Deepthi Bhogadhi, and Dr. Greenberg.References:1. Yavari, I., Roberts, J. D., J. Org. Chem., 1978 43: 4689-4690. 2. Jaszay, Z., Petnehazy, I., Toke, L., Szajani, B., Synthesis, 1987 5: 520-523.3. Enholm et al., Tetrahedron Letters, 2004 V45, page 8635-86374. Ilan Pri-Bara, I., Schwartz, J., Chem Commun, 1997. 5. Tang, J., Mohan, T., Verkade, J. G., J. Org. Chem., 1994 59: 4931-4938. 6. Frank, P. G., Tuten, B. T., Prasher, A., Chao, D., Berda, E. B., Macromol. Rapid Commun., 2014 35: 249–253.