DESIGN AND SYNTHESIS OF POLYMERIC NANOSTRUCTURES USING SINGLE-CHAIN TECHNOLOGY AND CONTROLLED ARCHITECHTURES
With the increasing appeal of nanotechnology, there is a demand for development of synthetic techniques for the fabrication of nanosized objects that allow for precise size control and tailored functionalization. To this end, the collapse or folding of single polymer chains into architecturally defined nanostructures is a rapidly growing research topic in polymer science. Many synthetic approaches have been developed for the formation of single-chain nanoparticles (SCNP), and a variety of characterization methods and computational efforts have been utilized to detail their formation and probe their morphological characteristics. Interest in this field continues to grow partially due to the variety of potential applications of SCNP including catalysis, sensors, nanoreactors, and nanomedicine. While numerous developments have been made, the field is continuing to evolve, and there are still many unanswered questions regarding synthesis and characterization of SCNP. This dissertation serves to first identify recent accomplishments in the synthesis and characterization of SCNP, then to distinguish areas that are in need of advancement and innovation that we focused on to move this field forward. This includes exploring more complex synthetic strategies, obtaining folding control, employing nanoparticle functionalization, developing scalable methods, investigating hierarchical self-assembly of SCNP, and exploiting unique characterization techniques and in-depth simulations.
In chapter 2, we present a scalable route to single-chain nanoparticles (SCNP) under mild conditions using intramolecular atom transfer radical coupling (ATRC). Typical methods to SCNP, a class of soft nanomaterials in the sub 10 nm size regime, rely on complicated synthetic techniques, high temperatures unsuitable to fragile functional groups, or ultra-dilute conditions (solutions less than 1 wt%), all of which can greatly complicate scale up. Our method uses a minimal number of synthetic steps and mild reaction conditions amenable to a wide array of solvents and tolerant to a variety of functional groups. Using this scalable method, gram quantities of nanoparticles in the 5-10 nm size regime are accessible.
Chapter 3 describes a method to fold single polymer chains into nanoparticles using simple thermal Diels-Alder (DA) chemistry. Two different folding strategies are explored, one employing “chain-internal folding” and the other using external, multi-functional cross-linkers. In the first strategy, random terpolymers were designed with varying incorporations of methyl methacrylate (MMA), furfuryl methacrylate (FMA) and a maleimide functionalized methacrylate (MIMA) to achieve internal folding through a thermal DA reaction between pendent furan and maleimide groups. In the second method, the synthesis of random copolymers of MMA and FMA form nanoparticles after effecting a thermal DA reaction between pendent furan groups and external bi- or tri-maleimide functionalized cross-linkers. This multifaceted approach compares different synthetic designs of linear polymers as well as multiple cross-linker species as a means to explore the effect these synthetic differences have on the resulting SCNP. The two polymer series designed in this study allow for a direct comparison between chain internal cross-linking of multiple internal pendent groups and external cross-linker mediated collapse.
Looking to explore a different method to obtain polymeric nanostructures, chapter 4 focuses on the self-assembly of a range of star polymers. Star polymers, particularly Miktoarm stars, are another approach to molecular level control of self-assembled nanostructures. They have potential as templates for hybrid materials when self-assembled in solution. Interest in star polymers continues throughout literature since they have the ability to transport and release guest molecules for use in areas including catalysis, imaging, drug delivery. In this study, we focus on the synthesis of star polymers to be used as single-molecule micelle-like structures with the ability to program multiple domains into both the core and corona through the introduction of monomers with varying solubility. In addition, we aim to place responsive segments, or linkages, at the interface of the core and corona to be selectively triggered using light, heat, and chemical stimuli at particular sites to promote a controlled self-assembly.