Synthetic strategies for control of structure from individual macromolecules to nanoscale materials to networks

Abstract

Chapter 1. Aqueous self-assembly of prodrug macromonomers. A series of highly tunable micelles for drug delivery were made from norbornene based poly(ethylene glycol) macromonomers with covalently linked drugs. A total of five macromonomers were made using three different drugs (telmisartan, paclitaxel, and SN-38) and three different drug loadings. Combinations of these macromonomers were then allowed to self assemble into micellar aggregates. The size, stability, and shape of these micellar aggregates were controlled with the highly versatile structure. Chapter 2. Post micellization modification of norbornene-containing prodrug macromonomers. Highly tunable micelles for drug delivery were functionalized after their selfassembly. Post-micellization inverse electron demand Diels-Alder reactions of norbornenes and tetrazines were used to signal changes in micelle size and stability through the addition of either hydrophilic or hydrophobic tetrazines.

Thiol-ene additions reactions were used to increase micelle size and form chemically crosslinked nanoparticles. These modifications of norbornene-containing prodrug macromonomer assemblies illustrate their versatility. Chapter 3. Synthesis of polymers by iterative exponential growth. A scalable synthetic route that enables absolute control over polymer sequence and structure has remained a key challenge in polymer chemistry. Here, we report an iterative exponential growth plus side-chain functionalization (IEG+) strategy for the production of macromolecules with defined sequence, length, and stereoconfiguration. Each IEG+ cycle begins with the azide opening of an enantiopure epoxide, followed by side chain functionalization, alkyne deprotection, and copper-catalyzed azide-alkyne cycloaddition (CuAAC). These cycles have been conducted to form unimolecular macromolecules with molar masses of over 6,000 g/mol.

Subsequent modifications to IEG+ allow for the functionalization of monomers prior to the IEG+ cycle, expanding the library of compatible side chain chemistries. Chapter 4. Introduction to elastomer toughening strategies. Silicone elastomers are ubiquitous. Here, silicone elastomers are discussed in terms of network structure, the impact of network structure upon physical properties, and modifications of network structure in order to achieve desired physical properties. Fillers, the standard toughening strategy, are discussed in conjunction with entanglement density. Focus is placed on the impact of entanglement density on material properties. Topological networks are discussed and noted for their stress dissipative properties. Chapter 5. Topology modification of polydimethylsiloxane elastomers through loop formation. Topological networks are well known for their stress dissipation through the pulley effect leading to soft, extensible materials.

Combining these properties with a traditionally crosslinked network to produce a hybrid material allows for enhanced extensibility without a loss in modulus. Here, such hybrid networks were made with poly(dimethyl siloxane) polymers of a range of molecular weights. Side-loop polymer brushes were synthesized and then crosslinked to create hybrid networks with the statistical formation of topological bonds. These materials were characterized through tensile testing. Elastomers formed with the same molecular weight polymer in both side-loops and network formation did not show mechanical properties that depended upon the fraction of networks used for brush formation. Elastomers made with long polymers in brush formation and shorter polymers for network formation resulted in highly extensible systems without significant loss in modulus.