UC Berkeley

Molecular weaving is the realization of a macroscopic principle on a molecular level. Whereas the concept of interlocking, as observed in chains and fences, can be translated to the molecular level by designing molecularly interlocked molecules (MIMs), the technique of weaving single threads into a pattern is not easily recreated. This can be attributed to the necessity for the formation of extended structures with a high degree of order as weaving fundamentally involves an ordered assembly of single strands into various patterns. Reticular chemistry is uniquely qualified to solve this problem as it involves the design and synthesis of multidimensional, crystalline, and porous extended framework structures by connecting different building blocks through strong bonds. By combining strategies from both MIMs and reticular chemistry, molecular weaving was first realized in 2016 in covalent organic frameworks (COFs) by the Yaghi lab. Because MIMs have been implemented as molecular machines and investigated for their mechanical behavior, the question of the effect of molecular weaving on the overall properties of the material remained unanswered.

This dissertation focuses on elucidating the effect of molecularly woven nanocrystals as additives in polymer matrices. The challenge of capturing how molecular weaving influences a material’s properties lies within the small size of the synthesized crystals. As many mechanical engineering techniques are designed to analyze macroscopic samples, the nanometer-sized woven crystals aren’t easily characterized. By utilizing them as fillers in polymers, we are able to study the effect of molecular weaving on a macroscopic scale.

Chapter I provides a general introduction into reticular chemistry and its potential to address important problems related to climate change and realize complex concepts such as molecular weaving. I will be discussing the history of reticular chemistry and its materials, followed by a clear definition of this field of chemistry. The chapter concludes with an outlook into the present and future of reticular materials in applications such as molecular weaving.

Chapter II introduces the core concept of molecularly woven nanoparticles as additives in different polymers. By leveraging molecular weaving and the inherent porosity of the COF, polymers are able to interact with the pore system by threading through the framework. This leads to the formation of so-called polymer-COF junctions that are able to template polymer entanglement and provide additional pathways for energy dissipation during stress.

Chapter III expands upon polymer-COF composites by investigating a molecularly interlocked framework and its effect on the mechanical behavior of the composites. By comparing the behavior of the interlocked COF as an additive both with the woven COF and the demetalated version of itself, more insight into the interactions between polymer matrix and mechanically bonded framework structure can be gained.

Chapter IV delves into the scaling of woven COFs and their translation into polymer-COF composites with polycarbonate (PC) and polydimethylsiloxane (PDMS). Additionally, the scaling of a series of mechanically bonded COFs is discussed, and a new pathway to accessing metal-free woven structures is presented.

Chapter V discusses the expansion of molecular weaving from three-dimensional (3D) to two-dimensional (2D) COFs. By controlling the angles of the linkers between the tetrahedral weaving nodes, the formation of 2D woven structures can be achieved from generally 3D-directing starting materials.

Chapter VI covers an educational research study that introduced a group of high school students to cutting-edge research through an accessible, low-tech synthesis of a water harvesting MOF. Additionally, the participants learned about concepts such as water scarcity and the importance of finding alternate ways to access clean drinking water.

Chapter VII serves as a conclusion to the topic of woven COFs and their ability to enhance the mechanical behavior of polymer-COF composites. This chapter also serves as a perspective for future investigations in this field of research.