Using Amines and Aldehydes as a Novel Crosslinking Method for Silicone Materials

Silicones are a class of polymer possessing polysiloxane bonds, with broad industrial and commercial applications that are distinct from organic polymers. Functional silicones made by combining polysiloxanes with other materials, such as small molecules or other polymers, allow for tailoring the silicone's properties to a specific application. These materials are synthesized t hrough well-established and specialized reactions specific to silicone polymers, and progress towards new crosslinking reactions is limited. The current methods of crosslinking silicones have several drawbacks, particularly: requiring harsh reaction conditions or poor tolerance towards many organic functional groups. The advent of novel crosslinking technologies is necessary for further innovation of silicones as materials such as functional coatings, polymers, and elastomers. Functional organosilicone materials leverage the known chemistry of organic moieties and reactions to derivatize or synthesize silicones. These materials combine the properties and reactivity of organic functionality with polysiloxanes, augmenting reactions specific to silicones. This diversifies the library of synthetic routes for silicone materials while also producing unique properties and additional value. In addition, t here is an opportunity to explore facile organic reactions as novel crosslinking chemistries. The condensation between amines and aldehydes to form imines is an attractive synthetic scheme for crosslinking silicones that can solve many problems associated with traditional methods. These moieties are commonly employed for their relatively simple reac tion conditions and high yields to assemble complex chemicals motifs. These features, along with the evolution of water as the only byproduct and tolerance to other organic functional groups, make the synthesis of imines ideal for crosslinking silicones into functional materials. This thesis explores the use of amine-functionalized silicone oils with various aliphatic and aromatic aldehydes as a novel method of crosslinking functional silicone materials via imines and the application of the resulting materials. These reactions overcome many of the drawbacks of traditional methods for crosslinking silicones and produces materials with novel properties that can enable their use in different applications. Furthermore, t he differences in reactivity between the two types of aldehydes lead to two unique crosslinking motifs. Aromatic aldehydes produce conjugated Schiff-base crosslinks, while the crosslinking with aliphatic aldehydes undergoes various condensation reactions to give novel silicone materials. The use of small aliphatic aldehydes such as formaldehyde, glutaraldehyde, and glyoxal was found to rapidly crosslink aminopropylsilicones into elastomeric materials . The high reactivity of the aldehyde towards the amine- moieties also allows for robust crosslinking into elastomers that can occur even in the presence of water, a remarkable feature for silicones that are normally water insoluble. These properties allowed for the application of the material as an ink for 3-D printing, where the rapid crosslinking allowed for the study of a novel free-space droplet merging printing method. Silicone materials crosslinked with aromatic aldehydes produce conjugated Schiff -base bonds. These crosslinks can undergo dynamic exchange reactions in the presence of an amine catalyst to alter bonding in the material. These reactions gave the silicone chemoplastic and thermoplastic properties , allowing the material to be remou lded and reprocessed. Naturally-derived aromatic aldehydes can also be used as the crosslinker, allowing for a multi-faceted approach to increasing the sustainability of silicone materials by increasing their utility, making them reprocessable, thus extending their lifespan while using sustainable materials as a filler.