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

Abstract

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, the 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 remoulded 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.