Aromatic Polyamide Brushes for High Young's Modulus Surfaces by Surface-Initiated Chain-Growth Condensation Polymerization

Since being developed over 50 years ago, aromatic polyamides have been used industrially for numerous high-performance applications due to their heat resistance, chemical stability, and high strength. Despite this extensive time span, limited applications as surface coatings have been explored due to most aromatic polyamides being insoluble in organic solvents and their extremely high melting temperatures. However, new polymerization techniques have been developed to overcome this insolubility, allowing applications such as reverse osmosis membranes and gas separation membranes to be developed. With the recent advancement of substituent effect chain-growth condensation polymerization, controlled growth aromatic polyamides have been shown to grow from flat and curved surfaces. In this study, aromatic polyamides with a protecting side chain were grown from flat and curved surfaces to allow for post polymerization deprotection and the introduction of hydrogen bonding along the backbone of the polyamide. The aromatic polyamide brushes formed were then characterized using transmission electron microscope and atomic force microscopy to explore important physical properties of the polymer brushes, including grafting density and Young's modulus. The introduction of hydrogen bonding dramatically increased the Young's modulus of the aromatic polyamide brushes from 5-6 to 22-32 GPa. Our results demonstrate the tunability of the aromatic polyamide brushes to achieve high mechanical strength and pave the way for their application in areas such as high-performance coatings.