In a secondary amide group containing polymer, hydrogen bonding forms as supramolecular crosslinking and contributes to regulate polymer properties, such as thermal property and mechanical property. The change of chain flexibility upon incorporation of amide groups also leads to different material behaviors. The two effects are sometimes difficult to observe simultaneously in many traditional polymers, such as polyamide and polyurethane, due to crystallization.<br/><br/>In this work, amorphous polyesters with the same backbone structure but different numbers of hydrogen bonding amide – propyl groups in the side chain were synthesized via carbodiimide coupling of succinic acid and various functionalized diols. The effect of temperature on hydrogen bonding between amide groups were studied by temperature-dependent infrared spectroscopy, and it showed that hydrogen bonding strength was proportional to amounts of amide groups and weakened with temperature in the testing range of 20 to 200. The polymer containing most amide – propyl groups had the largest amounts of amide groups where hydrogen bonding could form and act as supramolecular crosslinking. It had the highest Tg and Young’s modulus at room temperature indicating more supramolecular crosslinking made the material less flexible and stiffer. On the other hand, the material with longer flexible amide-propyl side chain turned to more flexible. Rheology measurements indicated the competing effects of side chain flexibility and supramolecular crosslinking on the material property. Hydrophilicity and hygroscopicity of the material increased with amide – propyl groups which were confirmed by water contact angle measurement and TGA.<br/><br/>The balance between side chain flexibility and hydrogen bonding interaction provides the material with different performances and it is environmentally sensitive. Thus through controlling the number of amide groups and selecting operating conditions, specific properties such as viscosity and complex modulus could be achieved. Exploiting the two handles of chain flexibility and hydrogen bonding, we present a good understanding of structure property relationship for this class of materials.

Combined effect of side chain flexibility and hydrogen-bonding originated supramolecular crosslinking on polyester properties

254th National Meeting (2017)

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