High-Performance Poly(amide-urea) via a Nonisocyanate Route with Simultaneously Improved Strength and Toughness

The synthesis of traditional polyurea (PUR) involves toxic, hazardous, and harmful isocyanates. Sustainable biobased feedstocks are significant for future industrial development. A range of nonisocyanate poly(amide-urea) (NIPURs) are obtained by melt polycondensation from biobased dicarboxylic acids, urea, and diamines without catalysts and high pressure. Excessive hydrogen bonding in NIPURs leads to high crystallinity, which renders it difficult to obtain a polymer material with both high strength and satisfactory toughness. The hydrogen bonding content and distribution can be regulated by changing the molar ratio of dicarboxylic acids/urea and the structure of the dicarboxylic acids. It is remarkable that NIPURs exhibit excellent mechanical and thermal properties. Its yield strength is up to 61 MPa, tensile strength is as high as 7069 MPa, and it maintains an elongation at break of 241%; its melting point ranges from 166 to 200 °C and it maintains initial decomposition temperature (T5%) higher than 345 °C. The adjustable mechanical and thermal properties of NIPURs offer significant potential for various applications. This work could provide new insights into designing PUR with enhanced mechanical properties.