Polyureas (PUrs) with excellent properties have been applied widely in many fields. These days attention has been turned to non-isocyanate routes for PUr preparation due to the toxicity and the high cost of isocyanates. Urea is a green chemcial which can be either from urine or from recycled carbon dioxide and ammonia. Here we introduce a urea-based route to prepare PUrs, by melt polycondensation of urea and 1,10-diaminodecane (DA-10) or/and 1,6-diaminohexane (DA-6) without catalyst, solvent, and high pressure. It is difficult to synthesize such thermoplastic PUrs from diisocyanate without any solvent since the melting point of PUr is normally higher than 170 C at which isocyanate is able to react with urea group to form biuret. The thermoplastic PUrs obtained in this study exhibit excellent mechanical and thermal properties. Furthermore, the properties can be adjusted by changing the feed ratio of diamines (DA-6/DA-10). The compression-molded PUrs show even better mechanical properties than ultra-high molecular weight polyethylene (UHMWPE). The values of Young's modulus, strength at break and elongation at break are found to be 230-300 MPa, 40-60 MPa and 200%-400%, respectively (except for PUr-6). Therefore, this facile, non-isocyanate approach provides a viable alternative to the current industrial process for highperformance PUrs.
The feedstocks for conventional polyurea foams (PUrFs) are limited but they have more choices in urea route as discribed in this work. Urea, ternary amine T403 and diaminodecane DA‐10 were used for the construction of self‐foaming PUrFs, in which the byproduct ammonia performs as a foaming agent. The influence of nano SiO2 content and feeding ratio of T403 to DA‐10 on the pore morphology and the properties of PUrFs were investigated. A feeding amount of 3 wt% nano SiO2 is found to be able to significantly improve the nucleation performance of PUrFs. If the nano SiO2 loading is higher (5 wt%) the melt strength will increase, which is not benefit for the foaming. An appropriate feeding ratio of T403 to DA‐10 (1/1, sample PUrF‐3‐50) can improve the crystallinity thus promoting the nucleation in foaming process. The comprehensive performance of PUrF‐3‐50 is found to be the highest, with an average pore size at 429 μm, an apparent density at 298 kg/m3, and a compressive strength (75% strain) at 3.2 MPa. It is worth noting that the hysteresis of PUrF‐3‐50 is high (>90%) and stable. This work provides a new strategy for the preparation of PUrFs and broadens the applications of urea‐based polymers.
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