Non-Isocyanate Aliphatic–Aromatic Poly(carbonate-urethane)s—An Insight into Transurethanization Reactions and Structure–Property Relationships

Abstract

This study reveals insights into the transurethanization reactions leading to the aliphatic–aromatic non-isocyanate poly(carbonate-urethane)s (NIPCUs) and their structure–property relationships. The crucial impact of the alkyl chain length in 4,4′‑diphenylmethylene bis(hydroxyalkyl carbamate) (BHAC) on the process of transurethanization reactions was proved. The strong susceptibility of hydroxyethyl‑ and hydroxybutyl carbamate moieties to the back-biting side reactions was observed due to the formation of thermodynamically stable cyclic products and urea bonds in the BHACs and NIPCUs. When longer alkyl chains (hydroxypentyl-, hydroxyhexyl-, or hydroxydecyl carbamate) were introduced into the BHAC structure, it was not prone to the back‑biting side reaction. Both 1H and 13C NMR, as well as FT-IR spectroscopies, confirmed the presence of carbonate and urethane (and urea for some of the samples) bonds in the NIPCUs, as well as proved the lack of allophanate and ether groups. The increase in the alkyl chain length (from 5 to 10 carbon atoms) between urethane groups in the NIPCU hard segments resulted in the increase in the elongation at break and crystalline phase content, as well as the decrease in the Tg, tensile strength, and hardness. Moreover, the obtained NIPCUs exhibited exceptional mechanical properties (e.g., tensile strength of 40 MPa and elongation at break of 130%).

Synthesis of non‐isocyanate polyurethanes with high‐performance and self‐healing properties

“…Several reports have also described the synthesis of poly(carbonate urethane)s based on carbamates and polycarbonate diols. 10,40,41 The obtained NIPUs had good mechanical properties but less concern about thermal stability. At the same time, PU is very susceptible to damage during use, which reduces its service life, so it is also very important to have a certain degree of recyclability and self-repairing ability.…”

“…Shen et al 39 proposed a “hard segment first” method to synthesize linear NIPUs through the reaction between bis‐hydroxyalkyl carbamate and oligodiols and further covalently self‐crosslinked at high temperatures, due to the reaction of the terminal methoxy–carbonyl group with the secondary amide group. Several reports have also described the synthesis of poly(carbonate urethane)s based on carbamates and polycarbonate diols 10,40,41 . The obtained NIPUs had good mechanical properties but less concern about thermal stability.…”