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Synthesis of Polyurea Thermoplastics through a Nonisocyanate Route Using CO2 and Aliphatic Diamines

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journal contribution
posted on 11.12.2020, 10:43 by Ruhui Shi, Shan Jiang, Haiyang Cheng, Peixuan Wu, Chao Zhang, Masahiko Arai, Fengyu Zhao
The transformation of CO2 can alleviate environmental problems and promote sustainable development. We prepared polyureas (PUas) from CO2 and diamines via an isocyanate-free route. PUas synthesized by the copolymerization of CO2 with 1,6-hexamethylene diamine (HMDA) and 1,12-diaminododecane (DAD) presented superior mechanical properties compared to the ones from CO2 with either DAD or HMDA alone. The PUas contained DAD and HMDA segments in the main polymer chains, and hydrogen bonds were formed between DAD and HMDA segments, in which the hydrogen bonds were distributed at regular and irregular intervals depending on the relative amounts of the two segments. For PUas synthesized from either DAD (x = 0) or HMDA (x = 100), hydrogen bonds were mostly present at regular distances, forming a regular hydrogen bond network and contributing to high crystallinity. For PUas of DAD100–xHMDAx (37 ≤ x ≤ 63), in contrast, irregular hydrogen bonds coexist with regular ones, so the crystallinity was lower compared to DAD100 and HMDA100. It is to note that the PUas synthesized are advantageous for postprocessing as their initial decomposition temperatures (Td,5% > 295 °C) are about 85 °C higher than the melting temperatures (Tm, 116–207 °C). Furthermore, mechanical properties were optimized by varying the chain length of aliphatic diamine used. The PUas (DAD50HMDA50 and DAD37HMDA63) obtained show mechanical properties superior to those of the previously reported polymeric materials, such as CO2-based PUas, isocyanate-free polyhydroxyurethanes, CO2-sourced polycarbonates, polyamide 6, and traditional PUas from diisocyanates. Hence, the present CO2-sourced PUas will find industrial applications in different fields.