A multi-scale investigation on effects of hydrogen bonding on micro-structure and macro-properties in a polyurea

• Published in: Polymer (Guilford) 2018-06, Vol.145, p.261-271
• Main Authors: Li, Ting, Zhang, Cheng, Xie, Zhining, Xu, Jun, Guo, Bao-Hua
• Format: Article
• Language: English
• Subjects: Bulk polymerization; Coarsening; Crosslinking; Destruction; Dynamic mechanical analysis; Elastomers; Energy loss; Fourier transforms; Hydrogen; Hydrogen bonding; Hydrogen bonds; Infrared spectroscopy; Mechanical properties; Microstructure; Modulus of elasticity; Morphology; Multiscale analysis; Polymerization; Polymers; Polyurea; Rubbery plateau modulus; Temperature dependence
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/j.polymer.2018.05.003

Effects of hydrogen bonding on the micro-structure development and mechanical properties of a bulk-polymerized Polyurea are systematically investigated from the perspective of temperatures. A two-stage temperature dependence of bidentate hydrogen bonding among hard domains, namely, slight dissociation from 85 °C to 165 °C and dramatic destruction above 165 °C, are revealed by Fourier transform infrared spectroscopy (FTIR). Morphology developments and mechanical properties also exhibit similar stages in consistent with hydrogen bonding evolution. At the first stage, even slight dissociation of hydrogen bonding can lead to the loss of long-range connectivity of hard domains, resulting in the decrease of "energy loss coefficient". At the second stage, dramatic destruction of hydrogen bonding above 165 °C facilitates the "coarsening" process, which undoubtedly poses the decline of physical cross-link density, leading to the steep decline of Young's modulus and rubbery plateau modulus in dynamic mechanical analysis (DMA). Multi-scale characterizations are employed during the investigation. [Display omitted] •Two stages of bidentate hydrogen bonding dissociation among hard domains are observed upon in-situ heating.•The two stages are slight dissociation from 85 °C to 165 °C and dramatic destruction above 165 °C.•The loss of long-range connectivity of hard domains is confirmed in the first stage, and "coarsening" in the second one.•Similar stages in mechanical properties are the decrease of "energy loss coefficient" and physical cross-link density.