Synthesis, characterization, and mechanical and dynamic mechanical studies of β-alanine trimer-grafted SBR

Publication date: 31 January 2018
Source:Polymer, Volume 136
Author(s): Yihong Zhao, Lin Fu, Li Jia
Two β-alanine trimer-grafted SBRs with varied grafting densities, 3a and 3b, have been synthesized. The grafting density of 3b is about twice of that of 3a. FT-IR and DSC evidences suggest that the β-alanine trimer segments in both 3a and 3b exist exclusively in the β-sheet secondary structure, and the β-sheets stack to form crystals in the continuous SBR phase. The Tm of the β-sheet crystals in 3b is higher than the Tm of those in 3a. This likely suggests that the size of the crystals is somewhat larger in 3b than in 3a. TEM revealed that the β-sheet crystals are rod-like, with lengths on the order of a few tens of nanometers and widths of a few nanometers. The aspect ratio is much lower than that of the β-sheet crystals in segmented TPEs. The most prominent difference in the tensile behavior between 3a and 3b is strain hardening. The former is devoid of strain hardening, while the latter displays strong strain hardening. Overall, the high β-alanine content in 3b leads to improvement of stiffness, ultimate strength and overall toughness at the sacrifice of extensibility and elastic recovery compared to 3a. Dynamic mechanical studies showed that both 3a and 3b display very low loss factors, typical for TPEs with monodisperse hard segments that form β-sheet crystals, at temperatures up to 105 °C.

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