Dual Covalent Cross-Linking Networks in Polynorbornene: Comparison of Shape Memory Performance

In this work, tetrakis(dimethyllamino)ethylene (TDAE) plasticized polynorbornene (PNB) was used as the matrix, sulfur (S) and dicumyl peroxide (DCP) were simultaneously used as crosslinking agents to construct dual covalent cross-linking networks in PNB. The effects of different amounts of cross-lin...

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Bibliographic Details
Published in:Materials 2021-06, Vol.14 (12), p.3249
Main Authors: Zhao, Haotian, Zhang, Qinghong, Wen, Xinlong, Wang, Gongliang, Gong, Xiaowen, Shi, Xinyan
Format: Article
Language:English
Subjects:
Bonding
Composite materials
Covalence
Covalent bonds
Crosslinking
Dicumyl peroxide
Elastic recovery
Fourier transforms
FTIR spectrometers
Glass transition temperature
Infrared spectrometers
Mechanical properties
Molecular weight
Networks
Polymers
Polynorbornene
Polysulfides
Reaction mechanisms
Shape memory
Sulfur
Tensile strength
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Summary:In this work, tetrakis(dimethyllamino)ethylene (TDAE) plasticized polynorbornene (PNB) was used as the matrix, sulfur (S) and dicumyl peroxide (DCP) were simultaneously used as crosslinking agents to construct dual covalent cross-linking networks in PNB. The effects of different amounts of cross-linkers on the crosslinking degree, mechanical property, glass transition temperature, and PNB shape memory performance were investigated. Two crosslinking mechanisms were examined by Fourier transform infrared spectrometer and Raman spectrometer. The results showed that sulfur-rich cross-linked PNB exhibited a higher crosslinking degree, tensile strength, and slightly higher glass transition temperature than the DCP-rich system. Cross-linked PNB presented better shape memory performance than the uncross-linked one. Sulfur-rich cross-linked PNB showed even better shape memory behavior than the DCP-rich system, both with a shape fixation ratio of over 99% and a shape recovery ratio of over 90%. The reaction mechanism of sulfur and DCP in cross-linking PNB was different. Sulfur reacted with the α-H in PNB to form monosulfide bonds, disulfide bonds, and polysulfide bonds in PNB and the number of polysulfide bonds increased with increased amounts of sulfur. DCP reacted with the double bonds in PNB to form C-C covalent bond crosslinking networks. The crosslinking mechanism revealed that the sulfur-containing cross-linked bonds, especially polysulfide bonds, were more flexible and bore large deformation, which gave the PNB excellent mechanical properties and ensured a higher shape entropy elastic recovery ratio.
ISSN:1996-1944
1996-1944
DOI:10.3390/ma14123249