The Effect of Branching Structure on the Properties of Entangled or Non-covalently Crosslinked Polyisoprene
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ARTICLE
POLYMER SCIENCE
https://doi.org/10.1007/s10118-020-2480-0 Chinese J. Polym. Sci.
The Effect of Branching Structure on the Properties of Entangled or Non-covalently Crosslinked Polyisoprene Mo-Kun Chen, Rong Zhang, Mao-Zhu Tang, Guang-Su Huang*, and Yun-Xiang Xu* College of Polymer Science & Engineering, State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu 610065, China
Electronic Supplementary Information Abstract The branching structures in natural rubber (NR) were believed to be critical for its superior mechanical properties. However, it is challenging to unravel the branching structure-function relationship of NR due to the complexity of the system. Herein, polyisoprene(polyisoprene-g-polylactide) (PI-PLA) as model compound containing branching structure was designed and synthesized, which can improve the modulus, strength and viscoelasticity activation energy compared to those of the pristine polyisoprene (PI). The reason is that the branching structure contributes to the entanglement between polyisoprene chains. In order to probe the effect of branching structure on noncovalently crosslinked system, the polyisoprene block of PI-PLA was epoxidized and mixed with Fe3+ ions to introduce coordination bonds. Compared with the linear counterpart, the branching structure obviously enhanced activation energy of coordinated polyisoprenes, remarkably improving the mechanical properies of elastomer. Keywords Natural rubber; Branching structure; Noncovalent interaction; Polyisoprene Citation: Chen, M. K.; Zhang, R.; Tang, M. Z.; Huang, G. S.; Xu, Y. X. The effect of branching structure on the properties of entangled or non-covalently crosslinked polyisoprene. Chinese J. Polym. Sci. https://doi.org/10.1007/s10118-020-2480-0
INTRODUCTION Natural rubber (NR) possesses excellent comprehensive properties such as high strength and toughness, crack resistance, antifatigue property and so on, which is widely used in various fields such as industry, agriculture, medical care and aerospace. The synthetic polyisoprene possesses similar main chain structure (e.g. molecular weight, stereoregularity) to NR, but its properties are still inferior to those of NR.[1−4] The main reason is ascribed to the nonrubber components in NR which formed natural network in polyisoprene matrix.[5] Both proteins at the ω-terminal and phospholipids at α-terminal formed branching structures by noncovalent bonding, which influence the entanglement or dynamic bonding between polyisoprene chains.[6] In the last decades, many researches have been carried out to study the effects of the nonrubber components on NR network.[1,7−13] It has been proved that the branching structure in NR makes transient entanglements into permanent entanglements, which can accelerate the strain induced crystallization and stress upturn during the extension. Besides, the curing behavior, crosslinking density, and fatigue resistance of NR are better than those of purified NR as well as the isoprene
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