Promoted strain-induced crystallization of cis-1, 4-polyisoprene with functional carbon nanodots

The excellent mechanical properties and fatigue-resistance of natural rubber (NR) are closely related to the strain-induced crystallization (SIC) capability of NR, which is originated from the unique network structure of NR. The synthetic counterpart of NR, cis-1,4-polyisoprene (IR) generally possesses inferior mechanical performance due to insufficient SIC capability. In this contribution, amino-functionalized carbon nanodots (CDs) were introduced as high-functionality cross-linkers into sulfur-cured sulfonated IR, aiming to improve the SIC capability of IR. The amino groups on CD surfaces are connected with the sulfonic acid groups on the IR backbones to form ionic bonds, and a covalent crosslinking is concurrently obtained by using sulfur vulcanization, thereby a dually crosslinked IR network is resulted. When the rubber is deformed, the ionic bond breaks preferentially prior to the rupture of covalent bond, leading to efficient energy dissipation. The preferential rupture of the ionic bonds also promotes the orientation process of IR chains and hence SIC capability, as evidenced by lowered onset strain for crystallization and increased crystallinity. The promoted SIC leads to remarkably improved tensile properties.