High-Performance Olefin Thermoplastic Elastomer Based on Dynamically Cross-Linking Crystalline Macromers and Elastic Backbones

Abstract

Developing novel olefin thermoplastic elastomers (TPE-Os) that outperform those with well-defined block or grafted chain structures is both highly attractive and challenging. Here, we report the preparation of high-performance TPE-Os in a combinatorial way. Semicrystalline ethylene/1-octene/diene copolymers with pendant vinyl groups and crystalline polyethylene macromers with terminal double bonds are synthesized, and they are dynamically linked with a dithiol-based cross-linker containing a boronic ester bond to form a new TPE-O. Due to the synergy between physical crystallization and dynamic cross-linking, it exhibits a significantly increased Young's modulus (E), elongation at break (ε), ultimate strength (σ), and tensile toughness (U T ) of up to 27.2 ± 3.8 MPa, 902 ± 28%, 26.7 ± 1.1 MPa, and 120.1 ± 9.5 MJ•m −3 , respectively, which are among the highest levels of the dynamically cross-linked elastomers and traditional well-defined TPE-Os. It also has good elasticity with a 10-cycle elastic recovery ratio of up to 71.4%; a high melting point of nearly 123.8 °C and the σ can even maintain 0.14−0.42 MPa at 200 °C. The new TPE-O also offers high reprocessing performance with a recovery ratio of 113.2% for E, 98.5% for ε, 95.8% for σ, and 92.5% for U T . We believe that our study will facilitate the development of next-generation TPE-Os with higher performance.

Commodity Rubber Material with Reversible Cross-linking Ability: Application of Boroxine Cross-links to Ethylene-Propylene Rubber

“…By using external cross-linking reagents corresponding to the functional groups, such as bis (maleimide) reagent to furans, boronic ester reagents to diol, , and thiols or Zn 2+ ion to dicarboxylic acid, , polyolefins are reversibly cross-linked. For polyolefins bearing CC double bonds on the side chain, epoxidation or thiol–ene reaction is applicable for introducing diols, which is further cross-linked with dicarboxylic acid, diol, or diboronic acid cross-linking reagents. − Besides, ethylene/vinyl acetate copolymer derivatives, which are accessible with the radical process, are also applied for introducing urethane- and silyl ether-based vitrimer functionalities. , However, most of the examples rely on external cross-linking reagents, which can be eliminated from the polymer structure after a repeated number of recycling processes. This causes deterioration of physical properties, i.e., tensile strength and elongation, along with the decrease of cross-linking density.…”

“…Therefore, we have designed a polyolefin with a boron atom covalently connected to the carbon in the polymer main chain, which can be synthesized by direct copolymerization, to attain repetitive durability for cross-linking. All the previous examples of boronic acid- or ester-cross-linked polyolefin rubber apply cleavable heteroatoms between boron and carbon in the polymer chain. ,,− ,− …”