The controllable introduction of dynamical chemical cross-linking into polymers permits the development of recyclable polymer products with high performance. However, challenges lie in chemically inert polyolefins, which are the largest polymer product in the world to date. Here, we demonstrate the preparation of polyolefin elastomers (POEs) with tunable dynamic chemical cross-linking, compatible with their industrial production. Boronic ester bond cross-linked POEs (BPOEs) present high mechanical performances with tensile strength (σ) up to 23.8 MPa, Young's modulus (E) up to 29.0 MPa, and toughness (U T ) up to 69.6 MJ•m −3 , far superior to those reported elastomers. BPOEs also demonstrate good thermal stability maintaining a steady storage modulus plateau of 2.9 MPa above 100 °C, instead of 0.2 MPa for pristine POEs. After reprocessing three times, BPOEs show a good reprocessability with a σ recovery of 85.6%, an E of 108.5%, a U T of 95.7%, and an elongation at break (ε) of 97.1%, even higher than that of commercial POEs such as POE-8150 of Dow Company. Our method thus permits the future development of higher-performance POEs and other polyolefins with good reprocessability and recyclability.
Polyolefin thermoplastic elastomers (TPE‐Os) are high‐performance polyolefins consisting of both plastic and rubber phases. Compared with other thermoplastic elastomers, the TPE‐Os possess better chemical stability, transparency, re‐processability, and electrical insulation, which renders their broad applications possible. By manipulating chain structures and topologies of the TPE‐Os, differently structured polyolefins with improved thermal and mechanical properties have been developed, including ethylene and α‐olefin random copolymers (POEs), olefin block copolymers (OBCs), comb‐shaped polyolefin elastomers (CPOEs), and dynamically cross‐linked polyolefin elastomers. Herein, we review the synthesis of the POE, OBC, CPOE, and dynamical cross‐linked polyolefin elastomer, including the catalyst systems, polymerization techniques, processes, and kinetic modelling. The characterization of the TPE‐Os and the relationships between the TPE‐O chain structure, aggregated state, and product performance are discussed. The future development of higher‐performance TPE‐Os is envisaged.
Comb-polyolefin elastomers (CPOEs) with crystalline long-chain branches (LCBes) demonstrate superior mechanical properties and processability. However, fully understanding the effect of LCBes on their material performance remains a huge challenge due to the residue of unreacted polyethylene macromers (PE-Ms). Here, we report a method of blending CPOEs with PE-Ms to study the structure–activity relationship of CPOEs via extrapolation. CPOE samples with different numbers of LCBes (q) between 0.0 and 9.9 and PE-Ms with an M w value similar to the LCBes were prepared and studied. Blending CPOEs with 20–40 wt % of PE-Ms increased the melt fluidity and reduced the zero-shear viscosity (η0) value from 4590 Pa·s to 980 Pa·s without causing phase separation. These CPOEs exhibit dynamic responses with a similar temperature dependence where the time shift factors could be fitted by the same Williams–Landel–Ferry parameters with C1 at 4.88 and C2 at 443 K. For CPOEs with LCBes, as q increased from 1.1 to 9.9, the number of entanglements between the graft points (Z g) decreased from 11.78 to 0.93, and the chain conformation changed from sparse comb (SC) to dense comb (DC), respectively. The maximum η0 value of CPOEs occurs at the turning point of SC and DC, where Zg is equal to the entanglement number of the branched chain −Z bc of 4.72. Our study distinguished the different effects between the grafted and free PE-Ms on the CPOEs, enabling an in-depth understanding of macromolecular engineering in polymer and facilitating the future development of higher-performance CPOEs or other grafted polymers.
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