Strengthening Polyethylene Thermoplastics through a Dynamic Covalent Networking Additive Based on Alkylboron Chemistry

Abstract

Polyethylene (PE) is the most heavily used polymer worldwide. Considerable efforts have focused on modifying properties of PE via cross-linking. In contrast to previous crosslinking methods, which generate PE thermosets of low processability, here, we report the development of a dynamic covalent networking additive (DCNA) that possesses the PE backbone and reconfigurable network with alkyl boronic esters as novel dynamic linkages. The addition of DCNA at 5 wt % provides PE materials with clearly improved mechanical (e.g., tensile strength, Young's modulus, and yield strength) and rheological (e.g., creep resistance) properties at elevated temperatures. Moreover, the obtained materials could be easily reprocessed, recycled, and 3D-printed, creating opportunities toward sustainable and high-performance PE materials.

Mechanically Robust, Heat-Resistant, and Reprocessable Polyethylene Vitrimers Cross-Linked by β-Hydroxy Ester Bonds via Reactive Processing

“…When the gel content is higher, the molecular chains get more difficult to stretch further due to the constrain of the high-density cross-linked network, which results in the deterioration in the tensile strength and elongation at break. Interestingly, ED0.5 displays superior mechanical properties as compared with those of reported (LD) PE vitrimers. ,, Besides, it is worth mentioning that our PE vitrimers show superior mechanical properties (tensile strength of 10–20 MPa) compared to to conventional XL­(LD)­PE cross-linked by peroxide. − …”

“…Polyethylene (PE), manufactured at a rate of more than 100 million tons every year, is the most extensively used thermoplastic worldwide, although it consists of the simplest repeating unit, i.e., ethylene (CH 2 CH 2 ). , Owing to its low cost, outstanding chemical resistance, ease of processing, and good electrical insulation property, PE is widely applied in many fields from everyday uses such as packaging and commodities to advanced applications like lithium batteries and biomedical implants. − However, its intrinsic defects such as low strength and modulus as well as poor thermal, creep, and environmental stress crack resistance largely restrict the wider application of PE. To solve these problems, PE is generally cross-linked with covalent bonds by peroxides, silane, or irradiation. , Because of the formation of a three-dimensional network, the cross-linked PE (XLPE), which exhibits a remarkably improved rigidity and heat, creep, and chemical resistance, is commonly employed as cable insulation, water pipes, and heat-shrinkable sleeving .…”

“…Such an appealing nature allows vitrimers to change their topology and rearrange the networks while maintaining their cross-link density and consequent structural integrity at elevated temperatures. − As a result, vitrimers behave like cross-linked polymers at service temperature, but they can be reprocessed and recycled via flow when heated above the temperature at which the bonds start exchanging. A variety of reactions have been designed to fabricate vitrimers originating from different polymer systems, including transesterification, ,, olefin metathesis, , disulfide metathesis, , boronic ester or boroxine exchange, ,, silyl ether exchange, , transiminination, transamination, , transcarbamoylation, , alkoxyamine exchange, and so on. As it is difficult to introduce dynamic covalent bonds to the nonpolar PE chains, only several reports exist with regard to the preparation of PE vitrimers or analogs via solution synthesis or melt reaction (reactive processing). ,,,,, Compared with solution synthesis, reactive processing has gained more interest due to its low cost, ease of scale-up production, and solvent-free conditions.…”

“…A variety of reactions have been designed to fabricate vitrimers originating from different polymer systems, including transesterification, ,, olefin metathesis, , disulfide metathesis, , boronic ester or boroxine exchange, ,, silyl ether exchange, , transiminination, transamination, , transcarbamoylation, , alkoxyamine exchange, and so on. As it is difficult to introduce dynamic covalent bonds to the nonpolar PE chains, only several reports exist with regard to the preparation of PE vitrimers or analogs via solution synthesis or melt reaction (reactive processing). ,,,,, Compared with solution synthesis, reactive processing has gained more interest due to its low cost, ease of scale-up production, and solvent-free conditions. The group of Nicolaÿ and Leibler reported a series of PE vitrimers of dioxaborolane metathesis from high-density polyethylene (HDPE) via one- or two-step reactive processing .…”

“…Polyethylene (PE), manufactured at a rate of more than 100 million tons every year, is the most extensively used thermoplastic worldwide, although it consists of the simplest repeating unit, i.e., ethylene (CH 2 �CH 2 ). 1,2 Owing to its low cost, outstanding chemical resistance, ease of processing, and good electrical insulation property, PE is widely applied in many fields from everyday uses such as packaging and commodities to advanced applications like lithium batteries and biomedical implants. 3−6 However, its intrinsic defects such as low strength and modulus as well as poor thermal, creep, and environmental stress crack resistance largely restrict the wider application of PE.…”