The design and synthesis of closed-loop recyclable polymers is a promising solution to address the large negative effects of plastic pollution problem and massive economic loss associated with single-use plastics. We demonstrate that ring-opening polymerization (ROP) of 6-alkyl-substituted morpholine-2,5-dione (MDs) leads to closed-loop recyclable aliphatic poly(ester-amide)s (PEAs) with tunable mechanical properties. The controlled ROP of these MDs was achieved using benzyl alcohol as an initiator and DBU/TU as a catalyst, affording various PEA homo- and copolymers with different molar masses and compositions. All these PEAs are amorphous and thermally stable with T d,5% values in the range of 267–292 °C. Their glass transition temperatures (T g) are in the range of 58–142 °C, being affected by the structure of pendent alkyl groups, the hydrogen bonding between amide groups, and the composition of copolymers. Tensile tests revealed that the structure of pendent alkyl groups exerts a significant effect on the mechanical property of PEAs, and they are brittle (n-butyl or cyclohexyl substituted) or ductile (n-hexyl or n-octyl substituted) plastics. In addition, the mechanical properties of PEAs could be finely adjusted by the copolymerization of different MD monomers. Of importance, both homopolymers and copolymers of these PEAs could be thermally depolymerized by sublimation to recover the corresponding monomers in high purity and efficiency. Given their good and adjustable thermal/mechanical properties, and excellent recyclability, these PEAs show promise as new close-loop recyclable polymers.
Polymer dielectrics with high energy density are of urgent demand in electric and electronic devices, but the tradeoff between dielectric constant and breakdown strength is still unsolved. Herein, the synthesis and molar mass control of three alternating [1.1.1]propellane‐(meth)acrylate copolymers, denoted as P‐MA, P‐MMA, and P‐EA, respectively, are reported. These copolymers exhibit high thermal stability and are semi‐crystalline with varied glass transition temperatures and melting temperatures. The rigid bicyclo[1.1.1]pentane units in the polymer backbone promote the orientational polarization of the polar ester groups, thus enhancing the dielectric constants of these polymers, which are 4.50 for P‐EA, 4.55 for P‐MA, and 5.11 for P‐MMA at 10 Hz and room temperature, respectively. Moreover, the high breakdown strength is ensured by the non‐conjugated nature of bicyclo[1.1.1]pentane unit. As a result, these copolymers show extraordinary energy storage performance; P‐MA exhibits a discharge energy density of 9.73 J cm–3 at 750 MV m–1 and ambient temperature. This work provides a new type of promising candidates as polymer dielectrics for film capacitors, and offers an efficient strategy to improve the dielectric and energy storage properties by introducing rigid non‐conjugated bicyclo[1.1.1]pentane unit into the polymer backbone.
1,3-Disubstituted bicyclo[1.1.1]pentane (BCP) is a rigid, linear, non-conjugated hydrocarbon unit that is usually transformed from [1.1.1]propellane. This unit has been introduced into drugs as mimics of 1,4-disubstituted benzene moieties and used as rigid linkers in small-molecule materials. However, the influence of this unique structure on the polymer properties has only been scarcely investigated. In this work, three symmetrical α,ω-diene monomers containing one and two BCP units were synthesized for the first time from [1.1.1]propellane. Three types of precise poly(1,3-bicyclo[1.1.1]pentane alkylene)s with BCPs located on every 11th and 21st chain carbons were obtained via acyclic diene metathesis (ADMET) polymerization and subsequent hydrogenation. All these polymers show higher thermal stability than linear polyethylene. For polymers containing one BCP moiety in their repeating unit, BCP acts as a defect to distort the PE crystals and decrease the melting temperature of PE. However, the polymer that containing a [2]staffane moiety (two jointed BCP units) in the polymer backbone forms a new crystalline morphology. This work elucidates the impact of BCP units on the thermal and crystallization behavior of PE, providing new insights of utilizing BCP unit to construct new polymer backbone, regulate the packing order of polymers and their properties.
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