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Creators/Authors contains: "Shi, Changxia"

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  1. Free, publicly-accessible full text available October 30, 2025
  2. Free, publicly-accessible full text available August 1, 2025
  3. Abstract

    Geminal (gem−) disubstitution in heterocyclic monomers is an effective strategy to enhance polymer chemical recyclability by lowering their ceiling temperatures. However, the effects of specific substitution patterns on the monomer's reactivity and the resulting polymer's properties are largely unexplored. Here we show that, by systematically installinggem‐dimethyl groups onto ϵ‐caprolactam (monomer of nylon 6) from the α to ϵ positions, both the redesigned lactam monomer's reactivity and the resultinggem‐nylon 6’s properties are highly sensitive to the substitution position, with the monomers ranging from non‐polymerizable to polymerizable and thegem‐nylon properties ranging from inferior to far superior to the parent nylon 6. Remarkably, the nylon 6 with thegem‐dimethyls substituted at the γ position is amorphous and optically transparent, with a higherTg(by 30 °C), yield stress (by 1.5 MPa), ductility (by 3×), and lower depolymerization temperature (by 60 °C) than conventional nylon 6.

     
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    Free, publicly-accessible full text available April 22, 2025
  4. Replacing reactive hydrogens in the monomer improves the properties of a type of polyester in multiple respects. 
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  5. Abstract

    Ring‐opening polymerization (ROP) of lactones or cyclic (di)esters is a powerful method to produce well‐defined, high‐molecular‐weight (bio)degradable aliphatic polyesters. While the ROP of lactones of various ring sizes has been extensively studied, the ROP of the simplest eight‐membered lactone, 7‐heptanolactone (7‐HL), has not been reported using metal‐based catalysts. Accordingly, this contribution reports the ROP of 7‐HL via metal‐catalyzed coordinative‐insertion polymerization to the corresponding high‐molecular‐weight polyester, poly(7‐hydroxyheptanoate) (P7HHp). The resulting P7HHp is a semi‐crystalline material, with aTmof 68 °C, which is ~10 °C higher than poly(ε‐caprolactone) derived from the seven‐membered lactone. Mechanical testing showed that P7HHp is a hard and tough plastic, with elongation at break >670%. P7HHp‐based polyesters with higherTmvalues have been achieved through stereoselective copolymerization of 7‐HL with an eight‐membered cyclic diester, racemic dimethyl diolide (rac‐8DLMe), known to lead to highTmpoly(3‐hydroxyburtyrate) (P3HB). Notably, catalyst's strong kinetic preference for polymerizingrac‐8DLMeover 7‐HL in the 1/1 comonomer mixture rendered the formation of di‐block copolymer P3HB‐b‐P7HHp, showing two crystalline domains withTm1 ~ 65 °C andTm2 ~ 160 °C. Semi‐crystalline random copolymers withTmup to 164 °C have also been obtained by adjusting copolymerization conditions. Mechanical testing showed that P3HB‐b‐P7HHp can synergistically combine the high modulus of isotactic P3HB with the high ductility of P7HHp.

     
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