Highly crystalline, heat resistant and biodegradable copolyesters from fully bio-based bis(pyrrolidone) monomer

Abstract

Improving the heat resistance of bio-based and biodegradable polyesters is of great significance to extend their applications. Herein, N,N’-trans-1,4-cyclohexane-bis(pyrrolidone-4-methyl carboxylate) (T-CBPMC) was prepared through efficient Michael-addition reaction between dimethyl itaconate and trans-1,4-cyclohexanediamine. The obtained T-CBPMC was copolymerized into aliphatic poly(butylene succinate) (PBS), and a series of PBSPs copolymers with T-CBPMC (BP) molar percentages between 41−80 mol % and weight average molecular weight (M_w) values ranging between 5.77*10⁴ and 6.67*10⁴ g/mol were prepared. BP units efficiently facilitated the melting temperature (203-251 °C) and isothermal-crystallization rate (t_1/2 < 20 s) of PBSPs, endowing the highest heat resistance among commercial biodegradable polyesters, which helps maintain stable in pasteurization, high-temperature disinfection, and microwave environments. Moreover, these copolymers displayed remarkable mechanical, gas barrier properties and degradability. PBSP40-PBSP60 obtained high elastic modulus (335–872 MPa) and tensile strength (24.7–31.5 MPa), and good toughness simultaneously. Multiple-ring structures and large steric hindrance of BP units resulted in superior O₂ barrier performance than that of non-degradable PET films. Importantly, the PBSP copolyesters showed obvious degradation in water environments and relatively better enzymatic degradation. It was interesting to find that even with 70 % of the BP units, the PBSP copolyesters still retained hydrolysis ability. The resulting PBSP copolyesters open the way for alternative candidates of biodegradable packaging materials with rapid crystallization, high heat-resistance and gas barrier.