Synthesis of Pyrrolidone-Based Copolyesters with Enhanced Glass Transition Temperatures and Abiotic Hydrolysability
Most degradable polymers are utilized in applications below 100°C. Developing materials with high thermal performance (specifically high glass transition temperature) is critical to expanding their application range. Here, N,N′-trans-1,4-cyclohexane-bis (pyrrolidone-4-methyl carboxylate) (T-CBPMC), a tricyclic diester, was prepared via Michael addition-cyclization of renewable feedstocks and further used as a monomer to synthesize poly (ethylene-co-cyclohexanedimethylene-1,4-cyclohexane-bis (pyrrolidone-4-methyl carboxylate)) (PECP) copolyesters, with 1,4-cyclohexanedimethanol (CHDM) molar content ranging from 0% to 95% relative to the total diol. The copolymerization of ethylene glycol (EG) significantly accelerated chain length, yielding PECP copolyesters with number average molecular weight (M n ) ranging from 29.1 kDa to 48.4 kDa. The T-CBPMC units effectively enhanced the glass transition temperature (119-133°C) and crystallization property of PECP, endowing it with superior thermal properties. Furthermore, the pyrrolidone ring exhibits outstanding ultraviolet shielding efficacy. Despite their steric hindrance, pyrrolidone rings also conferred hydrophilicity to the polymer. PECP copolymers exhibited adjustable hydrolysis rate at room temperature, by varying the CP compositions, with weight loss varying from 5% to 68% after 60 days. Structural, morphological, and molecular weight analyses after hydrolysis revealed that cleavage preferentially occurred at the ester bonds linking T-CBPMC and EG. Combining rigid T-CBPMC and CHDM with EG provided a better balance, the CP segments enhanced the T g and crystallization capabilities of the polyester, whereas the EP segments imparted hydrolysability.
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