关键词: 丝氨酸衍生物, 环内酯, 环碳酸酯, 开环聚合, 共聚, 聚酯

Serine is a naturally occurring amino acid, polyesters derived from serine exhibit inherent renewability and biodegradability, rendering them a promising class of eco-friendly polymers. In this work, two kinds of novel serine-derived cyclic ester monomers were synthesized, and their ring-opening polymerization (ROP) was systematically investigated. The four-membered cyclic lactones L- and D-3-(dibenzylamino)oxetan-2-one (L-M1, D-M1) were synthesized via three steps from serine methyl ester hydrochloride, benzyl bromide and 2-(1H-benzotriazole-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate (HBTU) in an overall yield of ~40%. The structure of M1 was further confirmed by NMR and X-ray single crystal diffraction study. The cyclic carbonate monomer 5-(dibenzylamino)-1,3-dioxan-2-one (M2) was prepared from serinol, benzyl bromide and N,N'-Carbonyldiimidazole (CDI) via a two-step procedure in an overall yield of approximately 53%. The ring-opening polymerization (ROP) of M1 was catalyzed by lanthanum complex La1, affording poly(M1)s [P(M1)] with narrow polydispersities (PDI = 1.02-1.08). The experimentally determined molecular weights of the resulting polymers closely match the corresponding theoretical values, with the highest achieved molecular weight reaching 1.28 × 10⁵ g/mol. The polymer P(D-M1) has a melting point at 210 ℃ and the melting process is accompanied by partial decomposition; moreover, two thermal decomposition stages are observed. The polymerization of racemic M1 (rac-M1) yielded a polymer predominantly with an isotactic sequence. Using N,N'-dibenzyl-serinol (IV) as the initiator, the ROP of M2 could be initiated by sodium complex Na1 efficiently to afford P(M2)s with molecular weights close to the theoretical values and relatively broad polydispersities (PDI = 1.35-1.69). P(M2) possesses one thermal decomposition stage and a melting point of T_m = 170.1 ℃. The copolymerization of M2 with 1,3-dioxan-2-one (TMC) was also realized successfuly by using complexes sodium complexes Na1-Na3 as catalysts, wherein TMC exhibited slightly faster initiation kinetics than M2. Regardless of the variations in polymerization time, monomer feed ratio, or catalyst structures, the molecular weights of the resulting polymers consistently approached their theoretical values. Analysis of the average number of units per chain segment and assessment of sequence distribution characteristics revealed that the resulting copolymers are predominantly random. The typical copolymer possesses three thermal decomposition stages and a melting temperature of T_m = 168.6 ℃.

Key words: serine derivatives, cyclic lactone, cyclic carbonate, ring-opening polymerization, copolymerization, polyester