A poly(L-lactide) with a trifluoro ethyl ester end group and an average degree of polymerization (DP) of 50 was synthesized by ROP of L-lactide initiated with trifluoroethanol. Small-angle X-ray scattering (SAXS) in combination with differential scanning calorimetry (DSC) measurements revealed an average crystal thickness of 13 nm, corresponding to 45 repeat units. This suggests that most crystallites were formed by extended PLA chains, and both flat surfaces were covered by CF3 groups. The crystalline PLAs were annealed at 140 or 160 °C in the presence of two catalysts: tin(II) 2-ethylhexanoate, (SnOct₂) or dibutyltin bis(pentafluorophenoxide) (BuSnPhF). The chemical reactions, such as polycondensation and cyclization, proceeded in the solid state and were monitored by matrix-assisted laser desorption/ionization time-of-flight (MALDI TOF) mass spectrometry and gel permeation chromatography (GPC) measurements. Under optimal conditions a large fraction of linear chains was transformed into crystallites composed of extended cycles. Additionally, MALDI TOF MS analysis of GPC fractions from samples annealed for 28 or 42 days detected chain elongation of the linear species up to a factor of 20.

中文翻译：

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由直链组成的聚(L-丙交酯)晶体转变为由环组成的晶体

以三氟乙醇为引发剂，通过L-丙交酯的ROP法合成了平均聚合度(DP)为50的具有三氟乙酯端基的聚( L-丙交酯)。小角 X 射线散射 (SAXS) 与差示扫描量热法 (DSC) 测量相结合显示平均晶体厚度为 13 nm，对应于 45 个重复单元。这表明大多数微晶是由延伸的 PLA 链形成的，并且两个平坦表面都被 CF3 基团覆盖。结晶 PLA 在两种催化剂存在下于 140 或 160 °C 退火：2-乙基己酸锡 ( II ) (SnOct ₂ ) 或二丁基锡双(五氟苯酚) (BuSnPhF)。缩聚和环化等化学反应在固态下进行，并通过基质辅助激光解吸/电离飞行时间 (MALDI TOF) 质谱和凝胶渗透色谱 (GPC) 测量进行监测。在最佳条件下，大部分直链转化为由延长的循环组成的微晶。此外，对退火 28 或 42 天的样品的 GPC 级分进行 MALDI TOF MS 分析，检测到线性物质的链伸长高达 20 倍。