In this work, a series of stereoblock polylactic acids chemically bonded by the two enantiomers of polylactic acid poly(L-lactic acid) (PLLA) and poly(D-lactic acid) (PDLA), C16-PLLA_m-b-PDLA_n and C16-PDLA_m-b-PLLA_n (m ≥ 200, n = 2m) with higher molecular weight (M_n ≥ 11.63 × 10⁴ g/mol, PDI ≤ 1.81), were synthesized via a two-step-controlled ring-opening polymerization reaction of first L-lactide and then D-lactide or, in turn, using hexadecanol (C16) as the initiator in the first step. Both synthesized stereoblock polylactic acids contain stereocomplex crystals (SCs) and homogeneous crystals (HCs), and the HCs were removed, while the SCs were retained during isothermal crystallization at 190 °C because the used crystallization temperature is higher than the melting temperature of HCs but lower than that of SCs. The crystallinity of the SCs (X_SC) has a significant effect on the barrier performances of the film. To illustrate, with the increase of X_SC of the stereoblock polylactic acid film C16-PLLA₃₀₀-b-PDLA₆₀₀ from 0.83% to 22.72%, the oxygen permeability (P_O2) and the water vapor permeability (P_H2O) of the film decrease from 1.59 × 10^–14 cm³·cm/(cm²·s·Pa) to 0.38 × 10^–14 cm³·cm/(cm²·s·Pa) and from 6.78 × 10^–14 g·cm/(cm²·s·Pa) to 2.04 × 10^–14 g·cm/(cm²·s·Pa), respectively, improving the oxygen barrier performance by 76.10% and the water vapor barrier performance by 69.91%. The stereoblock polylactic acid films not only have a high barrier performance but also maintain good tensile performance and degradability, providing a new strategy for developing degradable high gas barrier materials based on polylactic acid itself.

中文翻译：

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可降解立体嵌段聚乳酸的结构、性能及潜在包装应用


在本研究中，由聚乳酸聚（L-乳酸）（PLLA）和聚（D-乳酸）（PDLA）的两种对映异构体化学键合的一系列立体嵌段聚乳酸，C16-PLLA _{m-b-PDLA n}和C16-PDLA _{m-b-PLLA n}（m ≥ 200，n = 2m），分子量较高（M_n ≥ 11.63 × 10⁴ g/mol，PDI ≤ 1.81），通过先 L-丙交酯和 D-丙交酯或反过来使用十六醇 （C16） 作为第一步引发剂的两步受控开环聚合反应合成。两种合成的立体嵌段聚乳酸均含有立体复合晶体 （SCs） 和均相晶体 （HCs），由于使用的结晶温度高于 HCs 的熔融温度，但低于 SCs，因此在 190 °C 的等温结晶过程中保留了 SCs。SCs 的结晶度 （X_SC） 对薄膜的阻隔性能有显着影响。举例来说，随着立体嵌段聚乳酸薄膜 C16-PLLA_{300-b-PDLA 600} 的 X_SC 从 0.83% 增加到 22.72%，薄膜的透氧率 （P_O2） 和水蒸气渗透率 （P_H2O） 从 1.59 × 10^–14 cm³·cm/（cm²·s·Pa） 降至 0.38 × 10^–14 cm³·cm/（cm²·s·Pa） 和 6.78 × 10^–14 g·cm/（cm²·s·Pa） 更改为 2。04 × 10^–14 g·cm/（cm²·s·Pa） 的阻燃剂，分别使氧气阻隔性能提高了 76.10%，水蒸气阻隔性能提高了 69.91%。立体嵌段聚乳酸薄膜不仅具有高阻隔性能，而且保持良好的拉伸性能和降解性，为开发基于聚乳酸本身的可降解高气体阻隔材料提供了新策略。