L-Lactide was polymerized in bulk at 120, 140, 160 and 180 °C with neat tin(II) 2-ethylhexanoate (SnOct₂) as the catalyst. At 180 °C the Lac/Cat ratio was varied from 25/1 up to 8000/1 and at 160 °C from 25/1 up to 6000/1. The vast majority of the resulting polylactides consist of cycles in combination with a small fraction of linear chains having one octanoate and one COOH end group. The linear chains almost vanished at high Lac/Cat ratios, as evidenced by MALDI-TOF mass spectrometry and measurements of intrinsic viscosities and dn/dc values. At Lac/Cat ratios <1000/1 the number average molar masses (M_n) are far higher than expected for stoichiometic initiation, and above 400/1 the molar masses vary relatively little with the Lac/Cat ratio. At 180 °C slight discoloration even at short times and degradation of the molar masses were observed, but at 160 °C or below colorless products with weight average molar masses (M_w) up to 310 000 g mol⁻¹ were obtained. The formation of high molar mass cyclic polylactides is explained by a ROPPOC (Ring-Opening Polymerizatiom with simultaneous Polycondensation) mechanism with intermediate formation of linear chains having one Sn–O–CH end group and one mixed anhydride end group. Additional experiments with tin(II)acetate as the catalyst confirm this interpretation. These findings together with the detection of several transesterification mechanisms confirm the previous critique of the Jacobson–Stockmayer theory.

中文翻译：

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通过纯净的2-乙基己酸锡（II）制得的高摩尔质量环状聚（L-丙交酯）

用纯净的2-乙基己酸锡（II）（SnOct ₂）作为催化剂在120、140、160和180°C下将L-丙交酯本体聚合。在180°C时，Lac / Cat比从25/1到8000/1不等，在160°C时从25/1到6000/1。所得的大多数聚丙交酯由循环与小部分具有一个辛酸酯和一个COOH端基的直链组成。线性链在高Lac / Cat比下几乎消失了，这由MALDI-TOF质谱以及特性粘度和d n / d c值的测量证明。在Lac / Cat比<1000/1时，数均摩尔质量（M _n）远远高于化学计量引发的预期值，并且在400/1以上时，摩尔质量随Lac / Cat比的变化相对较小。在180℃下，即使在短时间内也观察到轻微的变色和摩尔质量的降解，但是在160℃或更低温度下，获得了无色产物，其重均摩尔质量（M _w）高达310 000 g mol ^-1。高摩尔质量环状聚丙交酯的形成是通过ROPPOC（同时缩聚的开环聚合）机理解释的，中间形成具有一个Sn-O-CH端基和一个混合酸酐端基的线性链。与锡另外的实验（II乙酸盐作为催化剂证实了这一解释。这些发现以及对几种酯交换反应机制的发现，证实了对雅各布森-斯托克梅尔理论的先前批评。