The viscosities of poly(3-hydroxybutyrate) (PHB) with mixed tacticities were determined as functions of temperature and shearing rate via plate–plate viscosimetry, and fitted by a combined Herschel–Bulkley–Cross–Doolittle model while applying Carvalho et al.’s single-point correction. They were compared to values of slit viscosimetry, obtained during processing at a temperature of 428 K. In both cases, measured values and fitted model parameters as a function of tacticity exhibited a discontinuous behaviour at a fraction of meso diads of 0.7. To further investigate, we calculated values of vibrational and excess free volume. We found that these correlate with structural and external properties, some of which were reported in earlier works, namely the paracrystalline contents and specific volumes of the materials at room temperature, as well as their energies of fracture during tensile testing. These, in turn, correlate with the statistical averages of relative lengths of chain segments of similar a- or iso-tacticity. Hence, we found that expressing changing tacticities simply by a continuous progression of the fraction of meso diads is insufficient to trace associated discontinuities of the flow behaviour in mixed-tacticity PHB. We conclude that free volume is generated by polymer chain conformational disorder, which should be treated on the oligomeric chain segment level.

中文翻译：

---

通过粘度测定法测定混合立构规整度聚 (3-羟基丁酸酯) 的自由体积及其与结构特征和机械性能的相关性

具有混合立构规整度的聚 (3-羟基丁酸酯) (PHB) 的粘度通过板-板粘度测定法确定为温度和剪切速率的函数，并在应用 Carvalho 等人时通过 Herschel-Bulkley-Cross-Doolittle 组合模型进行拟合。 s 单点校正。将它们与在 428 K 温度下加工过程中获得的狭缝粘度测定值进行比较。在这两种情况下，作为立构规整度函数的测量值和拟合模型参数在 0.7 的中间直径分数下表现出不连续的行为。为了进一步研究，我们计算了振动和过量自由体积的值。我们发现这些与结构和外部特性相关，其中一些在早期的作品中已有报道，即室温下材料的副晶含量和比容，以及它们在拉伸试验中的断裂能。这些又与具有相似α-或等规立构规整度的链段的相对长度的统计平均值相关。因此，我们发现仅仅通过连续增加中二元组来表达立构规整度的变化不足以追踪混合立构规整度 PHB 中流动行为的相关不连续性。我们得出结论，自由体积是由聚合物链构象紊乱产生的，应该在低聚链段水平上进行处理。我们发现，仅仅通过中间二元分数的连续进展来表达变化的立构度不足以追踪混合立构规整度 PHB 中流动行为的相关不连续性。我们得出结论，自由体积是由聚合物链构象紊乱产生的，应该在低聚链段水平上进行处理。我们发现，仅仅通过中间二元分数的连续进展来表达变化的立构度不足以追踪混合立构规整度 PHB 中流动行为的相关不连续性。我们得出结论，自由体积是由聚合物链构象紊乱产生的，应该在低聚链段水平上进行处理。