Heo Kyuyoung, Yoon Jinhwan, Jin Kyeong Sik, Jin Sangwoo, Sato Harumi, Ozaki Yukihiro, Satkowski Michael M, Noda Isao, Ree Moonhor
Department of Chemistry, National Research Lab for Polymer Synthesis & Physics, Pohang Accelerator Laboratory, Pohang University of Science & Technology, Pohang 790-784, Republic of Korea.
J Phys Chem B. 2008 Apr 17;112(15):4571-82. doi: 10.1021/jp711136x. Epub 2008 Mar 26.
The crystallization behavior of microbially synthesized poly(3-hydroxybutyrate) (PHB) and its copolymers [P(HB-co-HHx)] containing 2.5, 3.4, and 12 mol % 3-hydroxyhexanoate (HHx) comonomer and the melting of the resultant crystals were studied in detail using time-resolved small-angle X-ray scattering and differential scanning calorimetry. The polyesters were found to undergo primary crystallization as well as secondary crystallization. In the primary crystallization, the thicknesses of the lamellar crystals were sensitive to the crystallization temperature, but no thickening was observed throughout the entire crystallization at a given temperature. The thickness of the lamellar crystals in the PHB homopolymer was always larger than that of the amorphous layers. In the copolymers, by contrast, the randomly distributed HHx comonomer units were found to be excluded from the lamellar crystals into the amorphous regions during the isothermal crystallization process. This interrupted the crystallization of the copolymer chains, resulting in the formation of lamellar crystals with thicknesses smaller than those of the amorphous layers. The lamellar crystals in the copolymers had lower electron densities compared to those formed in the PHB homopolymer. On the other hand, secondary crystallization favorably occurred during the later stage of isothermal crystallization in competition with the continuous primary crystallization, forming secondary crystals in amorphous regions, in particular in the amorphous layers between the primarily formed lamellar crystal stacks. Compared to the primarily formed lamellar crystals, the secondary crystals had short-range-ordered structures of smaller size, a broader size distribution, and a lower electron density.
利用时间分辨小角X射线散射和差示扫描量热法，详细研究了微生物合成的聚（3-羟基丁酸酯）（PHB）及其含有2.5、3.4和12摩尔％3-羟基己酸酯（HHx）共聚单体的共聚物[P（HB-co-HHx）]的结晶行为以及所得晶体的熔融情况。发现聚酯会经历初级结晶和次级结晶。在初级结晶过程中，片晶的厚度对结晶温度敏感，但在给定温度下的整个结晶过程中未观察到增厚现象。PHB均聚物中片晶的厚度总是大于非晶层的厚度。相比之下，在共聚物中，发现随机分布的HHx共聚单体单元在等温结晶过程中从片晶中被排除到非晶区。这中断了共聚物链的结晶，导致形成厚度小于非晶层的片晶。与在PHB均聚物中形成的片晶相比，共聚物中的片晶具有较低的电子密度。另一方面，次级结晶在等温结晶后期与持续的初级结晶竞争时有利地发生，在非晶区，特别是在初级形成的片晶堆叠之间的非晶层中形成次级晶体。与初级形成的片晶相比，次级晶体具有较小尺寸、较宽尺寸分布和较低电子密度的短程有序结构。
