Metastability and transformation of polymorphic crystals in biodegradable poly(butylene adipate)
Metastability and transformation of polymorphic crystals in biodegradable poly(butylene adipate)
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DOI：
10.1021/bm0343850
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发表时间：
2004-03-01
影响因子：
6.2
通讯作者：
Doi, Y
中科院分区：
文献类型：
--
作者：
Gan, ZH;Kuwabara, K;Doi, Y
用广角X射线衍射(WAXD)、小角X射线散射(SAXS)和差示扫描量热法(DSC)研究了熔融结晶聚己二酸丁二醇酯(PBA)的晶型现象。研究发现，等温结晶只需改变结晶温度即可形成PBA多晶型晶体。PBAα晶体、β晶体和两种晶体的混合物分别在32摄氏度以上、27摄氏度以下以及这两种温度之间的结晶温度下生长。通过多个熔融峰的指认，分析了PBA多态与熔融行为的关系。因此，用Hoffman-Week方程和Gibbs-Thomson方程确定了α和β晶体的平衡熔化温度T(M)度，以了解结构的亚稳性。PBAα晶型的T(M)比β晶型的T(M)高，说明PBAα晶型是结构稳定相，β晶型是亚稳相。PBA多晶型晶体的生长动力学分析表明，亚稳的PBAβ晶体确实是动力学优先的结果。根据热力学和动力学结果，从PBAα和β晶体的生长机制和β晶体向α晶体的转变的角度，认识到PBA熔融结晶中的稳定性随晶体尺寸反转的现象。PBAβ-->；α相变发生在足够高的退火温度下，相变明显是伴随着片层晶体的增厚的固-相转变过程。讨论了聚合物链在晶相和非晶相中的分子运动，以了解聚合物的增稠和相变行为。
Polymorphism phenomenon of melt-crystallized poly(butylene adipate) (PBA) has been studied by wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), and differential scanning calorimetry (DSC). It has been found that the isothermal crystallization leads to the formation of PBA polymorphic crystals, simply by changing the crystallization temperature. The PBA alpha crystal, beta crystal, and the mixture of two crystal forms grow at the crystallization temperatures above 32 degreesC, below 27 degreesC, and between these two temperatures, respectively. The relationship between PBA polymorphism and melting behaviors has been analyzed by the assignments of multiple melting peaks. Accordingly, the equilibrium melting temperatures T(m)degrees of both alpha and beta crystals were determined by Hoffman-Weeks and Gibbs-Thomson equations for the purpose of understanding the structural metastability. The T(m)degrees of the PBA alpha crystal was found to be higher than that of the beta crystal, indicating that the PBA alpha crystal form is a structurally stable phase and that the beta crystal form is a metastable phase. The analysis of growth kinetics of PBA polymorphic crystals indicates that the metastable PBA beta crystal is indeed the kinetically preferential result. Based on the thermal and kinetic results, the phenomenon of stability inversion with crystal size in melt-crystallized PBA was recognized, in terms of the growth mechanisms of PBA alpha and beta crystals and the transformation of beta to alpha crystals. The PBA beta --> alpha crystal transformation takes place at a sufficiently high annealing temperature, and the transformation has been evident to be a solid-sol id-phase transition process accompanied by the thickening of lamellar crystals. The molecular motion of polymer chains in both crystalline and amorphous phases has been discussed to understand the thickening and phase transformation behaviors.