Crystallization and structure formation of block copolymers containing a rubbery amorphous component
Crystallization and structure formation of block copolymers containing a rubbery amorphous component
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DOI：
10.1021/ma0200118
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发表时间：
2002-10-08
期刊：
影响因子：
5.5
通讯作者：
Miya, M
中科院分区：
文献类型：
--
作者：
Shiomi, T;Takeshita, H;Miya, M
采用时间分辨同步辐射小角X射线散射（SR-SAXS）技术研究了聚乙二醇-聚丁二烯（PEG-PBd）二嵌段和三嵌段共聚物在微相分离熔体中等温结晶过程中的高阶结构变化。重分数fl'EG = 0.57和0.51的PEG-PBd的层状微相结构在结晶时被破坏，并转变为不同于熔体中的层状结构。具有f（PEG）= 0.34的二嵌段共聚物结晶，保持熔体中预先存在的圆柱形结构。另一方面，f（PEG）= 0.7的两嵌段共聚物，其熔体结构为圆柱形，显示出两种类型的结构变化：在低结晶温度T下，SAXS峰位不连续地变化，但结构保持圆柱形，而在高结晶温度T下，结构从圆柱形变为层状。具有f（PEG）= 0.67和0.42的三嵌段共聚物PBd-PEG-PBd显示类似于f（PEG）= 0.57和0.51的二嵌段共聚物的结构变化。所有样品在熔融过程中的结构变化行为均与晶化过程相反。结晶行为，特别是结晶动力学，也通过DSC和偏光显微镜（POM）进行了研究。用530 nm的延迟板。Avrami指数从DSC结果评价的嵌段共聚物几乎是相同的PEG均聚物，即使在结晶从圆柱形熔体，这是完全不同的结果从冷冻的微相分离的熔体结晶以前报道的。对于f（PEG）= 0.34的二嵌段和f（PEG）= 0.42的三嵌段共聚物，在熔体中具有小尺寸的微区，总体结晶速率被抑制，表观活化能高。POM没有观察到具有清晰的马耳他十字的球晶，但是对于包括f（PEG）= 0.34的二嵌段共聚物的所有嵌段共聚物，晶体区域传播有不规则分布的蓝色和黄色部分。对于f（PEG）= 0.34的共聚物，这种传播行为和Avrami指数的上述结果表明，结晶可以从一个圆柱体域穿越到另一个圆柱体域，同时保持熔体结构。动力学结果表明，三嵌段共聚物中的中间嵌段更容易成核。
Changes of higher-order structure of poly(ethylene glycol) - poly(butadione) (PEG-PBd) di- and triblock copolymers in isothermal crystallization from microphase-separated melts were studied using time-resolved synchrotron small-angle X-ray scattering (SR-SAXS) techniques. Lamellar microphase structure of PEG-PBd with weight fractions fl'EG = 0.57 and 0.51 was destroyed on crystallization and changed to a lamellar structure distinct from that in the melt. A diblock copolymer with f(PEG) = 0.34 crystallized, keeping the cylindrical structure preexisting in the melt. On the other hand, a f(PEG) = 0.7 diblock copolymer whose melt structure was cylindrical showed two kinds of structure changes: at low crystallization temperatures T, the SAXS peak positions changed discontinuously but the structure remained cylindrical, while the structure changed from cylindrical to lamellar at high T,. Triblock copolymers PBd-PEG-PBd with f(PEG) = 0.67 and 0.42 showed a structure change similar to the f(PEG) = 0.57 and 0.51 diblock copolymers. Behavior of structure changes in the melting process was the reverse of that in the crystallization process for all the samples. Crystallization behavior, in particular crystallization kinetics, was also investigated by DSC and polarized optical microscopy (POM.) with a 530 nm retardation plate. Avrami exponents evaluated from DSC results for the block copolymers were almost the same as those for PEG homopolymers even in crystallization from the cylindrical melt, which was quite different from the result in crystallization from a frozen microphase-separated melt reported previously. For the f(PEG) = 0.34 diblock and f(PEG) = 0.42 triblock copolymers with a small-sized microdomain in the melt, overall crystallization rates were suppressed and apparent activation energies were high. No spherulite with a clear Maltese cross was observed by POM, but the crystal region was propagated with irregularly distributed blue- and yellow-colored portions for all the block copolymers including the f(PEG) = 0.34 diblock copolymers. This behavior of the propagation and the above result of Avrami exponents for the f(PEG) = 0.34 copolymer suggest that crystallization can traverse from one cylinder domain to another with preservation of the melt structure. From the kinetic results obtained by both DSC and POM, it was suggested that nucleation was easy for the middle block in the triblock copolymers.