Crystallization-Driven Self-Assembly of Block Copolymers with a Short Crystallizable Core-Forming Segment: Controlling Micelle Morphology through the Influence of Molar Mass and Solvent Selectivity
Crystallization-Driven Self-Assembly of Block Copolymers with a Short Crystallizable Core-Forming Segment: Controlling Micelle Morphology through the Influence of Molar Mass and Solvent Selectivity
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DOI：
10.1021/ma402429d
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发表时间：
2014-04-08
期刊：
影响因子：
5.5
通讯作者：
Manners, Ian
中科院分区：
文献类型：
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作者：
Hsiao, Ming-Siao;Yusoff, Siti Fairus M.;Manners, Ian
三种定义明确的具有相似嵌段比（r = N-P2 VP/N-PFS = ca.）的不对称结晶线团聚（二茂铁基二甲基硅烷-嵌段-2-乙烯基吡啶）（PFS-b-P2 VP）二嵌段共聚物（PFS 44-b-P2 VP（264）、PFS 75-b-P2 VP（454）和PFS 102-b-P2 VP（625））。6.0+/- 0.1），但总摩尔质量不同（M1 = 38 700，65 800，和90 400 g mol（-1）），并探讨了它们的溶液自组装行为作为一个函数（i）摩尔质量和（ii）比例的共同选择性溶剂。当在异丙醇（i-PrOH），P2 VP的选择性溶剂中进行自组装时，随着分子量的增加，检测到从最初形成的球体（具有无定形PFS核）到圆柱体（具有结晶核）的结晶驱动过渡的速率降低。这种趋势可以通过PFS核形成嵌段的结晶速率随着链长增加而降低来解释。相反，当使用i-PrOH与增加量的THF（两种嵌段的共同溶剂）的混合物时，由相同的PFSx-b-P2 VP（6x）样品形成球体、圆柱体以及由夹在两个玻璃状冠状P2 VP层之间的结晶PFS薄片组成的窄透镜状片晶。最可能的解释涉及PFS核形成嵌段的增塑，其促进结晶，可能通过P2 VP冠状嵌段的线圈的收缩来补充，否则限制结晶PFS核的横向生长，因为THF是比i-PrOH差的P2 VP溶剂。选区电子衍射研究表明，PFS的球形胶束的核心是无定形的，但与那些存在于一个状态接近的单斜PFS单晶的圆柱形胶束是一致的。相反，在THF/i-PrOH中形成的片晶中，发现PFS核是多晶的。窄透镜状多晶片晶而不是规则的矩形单晶形态的形成归因于中毒效应，由此长P2 VP冠状块在矩形PFS单晶核的生长中的干扰在晶体生长前沿引入缺陷。
Three well-defined asymmetric crystalline-coil poly(ferrocenyldimethylsilane-block-2-vinylpyridine) (PFS-b-P2VP) diblock copolymers (PFS44-b-P2VP(264), PFS75-b-P2VP(454), and PFS102-b-P2VP(625)) with similar block ratios (r = N-P2VP/N-PFS = ca. 6.0 +/- 0.1) but different overall molar masses (M,, = 38 700, 65 800, and 90 400 g mol(-1)) were synthesized by sequential anionic polymerization, and their solution self-assembly behavior was explored as a function of (i) molar mass and (ii) the ratio of common to selective solvent. When self-assembly was performed in isopropanol (i-PrOH), a selective solvent for P2VP, a decrease in the rate of the crystallization-driven transition from the initially formed spheres (with amorphous PFS cores) into cylinders (with crystalline cores) was detected with an increase in molecular weight. This trend can be explained by a decrease in the rate of crystallization for the PFS core-forming block as the chain length increased. In contrast, when a mixture of i-PrOH with increasing amounts of THF, a common solvent for both blocks, was used, spheres, cylinders, and also narrow lenticular platelets consisting of crystallized PFS lamellae sandwiched by two glassy coronal P2VP layers were formed from the same PFSx-b-P2VP(6x) sample. The most likely explanation involves the plasticization of the PFS core-forming block which facilitates crystallization, possibly complemented by contraction of the coils of the P2VP coronal block which otherwise limit of the lateral growth of the crystalline PFS core as THF is a poorer solvent for P2VP than i-PrOH. Selected area electron diffraction studies indicated that the PFS cores of the spherical micelles were amorphous but were consistent with those of the cylindrical micelles existing in a state approximating to that of a monoclinic PFS single crystal. In contrast, in the platelets formed in THF/i-PrOH, the PFS cores were found to be polycrystalline. The formation of narrow lenticular polycrystalline platelets rather than a regular, rectangular single crystalline morphology was attributed to a poisoning effect whereby the interference of the long P2VP coronal blocks in the growth of a rectangular PFS single crystalline core introduces defects at the crystal growth fronts.