Self-Assembly and Chain-Folding in Hybrid Coil-Coil-Cube Triblock Oligomers of Polyethylene-b-Poly(ethylene oxide)-b-Polyhedral Oligomeric Silsesquioxane
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- 作者：Jianjun Miao ; Li Cui ; Henry P. Lau ; Patrick T. Mather ; Lei Zhu
- 刊名：Macromolecules
- 出版年：2007
- 出版时间：July 24, 2007
- 年：2007
- 卷：40
- 期：15
- 页码：5460 - 5470
- 全文大小：654K
- 年卷期：v.40,no.15(July 24, 2007)
- ISSN：1520-5835
文摘
Self-assembly and chain-folding in well-defined oligomeric polyethylene-block-poly(ethylene oxide)-block-polyhedral oligomeric silsesquioxane (PE-b-PEO-b-POSS) triblock molecules were studied by small-angleX-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD), and transmission electron microscopy (TEM).The triblock oligomers were synthesized by attaching two kinds of functional POSS molecules, namely,isocyanatopropyldimethylsilylisobutyl-POSS (Ib-POSS) and isocyanatopropyldimethylsilylcyclopentyl-POSS(Cp-POSS), to a hydroxyl-terminated PE-b-PEO-OH diblock oligomer (denoted as E39EO23) via urethane reactions.In these triblock oligomers, both PE and POSS were crystalline, whereas PEO became amorphous due to tetheringof its both ends to other two blocks. In the crystalline state, PE chains tilted 32
from the lamellar normal, andboth Ib-POSS and Cp-POSS molecules stacked into four-layer (ABCA) lamellar crystals, having the sametrigonal (R
m) symmetry as in pure POSS crystals. Because the cross-sectional area for a PE chain in the PEcrystals (0.216 nm2/chain) at the interface was much smaller than that for a POSS molecule in POSS crystals(1.136 nm2/molecule), the self-assembly and PE chain-folding were substantially affected by the sequence of PEand POSS crystallization when crystallizing from the melt. For example, PE crystallization induced the POSScrystallization in the bulk E39EO23-Ib-POSS, and thus extended-chain PE crystals were observed. The grains ofcrystalline lamellae again were small with often highly curved lamellar crystals. This could also be attributed tothe unbalanced interfacial areas for POSS and PE blocks (the interfacial area ratio being 2.6 for interdigitated PEcrystals, i.e., two PE chains per POSS molecule). For the E39EO23-Cp-POSS triblock oligomer, POSS moleculescrystallized before PE crystallization, forming a well-defined lamellar structure. The preexisting POSS crystalsconfined the PE crystallization, and thus almost once-folded PE crystals were obtained. Because the interfacialarea ratio between POSS and PE blocks decreased to 1.3, the crystalline lamellae were straight and their grainswere relatively large. On the basis of this study, we conclude that confinement effect plays an important role onchain-folding of crystalline block oligomers, which in turn determines the unbalanced cross-sectional areas betweenchemically different blocks and finally dictates their final crystalline morphology.
from the lamellar normal, andboth Ib-POSS and Cp-POSS molecules stacked into four-layer (ABCA) lamellar crystals, having the sametrigonal (Rm) symmetry as in pure POSS crystals. Because the cross-sectional area for a PE chain in the PEcrystals (0.216 nm2/chain) at the interface was much smaller than that for a POSS molecule in POSS crystals(1.136 nm2/molecule), the self-assembly and PE chain-folding were substantially affected by the sequence of PEand POSS crystallization when crystallizing from the melt. For example, PE crystallization induced the POSScrystallization in the bulk E39EO23-Ib-POSS, and thus extended-chain PE crystals were observed. The grains ofcrystalline lamellae again were small with often highly curved lamellar crystals. This could also be attributed tothe unbalanced interfacial areas for POSS and PE blocks (the interfacial area ratio being 2.6 for interdigitated PEcrystals, i.e., two PE chains per POSS molecule). For the E39EO23-Cp-POSS triblock oligomer, POSS moleculescrystallized before PE crystallization, forming a well-defined lamellar structure. The preexisting POSS crystalsconfined the PE crystallization, and thus almost once-folded PE crystals were obtained. Because the interfacialarea ratio between POSS and PE blocks decreased to 1.3, the crystalline lamellae were straight and their grainswere relatively large. On the basis of this study, we conclude that confinement effect plays an important role onchain-folding of crystalline block oligomers, which in turn determines the unbalanced cross-sectional areas betweenchemically different blocks and finally dictates their final crystalline morphology.