Orthogonal Crystal Orientation in Double-Crystalline Block Copolymer

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• 作者：Ming-Champ Lin ; Yi-Chin Wang ; Jean-Hong Chen ; Hsin-Lung Chen ; Alejandro J. Mu虉ller ; Chun-Jen Su ; U-Ser Jeng
• 刊名：Macromolecules
• 出版年：2011
• 出版时间：September 13, 2011
• 年：2011
• 卷：44
• 期：17
• 页码：6875-6884
• 全文大小：1077K
• 年卷期：v.44,no.17(September 13, 2011)
• ISSN：1520-5835

文摘

In this study, we explore the orientation of crystals formed within the lamellar domains of a diblock copolymer composed of two crystallizable blocks, that is, poly(l-lactide)-block-polyethylene (PLLA-b-PE). The orientation of both PLLA and PE crystals with respect to the lamellar interface was examined under two types of crystallization condition with a broad range of crystallization temperatures (T_c). The first type was the 鈥渢wo-stage crystallization鈥? where the PLLA block was allowed to crystallize before PE. The second was the 鈥渙ne-stage crystallization鈥? where PLLA and PE blocks competed to crystallize. A homeotropic crystal orientation was always observed for the PLLA crystals, with the crystalline stems lying parallel to the lamellar normal regardless of the crystallization condition, except when T_c approached the glass-transition temperature of PLLA, where the orientation became random. A homogeneous crystal orientation with the PE crystalline stems oriented perpendicular to the lamellar normal was always identified at low-to-intermediate degree of undercooling, whereas at large undercooling, the crystals showed random orientation. The 鈥渙rthogonal orientation鈥?disclosed here was preserved over a broad range of undercooling. Our results further demonstrated that the orientation of both PLLA and PE crystals depended mainly on T_c but was independent of the competitiveness of the two crystallization processes. This was a consequence of the strong segregation that made the two blocks crystallize independently within their respective microdomains.