結晶性嵌段式共聚物之結晶行為與階層性結構研究

Crystallization Behavior and Hierarchical Structure of Crystalline Block Copolymers

林明昌(Ming-Champ Lin)

指導教授 ： 陳信龍

國立清華大學/工學院/化學工程學系/博士(2012年)

https://doi.org/10.6843/NTHU.2012.00076

摘要

Crystallization of diblock copolymer composing one or two crystallizable components has attracted significant attention in recent decades. In this study, we center on the crystallization behavior and morphological structure of the diblock copolymers containing one crystalline and one amorphous block (i.e., the C-A diblocks) and two crystalline blocks (i.e., the C-C diblocks). We intend to unravel how the interplay between the crystallization event and the driving force of microphase separation influences the kinetics and thermodynamics of crystallization as well as on the hierarchical structure formation of the systems.
First of all, we investigate the crystallization behavior of isotactic polypropylene (iPP) under the influence of nanoscale confinement templated by the microphase-separated structure of an iPP-based C-A diblock copolymer system, isotactic polypropylene-block-atactic polystyrene (iPP-b-aPS). Three types of iPP microdomains, i.e., lamellae, cylinder and sphere, were generated by controlling the composition of the diblock. The effect of microdomain morphology on the nucleation mechanism, crystallization kinetics, self-nucleation behavior, the population of the helical sequence of iPP block in the melt state and crystal orientation have been systematically studied.
The strongly-segregated lamellae-forming poly (lactide)-block-polyethylene (PLA-b-PE) diblocks (including C-A polyethylene-block-poly(LD-lactide) (PE-b-PDLLA) and C-C poly(L-lactide)-block-polyethylene (PLLA-b-PE)) constituting analogous molecular weight of PE block have been systematically investigated and compared. In both systems, the crystallization process was virtually confined within the respective lamellar microdomains. Moreover, the microdomain morphology prescribed by the melt mesophase was essentially unperturbed upon crystallization, irrespective of the crystallization history, as a consequence of large segregation strength in nature.
In addition to the strongly-segregated C-C diblocks with a symmetric composition, we further focus on the crystallization kinetics and crystallization-induced morphological formation of a weakly-segregated asymmetric C-C diblock copolymer, syndiotactic polypropylene-block-poly(ε-caprolactone) (sPP-b-PCL). The system was subjected to crystallization over a broad range of conditions for tuning the competitiveness and interplay of the two crystallization events. It was found that the degree of morphological perturbation induced by sPP crystallization caused a special “interactive crystallization kinetics” in this type of material, where the crystallization temperature the leading crystalline component, sPP, drastically affected the crystallization kinetics of PCL block.
Apart from the correlation between crystallization behavior and morphological transformation, we further examined the preferential orientation of crystals (i.e., the crystalline molecular order) formed in lamellar microdomains of strongly-segregated PLA-b-PE diblocks. Orientation of PE crystals formed over a broad range of undercooling in a C-A PE-b-PDLLA diblock copolymer has been critically examined. It was found that the PE crystalline stems in the lamellar microdomains always orient parallel to the lamellar interface when there is a preferred orientational order. We have organized the thermodynamic and kinetic factors that may govern the preferred crystal orientation in diblock copolymers and concluded that the orientational order should be controlled by the competition between nucleation density and crystal growth kinetics.
Considering that most research so far has focused on the crystal orientation in C-A systems, here we investigate a C-C PLLA-b-PE diblock to explore the orientation of crystals formed within the lamellar domains over a broad range of crystallization conditions. It was found that the preferred crystal orientations were identical to those observed for the corresponding C-A systems and were not affected by the crystallization history, indicating that PLLA and PE blocks crystallized independently in their respective microdomains as a consequence of large segregation strength.

關鍵字

結晶性-無定形嵌段式共聚物 ； 雙結晶性嵌段式共聚物 ； 結晶行為 ； 階層性結構 ； 奈米結構 ； 晶體取向

並列摘要

無資料

並列關鍵字

crystalline-amorphous block copolymer ； crystalline-crystalline block copolymer ； crystallization behavior ； hierarchical structure ； nanostructure ； crystal orientation

參考文獻

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