結晶-無定形雙團鏈式共聚合物,Poly(e-caprolactone)-block-Polybutadiene,之結晶動力學與結晶誘導形態轉變研究

Crystallization Kinetics and Crystallization-Induced Morphological Formation of Crystalline-Amorphous Diblock Copolymer, Poly(e-caprolactone)-block-Polybutadiene

許仁勇(Jen-Yung Hsu)

指導教授 ： 陳信龍

國立清華大學/工學院/化學工程學系/博士(2007年)

摘要

無資料

關鍵字

雙團鏈式共聚合物 ； 結晶-無定形 ； 結晶動力學 ； 形態轉變

並列摘要

Diblock copolymers are known to be able to self-assemble into a variety of long-range ordered nanostructures. The formation of these nanostructures is driven by the segregation between the repulsive block chains. For crystalline-amorphous diblock copolymers, the crystallization driving force is usually strong enough to perturb the melt morphology if the system is weakly segregated. In the present work, we systematically study the morphological formation and crystallization kinetics of a relatively weakly-segregated diblock copolymer, poly(caprolactone)-block- polybutadiene (PCL-b-PB), under different environments, namely, the neat state, the blend with PB homopolymer (h-PB), and within confined space.
For the binary blend of PCL-b-PB and h-PB, the existence of h-PB significantly retarded the crystallization-driven breakout of the melt mesophase. As the breakout could not take place in time during cooling from the melt at 5 ℃/min, PCL crystallization was largely confined within the individual microdomains, leading to a distinct correlation between crystallization kinetics and microdomain morphology. The crystallization-induced breakout of the cylinder morphology in the melt at low to moderate undercooling was also investigated. A domain coalescence prior to the formation of extended lamellar stacks was observed. This process was attributed to the crystallization-induced deformation of microdomains coupled with the effect of conformational communication of PB block chains.
A slightly asymmetric PCL-b-PB was found to display equilibrium lamellar or metastable cylinder morphology in the melt. This offered a special system where the effect of melt morphology on the crystallization behavior can be studied based on a single sample. In the cylinder-forming PCL-b-PB, the crystallization was found to breakout the melt structure. However, the corresponding crystallization rate was significantly slower than the lamellar counterpart, signaling an additional energy barrier associated with the breakout of the cylindrical microdomains. This additional energy barrier was attributed to the diffusion of PCL blocks across PB matrix onto the growth front.
We further examined the crystallization behavior of PCL-b-PB under the influence of spatial confinement. Using an emulsion approach, the microdomains of PCL-b-PB were confined within nanoscale droplets. Both the melt morphology and the crystallization kinetics were found to be very different from those in the bulk state. The nearly symmetric PCL-b-PB exhibited a lamellar morphology in the bulk while in the space-confined state the system was in the disordered state. The crystallization kinetics in the confined space was dominated by homogenous nucleation, while in the bulk it was governed by crystal growth. Our study revealed that the mechanism and kinetics of crystallization of PCL-b-PB strongly depended on the external environment, so did the morphological transformation induced by the crystallization.
Finally, an anomalous helical-ribbon morphology was identified when a nearly symmetric PCL-b-PB crystallized at sufficiently large undercooling. This twisting structure was quite special compared to the common helical structure, since the supramolecular structure was derived from an achiral diblock copolymer and driven by the crystallization process. The twisting was proposed to be driven by the attractive interaction between PB brushes where the crystallization introduced a strong perturbation for the PB brushed to initiate the twisting.

並列關鍵字

diblock copolymer ； crystalline-amorphous ； crystallization kinetics ； morphological formaion