Birefringence of Crystalline Block Copolymers Templated by Crystallization

結晶行為對半結晶性團聯共聚物雙折射之調控

張光威(Guang-Wei Chang)

指導教授 ： 何榮銘

國立清華大學/工學院/化學工程學系/碩士(2008年)

https://doi.org/10.6843/NTHU.2008.00318

摘要

A series of semicrystalline block copolymers, poly(4-vinylpyridine) -block-poly(ε-caprolactone) (P4VP-PCL), with lamellar microstructure have been synthesized. Owing to the vitrified P4VP microdomains and strongly segregated microphase separation, the crystallization of the PCL blocks in P4VP-PCL can be carried out under nanoscale confinement at various temperatures. Specific PCL crystalline orientation can be achieved by confined crystallization under the vitrified P4VP microdomains. Considering the practical applications, large-scale oriented microphase-separated microdomains is required to provide well-defined structure for anisotropic macroscopic properties. A novel orientation process combining rimming coating and shearing was employed to achieve the large-scale orientation for microphase-separated microdomains.
Simultaneous SAXS and WAXD experiments are carried out to examine the anisotropic properties of microphase separated microstructure and corresponding crystalline orientation. The scattering results suggested that the crystalline chains are normal to microphase-separated lamellar microdomains at various temperatures from -10℃ to 40℃ because of the nanoscale confinement for crystallization; namely, a perpendicular orientation can be achieved. As evidenced by DSC measurements, the confined size effect varying from different molecular-weight samples is significant on confined crystallization. Interestingly, as observed by polarized light microscopy, uniform birefringence pattern can be identified in the oriented block copolymer thin films after crystallization.
The birefringence of the crystalline block copolymer thin films was examined as a function of crystallization temperature. Real-time birefringence measurement of the thin-film samples with the crystallization process was obtained by using a polarizer-sample-polarizer system. The enhancement on the birefringence of the block copolymer thin films corresponded well with the increase on the crystallinity of confined crystallization. We speculate that the growth of oriented crystallites with perpendicular morphology is attributed to the confinement effect. As a result, the birefringence of the thin-film samples increased with the crystallinity developing within the confined microdomains because of the specific anisotropic character.
Our results indicated that significant birefringence variation in the semicrystalline P4VP-PCL block copolymers can be templated by controlling the orientation and crystallinity of the crystalline microdomains due to the formation of preferential crystalline orientation. Also, it is noted that this birefringence variation is a reversible process by simply controlling the annealing temperature. Consequently, this block copolymer thin film can provide a temperature-controlled birefringence film and also a controllable birefringence film with the crystallization time because of the unique anisotropic crystallites of confined crystallization.

關鍵字

雙折射 ； 結晶 ； 團聯共聚物

並列摘要

無資料

並列關鍵字

birefringence ； crystallization ； block copolymer

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