本研究合成具有光異構化特性之偶氮苯單體，再經由原子轉移自由基聚合法製備雙團聯共聚物poly(ethylene glycol)methyl ether-block-poly(6-[4-(4'-methoxyphenylazo)phenoxy]hexylmethacrylate) (mPEG-b-PAzo)。本研究亦藉由氫鍵鍵結的方式混摻偶氮苯單體與PEG製備偶氮苯/PEG複合物，分別研究此兩種系統之光異構化行為並探討其對PEG結晶行為的影響。
我們將mPEG-b-PAzo溶在不同的中性溶劑及選擇性溶劑中，以紫外光-可見光分光光譜儀分析其光異構化行為，結果顯示偶氮苯鏈段的分子量及異構物型式可影響偶氮苯與溶劑的相容性，進而影響偶氮苯分子的聚集型態，導致光異構化速率的改變。在mPEG-b-PAzo塊材中，當偶氮苯團聯共聚物中含cis異構物時，所形成的微相結構較雜亂，且PEG鏈段具有較高的起始結晶溫度。
當偶氮苯/PEG複合物溶在溶劑中，觀察到偶氮苯以氫鍵鍵結於PEG鏈段時，會導致光異構化速率降低。觀察複合物的結晶行為，PEG與偶氮苯分子之間的氫鍵抑制了PEG的結晶，當混摻比例達1:1時，PEG無結晶發生。此外，cis異構物有利於PEG的結晶行為，可促使起始結晶溫度及結晶度上升，但熔融溫度則無明顯變化，顯示含cis及trans異構物不影響結晶層厚度。我們亦發現當偶氮苯分子添加量增加時，偶氮苯/高分子複合物相分離形成層狀結構。

In this study, azobenzene monomers and poly(ethylene glycol)methy lether-block-poly(6-[4-(4'-methoxyphenylazo)phenoxy]hexylmethacrylate) (mPEG-b-PAzo) block copolymers were synthesized through atom transfer radical polymerization. We also prepared azobenzene/PEG complexes through hydrogen bonding interaction. The photoresponsive behavior and its effects on the microphase separation and crystallization behavior of both systems were investigated.
The mPEG-b-PAzo block copolymers were dissolved in various neutral and selective solvents and the photoresponsive behavior was characterized by using UV-vis spectroscopy to investigate the photoresponsive and self-assembly behaviors of mPEG-b-PAzo in solutions. The photoisomerization rate of mPEG-b-PAzo was mainly determined by the aggregation state of azobenzene, which depended on the molecular weight of PAzo segments and the types of isomers. This was attributed to the increased miscibility of mPEG-b-PAzo in a solvent when the molecular weight of PAzo decreased and the cis-isomers increased. In bulk architecture, the presence of cis-isomers increased the onset crystallization temperature. However, cis-isomers disturbed the microphase separation of mPEG-b-PAzo, resulting in a poorly ordered morphology.
When the azobenzene/PEG complex was dissolved in a solvent, the hydrogen bonding between azobenzene and PEG caused a reduction of the photoisomerization rate. Regarding the crystallization behavior of azobenzene/PEG complexes, the hydrogen bonding between azobenzene and PEG prohibited PEG crystallization. When the content of PEG and azobenzene was 1:1, no PEG crystallization occurred. On the other hand, cis-isomers facilitated PEG crystallization, leading to an increase in the onset crystallization temperature and degree of crystallinity. However, the change in the melting temperature was not considerable, suggesting that the cis- and trans-isomers did not affect the lamellar thickness. Furthermore, the azobenzene/PEG complexes could phase separate to form a lamellar structure.

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