本研究合成具有光異構化特性之偶氮苯單體，再以原子轉移自由基聚合法製備一系列含不同偶氮苯鏈段比之三團聯共聚物poly(6-[4-(4-ethoxyphenylazo)phenoxy]hexyl methacrylate)-block-poly(ethylene glycol)-block-poly(6-[4-(4-ehoxypenylazo)phenoxyl]hexyl methacrylate) (PMMAzo-b-PEG-b-PMMAzo)，並研究其在溶液中之結構與光異構化行為。
PMMAzo-b-PEG-b-PMMAzo具有光異構化之行為，經由紫外光照射後，會由反式異構物轉換為順式異構物，照射可見光則會發生逆反應。利用紫外光-可見光分光光譜儀分析偶氮苯之光異構化行為，當團聯共聚物溶於中性溶劑(DMF)時，由於DMF對兩鏈段皆相容，因此團聯共聚物以random coil形式存在於溶液中；然而當選擇性溶液(H2O)加入DMF時，溶液對偶氮苯鏈段之溶解度降低，形成PEG鏈段在外而偶氮苯鏈段在內之微胞結構。從UV-Vis光譜中發現，當溶液之選擇性上升，吸收峰產生藍位移，代表偶氮苯分子之H-aggregation含量增加，其進行光異構化時結構轉換所需之空間會受到限制，因此偶氮苯分子於選擇性溶液中之光異構化速率會變慢。此外，我們也分析不同偶氮苯鏈段比之團聯共聚物於溶液中對光異構化與結構之影響，結果顯示，高偶氮苯鏈段比之團聯共聚物較容易受到溶液之選擇性影響而改變偶氮苯分子的排列型態，且光異構化速率也會隨著偶氮苯鏈段比上升而變慢。
本研究亦探討鹽類對於含偶氮苯團聯共聚物溶液中之結構影響，我們使用KCl與KSCN摻入含PMMAzo-b-PEG-b-PMMAzo之混合溶液中，當溶液的選擇性較低時，偶氮苯分子不會產生聚集，此時添加鹽類無法改變偶氮苯分子之排列型態。然而，若溶液的選擇性過高時，則會限制鹽類對於PEG鏈段的鹽析效應，此時偶氮苯分子的聚集型態也無明顯改變。在適當的混合溶液比例時，鹽類的摻入對PEG鏈段產生鹽析效應而萎縮，但微胞的尺寸則變大，我們可以推論位於微胞核的PMMAzo鏈段體積變大，因此偶氮苯分子較不會規則排列，以nonassociation形態存在的比例增加。

We synthesized a photoresponsive azobenzene monomer, which was used to synthesize azobenzene-containing triblock copolymers poly(6-[4-(4-ethoxy-phenylazo)phenoxy]hexyl methacrylate)-block-poly(ethylene glycol)-block-poly(6-[4-(4-ehoxypenylazo)phenoxyl]hexyl methacrylate) (PMMAzo-b-PEG-b-PMMAzo) through atom transfer radial polymerization. Their photoresponsive properties and structures in solutions were systematically investigated.
PMMAzo-b-PEG-b-PMMAzo exhibited the photoisomerization response. When PMMAzo-b-PEG-b-PMMAzo was irradiated by UV light, trans isomers converted to cis isomers. On the other hand, the reverse cis-to-trans photoisomerization was obtained after visible light irradiation. UV-Vis spectroscopy was carried out to examine the photoresponsive properties of PMMAzo-b-PEG-b-PMMAzo. When PMMAzo-b-PEG-b-PMMAzo was dissolved in a neutral solvent (DMF), both blocks were compatible with DMF, resulting in a random-coiled conformation. When a PEG-selective solvent (H2O) was added to DMF, the solubility of PMMAzo in the mixed solvents decreased, leading to the formation of micelles composed of PMMAzo in the core and PEG in the corona. When the solvent selectivity was increased, maximum absorbance in the UV spectra was blue-shifted, indicating an increase in the amount of H-aggregated azobenzene mesogens. The free volume of H-aggregated mesogens was limited during photoisomerization, causing a decrease in the photoisomerization rate. Furthermore, we investigated the effect of the weight fraction of the azobenzene block (fPMMAzo) on the structure and photoresponsive behavior of PMMAzo-b-PEG-b-PMMAzo. Results revealed that the copolymer with high fPMMAzo resulted in the aggregation of mesogens and the formation of micelles in selective solvents. Additionally, the photoisomerization rate increased with an increase in fPMMAzo.
The present study also investigated the effect of salt addition (KCl and KSCN) on the structure of PMMAzo-b-PEG-b-PMMAzo in solvents. When the solvent selectivity was low, mesogens were nonassociated, and the addition of salts showed little relation to the aggregation state of mesogens. However, when the solvent selectivity was too high, the salting-out effect on PEG chains was limited, resulting in little changes in the aggregation state of mesogens. In the mixed solvents with appropriate solvent selectivity, salts caused the shrinkage of PEG chains because of the salting-out effect. Conversely, the size of micelles increased. Such behavior was attributed to the expansion of PMMAzo chains in the core of micelles. As a result, the amount of nonassociated mesogens increased.

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