4-乙烯基吡啶高分子與扇狀苯甲酸衍生物形成之超分子的相分離行為與結構分析

Abstract

本研究探討扇狀苯甲酸衍生物與4-乙基吡啶高分子(P4VP與PS-b-P4VP)藉由氫鍵所組成之超分子的相行為與結構，其中使用的扇狀小分子包含 3,5-bis(hexadecyloxyl)benzoic acid (BA2) 與3,4,5-tris(hexadecyloxyl)benzoic acid (BA3)，分別帶有兩條與三條16個碳的長碳鏈。我們利用傅立葉轉換紅外光譜儀(FTIR)偵測P4VP鏈段上吡啶環之特徵吸收峰值變化來判定小分子在超分子結構中的氫鍵鍵結程度，發現在P4VP(BA3)系統中其鍵結程度並不是隨小分子的添加而單調增長，而是當添加的BA3:4VP莫爾比例達到~0.7時呈現最大值，隨後便隨小分子的增加而遞減。其主要原因是BA3小分子具有高度結晶性且容易自我聚集，過量的小分子將引發巨觀相分離並生成小分子的結晶相，使得BA3小分子與P4VP上之吡啶環的鍵結數目降低。我們進一步藉由示差掃描熱量分析儀(DSC)鑑定其相對應的超分子熱性質，亦利用小角/廣角X光散射儀器(SAXS/WAXS)與偏光顯微鏡(POM)分析其超分子結構，皆印證此巨觀相分離的發生。 此外，我們也探討超分子之形態：當添加的小分子達到P4VP鏈段所能氫鍵鍵結之最大劑量時，由均聚物(homopolymer)組成之P4VP(BA3)超分子會形成小尺度的六角最密堆積柱狀結構(~ 5 nm)；在小分子與嵌段共聚物PS-b-P4VP結合而成的超分子中，可藉由調控小分子的含量形成各種不同的嵌段共聚物形態，如層板結構、穿孔層板結構、柱狀結構以及球狀結構等。值得注意的是，P4VP(BA3)鏈段在共聚物中可以維持小尺度的六角最密堆積柱狀結構，因而形成球結構中有柱結構的階層式形態。本研究結果有助於調控超分子結構並避免巨觀相分離行為的發生。

In this work, we investigated the supramolecular complexes of fan-like small molecules and 4-vinylpridine based polymers via hydrogen bonding interactions. The fan-like molecules are the carboxylic acid derivatives with different number of hexadecyl tails, including 3,5-bis(hexadecyloxyl)benzoic acid (BA2) and 3,4,5-tris(hexadecyloxyl)-benzoic acid (BA3). We firstly used FTIR to investigate the degree of small molecules associated onto pyridine groups in the complexes of BA and homopolymer poly(4-vinylpyridine)(P4VP). It is interesting to find that for P4VP(BA3)x, where x is the molar ratio of added BA3 to P4VP repeating unit, the degree of complexation is not monotonically increased with x but reaches a maximum at x ~ 0.7 and then decreased as x is increased. Since BA3 is highly crystalline and tends to self-aggregate, an excess BA3 induces a macrophase separation that leads to the formation of a pure BA3 crystalline phase, thus reducing the number of BA3 molecules hydrogen-bonded with pyridine. The corresponding thermal behaviors of the supramolecules are confirmed by differential scanning calorimetry (DSC) measurements and the resulting structures are verified by X-ray scattering and polarized optical microscopy (POM) measurements. In addition, we have studied the morphology of the supramolecules. Around the upper limit of complexation without macrophase separation, the homopolymer supramolecules P4VP(BA3) form small-scaled hexagonally packed cylinders, ~ 5 nm. When BA3 is incorporated into polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP), a variety of block copolymer-scaled structures, including lamella, perforated lamella, cylinder, and sphere are formed dependent on the amount of incorporated BA3. Furthermore, the small-scaled hexagonally packed cylinders can be maintained in the P4VP(BA3) blocks and a rarely seen hierarchical cylinder-within-sphere can be obtained. The present studies provided a better understanding of supramolecules containing highly crystalline components and demonstrated the feasibility of tailoring supramolecules without macrophase separation.