藉由可調控氫鍵作用力控制嵌段式共聚高分子摻合系統之自組裝行為與相行為之探討

Abstract

在高分子材料研究領域中，高分子混摻一直是一個被廣泛研究的課題，由於高分子摻混時，整個系統會產生很低的熵(entropy)值，使得絕大部分的高分子混摻系統都呈現著很差的相溶性。透過引入高分子間特殊作用力，使得高分子混摻系統相溶性顯著的提升，其中，又以氫鍵作用力被應用的最為廣泛。 在具有氫鍵作用力的的高分子摻合系統中，有各種理論去描述系統中的作用利行為及相溶性相圖，其中，以Painter-Coleman association model (PCAM)最能準確的闡述高分子氫鍵摻合系統的行為。因此，在本研究中，我們用利用陰離子活性聚合法合成一系列的poly(vinylphenol-b-2-(dimethylamino)ethyl methacrylate) (PVPh-b-PDMAEMA)，並製備一系列PVPh/PDMAEMA混摻比例，探討在嵌段式共聚高分子及聚摻高分子在具有同樣氫鍵作用力時的行為。在比較終可發現，嵌段式共聚高分子會展現出緊密作用的高分子鏈行為導致分子間複雜體(complexation)產生，反之，在聚摻高分子系統中僅僅展現出高分子相溶的行為。 近年來，由於奈米級階層性自組裝之材料被廣為應用在許多領域之中，使得嵌段式共聚高分子(diblock copolymer)在固態與液態下的自組裝行為之研究亦備受許多矚目與探討。一般軟段－軟段嵌段式共聚高分子的自組裝行為大部分藉由一短程吸引力(short-range attraction, covalent bond)以及一長程排斥力(long-range repulsion, block incompatible)之間平衡所導致，並形成各式各樣的奈米結構，而創造出多樣性的超分子材料(supramolecular material)。而藉由加入一均聚高分子(homopolymer)來控制嵌段式共聚高分子之微相分離(microphase-separation)行為在近年也廣為研究。 在研究中，我們將系統性的研究A-b-B/C嵌段式共聚高分子/均聚高分子在具有不同強度氫鍵作用力時之聚摻之相行為變化。我們利用陰離子活性聚合方式合成poly(vinylphenol-b-styrene) (PVPh-b-PS)嵌段式共聚高分子、poly(4-vinylpyridine) (P4VP) 、poly(methyl methacrylate) (PMMA)、poly(vinylphenol) (PVPh)均聚高分子，由於PVPh-b-PS中的PVPh鏈段會和P4VP產生強氫鍵作用力，相對地，和PMMA產生弱氫鍵作用力，故在PVPh-b-PS/P4VP的混摻系統會跟PVPh-b-PS/PMMA混摻系統產生截然不同的相行為。PVPh-b-PS/P4VP系統會隨著P4VP量在系統中的增加而展現出一系列相變化，由原先的層狀結構(lamella)依序變成雙連續相結構(gyroid)、六角圓柱(hexagonal packed cylinder)、最後變成體心立方排列球結構(body-central cubic sphere)；而PVPh-b-PS/PMMA系統並不會隨著PMMA量在系統中的增加而產生任相變化。並也以PVPh-b-PS/PVPh混摻系統作為比較，發現此系統亦無任何相變化產生。最後，提出一新的參數(KA/KB)來預測是否有像變化產生之可能；如果此參數大於一相變化變化產生，反之，便無相變化。 此外，我們研究一嵌段式高分子混摻一小分子(poly(4-vinylpyridine-b-styrene)/octyl- gallate系統在不同共同溶劑下之液態自組裝行為。在不同的共同溶劑之下，由於生成不同的氫鍵作用力強度的氫鍵導致會有不同的自組裝聚集行為產生，而調控的液態下的聚集結構。

The miscibility and interaction in polymer blends have been a topic and intense interest in polymer science. The miscibility of an immiscible blend was promoted by introducing one component which can form hydrogen bonded with another component. It is the one of the major achievements during last twenty years in polymer blend. This type of interaction has been widely described in terms of Painter & Coleman association model due to exactly prediction in most systems. We have used anionic polymerization to prepare a series of poly[vinyl phenol-b-2-(dimethylamino)ethyl methacrylate] (PVPh-b-PDMAEMA) block copolymers. These block copolymers are miscible, with strong specific interactions occurring between the OH groups of the PVPh segments and the tertiary ammonium groups of the PDMAEMA segments. These PVPh-b-PDMAEMA diblock copolymers exhibit higher glass transition temperatures than do the corresponding PVPh/partially protonated PDMAEMA blends obtained from DMSO solution, which we suspect exist in the form of separate coils. The blocks of the PVPh-b-PDMAEMA diblock copolymers interact strongly, resulting in polymer complex aggregation similar to the behavior of PVPh/partially protonated PDMAEMA blend complexes obtained in methanol. In addition, these PVPh-b-PDMAEMA diblock copolymers exhibit a novel type of pH-sensitivity: at low pH, compact spherical micelles are formed possessing PDMAEMA coronas and PVPh cores; at medium pH, vesicles are observed, consisting of partially protonated hydrophilic PDMAEMA shells and hydrophobic PVPh cores; at high pH, the spherical micelles that formed comprised ionized PVPh coronas and deprotonated hydrated-PDMAEMA cores, i.e., phase inversion of the micelles formed at pH 2. The self-assembly of block copolymers in solution and solid state is attracting intense current attention as a route to nanostructured and hierarchical materials with variety of potential applications. Block copolymers display interesting self-assembly phenomena and allow the creation of hybrid supramolecular material. Furthermore, it is also interesting to control the morphology of microphase separated block copolymers by adding a homopolymer or other block copolymer. In this thesis, we have investigated the phase behavior of poly(4-vinylphenol-b-styrene) (PVPh-b-PS) when respectively blended with poly(4-vinylpyridine) (P4VP), poly(methyl methacrylate) (PMMA), and PVPh homopolymers, of systematically decreased hydrogen-bonding strengths with the PVPh block of the copolymer. The PVPh-b-PS/P4VP blend has a much higher fraction (fH) of hydrogen bonded PVPh blocks for a significantly higher miscibility, compared to the blends with PMMA and PVPh homopolymers. Consequently, the PVPh-b-PS/P4VP blend, behaving as a neat diblock copolymer, exhibited a series of order-order phase transitions from the lamellar, gyroid, hexagonally packed cylinder, to body-centered cubic structures. In contrast, both the PVPh-b-PS/PMMA and PVPh-b-PS/PVPh blends maintained essentially the lamellar structure; the lamellar structure, depending on the hydrogen bonding strength. The ratio of inter-association equilibrium constant (KA) over self-association equilibrium constant (KB), KA/KB, is introduced as a convenient guide in estimating the phase behavior of similar polymer blends, featuring hydrogen bonding interactions between the homopolymer additive and copolymer: with a KA/KB ratio much larger than unity, the blend system tends to behave as a neat copolymer; with a KA/KB ratio significantly smaller than unity, phase separation instead of order-order phase transitions can be expected for the blend above certain volume fraction of homopolymer additive. In addition, we have investigated the complexation-induced phase behavior of the mixtures of poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) and octyl gallate (OG) due to hydrogen bonding in different solvents. For PS-b-P4VP/OG mixture in chloroform, the morphological transitions were induced from the unimer configuration to swollen aggregate and complex-micelles by adding OG. Interestingly, the complex-micelles can lead the formation of the honeycomb structure from chloroform solution. The PS-b-P4VP/OG mixture in THF, behaving an amphiphilic diblock copolymer in solution state, exhibited a series of morphological transitions by increasing the OG content. In contrast, the PS-b-P4VP/OG mixture in DMF maintained the unimer configuration upon adding OG. Therefore, the complexation-induced morphology of the mixtures of PS-b-P4VP and OG can be mediated by adopting different common solvents to affect the self-assembly behavior.