活性聚合具有環境刺激響應共聚高分子與分析其組裝結構與環境敏感智能行為

Abstract

隨著奈米科技的發展以及對能源與能源應用上的需求，具有精確結構設計的功能性軟物質材料已被廣泛的研究。近年來，活性高分子聚合技術的發展，使得我們可以得到具有可控制分子量分佈、複雜結構與控制組成比例的高分子材料。自然界生物為了維持生命與生理機能，生物體內的高分子與細胞必須隨著外在環境的變化來改變其化學性質與結構。由此概念所發展出具有刺激響應的仿生高分子材料已運用在許多生醫方面的應用。 自然界生物為了維持生命與生理機能，生物體內的高分子與細胞必須隨著外在環境的變化來改變其化學性質與結構。由此概念所發展出具有刺激響應的仿生高分子材料已廣泛運用在生醫材料。 本研究中，我們利用活性聚合出具有刺激響應共聚高分子，並且加以研究這些高分子在固態或液態中的自組裝結構: (1) 活性聚合聚胜肽嵌段式共聚高分子 poly(N-isopropylacrylamide)-b-poly(Z-L-lysine) (PNIPAm-b-PZLys) 及其性質研究: 聚胜肽(polypeptide)嵌段共聚高分子是利用具有雙官能基起始劑，一端進行原子轉移自由基聚合(atom transfer reversible polymerization)具有溫度響應的軟鏈段聚異丙基丙烯醯胺poly(N-isopropylacrylamide)，另一端則進行開環反應聚合硬鏈段聚胜肽polylysine高分子。藉由此種雙親性嵌段式共聚高分子的親疏水鏈段在極性上的差異，我們發現可以藉由改變共聚高分子的組成以及共溶劑極性，在形成各種型態熱力學穩定的高分子微胞。利用小角度(SAXS)、廣角度X光繞射儀(WAXS)與穿透式電子顯微鏡(TEM)觀察此種嵌段共聚物的微相自組裝相分離結構。在移除胺基保護基苄氧羰基後，我們利用核磁共振儀觀察此共聚物在改變環境溫度與pH值的刺激響應行為。 (2) 利用逐層組裝與點擊化學製備共價鍵穩定超薄殼層溫度敏感微膠囊中空球 本研究中，我們利用原子轉移自由基聚合聚合出具有疊氮以及炔基官能基的熱敏感聚異丙基丙烯醯胺共聚物，接著利用表面改質疊氮官能基的二氧化矽微米球當作基板進行逐層組裝並同時進行1,3-偶極環加成點擊化學反應形成共價鍵穩定的多層薄膜結構。利用稀釋氫氟酸水溶液移除模板，我們可得到一個穩定型態具有可逆溫度響應的高分子中空囊球。進一步藉由控制多層薄膜的交聯度以及反應溫度可以得到不同厚度及表面粗糙度的高分子膠囊中空球。 (3) 利用逐層組裝與點擊化學製備共價鍵穩定雙刺激響應超薄高分子液胞 傳統上高分子液胞(polymer vesicles)是利用兩性嵌段共聚物在水溶液下相分離所產生的自組裝結構。我們以第二部分研究作為基礎，進一步導入酸鹼敏感聚丙烯醯丙氨酸共聚物，與熱敏感聚異丙基丙烯醯胺共聚物交替進行交替逐層組裝反應。我們藉由此技巧制備出具有類似高分子液泡結構，並可控制尺度大小與殼-核層薄膜厚度。利用共軛焦顯微鏡(CLSM)、TEM與原子力顯微鏡(AFM)可觀察此高分子液泡對溫度與酸鹼值之刺激響應行為。

Applications for advanced functional soft materials that possess precisely engineered properties and functional groups have been expanding significantly with the development of nanotechnology and the growing need to address resource, health, and energy issues. Recent advances in living/controlled polymerization techniques have facilitated access to (co)polymers with controlled molecular weights, complex architectures, and precisely positioned functional groups. To sustain life and maintain biological function, nature requires selectively tailored molecular assemblies and interfaces that provide a specific chemical function and structure, and which change in their environment. Synthetic materials that change properties in response to local environmental stimuli with very similar attributes are often prepared for a broad range of biomedical applications. In this study, we synthesized well-defined stimuli-responsive copolymers by controlled/living polymerization and investigated their assembled nanostructures in the solid-state or in solution: (1) Polypeptide diblock copolymers: syntheses and properties of poly(N-isopropylacrylamide)-b-polylysine: A hydrolysis-resistant amide-linkage hetero-functional initiator was synthesized and used successfully for polymerization of well-defined rod-coil block copolymers poly(N-isopropylacrylamide)-b-poly(Z-L-lysine) (PNIPAm-b-PZLys) by combination of atom transfer radical polymerization (ATRP) and amine hydrochloride mediated ring-opening polymerization (ROP). These amphiphilic block copolymers are able to form universal micelle morphologies of spherical micelles, wormlike micelles, and vesicles by varying the polymer compositions and the helicogenic common solvents. From synchrotron SAXS, WAXS, and TEM results, the PNIPAm-b-PZLys microphase self-assembly morphology in solid state is a hierarchical lamellar-in-hexagonal structure. After removing the protective ε-benzyloxycarbonyl group, the dual stimuli-responsive behaviors of the PNIPAm-b-PLys investigated by nuclear magnetic resonance spectroscopy in aqueous solution resulted in either coil-to-helix or coil-to-globule transition by changing the environmental condition of elevating the temperature or increasing the pH value. (2) Using click chemistry to fabricate ultrathin thermoresponsive microcapsules through direct covalent layer-by-layer (LbL) assembly We report the syntheses of azido- and acetylene-functionalized PNIPAm copolymers and their use in the fabrication of ultrathin thermoresponsive microcapsules through direct covalent LbL assembly using click chemistry. These clickable copolymers were prepared through ATRP at 0 °C using a synthesized dansyl-labeled initiator and the CuBr/Me6TREN catalyst complex in 2-propanol. These clickable PNIPAm copolymers assemble alternately onto azido-modified silica particles in aqueous media through click reactions catalyzed by copper sulfate and sodium ascorbate. After removing the template, the microcapsules remained stable because of the presence of the covalently bonded triazole units; the microcapsules exhibited thermoresponsive and thermo-reversible swelling/de-swelling behaviors upon changing the temperature of the medium. Adjusting the number of clickable functionalities resulted in changes to the degree of cross-linking, thereby allowing control over the surface morphology and thickness of the covalently stabilized PNIPAm multilayer thin films. The microcapsules fabricated close to the lower critical solution temperature of PNIPAm exhibited extremely low surface roughnesses and thick multilayer films as a result of their compact chain conformation in aqueous solution, leading to tighter packing of the PNIPAm structure. (3) Fabrication of vesicle-like dual-responsive click capsules by direct covalent LbL assembly We report a click chemistry approach for the consecutive LbL assembly of thermo and pH-sensitive clickable copolymers on silica particles and the subsequent formation of a vesicle-like dual-responsive click capsules. This click capsules exhibit both thermo and pH-responsive behaviors by elevating the solution temperature and incubating in acidic or basic solutions respectively. These stimuli-responsive behaviors were examined by using confocal laser scanning microscopy (CLSM), TEM, and atomic force microscopy (AFM). This approach provides potential applications in preparing well-defined vesicle-like capsules with covalent stabilization and flexibility in introducing a range of new materials including different functional polymers.