新穎生物相容型團聯式共聚高分子之自組裝結構與相行為研究

Abstract

近年來，由於具有奈米階級性自組裝之材料被廣為應用在許多領域中，使得團聯式共聚高分子(diblock copolymer)在固態與液態下的自組裝行為之研究亦受到許多矚目與探討，其中以結合生物高分子與一般高分子所形成之團聯式共聚高分子尤其受到重視。一般高分子大部分藉由非特定的作用力進行自組裝，而生物高分子(例如: 蛋白質或聚胜肽(polypeptide))則可直接藉由分子間與分子內的氫鍵作用力或是靜電力直接進行自組裝。因此，可藉由結合不同生物高分子與一般高分子所形成之團聯式共聚物來創造具有不同自組裝特性之超分子材料(supramolecular materials) 。 本研究中，我們合成出三種新型以聚胜肽為主之團聯式共聚高分子，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) Poly(□-benzyl-L-glutamate)-block-Polypseudorotaxane 此團聯式共聚高分子是由一端具有alpha-螺旋形之硬段聚胜肽Poly(□-benzyl-L-glutamate)與經由軟鏈段P(EO19-r-PO3)與環糊精進行包覆錯合(inclusion complex)形成之硬段polypseudorotaxane所組成。藉由此種團聯式共聚高分子之間本身具有的作用力(包含polypseudorotaxane形成通道狀之結晶、聚胜肽之二級結構、與微相分離)，此種分子將產生階級性自組裝而形成雙層並排之特殊結構。 (2) Poly(2-ethyl-2-oxazoline)-block-Poly(□-benzyl-L-glutamate) (PEtOz-b-PBLG) 本研究中，我們研究此團聯式共聚高分子在固態與不同溶劑下之自組裝結構。固態中，PEtOz-b-PBLG具有熱向性液晶(thermotropic liquid crystal)之特性。在水溶液中，由於PEtOz-b-PBLG本身具有之親水-疏水雙親性特質，而會產生微胞狀與泡囊狀結構。而在會促使PBLG端產生alpha-螺旋二級結構之溶劑中，由於PEtOz-b-PBLG具有軟段-硬段(coil-rod)高分子特性，造成多樣化的自組裝結構(例如:球狀、泡囊狀、帶狀、中空管狀)與熱可逆性之成膠(gelation)狀態。 (3) Polyhedral oligomeric silsesquioxanes(POSS)-Poly(□-benzyl-L-glutamate) 結合無機奈米小分子多面體倍半矽氧烷寡聚體(POSS)與具alpha-螺旋形之聚胜肽Poly(□-benzyl-L-glutamate)形成之新型複合材料，我們成功製備出在溶劑Toluene中具有3-D帶狀之自組裝性材料。 此外，藉由加入一單聚高分子(homopolymer)來控制團聯式共聚高分子之微相分離(microphase separation)行為在近年來也廣被研究。 我們亦研究一新型A-B/C 團聯式共聚高分子/單聚高分子(poly(methyl methacrylate-b-vinylpyrrolidone)/poly(vinylphenol))聚掺之相行為變化。在此聚掺系統中，當PVPh含量在20%~60%時，由於不同強弱之分子間氫鍵作用力影響，會產生一特殊由微胞狀與基質組合成之微相分離結構。

The self-assembly of block copolymers in solution and the solid state is attracting intense current attention as a route to nanostructured and hierarchical materials with a variety of potential applications. Hybrids of synthetic and biological polymers are of particular interest. Typically, synthetic macromolecules differ with respect to their biological counterparts such as proteins and polypeptide in that their self-assembly is usually driven by largely unspecific interactions. In contrast, the self-assembly of biopolymers such as polypeptides involves directed hydrogen bonding and both electrostatic and hydrophobic interactions. Block copolymers with synthetic polymers and polypeptides display interesting self-assembly phenomena and allow the creation of hybrid supramolecular materials. In this thesis, we synthesized three kinds of novel polypeptide-based diblock copolymers and investigated their self-assembled nanostructures in the solid-state or in solutions: (1) Poly(□-benzyl-L-glutamate)-block-Polypseudorotaxane This diblock copolymer is comprised of an □-helical polypeptide rod, based on □-benzyl-L-glutamate, and an originally coiled segment P(EO19-r-PO3); it forms inclusion complexes with □-cyclodextrins (□-CDs) to give crystalline polypseudorotaxanes. Intrinsic interactions (e.g., the polypseudorotaxane’s channel-type crystallization, the polypeptide’s secondary structure, and microphase separation) within and between these rod–rod diblock copolymers contribute to their hierarchical self-assembly into juxtaposed bilayer-like nanostructure featuring hexagonally packed PBLG stacks and channel-type polypseudorotaxane moieties. (2) Poly(2-ethyl-2-oxazoline)-block-Poly(□-benzyl-L-glutamate) (PEtOz-b-PBLG) In bulk, the PEtOz-b-PBLG copolymers show thermotropic liquid crystalline behavior. Morphologies of self-assembled aggregation of these diblock copolymers in aqueous solution and in □-helicogenic solvents, in which PBLG blocks adopt rigid □-helix conformation, were investigated. In aqueous solution, these block copolymers self-assemble into spherical micelles and vesicular aggregates due to the amphiphilic nature. In helicogenic solvents for PBLG blocks, toluene and benzyl alcohol, the PEtOz-b-PBLG exhibits coil-rod chain properties that lead to interesting effects such as diverse aggregate morphologies (spheres, vesicles, ribbon, and tube nanostructures) and thermoreversible gelation behavior. (3) Polyhedral oligomeric silsesquioxanes (POSS)-Poly(□-benzyl-L-glutamate) New macromolecular self-assembling building blocks, polyhedral oligomeric silsesquioxanes-helical polypeptide copolymers, have been synthesized; these materials possess a well-defined 3-D shape and self-assemble in toluene solution to form nanoribbon structure. It is also interesting to control the morphology of microphase separated block copolymers by adding a homopolymer or another block copolymer. We have investigated a new type of A-B/C blend—formed between poly (methyl methacrylate-b-vinylpyrrolidone) and poly(vinylphenol) (PMMA-b-PVP/PVPh)—that displays unusual phase behavior. The proton spin-lattice relaxation time in the rotating frame (T1□H), which we determined using 13C NMR spectroscopy, indicates that microphase separation occurs for blends containing ca. 20–60 wt% PVPh. TEM images indicated clearly that the morphology of this microphase separation consists of a matrix of homogeneous mixed PVP/PVPh and micellar domains of excluded PMMA. This special phase behavior and miscibility is due mainly to the diversity of interactions that exist between the PMMA/PVPh and PVP/PVPh units.