含DEH-PPV結構之剛-柔團聯共聚高分子的合成與自組裝之研究

Abstract

Rod-coil block copolymers consisted of semiconducting polymers have been extensively studied due to their great potential in optoelectronic applications such as organic light-emitting diodes, thin-film transistors, and photovoltaic cells. Control of the morphology in 10-nm length scale is extremely important for optimizing the efficiency of these devices. In this dissertation, the synthesis of DEH-PPV-b¬-PMMA and DEH-PPV-b-PLLA by “click” chemistry is explored. The method has been expanded to the synthesis of high yield of end-functionalized PMMA. The self-assembly behaviors of DEH-PPV-b¬-PMMA and DEH-PPV-b-PLLA are thoroughly investigated. A series of DEH-PPV-b-PMMA polymers with narrow polydispersity (PDI < 1.1) were synthesized using Siegrist polycondensation and anionic polymerizations followed by “click” chemistry. Alkyne-terminated DEH-PPV and azido-terminated PMMA were synthesized first, and then the two functionalized polymers underwent 1, 3-cycloaddition reaction to obtain copolymers. Both the conversion of the end-functionalization of the homopolymers and the yield of the “click” reaction were higher than 98% as determined by 1H NMR and GPC. TEM and SAXS studies reveal the details of copolymer morphology. The DEH-PPV-b-PMMA system presented here has higher block segregation strength than many previously studied rod-coil block copolymers yet still shows experimentally accessible phase transitions with respect to temperature. As a result, this molecule offers new insight into the competition between rod-rod and rod-coil interactions that occurs in the system. The DEH-PPV rods are organized as a monolayer that is inclined with the lamellar normal (smectic C) for the copolymers containing low volume fraction of PMMA coil (<54%). However, as the coil fraction increases, the strips containing DEH-PPV pack into hexagonal lattice. In contrast to previous work which demonstrated similar morphologies, the sequence of reversible liquid crystalline and microphase phase transitions is altered as a result of the increased block segregation. Upon heating the low coil fraction copolymers exhibit a series of clear transitions of smectic-lamellar to amorphous-lamellar to disordered structures. In high coil fraction copolymers, the transitions between smectic-hexagonal to amorphous-hexagonal and smectic-hexagonal to disorder structures could not be clearly differentiated. The order-to-disorder temperature (ODT) decreases slowly with increasing coil fraction while the smectic-to-isotropic transition (SI) temperature stays relatively unchanged. The steady SI temperature suggests that the strong rod-rod interaction keeps the liquid crystalline rod in the nanodomain structure regardless of the amount of coil segment in the copolymers. A rod-coil block copolymer, DEH-PPV-b-PLLA (PDI < 1.2) with biodegradable and crystalline coil segment, was synthesized using Siegrist polycondensation and ring-opening polymerization followed by “click” chemistry and exhibits the long-range ordered nanostructure. Alkyne-terminated DEH-PPV and azide-terminated PLLA were synthesized first, and then the two functionalized polymers underwent 1, 3-cycloaddition reaction to obtain copolymers. Both the conversion of the end-functionalization of the homopolymers and the yield of the “click” reaction were higher than 98% as determined by 1H NMR and GPC. TEM, SAXS, and WAXS studies reveal the details of the copolymer morphologies. Without annealing, DEH-PPV-b-PLLA exhibits less ordered lamellar nanostructure as compared with DEH-PPV-b-PMMA due to the crystalline characteristic of PLLA influences the self-assembled behavior of the DEH-PPV-b-PLLA. With annealing, DEH-PPV¬-b-PLLA and DEH-PPV-b-PMMA exhibit similar ordered lamellar structure because the extent of the influence of PLLA crystalline characteristic is less. Well-defined poly(methyl methacrylate) (Mn = 3630 g mol-1, PDI = 1.06) with a primary benzylic bromide prepared using anionic polymerization was successfully transformed into diverse end-functionalities (ω-carboxyl, ω-hydroxy, ω-methyl-vinyl, ω-trimethylsilane, and ω-glycidyl-ether) via “click” reaction. The bromine end-terminated poly(methyl methacrylate) first was substituted by an azide function and sequentially was reacted with various functional alkynes (propiolic acid, propargyl alcohol, 2-methyl-1-buten-3-yne, propargyl trimethylsilane, and propargyl glycidylether). In all cases, 1H NMR, 13C NMR, FT-IR, and GPC measurements shows qualitative and quantitative transformation of the chain-end poly(methyl methacrylate) into the desired functionalities with high conversion (above 99%). The “click” chemistry is a very useful method to obtain well-defined copolymers and functionalized polymers. The differences of self-assembled behaviors between DEH-PPV-b-PMMA and DEH-PPV-b-PLLA are due to the crystalline characteristic of PLLA.