Synthesis, Morphology, and Applications of Block Copolymers with Different Architectures:PS-b-P4VP and F-b-P2VP
Date Issued
2009
Date
2009
Author(s)
Lin, Chia-Hung
Abstract
Block copolymers have attracted extensive research activity in contemporary macromolecular science. This is attributable to a range of fascinating fundamental issues associated with understanding self-assembly processes in both solution and in bulk. One of the main issues on block copolymers requires further exploration is the polymer architecture effect, especially on the conjugated rod-coil systems. The research objectives of this thesis are to explore the synthesis, morphology (solution, film, or fiber), and properties of block copolymers with different polymer architecture, including coil-coil, rod-coil, coil-rod-coil, and star block structures. The following summarize the important discovery of this thesis.n 1st part (Chapter 2), new hetero-arm star amphiphilic block copolymers of polystyrene-block-poly(4-vinylpyridine) (PS4-P4VP4) with four different mole ratios of 4VP moiety (f4VP) were synthesized by sequential living anionic polymerization. Micellar morphologies of the synthesized copolymers in dilute solution were explored through the variation of polymer architecture, selective solvent content, common solvent polarity, and block ratio. Dynamic/static light scattering (DLS and SLS), transmission electron microscopy (TEM) and atomic force microscopy (AFM) were used to characterize the micellar morphologies. The experimental results suggested that the aggregation size and number of PS4-P4VP4 solution micelles were smaller than those of the linear analog. Morphological transformation of hetero-arm PS4-P4VP4 from spheres to cylinders, vesicles, and large compound vesicles was observed as the water content increased. The morphology of PS4-P4VP4 in the solvent mixture of DMF/water or 1,4-dioxane/water was shown sphere but changed into large compound micelles in the THF/water due to the different degree of swelling on the PS block. As the P4VP molar ratio decreased from 0.37 to 0.24, 0.12 and 0.07, the morphology changed from spherical mixed with cylindrical, to vesicles, giant vesicles, and then to large compound micelles due to the core chain stretching.n 2nd part (Chapter 3), new rod-coil diblock and coil-rod-coil triblock copolymers containing conjugated poly[2,7-(9,9-dihexylfluorene)] (PF) and coil-like poly(2-vinylpyridine) (P2VP) were synthesized by combining coupling reaction and living anionic polymerization. The experimental results showed that the diblock PF-b-P2VP maintained spherical micellar aggregates as the methanol content increased. However, the triblock P2VP-b-PF-b-P2VP were found to readily aggregate in elongated cylinders due to its symmetric structure. Consequently, P2VP-b-PF-b-P2VP polymer chains could stack together favorably and have stronger π-πinterchain compared with diblock PF-b-P2VP, leading to the higher absorption maximum. The quantum efficiencies were gradually quenched with increasing the MeOH content for both copolymers. Moreover, for diblock PF-b-P2VP, the increase of the MeOH content induced a blue shift in both absorption and PL spectra, suggesting an “H-type” aggregation. However, triblock P2VP-b-PF-b-P2VP exhibited a blue shift in absorption but a red shift in PL by increasing the MeOH content, which reflected a different type of aggregation. n 3rd part (Chapter 4), we developed the synthetic routine for preparing new rod-coil star-like poly[2,7-(9,9-dihexylfluorene)]-block-Poly(2-vinylpyridine) block copolymer (star-PF-b-P2VP) by cross linking of living anionic PF-b-P2VP chain ends, according to synthetic concepts of preparation of diblock PF-b-P2VP. The morphologies of the copolymers in spin-coated thin films were analyzed via atomic force microscopy (AFM). The annealing treatment, substrate, initial polymer concentration and mixed solvent effects are applied to research to obtain tunable aggregated structures. In order to gain further insight of aggregation behavior, the morphological results are then combined with photoluminescence spectra (PL). By comparing the experimental results with diblock PF-b-P2VP copolymers in solution, star copolymers exhibit different aggregation behavior due to symmetric/asymmetric architectures for two kinds of architectures.n 4th part (Chapter 5), morphology and photophysical properties of electrospun (ES) nanofibers prepared from the blends of conjugated rod-coil diblock PF-b-P2VP and triblock P2VP-b-PF-b-P2VP copolymers with PEO were studied. Well-produced ES fibers are confirmed by field-emission scanning microscopy (FE-SEM) and transmission electron microscopy (TEM), and uniform blue emission is appeared in confocal images for all samples. The prepared ES fiber diameters were around 600-1000 nm using the processing solvent of MeOH/H2O while those from CHCl3 were a few thousands of nm, due to the difference on the dielectric constant. The PF aggregation domain increased with enhancing the block copolymer composition in the ES fibers. In copolymer/low Mw of PEO (Mn~100,000) blending system, it has red-shifting of emission peak from fibers to films, which is different from high Mw of PEO (Mn~2,000,000) blending system, displaying no obvious shifts of emission peaks between films and fibers in both diblock and triblock systems. Furthermore, the PF aggregated domain was larger in the PF-b-P2VP/PEO ES fibers than that of P2VP-b-PF-b-P2VP and led to much reduced aggregation emission, which suggested the importance of polymer architecture.
Subjects
block copolymer
morphology
conjugated polymer
rod-coil
architecture
anionic polymerization
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-98-F93524031-1.pdf
Size
23.53 KB
Format
Adobe PDF
Checksum
(MD5):9460ebe67cd766910ac1566ad508ee4f