Association and disassociation of polymer chains in dilute and semidilute solutions

In this thesis, we did the following studies: (1) The association of two rod-coil triblock copolymers: polystyrene-oligo(p-phenyleneethynylene)-polystyrene (PS-OPE-PS) and oligo(p-phenyleneethynylene)-polystyrene-oligo( p-phenyleneethynylene) (OPE-PS-OPE) in a toluene/hexane mixture as well as of C60-Poly(ethylene oxide)-C60 in a chloronaphthalene/benzene mixture. (2) The formation and fragmentation of 4-arm-PS-SH cluster in toluene via the oxidization in air to form disulfide crosslink as well as the decomposition of the resultant cross-linked 4-arm star polystyrene clusters with reversible disulfide groups in toluene via reduction to thiol group by 2,3-dihydroxy-1,4-butanethiol (DTT).; In Chapter 1, theories cited background of these studies as well as chemical synthesis methods used are introduced.; In Chapter 2, theories of static and dynamic light scattering (LLS) as well as details of the LLS instrumentation are introduced, especially the application of LLS to polymer solutions.; In Chapter 3, we present the study of the self-assembly of oligo( p-phenyteneethynylene)-based coil-rod-coil and rod-coil-rod triblock copolymers in the solvent mixture of toluene and hexane by using a combination of static and dynamic laser light scattering. UV-vis spectroscopy and fluorescence spectroscopy. Our results reveal that the aggregation in the solvent mixture is strongly influenced by the triblock copolymer structure. For the coil-rod-coil (PS-OPE-PS) triblock copolymer, small well-defined aggregates are formed in the solvent mixture with different toluene/hexane ratios. The coiled PS blocks entangle with the OPE block to restrict possible pi-pi stacking and make the OPE chain backbone more planar. The red-shift in the UV-vis and fluorescence spectra indicates the formation of 3-type aggregates. The rod-coil-rod (OPE-PS-OPE) triblock copolymer chains form large "disk-like" micelles with an ordered OPE core and a collapsed PS shell. The blue-shift in the UV-vis and fluorescence spectra shows the formation of H-type aggregates; namely, the OPE block in the core are parallel to each other so that there is stronger interchain pi-pi interaction.; In Chapter 4, we present the study of the aggregation of C60-PEO-C 60 chains in the chloronaphthalene/benzene solvent mixture with different ratios by using a combination of static and dynamic laser light scattering. Chloronaphthalene is a good solvent for C60 but a poor solvent for the PEO chain. On the other hand, benzene is a good solvent for the PEO chain but a poor solvent for Co. Individual polymer chains or small micelles coexist with large aggregates in solvent mixture. Our results show that the structures of the aggregates strongly depend on the composition of the solvent mixtures, which reflects in different ratios of <Rg>/<R h>, where <Rg> and <Rh> are z-average root-mean-square radius of gyration and hydrodynamic radius, respectively.; In Chapter 5, we present a study of reversible formation and decomposition of star polymer clusters. First, we synthesized 4-aim bromide-end star polystyrene chains by using atom transfer radical polymerization (ATRP), and then modified the end group from bromide to thiol since it can be slowly oxidized in air to induce the clustering among 4-arm star polystyrene chains. The clustering is reversible under a reduction condition. Such formation and fragmentation (decomposition) of the polymer clusters in toluene was followed by LLS. To induce the reduction, DTT was added. Our results reveal that in the clustering, the fast mode is attributed to the cooperative diffusion of individual 4-arm star polystyrene chains (unimers), while the slow mode is related to the diffusion of large clusters. In the fragmentation, the slow mode becomes fast and its intensity contribution decreases as the reduction time increases, reflecting the decreases of the size and the number of large polymer clusters. Our results suggest that the clusters fragmentation indu...