Control Of Morphologies Of Polymeric Aggregates

Block copolymers have drawn much attention due to their unique behaviors and potential applications, such as thermoplastics, modifiers, solubilizers, and surfactants etc in industry. It is well known that the properties of polymer materials mainly depend on their architectures and morphologies. So investigation on their relationships and fabrication of polymer materials with expected properties for special application are very meaningful. Therefore, this dissertation focuses on the preparation of various polymeric aggregates and the possible factors that will affect the morphologies of polymeric aggregates. The main results achieved in this dissertation are as follows:1) Amphiphilic block copolymers, PEO-b-PNAS have been successfully prepared by ATRP of NAS using PEO-Br as macro initiator. The stable core cross-linked micelles were obtained via the substitution reaction of oxysuccinimide of NAS units in the cores of micelles by ethylenediamine. The self-assembling of the core cross-linked PAM-b-PEO micelles on silicon wafers or glass slides formed flower-like aggregates. The possible factors such as the evaporation rate of solvent, relative chain length ratio of PNAS and PEO, and various substrates that will influence the formation of ordered aggregates have been discussed in detail. And this study will help us to understand the relationship between morphologies prepared from the micelles and self-assembling conditions. Meanwhile, one route is provided for preparation of various interesting morphologies.2) Various morphologies formed by PS-b-PEO have been successfully prepared by RAFT dispersion polymerization of St in methanol using PEO-TC and AIBN as macro RAFT agent and initiator, respectively. During the polymerization, formation and self-assembling of PS-b-PEO, and morphology transition have been achieved in one-pot. The determinant for morphology transition is the chain length ratio increase of PS to PEO blocks. By changing the feed molar ratio, the polymerization time, and concentration of St in methanol, the spherical micelles, nanowires and vesicles can be prepared. Thus we provide a feasible strategy for preparation of predeterminant polymeric morphologies.3) The RAFT polymerization of St in methanol using PDMAa-SC(S)S-PDMAa as macro RAFT agent can produce various morphologies including spherical micelles, nanorods, vesicles and large compound vesicles formed by PDMAa-b-PS-b-PDMAa. In this PISR system, the formation of PDMAa-b-PS-b-PDMAa, self-assembling and morphology transitions are successfully achieved in one-pot. In comparison with the diblock copolymer-formed RAFT polymerization, the triblock copolymer-formed polymerization showed different morphology transition behaviors, the sphere-to-rod, rod-to-vesicle and vesicle-to-large compound vesicle transitions occurred at low chain length ratio of PS/PDMAa. These are related to the bent triblock copolymer chains in the aggregates, but the diblock copolymer chains are extended in the aggregates. The triblock copolymer chains in the folder form or in the extended form can be controlled by changing feed molar ratio and St concentration.4) A facile method for direct preparation of functional polymeric nanomaterials based on living radical polymerization is developed. Spiropyran-based photochronic polymer vesicles have been produced via RAFT dispersion polymerization of St in methanol using P(4VP-SPMA)-TC as macro RAFT agent and stabilizer. In comparison with the polymer in DMF solution, P(4VP-SPMA)-b-PS in vesicles after UV irradiation showed stronger fluorescence and more excellent reversible photochromism in the same concentration of polymer. One factor contributing to these phenomena may be that the conformational flexibility of the polymer chains was restricted and bimolecular photodegradation reactions that involve the triplet excited states were minimized when the photochromic polymers were attached in vesicles.5) A convenient approach for preparation of ring-shaped polymeric aggregates has been introduced. Triblock copolymer, PS-b-PEO-b-PS has been successfully synthesized via RAFT dispersion polymerization of St in methanol using TC-PEO-TC and AIBN as macro RAFT agent and initiator, respectively. For the first time we found an interesting morphology transitions, the sphere to rod, then to ring, and finally to vesicle. The chain length ratio increase of PS to PEO blocks plays an important role in the morphology transitions. By altering the feed molar ratio, concentration of St, the polymerization time, aggregates with various morphologies can be obtained easily. Meanwhile, the possible mechanism of the formation of ring-shaped aggregates was discussed.