Investigation On Conductivity And Self-Assembly Of Amphiphilic Copolymers Prepared By RAFT Polymerization

Reversible addition-fragmentation chain transfer polymerization (RAFT) has been utilized to design and synthesize copolymers with well-defined structures and the incorporation of RAFT approach into dispersion polymerization allows for facile, direct and highly efficient in situ preparation of self-assembled nanoparticles with various morphologies including even uncommon ones in polar or nonpolar media. The ease of execution, solid content varied in a relative wide range and the long term stable structures highlight this technique. Producing such nanostructures with different shapes has significantly broadened its applications as catalysts, delivery vehicles, nano-reactors, etc. Although large amounts of polymeric species with different shapes and morphologies have been reported recently, it is essential to continuously investigate the properties of amphiphilic diblock copolymers in the solution.This thesis mainly discusses the relationship among the length of blocks, conductivity of polymerization systems and self-assembly behavior. The main outlines are listed below.(1) Water soluble dithiobenzoate-terminated polymethacrylic acid (PMAA-CADB) was synthesized by RAFT polymerization of MAA using 4-cyanopentanoic acid dithiobenzoate (CADB) as chain transfer agent. RAFT dispersion polymerizations of MMA were carried out in ethanol by using PMAA-CADB (Degree of polymerization is 30,122 and 450) as macro chain transfer agent (CTA) and V-65 as initiator. The variation of electric conductivity was traced during RAFT polymerization and the products of polymerization were characterized by 1H NMR, SEC and SEM/TEM. In contrast to the random copolymerization systems, the dramatic increase of conductivity at the beginning stage of RAFT polymerization was contributed by the charged solvophobic blocks in the soluble diblock copolymers. The conductivity increased as the length of PMMA block increased.(2) Objects of PMAA-b-PMMA were prepared by three methods i.e. the polymerization-, temperature- and ion-induced self-assembly. One was the spherical particles directly created during the dispersion polymerization at the high content of MMA. Secondly, temperature-induced self-assembly occurring at 0℃ produced self-assembled objects as spheres, worms and the mixture of spheres and worms. This process was controlled by both the length of PMAA block and total solid content of copolymers. Thirdly, diblock copolymers were deposited on the electrodes in the DC field and formed membranes or flat objects by adding saturated solution of KCl/ethanol. As a result, the proceeding of self-assembly resulted in the dramatic decrease of conductivity. It is obvious that electrostatic interaction played a role in the process of self-assembly.