The study of dendritic block copolymers having cross-linkable polyisoprene blocks

Abstract

Block copolymers (BCPs) are macromolecules composed of two or more distinct polymer blocks joined together by covalent bonds. BCPs have been highlighted as self-assembling molecules for creating well-defined nanostructures in bulk and solution, which are potentially valuable materials for drug delivery system, catalyst carrier, and separation membrane. Well-defined mesoporous structures can be directly created by self-assembly of BCPs in solution. For the formation of well-defined porous structures by self-assembly, the architectures, molecular weight of constituting blocks, and their molecular weight ratios have to be carefully adjusted. Also, the conditions for self-assembly have to be optimized. By carefully design and synthesis of the structural components of BCPs, preferential self-assembly in solution into well-defined porous structures has been demonstrated. However, the BCPs in the well-defined nanostructures are only held by non-covalent interaction. These porous nanostructures are unable to be used under harsh environments. Therefore, it is desirable that the self-assembled mesoporous structures are covalently stabilized to resist harsh conditions such as the presence of organic solvents, high temperature, extreme pH, and physical stress. In this thesis, I show the synthesis of block copolymers composed of a branched hydrophilic poly(ethylene glycol) (PEG) block and branched hydrophobic polyisoprene (PI). PI possesses a low glass transition temperature (Tg) and main-chain and pendant vinyl groups that can be used for cross-linking. I investigated the effect of architecture and block ratio of these BCPs on their self-assembly behaviors in solution. The covalent stabilization of the self-assembled structures of these block copolymers was carried out by cross-linking of PI blocks. The effect of the cross-linking of the PI domain on the structural stability of the nanostructure was investigated under harsh conditions.