Title

Morphology and Properties of Styrene-Based Block Copolymers (BCPS) and Self-Assembled Hybrid BCP/Inorganic Nanocomposites

Author

Tety Kwee

Date of Award

2005

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Polymers and High Performance Materials

First Advisor

Kenneth A. Mauritz

Advisor Department

Polymers and High Performance Materials

Abstract

Due to the ability of block copolymers (BCPs) to self-assemble and form microphase separated morphologies, a great deal of interest has been focused on developing unique materials utilizing this self-assembly behavior. Substantial research in this area has led to new opportunities to create novel organic/inorganic nanocomposites, in a sense that an inorganic phase that imparts certain characteristics or properties can be selectively incorporated into a specific domain. Ultimately, the central theme of this research involves creating BCP/inorganic nanocomposites based on a sol-gel process, and subsequently evaluating the morphology and thermo-mechanical properties of these nanocomposites. BCP/inorganic nanocomposites were created in-situ based on the sol-gel polymerization of hydrolyzed tetraethylorthosilicate (TEOS) monomers and other types of organo-alkoxysilane monomers using sulfonated BCP as morphological template. Several types of BCPs are used as morphological template to create these nanocomposites. Linear poly(styrene- b -maleated ethylene-co -butylene-b -styrene) (mSEBS) that consists of 28 wt% of PS in the outer block and ethylene-co -butylene mid-block. In addition, various architectures of BCPs based on polyisobutylene (PIB) middle block and PS outer blocks were also used in this regard. The morphologies of these BCPs were evaluated prior to nanocomposite fabrication. The unmodified mSEBS, assumed hexagonally packed PS cylinders (HPC), and this morphology remained unperturbed at low sulfonation levels. As the sulfonation level increases, these PS cylinders become 'frustrated' implying that there are chain associations in the form of hydrogen bonding within the sulfonate groups. The sulfonated mSEBS (smSEBS) morphologies become further 'frustrated' upon inclusion of the silicate phase, suggesting that the formation of the silicate quasi-network impedes the kinetic mobility of the sulfonated PS (sPS) chains during film formation, consequently disrupting the long-range equilibrium microstructures. The types of silicate monomers and BCP architecture also influence the size, shape, and distributions of the silicate particles. Large and non-uniform silicate particles were seen in the nanocomposites derived from semi-organic monomers with large pendant groups. Similarly, the silicate structures also became increasingly irregular with increasing number of arms in BCPs. These results suggest that there is an inherent competition between the diffusion rate of the silicate monomers and BCP film formation. (Abstract shortened by UMI.)