Synthesis, Structure and Dynamics of Block Copolymer Based Organic Inorganic Hybrid Materials

Cornell University, Ithaca NY

Investigators

Abstract

In this research the synthesis, structure, structur-formation and dynamic mechanical behavior of block-copolymer-based, nano-structured organic-inorganic hybrid materials from organically modified ceramic (ORMOCER) precursors will be studied. To this end first a whole range of poly(isoprene-block ethyleneoxide) (PI-b-PEO) diblock copolymers with varying PEO volume fraction and narrow molecular weight distribution will be synthesized by anionic polymerization. These will be used as structure directing agents in the sol-gel process of a mixture of two metal alkoxides, added to the block copolymers in different amounts. In this way the full phase space for the mixture of PI-b-PEO diblock copolymers of various compositions with the inorganic materials will be explored. Special emphasis will be put on the synthesis of organic-inorganic hybrid materials with the bicontinuous gyroid morphology, a particularly interesting structure in block copolymers. The resulting structures will be analysed by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) measurements. Results of this part will lead to a phase diagram comparable to that of diblock copolymer/homopolymer mixtures. Analysis of details of the phase diagram will be facilitated by the possibility to look at frozen-in, local transition domains in biphasic regions of the phase diagram simply by dissolution of block copolymer rich bulk samples. Furthermore, the large variability in the polymer as well as the sol-gel chemistry will be explored to synthesize hybrid materials with unknown property profiles. For particular compositions of the mixtures of organic and inorganic precursors the structure formation process during evaporation of the solvent under heating will be investigated using in-situ SAXS. By correlating these results with solid-state NMR measurements on silicon and aluminum, insights into the interplay between sol-gel chemistry and phase separation as well as into the pathways towards the final morphologies will be obtained. Finally, the present study will allow for a systematic investigation of the dynamic mechanical behavior of the resulting organic-inorganic hybrid materials. These materials can be looked at as model systems for the understanding of the mechanical behavior of commercially important polymer-clay nanocomposites. It is expected that this program will lead to advances in the fundamental understanding of the mechanisms of formation and behavior of structured block copolymer-silica hybrid materials. At the same time it will provide student training and learning at the interface between polymer science and inorganic chemistry.