Supramacromolecules: Structure/Property Control via Self-Assombly with Well Defined Macromolecules

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

Macroscopic properties of solids, e.g., polymeric materials, result from the combination of molecular structure and macroscopic organization or order. Polymer chemists have become adept at covalent synthesis of macromolecules that can be designed to be amophous, crystalline, bi- or tri-phasic, etc. On the other hand the central aim of supramolecular science is to design building blocks with the proper structure that allows them to self-assemble by noncovalent boding at the molecular level. Synergistic combination of the principles of these two fields should enable more precise design and control of macroscopic structure and properties by utilizing properly designed macromolecular building blocks, i.e., more macroscopic control should result from the use of such precisely defined structural units. %%% The primary goals of this project are to apply self-assembly, to form pseudorotaxane structures, to well defined macromolecular host and guest species and study the structures and properties of the resultant supramacromolecular materials. Using living polymerization protocols constructed and then allowed to self-assemble into a variety of noncovalent analogs of various types of block and graft copolymers, which will be studied and compared to the corresponding covalent analogs when these are available. Pseudorotaxane formation is reversible and this feature can be exploited to enable facile melt processing of mechanically linked (vs. Covalently linked) polymeric systems, which disassemble upon heating to lower molecular weight and lower viscosity building blocks; upon cooling self-assembly is expected to produce solid state features of phase separation, blend compatibilzation and enhanced mechanical properties associate with classical covalent block and graft copolymers. Additionally a great advantage of this modular approach is that from a few precisely defined macromolecular building blocks a large library of two and three dimensional structures can be self-assembled without further synthetic effort. Furthermore, the pseudorotaxane linkage is selective in terms of the cyclic/linear components (in a complementary lock and key fashion) and this gives rise to the possibility of control over the orientation and connectivity of building blocks, allowing construction of novel ensembles, including noncovalent analogs of ABC triblock copolymers.