Polymers with Mechanically Linked Architectures

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

TECHNICAL SUMMARY: The goals of this project are to produce and characterize for the first time prototypes of two distinct classes of mechanically linked macromolecular structures: 1. supramolecular block copolymers in which the linkage between the blocks consists of pseudorotaxane or rotaxane units 2. polymeric catenanes in which the integrity of the polymer is due to mechanical linkages between adjacent cyclic units, i. e., true "polymer chains". To achieve these aims aspects of modern polymer chemistry will be combined with recent advances in supramolecular chemistry. A combination of anionic, atom transfer radical and nitroxide-controlled free radical polymerizations will be employed to prepare well-defined macromolecules with terminal host and guest functionalities; these will then be self-assembled into a variety of non-covalent block copolymers and in some cases compared to covalent analogs. The pseudorotaxane structures will be "locked-in" by conversion to rotaxanes through covalent attachment of stoppers. These well-defined new systems are expected to provide unique, reversible control of structure, morphology, rheology and mechanical behavior by response to external stimuli, such as heat, shear, pH, light and solvents. A novel approach to polymeric catenanes or polycatenanes, true polymer "chains", in which each cyclic repeat unit is connected to its neighbors only by mechanical linkages, is expected to produce uniquely flexible macromolecules with a built-in capacity for externally stimulated responses. NON-TECHNICAL SUMMARY: Traditional covalent block copolymers provide multiphase materials with high performance parameters such as appearance, strength, flexibility, barrier properties, retention of shape, etc. for materials used in everyday life, e. g., in adhesives, packaging films, rubbers and impact resistant plastics. The unique mechanically linked supramolecular block copolymers prepared in this effort will provide an entirely new class of such materials, and potentially will greatly improve their processability, recyclability and range of applications, e. g., synthetic muscles, gene and drug delivery, due to sensitive responses to external stimuli. The entirely new class of chain-like materials, the polycatenanes, are expected to exhibit unique mechanical properties, e. g., superb flexibility, again combined with sensitive responses to external stimuli, making them of interest in sensors and actuators, among other applications. The PI is actively associated with graduate and REU programs that successfully seek under-represented minorities and women students. This effort provides research-education opportunities for students in terms of both supramolecular and polymer sciences so that they will acquire a creative, interdisciplinary problem-solving approach, enabling them in their future careers to design, synthesize and implement enabling materials for practical applications such as in the bio- and nano-technology and energy fields.