DESIGN OF MECHANOPHORE-CONTAINING PIB-PS BLOCK COPOLYMERS FOR DETERMINATION OF MOLECULAR-LEVEL STRUCTURE/PROCESSING/PROPERTY RELATIONSHIPS UNDER IMPACT

The focus of this dissertation is to design and synthesize model systems that can be used to determine the influence of polymer architecture and morphology on high shear rate impact response. This was done by creating a series of phase separated polyisobutylene (PIB)-polystyrene (PS) block and graft copolymers with and without an anthracene-maleimide mechanophore at the soft segment/hard segment interface. Studying the fundamentals of polymer architecture and morphology to establish the structure-processing-property relationships is critical for the rational development of protective coatings and blast mitigation. The first chapter provides an introductory overview on many of the parameters that govern high impact response and some of the tools used, such as laser induced projectile impact test (LIPIT), Split Hopkinson bar, and the use of mechanophores to probe stress concentration under extreme conditions. In the second chapter, the synthesis and morphology of high molecular weight mechanophore containing PIB-b-PS block copolymer is presented to investigate how the incorporation of the mechanophore units affects the resultant morphology. The addition of a mechanophore does not significantly change the morphology but other parameters such as annealing time, solvent and dispersity have a profound effect. In the third chapter, a series of multi-mechanophore graft copolymers is synthesized and characterized to investigate the effect polymer architecture has on morphology and scission events. The graft copolymers do not form well-ordered morphologies but there is a significant influence on phase separation and domain size with different grafts. Using pulsed ultrasound experiments, we found greater backbone scission occurs for polymers with a greater number of short grafts per chain than those with fewer, long grafts. In the fourth chapter, the tensile properties of block copolymers are related to their morphologies. Young’s modulus is shown to increases in the order: disordered \u3c cylindrical \u3c lamellar morphology, which corresponds to an increase in the connectivity of the PS domains. Methods for solid state mechanophore activation and preliminary data from high strain rate impact testing are discussed. Finally, chapter five looks at the major conclusions from this work and suggests future work that would be of interest to explore