Controlling Polymer Molecular Structure and Morphology: From Illumination of Conjugated Polymers to Polymer Chain Depolymerization

Polymers remain a prominent component of our lives, and finding methods to control their structure or morphology are needed to tune material properties. This dissertation reports methods to alter the conformation, morphology, or structure of polymeric materials. Chapter two describes the impact of exposure to white light during annealing of conjugated polymer blends on their morphology and optoelectronic performance. The observed changes in the morphology correlate strongly to the variation in photoluminescence (PL) with illumination, including that the PL varies less with illumination at higher Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] loadings, offering foundational understanding to guide the structure and optoelectronic performance of conjugated polymer blend films with illumination.

Chapter three describes the impact of exposure to synchrotron X-rays on the molecular structure of conjugated polymer solutions. These studies show that exposure of poly(3-hexylthiophene) in d-styrene to X-rays during synchrotron SAXS experiments results in the formation of radicals on the poly(3-hexylthiophene) (P3HT) that react to increase the polymer chain size, and continue to cascade long after the sample is removed from the X-ray beam. Supporting experiments reinforce the interpretation that deuterated polystyrene grafts to the P3HT, where the grafting reaction is dominated by X-ray exposure time. This reaction involves the rapid formation of graft points followed by the growth of deuterated polystyrene grafted chains. This study exemplifies the need to carefully plan synchrotron experiments, so as not to unexpectedly alter the structure of the targeted system.

Chapter four examines the evolution of chain structure during the glycolysis depolymerization of polyethylene terephthalate. We hypothesize that by intercepting intermediates in the depolymerization, telechelic oligomers can be captured that can also be used as reactants to produce value-added goods. These results show that a broad range of molecular weights (3,000 – 10,000 Daltons) are accessible at high yields with the heterogeneous reaction at lower temperatures, while increasing the temperature or using a homogeneous reaction limits accessible molecular weights and limits yield. This study shows that controlling the glycolysis depolymerization offers pathways to isolate targeted value-added oligomers. These materials can then serve as reactants to produce block copolymers, which are potential compatibilizers of PET blends.