Surface initiated polymerization of conjugated polymers by KCTP (Kumada Catalyst Transfer Polycondensation) efficient grafting methodologies, structure function relationship and organic electronic device fabrication
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In this dissertation, synthesis of conjugated polymer brushes of poly(3-methylthiophene) (P3MT) via SI-KCTP (Surface Initiated Kumada Catalyst Transfer Polycondensation) and their applications is discussed. These conjugated polymer brushes have unique optical and electronic properties and hence they are thoroughly investigated for applications in fabrication of more efficient organic electronic devices (OEDs). These devices have definite requirements in terms of grafting densities and directionality of polymer brushes. Therefore to have a thorough understanding, their unique properties are evaluated by systematic analysis of their structure-function relationship and limitations. The current problems associated with their limited applicability in OED fabrication are also studied. With this thorough understanding, optimal P3MT brushes have been developed and applied for successful OED fabrication. Covalent immobilization of polymer chains to substrates prevents delamination and provides a method to make uniform coatings on objects of complex geometries. Utilization of “grafting from” approach has proved to be efficient towards producing uniform and mechanically robust films. SI-KCTP begins with fabrication of reactive initiator monolayers from substrate surfaces and uses highly reactive catalysts like Ni(0) or Pd(0). The catalyst centers are prone to enter into a competitive side reaction called disproportionation, whereby catalyst concentration on the surface is reduced. This reduces grafting density and also indirectly affects the directionality of polymer brushes. The structure of these monolayers highly influences the rates of disproportionation reactions. A detailed systematic study is performed in order to understand the structure-function relationship of reactive initiator monolayers to the nature of P3MT brushes grown. This led us to develop the optimal initiator monolayer which produced P3MT brushes, appropriate for usage in OEDs. To prove the efficiency of the new reactive initiator monolayer towards OED fabrication, organic spin valve devices (OSVs) are fabricated with P3MT brush acting as the non-magnetic spacer layer covalently bound to ferromagnetic electrode. The device showed highly enhanced magnetoresistance response. This encouraging result proves the potential of the new monolayer. It also justifies the hypothesis that spin coating produces more disordered layers, reducing device efficiency by poor contact with surfaces and enhancing intermolecular rather than intra molecular carrier transport. Further, these brushes are considered for potential application towards heat conducting devices since they have shown high thermal conductivities on measurement by the time domain thermoreflactance (TDTR) technique. Rapid and efficient electrochemical techniques are also examined to overcome problems associated with traditional solution deposition ones.