Synthesis, morphologies and applications of polyoxometalate-containing diblock copolymers
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Block copolymers by virtue of their ability to self assemble and microphaseseparation due to the contrast in chemical and physical properties of the covalently linked blocks constitute the essential building blocks towards various nano or micro sized architectures. Polyoxometalates (POM), on the other hand, being an interesting class of metal-oxygen nanometer-sized anionic clusters, are regarded highly due to their excellent electron accepting capability. Combining POM clusters with diblock copolymers can lead to a fascinating class of hybrid materials where the POM cluster not only affect the selfassembly process of various diblock copolymers but also brings its unique electronic properties into the hybrid system. Herein we report the detailed synthesis and characterizations of two hybrid coil-coil diblock copolymers along with two hybrid rodcoil diblock copolymers through polymerization-hybridization approach. The coil-coil diblocks were synthesized via atom transfer radial polymerization (ATRP) of styryl-type monomers and 4-vinylpyridine in sequence. For rod-coil diblock copolymers, the coil block was synthesized through ATRP, followed by the conversion of the terminal bromide to an azide. Ethynyl terminated poly (p-phenylenevinylene) (PPV) and poly (3-hexylthiophene) (P3HT) were prepared separately as the rod blocks. The rod block and the coil block were connected through click chemistry to yield rod-coil diblock copolymers. After removing the phthalimide protecting groups to regenerate aryl amines, POM clusters were finally linked to the coil block of all diblock copolymers to yield the targeted hybrid diblock copolymers. The covalent cluster attachment was confirmed by UV-Vis spectroscopy, FTIR and cyclovoltammetry measurements. The structures, solution and film optical properties, self-assembled morphologies and solar cell performances of these hybrids have been studied. It has been found that solar cell devices based on hybrid P3HT exhibited rather poor performances. Fluorescence dynamic studies indicate that the photoinduced electron transfer process from the rod block to pendant POMs is quite inefficient which may account for the poor device performance. Though the self-assembly process of these hybrid diblock copolymers and the preliminary morphologies has been demonstrated, detailed and systematic study of morphological control requires further extensive research.
Table of Contents
Introduction -- Atom transfer radical polymerization of functionalized monomers -- Synthesis of coil-coil diblock copolymers with covalent attachment of polyoxometalate clusters to coil blocks -- Synthesis and optoelectronic properties of a PPV-based rod-coil diblock copolymer with polyoxometalate clusters covalently attached to the coil block -- Synthesis and thin film morphological studies of P3HT-based rod-coil diblock copolymer with polyoxometalate clusters covalently attached to the coil block