Molecular Bottlebrushes with Controlled Architectures: Synthesis and Self-Assembly
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Molecular architecture plays an important role in bottlebrush copolymer self-assembly. Using the ‘grafting-through’ approach, multicomponent bottlebrush copolymers with highly controlled architectures were synthesized and characterized by SEC and 1H NMR. Their self-assembly behavior was subsequently investigated with SAXS and electron microscopy. In the first part of this work, detailed synthesis of gradient bottlebrush copolymers is described. Compositional gradient was readily introduced by copolymerization of exo- and endo-norbornene capped macromonomers through ROMP. Kinetic studies confirmed spontaneous formations of bottlebrush copolymers with gradient interface. A series of PS-PLA gradient bottlebrush copolymers were synthesized using the developed protocol. When side chain lengths were kept uniform, PS-PLA gradient bottlebrush copolymers exhibited rich phase behavior producing lamellar, gyroid and cylindrical morphology contrasting the lamellae-dominant phase behavior of their block analogues. In the second part of this dissertation, syntheses of block-statistical hybrid and multiblock bottlebrush copolymers are described. In block-statistical hybrid bottlebrush copolymer, three components were distributed in two segments. PLA and PnBA side chains were statistically distributed along the backbone in the first segment while the second segment consisted of exclusively PS side chains. Such side chain arrangement led to the formation of hierarchical lamellar morphology with two distinct domain spacings. One domain spacing reflected the phase separation within the first segment between statistically distributed PLA and PnBA side chains and the other corresponded to the phase separation between the PLA-PnBA segment and the PS-exclusive segment. Multiblock bottlebrush copolymers were synthesized by sequentially polymerizing PS and PSM macromonomers. Tetrablock and hexablock PS-PSM bottlebrush copolymers were prepared and their self-assembly behavior was explored. Upon hydrolysis of PSM component, both samples self-assembled into well-ordered lamellar morphology. These studies together with the first part of this dissertation show how bottlebrush architecture can be used to manipulate the polymer self-assembly behavior.The last part of this thesis describes ‘grafting-from’ synthesis of ABA triblock bottlebrush copolymers with reactive end blocks. In this work, we took advantage of the rigidity of bottlebrush polymers to construct polymer networks with persistent and tunable pore sizes. Polymeric backbones were first prepared by ROMP and subsequently grafted with various types of side chains using ATRP. Cross-linking of end-reactive triblock bottlebrush copolymers with PMMA side chains produced polymer gels.