Helices and Hamburgers from the Assembly of Linear ABC Triblock Copolymers in Block-Selective Solvents
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This Ph.D. thesis reports the discovery and study of several morphologies of ABC triblock copolymer assemblies in block selective solvents. One block copolymer self-assembled into helices (mostly double and some triple helices), and the other block copolymer formed a mixture of structures resembling hamburgers and striped cylinders. The helices, biomimmetic structures which are unusual from block copolymer self assembly, were prepared from the triblock copolymer poly(n-butyl methacrylate)-block-poly(2-cinnamoyloxyethyl methacrylate)-block-poly(tert-butyl acrylate) (PBMA-b-PCEMA-b-PtBA). They were formed spontaneously in several binary solvent mixtures including dichloromethane/methanol, tetrahydrofuran (THF)/methanol, and chloroform/methanol. They were formed in the composition ranges where the mixtures were good for the PtBA block, poor for the PCEMA block, and marginal for the PBMA block. The structure was studied and established by TEM, AFM, DLS and 1H NMR and by TEM tomography. The mechanism and kinetics of helix formation was examined. The Hamburger and striped cylinder structures were produced from poly(tert-butyl acrylate)-block-poly(2-cinnamoyloxyethyl methacrylate)-block-poly(succinated glyceryl monomethacrylate) or (PtBA-b-PCEMA-b-PSGMA) in mixtures of THF, (-)-sparteine and 1- or 2-propanol. Here THF solubilized all the blocks of the copolymer, while propanol was a precipitant for the middle block (PCEMA), and the chiral amine, (-)-sparteine, complexed with PSGMA and made it insoluble. Within the Hamburger-like structure, the “filling” was made of the complexed PSGMA chains and the "buns" were made of PCEMA. The striped cylinders were made of stacking alternating PCEMA and PtBA stubs. The PtBA chains were located on the outer surfaces of both of these structures. With the hamburger structures, after PCEMA crosslinking, we were able to remove the chiral amine by dialysis and make the PSGMA chains soluble again in solvents such as N, N dimethylformamide. The hamburgers were thus separated into two halves, with each half existing as a Janus particle, which had PtBA chains on one side and PSGMA chains on the other side. The Janus particles might have interesting applications, such as in Pickering emulsion stabilization.