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Abstract

A series of amphiphilic ortho-phenylene ethynylene oligomers has been synthesized from a tetramer to a hexadecamer. Several synthetic approaches have been investigated including (i) a classic iterative convergent/divergent synthesis, (ii) a stepwise synthesis on a soluble support resembling Merrifield’s solid-support methodology, and (iii) the controlled oligomerization of a suitable shorter oligomer to access longer oligomers and their subsequent isolation from the reaction mixture. The oligomers were designed with suitable side chains contributing amphiphilicity as well as chirality and enabling helical folding among these oligomers as demonstrated by optical spectroscopy.
A novel π-conjugated polymer based on an ortho-alternating-para-phenylene ethynylene backbone was designed, successfully synthesized, and spectroscopically analyzed. An adequate multi-purpose side chain based on a natural amino acid was synthesized fulfilling the requirements of polarity, chirality, and branched structure. The results from absorbance and emission spectroscopy strongly point towards helical folding in polar solvents.
The construction of a series of amphiphilic block copolymers based on a flexible PPO segment and an aromatic PE segment was achieved. The PPO segment was polymerized from enantiopure propylene oxide and optimization of reaction conditions yielded highly isotactic, non-racemic and thus optically active polymeric material of controlled length and low polydispersity. Para-PE and meta-PE monomers were successfully grafted from PPO segments of different lengths generating block copolymers of distinct architectures, i. e. rod-coil copolymers with π-conjugated aromatic blocks in the case of pPE repeat units and switchable segments of differing aspect ratios in the case of mPE repeat units undergoing helix-coil transitions. The influence of the connectivity among the aromatic segments as well as the influence of the length of the PPO segment on the block copolymers’ solution properties was analyzed in extensive spectroscopic studies.
Finally, the architectural modification of attaching PPO segments on trifunctional PE monomers and their subsequent polymerization lead to graft copolymers of respectable molecular weight. Spectroscopic characterization demonstrated the ability of the PE-backbone to fold.