Development of supramolecular structuredbenzoxazine dimers and their potential applications

Abstract

The present work focuses on molecular design and development of benzoxazine dimer structures for their potential applications. In the first part, a series of N,N-bis(2-hydroxybenzyl) alkylamine, so called benzoxazine dimers, are prepared via a simple and selective ring-opening reaction of benzoxazines with the yield as high as 90%. These compounds perform dual functions as initiator and catalyst for ring-opening polymerization of lactide. Two hydroxyl groups of benzoxazine dimers are initiated by organocatalyst to be initiator. By simply varying methylene bridge, very active ligands for alkyl/alkoxide aluminium complex formation can be clarified. Metal-ligand complexes are proved to be catalysts in ring-opening polymerization of lactide. Polylactides obtained are polymerized with narrow polydispersity index and well controlled molecular weight. In the second part, for the first time, a thermochromic free-standing poly(ʟ-lactic acid) film is studies. By simply constructing tetra-branched benzoxazine dimers from pentaerythritol followed by ʟ-lactide ring opening polymerization initiated by organocatalyst as well as the conjugation with diacetylene at terminal, a precise eight-armed poly(ʟ-lactide) conjugated diacetylene can be obtained. The blend with poly(ʟ-lactic acid) followed by solution casting leads to the thermochromic free-standing film. The comparative studies declare that bulk diacetylene and other linear-, four- and multi-armed poly(ʟ-lactide) terminated polydiacetylene do not show thermochromic property. The microstructure analysis indicates the symmetric eight-armed structure controls the packing of polydiacetylene in poly(ʟ-lactic acid) matrix upon heating and cooling. From these two works, the benzoxazine dimers can be noticed to be one of the choices for decorating star and/or multi-branched polylactide. In the final part, the work covers a convenient, environmentally friendly, and simple procedure to obtain benzimidazoles through the cyclization between aldehyde and phenylenediamine derivatives under reduced pressure. This synthesis pathway not only gives the benzimidazoles with high yield from the mild condition but also the selection of benzaldehyde and phenylenediamine with reactive functional group leads to the precursor for synthesis a new class of benzoxazine dimer with pH-sensitive fluorescent intensity and multichromatic emissions.