Two-dimensional organic molecules for two-photon absorption, aluminum alkyl complexes initiated polymerizations, and unimolecular living radical polymerization initiators

A study of structure-property relationship on two-photon absorbing chromophores showed that highly symmetric and conjugated molecular structures exhibited larger two-photon absorption cross-section in comparison to their counterparts with lower symmetry. A number of symmetric two-photon absorbing chromophores were developed. Measurements of their optical properties showed that cross-sections were further enhanced upon (i) attachment of electron donating groups, such as substituted amino groups, to the symmetric structures; (ii) extension of the conjugation length; and (iii) replacement of conjugated π center with an sp3 hybridized nitrogen atom. Two-photon absorbing polymers and a dendritic structure of symmetric molecules were also synthesized and characterized.; A series of bulky aluminum complexes were synthesized and characterized. For the first time, they were found to be active initiators towards the polymerization of acrylates. Coordination of methyl acrylate to aluminum complexes was observed by variable-temperature nuclear magnetic resonance spectroscopy. Adducts of methyl acrylate to aluminum complexes were isolated and characterized by both 1H and 13C nuclear magnetic resonance spectroscopy. The proposed mechanism involved a radical process where the radicals were produced by an assisted homolysis of the Al-alkyl bond. A kinetic study of the methyl acrylate polymerization initiated by bulky aluminum complex showed that the rate of polymerization was first-order with respect to the monomer concentration and half-order with respect to the concentration of aluminum initiator. Further investigation showed bulky aluminum complexes were also active in the initiation of the polymerization of styrene and some other monomers.; A facile one-step synthesis of an unimolecular initiator, 2,3-dimethyl-4-phenyl-4-(2 ′,2′,6′,6′ -tetramethylpiperidinoxy)butanitrile, was developed for “living” radical polymerization study. A “living” polymerization of styrene was observed by the initiation of the synthesized initiator. Functional polymers, such as polyacrylamide and polyacrylic anhydride, were also synthesized in the presence of the above initiator. However, further study showed that the polymerizations were not “living”.