Acrylic Polymers Containing a Nickel Salphen Complex: An Approach to Supramolecular and Macromolecular Systems

Abstract

The synthesis, characterization and crystallographic analysis is reported of a new Nickel Salphen complex and its radical copolymerization with n-butyl acrylate and methyl methacrylate to produce novel host macromolecules with tunable association against guest anions. Spectrophotometric titrations of the complex and of the polymers revealed that a supramolecular regulation of guest-binding accessibility was enabled by the number of Ni-Salphen units per chain. The latter content in turn, determined the chain size and molecular weight uniformity upon polymerization, and likely increased the strength in interchain/intrachain non-covalent interactions over the nickel center and the acrylic domains. The study also showed that incorporation of the monomer into the acrylic polymer backbone opened the possibility for the nickel binding site to gain access to host:guest stoichiometric discrimination, switching from 1 : 1 (major) and 1 : 2 (minor) both coexisting for the host when in the free form, to mostly 1 : 2 when in the polymerized version.

Enhanced Host‐Guest Association and Fluorescence in Copolymers from Copper Salphen Complexes by Supramolecular Internalization of Anions

“…Previous reports on copolymers integrated by minor compositions of one monomer and a major composition of a different monomer that occupied larger regions in the chains demonstrated that even subtle compositional variations rendered strong supramolecular effects that proceeded cooperatively. In these cases, the chain domains occupied by the major component in the macromolecule showed a strong susceptibility to conformational alterations produced by supramolecular contributions from the minor components to the rest of the structure [40,49] . Thus, we could assume a similar contribution from the Cu−Salphen monomer to the overall chain conformation not only in the solid state, but also in suitable solutions.…”

“…[53] Complex 1 and polymers 2 and 3 were synthesized following previously reported methodologies with some modifications. [37,40,43] TGA experiments were carried out under 2 flow at 10 °C min À 1 on a Perkin Elmer TGA4000 apparatus; T i = 30 °C, T f = 460 °C. DSC data was achieved under N 2 at 10 °C min À 1 on a Mettler Toledo DSC1 calorimeter at Unidad de Servicios de Apoyo a la Investigación y a la Industria (USAII) of the School of Chemistry-UNAM; conditioning cycles: 1) r.t. to 100 °C, 2) isothermal at 100 °C for 10 min, 3) 100 °C to À 100 °C, 4) isothermal at À 100 °C for 10 min; measurement cycle: 5) À 100 °C to 250 °C.…”

“…In these cases, the chain domains occupied by the major component in the macromolecule showed a strong susceptibility to conformational alterations produced by supramolecular contributions from the minor components to the rest of the structure. [40,49] Thus, we could assume a similar contribution from the CuÀ Salphen monomer to the overall chain conformation not only in the solid state, but also in suitable solutions.…”

“…We have previously exploited the great flexibility of Salphen compounds as supramolecular synthons in programmable soft‐matter [34] and self‐assembled materials, [35] optically transparent electroconducting composites, [36] solid‐state potentiometric sensors, [37] catalysis, [38] chirogenesis, [39] etc. Furthermore, we have recently shown that unsymmetrical allyl‐functionalized Ni−Salphen complexes can be readily polymerized under environmentally friendly conditions via radical initiation together with acrylic monomers such as methyl methacrylate (MMA) and n ‐butyl acrylate ( n BuA) at variable ratios [40] . In such work, we reported that the incorporation of the Ni−Salphen into a larger acrylic polymer chain rendered a stoichiometrically different host‐guest chemistry with benzoate anions than that of the non‐polymerized metal complex, without depending on the classical iterative ligand‐modification approaches.…”

“…Furthermore, we have recently shown that unsymmetrical allyl-functionalized NiÀ Salphen complexes can be readily polymerized under environmentally friendly conditions via radical initiation together with acrylic monomers such as methyl methacrylate (MMA) and n-butyl acrylate (nBuA) at variable ratios. [40] In such work, we reported that the incorporation of the NiÀ Salphen into a larger acrylic polymer chain rendered a stoichiometrically different host-guest chemistry with benzoate anions than that of the non-polymerized metal complex, without depending on the classical iterative ligand-modification approaches. The polymer chain facilitated the association of this carboxylic guest to the Nickel center giving 1 : 2 host-guest stoichiometry as a major product, contrarily to the native association for the nonpolymerized complex that rendered otherwise the 1 : 1 product as the predominant one.…”