Preparation And Properties Of Carboxyl-functionalized Poly (Arylene Ether Nitrile) Rare Earth Coordination Polymer

With the continuous advancement of the"Industry 4.0"and"Made in China 2025"strategies,high-end manufacturing fields had increasingly high requirements for the functionality of special engineering plastics,especially in optical,electrical,magnetic and other fields.The development of these fields provided new ideas for the development and application of new materials.In this paper,a series of rare earth coordination polymers were prepared by utilizing the copolymerization method to introduce functional carboxyl groups into the poly(aryl ether nitrile)molecule,the rare earth ions were coordinated with the carboxyl-functionalized poly(arylene ether nitrile)(CPEN),and the structure,properties and applications of rare earth coordination polymers were also investigated in detail.Firstly,the functional monomer phenolphthalin was synthesized based on the molecular structure design,which reacted with 2,6-dichlorobenzonit-rile and bisphenol A through the nucleophilic aromatic substitution polymerization to afford CPEN.The FTIR showed that the stretching vibration peak of carbonyl group in the free carboxyl group(-COOH)appeared at 1725 cm^-1,which confirmed that the carboxyl group was successfully introduced into the structure of poly(arylene ether nitrile).At the same time,the NMR further confirmed the structure of the polymer was consistent with molecular structure design.The weight average molecular weight(Mw)was 64.88 Kg/mol.The polymer possessed a high glass transition temperature(T_g=195°C)with good thermal-oxidative(T_5%=426°C)and pretty tensile strength(80MPa).The strongest peak of emission spectrum was located at 457nm,showing blue fluorescence.Besides,the fluorescence emission intensity increased with the increase of solvent polarity.Secondly,a series of rare earth coordination polymers were assembled by employing CPEN was used as a polymer ligand,europium(Eu³⁺)and terbium(Tb³⁺)ions were luminescent centers,and 1,10-phenanthroline(Phen)and 8-hydroxyquinoline(HQ)were served as small molecular ligands.FTIR,UV-vis and XPS proved that rare earth ions were coordinated simultaneously with the oxygen atoms in the carboxyl group of CPEN and the nitrogen atoms of Phen.CPEN-Eu³⁺-Phen had a high T_g(251°C)and excellent thermal stability(T_5%exceeded 320°C),which was mainly due to the excellent thermal properties of the macromolecular ligand CPEN.The emission intensity of CPEN-Eu³⁺-Phen was about 70 times higher than that of CPEN-Eu³⁺-HQ owning to much better match between the lowest triplet energy level of Phen and the vibrational energy level of Eu³⁺in comparison with HQ.Compared with the binary complexes,the emission intensity of the ternary coordination polymers were significantly improved due to the synergistic effect of CPEN and Phen ligands,which could effectively transfer the energy of the ligands to Eu³⁺through non-radiation,thereby significantly enhancing the intrinsic emission intensity of Eu³⁺.In addition,the emission intensity of CPEN-Eu³⁺-Phen increased with the enhancement of Eu³⁺ion content,then the emission intensity started to decrease until the critical concentration reached 11.5wt%,which was due to the fluorescence concentration quenching effect.Afterwards,a series of color-tunable(from red to green)coordination polymers had been developed by adjusting the Eu³⁺/Tb³⁺ratio on the basis of RGB trichromatic principle.Therefore,the coordination polymers had great applications in luminescent devices,which could serve as a luminescent detection sensor in special environments(such as high temperature environments,extreme environments).Finally,a kind of novel nanofibers prepared by electrospinning utilizing aforementioned CPEN-Eu³⁺-Phen as fluorescent probe could serve as a simple and reliable light-emitting platform for identifying selectively Fe³⁺ions.The micromorphology showed that the nanofibers were evenly distributed and the surface was smooth.The normalized fluorescence intensity of CPEN-Eu³⁺-Phen nanofibers remained basically unchanged under the Na Cl concentration of 0-1.0 M and p H between 1to 14,exhibiting excellent fluorescence stability.In addition,the nanofibers presented moderate hydrophobicity,which was conducive to improve the reproducible stability of the sensor.More importantly,the titration experimental results showed that the red fluorescence was notablely quenched with addition of Fe³⁺ions,which was attribute to the competition absorption effect between Fe³⁺ions and CPEN-Eu³⁺-Phen nanofibers.The Stern-Volmer equation was used to evaluate the fluorescence quenching process,and the detection limit for Fe³⁺ions in aqueou solution was as low as 3.4?M.It was noteworthy that the CPEN-Eu³⁺-Phen nanofibers implied excellent cycling performance for Fe³⁺ions with less loss of fluorescence intensity after eleven consecutive quenching and recovery cycles on account of its surface hydrophobicity.In brief,these results indicated that CPEN-Eu³⁺-Phen nanofibers were expected to serve as an excellent luminescent sensor for Fe³⁺ions detection selectively in aqueous solution.