Design, Synthesis, Properties And Applications Of Linear Conjugated Polymers Without Transition Metal Catalysis

Interest in the design and synthesis of ?-conjugated polymers has increased considerably over the past decades due to a variety of potential applications in various electronic devices.Conventionally,?-conjugated polymers are often synthesized by polycondensation processes based on the transition metal-catalyzed cross-coupling reactions.Unfortunately,these methods usually suffer from some drawbacks such as use of environmentally harmful transition-metal catalysts,costly,air sensitivity and extra synthetic steps.Moreover,the trace residues of transition-metal catalysts in the polymeric products can seriously affect the efficiency and service life of the end-use devices.Therefore,it is desirable to develop a transition-metal-free process for the preparation of high-quality,high-purity new conjugated polymers.Since the properties and usage of the conjugated polymers are highly dependent on the chemical structure of the repeating units in the polymers.Therefore,designing poly?arylene?s and poly?arylene-vinylene?s usually require lipophilic side group to be attached or incorporated 1,3-butadiene units into the polyphenylene backbone,which would be broaden properties and applications of the new polymers.And exploring a cheaper,lower toxicity,more convenient process and transition-metal-free controlled polymerization method toward conjugated polymers with many properties is of great academic significance and industrial implication.Herein is described a new and efficient method to synthesize a new class of conjugated polymers containing 1,3-butadiene units by polycondensation using an organic base as the catalyst instead of toxic transition metalbased catalysts.The synthetic strategy is based on the reaction of ?,?-unsaturated compounds containing y-H with aldehyde compounds.The optimal polymerization conditions,the possible mechanism,the other conjugated polymers and their properties and applications were explored and studied.The specific contents as follows:1)4-?4-formylphenyl?-2-butylene acid ethyl ester was designed as a model monomer and polymerized to obtain the alternating poly?phenylene-1,3-butadiene?.Various conditions,such as catalyst,catalyst amount,solvent,monomer concentration temperature and time were investigated to explore the optimal reactions.Based on the experiments,the polymerization proceeds efficiently in the optimal reaction conditions:0.1M monomer in the ethanol solvent with 0.2 equiv.DBU catalyst under reflux for 72 h can afford polymers with relatively high molecular weight and low PDI in high yields.2)Based on our previous work and a serious of exploring,a possible mechanism of the polymerization through a six-membered ring transition state and then a 1,5-H shift intermediate is proposed.3)With the optimized reaction conditions,a new series of conjugated polymers containing butadiene units with different substituent were synthesized,such as the conjugated polymers incorporating electron-withdrawing groups in side chains P1,P2 and P3),incorporating thienyl group in the backbone?P4,P5 and P6?,and incorporating phenyl group in the backbone?P7,P8 and P9?.The structure of the conjugated polymers was determined by 1H Nuclear Magnetic Resonance spectrum,Fourier Transform Infrared spectrum and Viscotek gel permeation chromatography.The properties of the polymers were characterized by TGA,DSC,UV-vis absorption,phololuminescence emission spectroscopy,and cyclic voltammetry.From the results,the thermal stability of these polymers is adequate for their applications in optoelectronic devices.All the results illustrate that the optical properties of these copolymers are useful for blue light emitting materials.The HOMO energy levels and the electrochemical energy gaps of these polymers are lowered gradually from cyclic voltammogram.In the presence of lots of metal cations,the fluorescence intensity of these copolymers was quenched,and the highest quenching effet was observed in the presence of Fe³⁺ ions.The results revealed that these polymers had a high selectivity to Fe³⁺ ions and could be a potential sensor for Fe³⁺ ions.