Study On Kinetics Of Ultrasonic Atom Transfer Radical Polymerization Regulated By Sodium Bismuth Titanate

As one of the most widely used living/controlled radical polymerization methods,atom transfer radical polymerization(ATRP)is a research hotspot in the field of polymerization reaction engineering.The core of the technology is to reduce the concentration of free radicals through the activation/deactivation equilibrium of the polymerization,thereby inhibiting side reactions such as termination of free radicals.Combining light,electricity,ultrasound and other external field control methods,the activation/deactivation process of the polymerization can be controlled.Meanwhile,the spatiotemporal control of the polymerization process can be realized.Compared with other external field control methods,the advantage of ultrasound control is that ultrasound can enhance the mass transfer.On the one hand,it can accelerate the reaction rate of polymerization,and on the other hand,it can significantly reduce the auto-acceleration phenomenon caused by the gel effect.However,the piezoelectric materials currently used such as barium titanate(BTO)or zinc oxide have low piezoelectric efficiency,which leads to problems such as a large loading of piezoelectric materials and low activity in the polymerization.This report uses sodium bismuth titanate(NBTO)with high piezoelectric coefficient and high mechano-electric conversion efficiency as the mechano-electric transducer to activate the Cu(II),and an efficient method of mechano-ATRP was proposed.Compared with the results reported in the literature,the polymerization process has been significantly strengthened.The main research contents and innovative research results are as follows:(1)An efficient and controllable mechanochemically mediated ATRP(mechano-ATRP)was developed by using NBTO as mechano-electric conversion material.Compared with traditional piezoelectric materials like barium titanate or zinc oxide,NBTO has higher piezoelectric coefficient and mechano-electric conversion efficiency.The effects of the properties of piezoelectric materials,the loadings of NBTO,the concentration of Cu and the concentration of initiator on the polymerization kinetics were investigated.The NBTO with different morphology was prepared by changing the concentration of mineralizer.When the mineralization concentration was higher than16M,the NBTO showed prominent performance of regulation;With the 2.5 wt%loading of sodium bismuth titanate,and 150 ppm concentration of Cu,the conversion of polymerization in 2h was over 90%.The polymerization products has high end-group fidelity,predetermined molecular weight,and low dispersity,and the results are obviously better than those reported in the literature.The electrochemical impedance test results of NBTO and BTO show that the electron migration rate of NBTO at the solid-liquid interface is significantly higher than that of BTO.Moreover,the high responsiveness of mechano-ATRP to ultrasonic spatiotemporal control was verified by ultrasonic on/off experiments,and the high retention of end-group functionality was verified by chain extension experiments.(2)Based on the method of moments,an ultrasonic-controlled ATRP model was established,and the kinetic modeling of mechano-ATRP regulated by NBTO was carried out.Through reverse fitting of the aforementioned experimental data,key kinetic parameters such as the activation/deactivation reaction rate constant(k_a/k_da)and the ultrasonic reduction reaction rate constant(k_r,e)were obtained.The results show that the k_r,e of NBTO is 51 times that of BTO,which significantly increases the catalyst reduction reaction rate,strengthens the polymerization process and conforms to the above-mentioned experimental conclusions.Furthermore,the evolution of concentration of each species and the elementary reaction rates with time in the mechano-ATRP were simulated,verifying that the concentration of reaction species and elementary reaction rate changes in accordance with the basic law of living/controllable free radical polymerization.In addition,the kinetic behavior of mechano-ATRP under different polymerization degrees and different k_r,e was simulated.The simulation results show that the initiator concentration has little effect on the polymerization rate,but has a greater impact on the molecular weight distribution and end group retention of the polymerization product;increasing k_r,e can significantly accelerate the polymerization reaction rate,but has an impact on the molecular weight and molecular weight distribution of the polymerization products.