Study On The Pyrolysis Mechanisms Of PEK-C Based Membrane

The polymer based carbon membrane which is prepared with phenolphthalein-based cardo poly(arylene ether ketone)(PEK-C)as precursor has good separation performance for small molecule gas mixing system.However,the unclear preparation mechanism,especially the pyrolysis crosslinking reaction mechanism,limits its further improvement.By studying the reaction mechanism of preparation,the influence trend of preparation conditions on the properties of the membrane can be obtained,so as to explore the optimal preparation conditions for the preparation of excellent gas separation membrane.In this paper,polymer film was prepared with PEK-C polymer materials as the precursor,pyrolysis crosslinking experiment and molecular simulation were carried out to investigate the mechanism of pyrolysis crosslinking reaction.Firstly,the effects of reaction conditions,such as reaction temperature and molecular weight of precursor,on the crosslinking degree of pyrolysis crosslinking reaction of PEK-C membrane were studied through experiments,and the membrane before and after reaction were characterized by infrared spectrometer which can investigate the structural changes of PEK-C based membrane during pyrolysis crosslinking process.Secondly,a molecular simulation model was set up in order to simulate the variation rules between reaction temperature T and reaction intermolecular distance Rc and degree of crosslinking D_T in PEK-C based film pyrolysis crosslinking reaction process,so as to explore the reaction mechanism of pek-c membrane pyrolysis crosslinking process.Finally,the numerical laws were obtained by fitting the experimental and molecular simulation results of PEK-C based membrane pyrolysis crosslinking reaction process,the laws can be used to determine the starting and ending temperatures of PEK-C based membrane pyrolysis crosslinking reaction.The experimental study of PEK-C based membrane pyrolysis crosslinking reaction process shows:Firstly,the peak area of the inner ring ester bond of PEK-C molecule in the infrared spectrum gradually decreased with the temperature rising when the reaction temperature was higher than 643K and basically reduced to 0 when the reaction temperature was 748K,it means PEK-C based membrane pyrolysis crosslinking reaction was promoted by temperatures;Secondly,the higher the molecular weight was,the more thoroughly PEK-C based film pyrolysis crosslinking was carried out at the same reaction temperature in the process of pyrolysis crosslinking,moreover,the higher the molecular weight was,the more obvious promoting effect of reaction temperature in the process of pyrolysis crosslinking;Thirdly,by analyzing the infrared spectrum of PEK-C based film pyrolysis crosslinking,it can be seen that the inner ring ester bond breaks and exposed aromatic carbonyl and oxygen atoms were formed,then all of exposed aromatic carbonyl and part of exposed oxygen atoms fall off to form carbon dioxide,then PEK-C molecules which have lost oxygen atoms form new bonds with PEK-C molecules which haven't lost oxygen atoms and the two polymer chains were are at an Angle to each other in order to reduce steric hindrance.The Molecular simulation study of PEK-C based membrane pyrolysis crosslinking reaction process shows:Firstly,molecular simulation of PEK-C based membrane pyrolysis crosslinking process can be divided into four steps:searching for labeled reactive atoms,judging whether the reaction can be carried out,breaking the original bond to form a new"carbon-oxygen bridge",and counting the number of atoms involved in the reaction.Secondly,the higher the temperature was,the higher the MSD value would be,it means The more the atoms move,so it's greater probability that the distance between reactive functional groups was less than the reaction intermolecular distance Rc,therefore PEK-C based membrane pyrolysis crosslinking reaction was more likely.Thirdly,the crosslinking degree D_T increases with the increase of the reaction intermolecular distance Rc,there's a linear relationship between each other.The results of molecular simulation of PEK-C based membrane pyrolysis crosslinking reaction can be used for further theoretical interpretation of the experimental results.Fitting experiment and molecular simulation results shows:Firstly,it was found that the linear relationship between the crosslinking degree D_T and reaction temperature T,the linear relationship between the crosslinking degree D_T and reaction intermolecular distance Rc,the linear relationship between the reaction intermolecular distance Rc and reaction temperature T in PEK-C based film pyrolysis crosslinking reaction process;Secondly,the starting temperature of pyrolysis crosslinking reaction of PEK-C based membrane with low molecular weight(LMW),medium molecular weight(MMW)and high molecular weight(HMW)can be calculated as 655K,654K and 652K respectively,while the final temperature of pyrolysis crosslinking reaction is 745K,744K and 742K respectively.The experimental and simulation results in this paper mutually prove their correctness,and provide theoretical support for optimizing the preparation process of PEK-C based membrane and improving its membrane separation performance.