| Isoprene rubber(IR)is a synthetic rubber with the best comprehensive performance among its kind and is produced through stereopolymerization of isoprene catalized by coordination polymerization catalysit.IR is the best available substitute of natural rubber(NR),which means that it is of strategic signifincance in China,whose NR comsumption mainly depends on import from outside,to develop IR industry.Neodymium-catalized IR(Nd IR)is usually produced by neodymium catalyst with neodymium carboxylate as a major component.NdIR is becoming a prospective IR due to the easiness of its catalyst preparation,high activity of its catalyst,excellent performance of produt and enviorenment-friendly production process.The development of IR industry in China is later but from a higher starting point than other countries in the world,therefore,the NdIR is the dominant type of IR produced in China.Though the neodymium catalyst used to produce Nd IR is more active than tinanium catalyst used to produce titanium IR(Ti IR),the utilization efficiency of Nd is less than 10%,and there is much room for improvement of activity.Therefore,it is not only of theoretical importance but also of practical value to study the quantitative structure activity relationship(QSAR)of catalyst used to produce NdIR,so as to disclose the mechanism of catalyst activity and direct to design new catalysts with higher activity to lower production cost of NdIR.QSAR of a catalyst is a mathmetic model to express the relationship between its molecular structure and its catalytic activity.This study first computed a number of quantum chemical descriptors of 17 neodimium carboxylates with different number of carbon atoms and isomerization structure,using ADF2014,quantum chemistry software based on density functional theory(DFT).Key descriptors related to activity were selected as independent variables for QSAR model building.Secondly,methods for synthesis and characterization of the 17 neodymium carboxylates were studied,and their samples were synthesized and characterized through experiments.And then,their catalytic activities towards coordination polymerization of isoprene were studied and determined through polymerization experiments,from which the data of dependent variable for QSAR modeling were obtained.In the end,QSAR models for Nd IR catalyst were built with adequate modeling methods and were applied to explain the mechanism that causes the activity of neodymium carboxylate catalysts to be high or low as well as to predict the catalytic activity of catalysts.As to such compound systems as neodymium carboxylates with rare earth atoms in their molecules,ADF2014 can compromise well between accuracy and efficiency of computation.Detailed computation methods were studied and determined,including how to build an initial molecular geometry,how to set the computing parameters in the software,the simplication of the initial geometry,the omitting of conformation search,etc.The result indicates that the reproducibility of the computation methods is well and the variation among computed values of a quantum chemical descriptor of neodymium carboxylates with different structures is outstanding,which meets the requirement for QSAR modeling.Four descriptors including the HOMO energy ?HOMO,the LUMO energy ?LUMO,the dipole moment ? and the polarizability ? of ligand were selected according to the variation percentage and the correlation matrix.The four descriptors of the above 17 neodymium carboxylates were computed.Methods of synthesis and characterization for the 17 neodymium carboxylates were studied by experiments and their samples with high purity were synthesized.According to the differences of ligands and their complexes in physical and chemical properties,the synthesis methods of the 17 neodymium carboxylates were classified into three categories: the neodymium hydroxide water phase method,the neodymium chloride water phase method and the neodymium chloride oil-water dualphase method.The detailed operation procedure,process controlling conditions,as well as methods for product separation,purification and drying,were studied and determined.When neodymium carboxylates easy to desolve in water were synthesized with the neodymium hydroxide water phase method,the purity of product from crystallization under reduced pressure is higher than that from crystallization under normal pressure,and the purity of product from filer cake drying under reduced pressure is higher than that from filter liquor drying under reduced pressure.When neodymium carboxylates difficult to desolve in water were synthesized with the neodymium chloride oil-water dualphase method,the purity of product was strongly affected by the PH value of water phase,and high purity was obtained with PH value of water phase between 5.5 and 6.0.Strict experimental methods for coordination polymerization of isoprene with neodymium catalyst were studied and determined.Accuracy and comparability of experiment resuls were assured by means of the following measures:(1)Strict treatment of monomer,solvent,polymerization flask,etc.(2)To control the conversion of polymerization within the range from 30% to 70%.(3)To repeat experiment for several times and average the experiment results.(4)To keep the data from each batch of experiments comparable among different batches.Catalytic activity data of 17 neodymium carboxylates were obtained from experiments.Their relative activity data are changing from 2.21% to 100%,which is wide enough,and the differences among their absolute values of activity are also large enough,to be used for QSAR study.After statistic treatment of the number of independent variables and the data of dependent variable,QSAR models of catalyst for Nd IR production were built with a linear approch and a nonlinear approach,respectively.The linear model built with the partial least square(PLS)approach is: A = 56054.39 ?HOMO+ 46.18 ? + 5.94 ? + 13603.81,which indicates that the catalytic activity A is positively correlated with the HOMO energy ?HOMO and the dipole moment ? of neodymium carboxylate molecules,and the polarizability ? of ligand,with the influence of ?HOMO being the biggest,? the second biggest,and ? the smallest.This QSAR model can be used to explain why the catalytic activity of a neodymium carboxylate is high or low,further more,its coefficient of determination r2 = 0.9620 and that of cross validation r2(CV)= 0.9412,both being close to 1,which means that its quality is well and its predictive power is strong.The nonlinear model built with a neural network analysis(NNA)approach has a good quality and a reasonable predictive power,whose coefficient of determination r2 = 0.9737 and that of cross validation r2(CV)= 0.7947.In the last chapter,the QSAR models obtained from this study were successfully applied to explain why the catalytic activity of a neodymium carboxylate is high or low,and also to predict the catalytic activity of neodymium carboxylate catalysts.The linear model can explain the mechanism of Nd IR catalyst activity,that is,neodymium carboxylates with higher HOMO energy,larger dipole moment and larger polarizabilty of ligand are easier to react with the co-catalysts to produce more active centers of catalyst,resulting in a higher activity.Both the linear model and the nonlinear model can be applied to predict quantitatively the activity of catalyst with a reasonable accuracy,the relative error between the experiment value and the predicted one is within ±10%. |
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