【作者】 王龙；

【导师】 何学浩；

【作者基本信息】 天津大学 ， 材料化学工程， 2009， 硕士

【摘要】 本论文采用反应型八位置键涨落格子模型和Monte Carlo方法研究了三维空间下的ABn（n=2, 4）型超支化聚合反应。在考虑了分子内成环、空间效应、分子扩散及分子链松弛等因素影响的情况下系统研究了超支化聚合反应动力学及超支化分子的构象特征。在动力学研究中,分析了单体浓度、反应活性和取代基效应对聚合度、分子量分布及支化点密度的影响。在零反应活化能的条件下研究了浓度对参数的影响,浓度变化范围为0.1～0.95。结果显示数均聚合度、重均聚合度和多分散指数PI均随浓度的升高而增大。在A官能团转化率趋近于1时,平均场理论预测聚合度及分子量分布将趋于无穷大,而在我们的模拟中各参数的最大值均为有限值。比如AB₂和AB₄型超支化聚合反应中最大的PI值分别为3.50和3.42。在A官能团转化率为1时,平均支化点密度FB开始随着单体浓度的升高而增大,然而在高浓度体系下FB反而下降。在AB2型单体的反应体系中单体浓度c0=0.8时FB达最大值0.298;在AB4型单体的反应体系中c0=0.75时FB达最大值0.263。在反应活化能不为零时,随着反应活性降低PI逐渐变大,而平均FB则基本保持不变。相比而言,取代基效应对PI和FB具有显著影响。模拟结果与实验数据非常接近,这些结论将有助于对AB_n型超支化聚合反应进行预测。在AB₂型超支化聚合反应中,研究了单体浓度和取代基效应对分子构象的影响。系统研究了分子的尺寸与聚合度的标度规律,此规律可表示为R～Nβ,式中R为回转半径R_g或流体力学半径R_h,N为聚合度。研究发现标度指数β随着单体的转化率升高而减小,并且满足关系式β=H+K·CA,式中CA是A官能团的转化率,H和K是与单体浓度和B官能团活性比相关的常数。反应活性比在低转化率下对β具有显著影响,然而当转化率趋近于1时活性比的影响变得很小。C_A=1时β_g和β_h的取值范围分别为0.37<β_g<0.50、0.35<β_h<0.44。随着反应进行z-均半径之比γ=R_gz/R_hz逐渐增大,在各种反应条件下γ的变化范围为0.99～1.14。这些结果将有助于深入了解超支化分子构象的基本性质。更多还原

【Abstract】 In this dissertation, ABn（n=2, 4）type hyperbranched polymerization is investigated using Monte Carlo method with a reactive 3d bond fluctuation lattice model. With the considerations of intramolecular cyclization, steric factor, diffusion of molecules, and polymer chain relaxation, the kinetics of polymerization and the conformational properties of hyperbranched polymers are systematically studied.In the kinetic study, the influences of monomer concentration, reaction activity and substitution effect on the degree of polymerization, molecular weight distribution and branching degree are investigated. In the case of zero activation energy, the number- and weight-average degrees of polymerization, and polydispersity index, PI, increase with the rise of monomer concentration which ranges from 0.1 to 0.95. However, different from the infinite value obtained in mean-field theory when the conversion of A groups approaches one, the maximal value of these three parameters are finite, for instance the maximal value of PIs are 3.50 and 3.42 for AB2 and AB4 type hyperbranched polymerizations respectively. The average fraction of branching point, FB, initially elevates with the increase of monomer concentration and then decreases at high concentration, with the maximal values of 0.298 and 0.263 at c0=0.8 and c0= 0.75 for AB2 and AB4 type polymeizations at full conversion of A groups. In the case of non zero activation energy, the PI increases slowly with the decrease of reaction activity, but the average FB keeps nearly unchanging. In comparison, the substitution effect has significant influence on PI and FB. The simulation results show excellent agreement with experimental data and are helpful to make great progress in prediction for ABn type hyperbranched polymerizations.The influences of monomer concentration and substitution effect on the conformation of hyperbranched polymers are studied in one-pot AB₂ type hyperbranched polymerization. The scaling relationship of the conformation size of hyperbranched polymer with the polymerization degree, R～N^β, where R is the gyration radius （R_g） or the hydrodynamic radius （Rh） of macromolecule and N the degree of polymerization, were systematically studied. It is discovered that the scaling exponentβdecreases with the increase of the monomer conversion and satisfies a simply relation,β=H+K·C_A, where CA is the conversion of A functional groups, and H and K are constant coefficients relevant with the initial monomer concentration and the reactivity ratio of B groups. The influence of the reactivity ratio of B groups onλis strong at the lower conversion of reaction but becomes weak when the conversion approaches one. Theβ_g andβ_h are at the ranges 0.37<β_g<0.50 and 0.35<β_h<0.44 when CA=1. The ratio of z-average radius,γ=R_gz/R_hz, increases from 0.99 to 1.14 with the reaction conversion in various reaction conditions. These results are valuable to have deeply understanding to the fundamental property of hyperbranched polymer.更多还原