特异性超支化聚合反应模拟以及超支化大分子热力学行为研究

The reactive coarse grained (CG) force field is constructed using Inversion Boltzmann Iterative method combining with a smooth transition function. Further, the framework for the reactive coarse grained molecular dynamics is built. Based on the new reactive CG force field, the potential type and its parameters are studied to demonstrate its ability to reflect the specificity of hyperbranched polymerization such as reaction reversibility and the activation energy. After that, the different simulations using reactive MD or reactive MC methods are compared to test the advantage of reactive coarse grained (CG) force field developed by us. Using the experimental data, the influence of molecular specificity on the reaction kinetics, molecular weight and distribution and degree of branching in hyperbranched polymerization are studied. A deep understanding to the effects of steric hindrance and intramolecular cyclization on hyperbranched polymerization is obtained. Further, Wang-Landau sampling method is applied to study the phase transition behavior of hyperbranched polymer. Some experiments are carried out and its results are compared with simulation. Though this project, we hope to improve the ability of coarse grained molecular simulation to quantitatively predict the kinetics of hyperbranched polymerizatioan and thermodynamics of hyperbranched polymers in reality.

采用迭代反演玻尔兹曼方法和反应平滑过渡函数法构建反应性大分子粗粒化力场，进而构建反应性粗粒化分子动力学模拟框架；研究粗粒化力场形式和参数对超支化反应特异性、可逆性、反应活化能调控的影响；比较动力学方法和Monte Carlo 方法在超支化聚合反应动力学模拟的结果差异；结合实验研究认识分子特异性对线性和非线性聚合反应中反应动力学、分子量和分布、支化度的影响；进一步认识空间位阻和分子内环化效应在超支化聚合反应的结构特异依赖性；采用Wang-Landau方法系统研究超支化大分子的热力学性质，开展部分实验研究，同模拟结果相比较。通过该项目的研究，推进对近真超支化聚合反应体系和特异性大分子热力学性质的定量研究和预测。

建立了一套高效的反应型粗粒化分子模拟方法，该模拟方法结合了玻尔兹曼反演迭代粗粒化力场提取技术和蒙特卡洛算法模拟化学反应算法。采用该模拟方法，我们对特异性超支化聚合反应对3,5-二(三甲基硅氧烷基)苯甲酰氯超支化聚合反应和对氯甲基苯乙烯ATRP超支化聚合反应进行了定量模拟研究，研究了官能团活性、催化剂与单体比例、自由基增长速率常数、ATRP平衡常数对反应动力学的影响；深入认识了空间位阻和分子内成环对特异性超支化聚合反应动力学及聚合物分子量和分子量分布的影响；通过拟合实验数据，我们成功获得了实验相关特异性聚合体系中的ATRP平衡常数和自由基链增长速率常数，进而获得超支化聚合物分子详细结构参数；在该项目中，我们还进一步发展了粗粒化反应平滑函数模拟方法，并在简单反应体系中进行了检验，证实采用平滑函数方法可以实现完全分子动力学架构下的粗粒化可逆化学反应模拟；在该项目第二部分，我们采用Wang-Landau抽样算法和副本交换分子动力学模拟方法系统研究了单链超支化大分子的热力学性质，针对超支化和树枝形两类大分子，通过模拟研究阐明了超支化大分子的coil-globule和liquid-solid相转变与支化度的依赖关系；最后，我们采用超快升温分子动力学模拟方法，研究了特异性短支链高分子（等规聚丙烯iPP）的熔融行为，阐明了升温速率和分子链长度对iPP高分子两种晶型熔融行为的影响。我们的研究加深了人们对大分子支化结构和热力学性质依赖关系的认识。