聚酯共聚物序列结构的理性设计和高效形成策略

Copolycondensation is one of the most important polymer synthesis reactions which can obtains high performance modified polycondensation macromolecules through the regulation of main chain composition and sequence structure. In this project, the regulation of short-range structures and engineering formation of the tailored molecular chain in poly(ethylene terephthalate) copolycondensation process will be studied using molecular simulation combined with copolycondensation experimental verification. The molecular dynamic simulation of characteristic copolycondensation reactions is based on the molecular dynamics software of LAMMPS. According to the transition state theory, the contributions of different components to the pre-exponential factor and activation energy can be obtained so that the reaction activity of each component can be quantified. Then the intrinsic rate constant and activation energy of each reaction can be calculated using group contribution method. With the kinetic parameters achieved above, a stochastic kinetic Monte Carlo simulation method can be conducted to establish a ternary copolycondensation model and then to calculate the effects of different functional groups, chain lengths and segment structures on the chemical composition, sequence structure and the change behavior of the copolymer chain in a no thermal system. Parameters obtained by LAMMPS can also be further applied to establish a macroscopic reaction kinetics model for PET copolycondensation process. Besides, the effect of the operation conditions such as temperature and feeding way on the composition and sequence structure of the polymer chain will also be simulated to obtain the efficient engineering strategy for controlling the formation of short-range structure of copolyester molecular chain. Corresponding to the multiscale kintic model building and simulation, adipic acid, hexylene glycol, hexamethylene diamine, 1,4-butanedioic acid and naphthalenedicarboxylic will be used as functional monomers to conduct three kinds of characteristic copolycondensation experiments, including ternary monemors, prepolymer with monemor, and the prepolymer with prepolymer. The influences of different functional end groups, chain lengths and segment structure on the chemical composition, sequence structure and their changing behavior along with the progress of copolycondensation process can be characterized by two-dimensional nuclear magnetic resonance and infrared spectrum analysis to verify the reliability of molecular dynamics model and Monte Carlo simulation. After that, the rational regulation mechanism of the copolymer sequence structure will be finally presented. This project reveals the multi-scale complex interactions in the copolycondensation proceess from molecules, chain segments to the condensed state macromolecular chains and analyzes the key regulation mechanisms of the copolymer chain structure. The controlled realization of the copolycondensation process and its product sequence structure is expected to carry out efficiently. This work can provide the rational design and engineering regulation strategies for the segment sequence structure of both copolyesters and other copolycondensation reaction systems.

共缩聚反应通过聚合物主链组成和序列结构的调控获得高性能化和功能化的改性高分子。拟以聚酯共缩聚为典型对象，分子模拟与共聚实验相结合，开展聚酯共缩聚过程多尺度反应机理以及聚酯共聚物分子链近程结构设计和高效形成的共性基础研究。利用LAMMPS分子模拟结合过渡态理论定量不同分子结构共聚反应物的官能团效应及其反应活性，并根据基团贡献法获得其本征动力学常数及相应活化能；采用蒙特卡罗方法，实现无热环境下不同共聚酯体系链段近程结构的模拟，设计聚酯共聚实验验证模拟计算的合理性和准确性；建立共聚体系宏观动力学模型，确定共聚酯特定序列分子链形成的优化工程策略，实现聚酯共聚过程与产品可控高效实施。本项目从分子、链段到大分子链凝聚态揭示共聚过程多尺度复杂相互作用，解析聚酯共聚物链段结构调控的关键机制，不仅为聚酯共聚物的设计和高效制备提供理论方法和基础数据，也可为其他共缩聚反应体系的构建和实现提供理论指导。

利用两种或两种以上不同类型的二元酸/醇类功能单体进行共缩聚反应是制备功能聚酯等高性能化工新材料的重要方法。共缩聚过程中，不同链结构单体的端基官能团活性存在差异，反应行为不同。因此，引入共聚单体的种类、方式和反应条件不同，将显著影响共聚物分子链的近程结构，特别是链结构单元的化学组成和序列结构，进而影响共聚物凝聚态结构与性能。.本项目以典型聚酯的共缩聚过程为对象，通过分子模拟、共聚实验以及流程模拟等多个尺度研究手段相结合，开展了聚酯共缩聚过程功能单体端基活性辨识、反应机理与行为研究、共聚物复杂构效关系解析以及特定链结构共聚酯的可控制备等共性基础研究。.首先，基于密度泛函理论，计算了不同分子结构二元酸/醇单体和反应中间产物的最优几何构型、轨道能量和表面静电势等，分析了相应的质子化与酯化反应路径，在分子层面探讨了的环状等主链结构作用下的官能团效应与端基特性，分析了端羧基和端羟基间双分子基元反应的振动频率、自由能、透射系数等参数随主链分子结构的变化，从分子尺度辨析了不同共聚体系的官能团反应活性计算方法及其与单体结构间的关系，实现了低聚合度时的端基反应活性量化分析与计算。.其次，针对典型二元均聚、三元共聚等体系，开展了系列端基反应动力学实验研究，分别考察了不同功能单体作用下的酯化、聚合反应动力学行为，辨识了不同结构二元醇端羟基的反应活性差异，基于不同端羟基活性差异建立了二元酯化与复杂三元共酯化、共缩聚动力学模型。利用所建立的动力学模型及参数，在Aspen平台实现了PTA-EG-CHDM典型三元共聚反应体系的流程建模，模拟分析了无规共聚酯PCTG连续制备过程进料醇酸摩尔比、各阶段反应温度以及停留时间等工艺过程影响因素，获得了相应的工程制备与调控策略，从而形成了万吨级高性能共聚酯PCTG工艺包技术。.进一步，通过设计的两步法路线，可控制备了一系列不同分子链组成与结构的PTA-EG-CHDM三元嵌段共聚酯，对比研究了共聚酯复杂的分子链组成及序列分布对材料聚集态结构以及宏观热物理性能的影响，解析了嵌段共聚酯的复杂构效关系，发现通过调控共聚酯链段序列分布可以改变共聚物结晶性能，成功实现了15mol%CT含量的共聚物由无定型向结晶态的转变。.本项目对于功能单体端基反应行为辨识方法以及共聚物序列结构调控策略对于高性能聚酯、聚酰胺、弹性体等新材料可控制备具有重要意义。