环状聚合物与线型、星型聚合物拓扑共混的流变学研究

Rheology of ring polymers and their blends is one of the most challenging topics in polymer physics. Especially, as one of the unsolved problem in topological polymeric blends, the dynamics of ring-linear and ring-star blends is still not well understood. Heretofore, most studies on ring-based topological blends are based on simulation, but the evidences from rheological experiments are very limited. In this project, we will mix ring polymers with both linear and star polymer matrix to investigate the effect of ring addition on linear and nonlinear rheological behavior of topological blends. We will employ the Rouse and tube model formulated by time-marching algorithm to fit the rheological data of unentangled and entangled topological blends, respectively. In this way, we can quantitatively evaluate the effect of multiple threading through rings by matrix chains, and establish its relation with rheological behavior. In addition, this study would clarify the dependence of multiple threading on chain size and topology of matrix by tuning the parameters like molecular weight and degree of branching. This research will establish the molecular dynamic picture behind the rheology of “ring-linear” and “ring-star” blends, and improve the understanding about dynamics of topological mixture. The results can be used to analyze the rheological influence from cyclic-byproduct after ring-opening polymerization, and to guide the fabrication of ring-based topological polymer blends.

环状聚合物及其共混物的流变学研究，是高分子物理中的前沿领域。尤其是环状链与线型、星型链的共混，是拓扑共混动力学中尚未解决的问题。目前为止，环状链拓扑共混动力学的研究主要依靠计算机模拟，而流变实验证据却严重不足。本项目拟将少量环状高分子分别加入线型及星型聚合物基体中，考察环状高分子对基体聚合物线性及非线性流变行为的影响，并利用Rouse和基于时间推进算法(TMA)的管状模型，分别拟合非缠结和缠结共混物的线性流变数据，定量地评估线、星型链穿过环孔洞所导致的“多链穿插”效应，从而建立“多链穿插”与流变行为之间的关系。通过调节分子量、支化度等参数，还将揭示链尺寸、链拓扑结构等因素对“多链穿插”的影响。本项目的开展，将建立环-线、环-星聚合物共混物流变行为的分子动力学基础，丰富拓扑共混动力学的实验现象与理论认识，研究结果还有望用于评估开环聚合中环状副产物的影响、指导环状聚合物的应用等，具有实际意义。

环状聚合物由于特殊的闭环结构，具有不同于线性链的分子动力学特性，阐明环状-线性、环状-支化共混物的分子动力学，是理解环状拓扑效应、发展含环共混体系分子本构方程、开发环状链作为流变学改性剂的关键。本项目针对上述问题开展了以下研究：1.研究了环-线、环-支化、支化-线性共混体系的整链分子动力学行为，结合流变实验与模拟，阐明了环线穿插效应在共混物流变行为中的关键作用及其分子量依赖性，并发展了分子本构方程描述不同拓扑共混物的流变行为；2.比较了环-环、环-线、线-线相容性共混物的组分动力学行为，阐明了环状结构对相容性共混中链段松弛的影响，通过将“回咬效应”引入自浓度模型，成功预测了相容性共混中的环状链动力学；3.发现打结环与链锁环具有相同的静态性质与分子量依赖性，但在动力学上，链锁环表现出链接区域随时间而改变的“呼吸”现象。通过这些研究所取得的成果，我们阐明了环线穿插、环状链回咬、环状链打结等效应对环状链分子动力学的影响，实现了对含环共混体系流变性质的准确预测。