Department of Chemistry, The University of Virginia, Charlottesville, Virginia 22904, United States.
J Phys Chem B. 2021 Apr 8;125(13):3426-3437. doi: 10.1021/acs.jpcb.1c00873. Epub 2021 Mar 29.
Synthetic copolymer sequences remain challenging to control, and there are features of even simple one-pot, solution-based copolymerizations that are not yet fully understood. In previous simulations on step-growth copolymerizations in solution, we demonstrated that modest variations in the attractions between type A and B monomers could significantly influence copolymer sequence through an emergent aggregation and phase separation initiated by the lengthening of nascent oligomers. Here we investigate how one aspect of a copolymer's geometry-its flexibility-can modulate those effects. Our simulations show the onset of strand alignment within the polymerization-induced aggregates as chain stiffness increases and demonstrate that this alignment can influence the resulting copolymer sequences. For less flexible copolymers, with persistence lengths ≥10 monomers, modest nonbonded attractions of ∼ between monomers of the same type yield A and B blocks of a characteristic length and result in a polydispersity index that grows rapidly, peaks, and then diminishes as the reaction proceeds. These results demonstrate that for copolymer systems with modest variations in intermonomer attractions and physically realistic flexibilities a nascent copolymer's persistence length can influence its own sequence.
合成共聚物序列仍然难以控制，即使是简单的一锅法、溶液共聚合，也有一些特征尚未完全理解。在之前关于溶液中逐步增长共聚合的模拟中，我们证明了 A 型和 B 型单体之间适度的吸引力变化可以通过引发聚合诱导的聚集和相分离，显著影响共聚物序列，而这种聚合诱导的聚集和相分离是由新生低聚物的延长引起的。在这里，我们研究了共聚物几何形状的一个方面——其柔韧性——如何调节这些影响。我们的模拟表明，随着链刚性的增加，聚合诱导的聚集体内的链排列开始出现，并且证明这种排列可以影响最终的共聚物序列。对于柔韧性较低的共聚物，其持久长度≥10 个单体，同种类型单体之间适度的非键相互作用约为∼，会产生具有特征长度的 A 和 B 嵌段，并导致多分散指数迅速增长、峰值，然后随着反应的进行而减小。这些结果表明，对于单体间相互作用具有适度变化和物理上合理柔韧性的共聚物体系，新生共聚物的持久长度可以影响其自身的序列。
