Hamblin Ryan L, Zhang Zhongmin, DuBay Kateri H
Department of Chemistry, University of Virginia, Charlottesville, Virginia 22903, United States.
Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States.
Macromolecules. 2024 Oct 15;57(21):9984-9998. doi: 10.1021/acs.macromol.4c01047. eCollection 2024 Nov 12.
The sequence of copolymers is of significant importance to their material properties, yet controlling the copolymer sequence remains a challenge. Previously, we have shown that polymer chains with sufficient stiffness and intermolecular attractions can undergo an emergent, polymerization-driven nematic alignment of nascent oligomers during a step-growth polymerization process. Both the extent of alignment and the point in the reaction at which it occurs impact the kinetics and the sequence development of the growing polymer. Of particular interest is the emergence of a characteristic block length in the ensemble of sequences, resulting in unusually peaked block length distributions. Here we explore the emergence of this characteristic block length over time and investigate how changes in activation energy, solution viscosity, and monomer density influence the sequence and block length distributions of stiff copolymers undergoing step-growth polymerization. We find that emergent aggregation and nematic ordering restrict the availability of longer chains to form bonds, thereby altering the propensity of chains to react in a length dependent fashion, which changes as the reaction progresses, and promoting the formation of chains and blocks of a characteristic length. Further, we demonstrate that the characteristic length scale which emerges is sensitive to the relative time scales of reaction kinetics and reactant diffusion, shifting in response to changes in the activation energy of the reaction and the viscosity of the solvent. Our observations suggest the potential for biasing characteristic lengths of sequence repeats in stiff and semiflexible copolymer systems by targeting specific nonbonded interactions and reaction kinetics through the informed adjustment of reaction conditions and the selection or chemical modification of monomer species.
共聚物的序列对其材料性能至关重要，但控制共聚物序列仍然是一项挑战。此前，我们已经表明，具有足够刚度和分子间吸引力的聚合物链在逐步增长聚合过程中，新生低聚物会发生一种由聚合驱动的向列取向。取向程度及其发生反应的时间点都会影响生长聚合物的动力学和序列发展。特别值得关注的是，在序列集合中出现了特征嵌段长度，导致嵌段长度分布出现异常的峰值。在这里，我们探讨了这种特征嵌段长度随时间的出现情况，并研究了活化能、溶液粘度和单体密度的变化如何影响进行逐步增长聚合的刚性共聚物的序列和嵌段长度分布。我们发现，自发聚集和向列有序排列限制了较长链形成键的可用性，从而改变了链以长度依赖方式反应的倾向，这种倾向会随着反应的进行而变化，并促进形成具有特征长度的链和嵌段。此外，我们证明出现的特征长度尺度对反应动力学和反应物扩散的相对时间尺度敏感，会随着反应活化能和溶剂粘度的变化而移动。我们的观察结果表明，通过明智地调整反应条件以及选择或化学修饰单体种类来靶向特定的非键相互作用和反应动力学，有可能使刚性和半柔性共聚物体系中序列重复的特征长度产生偏差。
