Department of Chemistry, University of Virginia, Charlottesville, Virginia 22904, United States.
J Phys Chem B. 2022 Sep 1;126(34):6585-6597. doi: 10.1021/acs.jpcb.2c04092. Epub 2022 Aug 15.
The phase behavior and material properties of copolymers are intrinsically dependent on their primary comonomer sequences. Achieving precise control over monomer sequence in synthetic copolymerizations is challenging, as sequence determination is influenced not only by the reaction conditions and the properties of the reactants but also by the statistical nature of the copolymerization process itself. Mayo-Lewis reactivity ratios are often used to predict copolymer composition and sequence and are based on ratios of static reactivity constants. However, prior results have demonstrated that in a generic, solution-based step-growth A,B-copolymerization, relatively weak non-bonded attractions between certain monomer pairs induce emergent microphase separations. Such polymerization-driven separations lead to deviations from standard kinetics due to the emergent heterogeneities in reactant concentrations, which can also cause significant shifts in the resulting copolymer sequences. Previously, these effects were observed in systems where the activation energies were equal for all reaction pathways, that is, between all monomer pair combinations. In this work, we explore the combined effects on copolymerization kinetics of differences in both activation energies and non-bonded attractions between monomers and examine the sequences produced within this same step-growth copolymerization model. Our results indicate that altering activation energies influences the kinetics and sequences in a manner that also depends on the non-bonded attractions, showing that these effects may work in concert or in opposition to one another to bias the sequences formed. Non-standard kinetic behaviors and long-range sequence biasing are observed under certain conditions, and the extent of each clearly shifts as the reaction proceeds. These findings provide insight into the complex interplay between sequence and nascent oligomer phase behavior, highlighting the potential for exploiting emergent phase properties in the informed design of advanced sequence-biased materials.
共聚物的相行为和材料性质本质上取决于其主要共聚单体序列。在合成共聚物中实现对单体序列的精确控制具有挑战性，因为序列的确定不仅受到反应条件和反应物性质的影响，而且还受到共聚过程本身的统计性质的影响。梅奥-刘易斯反应性比通常用于预测共聚物组成和序列，并且基于静态反应性常数的比值。然而，先前的结果表明，在通用的、基于溶液的逐步 A，B-共聚中，某些单体对之间相对较弱的非键相互作用会引起新兴的微相分离。这种聚合驱动的分离会导致偏离标准动力学，因为反应物浓度出现新兴的非均相，这也会导致所得共聚物序列发生显著变化。以前，这些效应在所有反应途径（即所有单体对组合）的活化能相等的系统中观察到。在这项工作中，我们研究了单体之间的活化能和非键相互作用的差异对共聚动力学的综合影响，并在相同的逐步共聚模型中研究了所产生的序列。我们的结果表明，改变活化能会以依赖于非键相互作用的方式影响动力学和序列，表明这些效应可能协同或相互抵消以偏向形成的序列。在某些条件下会观察到非标准动力学行为和长程序列偏置，并且随着反应的进行，每种情况的程度显然会发生变化。这些发现深入了解了序列和新生低聚物相行为之间的复杂相互作用，突出了在设计先进的序列偏置材料时利用新兴相性质的潜力。
