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Formation and thermodynamics of heteropolymers with adjustable monomer sequence distribution.

机译：单体序列分布可调的杂聚物的形成和热力学。

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Over the past few decades, multiple experimental and theoretical studies have reported on the formation and thermodynamics of copolymers with ordered sequences. Because of challenges associated with synthesizing random copolymers (RCPs) with tunable co-monomer sequences and analyzing their co-monomer sequence distribution, only a few computer simulations and sophisticated theoretical approaches have been employed that provided insight in the thermodynamical behavior of such RCPs. Recently, we developed a methodology facilitating the formation of RCPs with tunable co-monomer sequence distributions by invoking the "coloring scheme" suggested Khokhlov and coworkers in their computer simulations. The RCPs considered in this work are prepared by bromination of polystyrene (PS) with bromine leading to poly(styrene-co-4-bromostyrene) (PBrxS) RCPs, where x is the mole fraction of the 4-bromostyrene (4-BrS) segments in PBrxS.;In this Thesis, we demonstrate that the co-monomer sequence distribution in PBrxS can be adjusted by carrying out the bromination reaction in solutions of various solvent quality and reaction geometry. By adjusting the solvent quality during the bromination reaction, either random or random blocky PBrxS, (r-PBrxS or b-PBrxS, respectively), are synthesized. We find that: (1) the bulk bromination of PS follows the second-order kinetic in bromine, (2) the reaction rate increases with increasing the solvent dielectric constant, and (3) decreasing the solvent quality decreases the bromination reaction rate. In addition, we report that the reaction rates for brominating PS brushes are much smaller than those of free PS chains in solution. We attribute this latter behavior to steric hindrance due to PS confinement on the substrate.;We also report on the effect of chemical composition, co-monomer distribution, and H/D isotopic substitution in the RCP and the solvent on the phase behavior of PBrxS in cyclohexane (CH). We use turbidity and small angle neutron scattering measurements to assess the temperature-dependence of phase behavior of PBrxS with various x as a function of polymer concentration in CH. Our results reveal that while r-PBrxS chains collapse as individual coils during the coil-to-globule transition, the 1-phase to 2-phase transition in b-PBrxS is very complex. Specifically, we report that larger macromolecular aggregates comprising multiple b-PBrxS chains form in solution well above the coil-to-globule transition observed in r-PBr xS having the same x, and that this assembly acts as a precursor to the "true phase transition". This complex phase behavior of b-PBr xS is associated with the existence of inter- and intra-chain contacts acting among styrene and 4-BrS units ("pattern recognition") leading possibly to "flower-like" micelle formation.;Finally, we report on the adsorption kinetics of PBrxS on flat substrates by monitoring the adsorption of PBrxS from various solvents on flat silica surfaces. The PBrxS adsorption is driven by the strong affinity of the 4-BrS units towards silica while the interaction between styrene and the surface is nearly athermal. For a given solvent the amount of PBrxS adsorbed onto the surface increases with increasing the 4-BrS content and the blockiness in the monomer distribution in the RCP. Concurrently, the amount of PBrxS on the substrate also increases with decreasing the quality of the solvent, from which the copolymer is adsorbed. We provide theoretical insight into the various molecular phenomena that govern both the kinetics and the equilibrium amount of the RCPs on the surface as a function of the co-monomer distribution in the RCPs.
机译：在过去的几十年中，已进行了许多实验和理论研究，报道了有序序列的共聚物的形成和热力学。由于合成具有可调共聚单体序列的无规共聚物（RCP）并分析其共聚单体序列分布带来的挑战，因此仅采用了一些计算机模拟和复杂的理论方法，为此类RCP的热力学行为提供了见识。最近，我们开发了一种方法，该方法通过调用Khokhlov及其同事在计算机模拟中提出的“着色方案”来促进具有可调共聚单体序列分布的RCP的形成。本工作中考虑的RCP是通过将溴与聚苯乙烯（PS）溴化而生成聚（苯乙烯-co-4-溴苯乙烯）（PBrxS）RCP制备的，其中x是4-溴苯乙烯（4-BrS）的摩尔分数在本文中，我们证明了可以通过在各种溶剂质量和反应几何形状的溶液中进行溴化反应来调节PBrxS中的共聚单体序列分布。通过在溴化反应过程中调节溶剂质量，可以合成无规或无规嵌段的PBrxS（分别为r-PBrxS或b-PBrxS）。我们发现：（1）PS在溴中的本体溴化反应遵循二级动力学；（2）反应速率随溶剂介电常数的增加而增加；（3）溶剂质量降低会降低溴化反应速率。此外，我们报道溴化PS刷的反应速率比溶液中游离PS链的反应速率小得多。我们将后者的行为归因于由于PS限制在底物上而引起的位阻。;我们还报告了RCP中化学成分，共聚单体分布和H / D同位素取代以及溶剂对PBrxS的相行为的影响在环己烷（CH）中。我们使用浊度和小角度中子散射测量来评估具有各种x的PBrxS的相行为与温度的相关性，其作为CH中聚合物浓度的函数。我们的结果表明，尽管r-PBrxS链在线圈到球的过渡过程中因单个线圈而崩溃，但b-PBrxS的1相到2相过渡非常复杂。具体而言，我们报告说，在多个具有相同x的r-PBr xS中观察到的线圈-小球过渡上方的溶液中，形成了包含多个b-PBrxS链的较大的高分子聚集体，并且该组装体充当“真相”的前体过渡”。 b-PBr xS的这种复杂的相行为与在苯乙烯和4-BrS单元之间起作用的链间和链内接触的存在（“模式识别”）有关，最后可能导致“花状”胶束的形成。我们通过监测平面二氧化硅表面上各种溶剂对PBrxS的吸附，来报告PBrxS在平面基材上的吸附动力学。 PBrxS的吸附是由4-BrS单元对二氧化硅的强亲和力驱动的，而苯乙烯与表面之间的相互作用几乎是无热的。对于给定的溶剂，吸附在表面上的PBrxS的量随4-BrS含量的增加以及RCP中单体分布的嵌段性而增加。同时，基材上PBrxS的量也随着吸附共聚物质量的溶剂质量的降低而增加。我们提供了对各种分子现象的理论见解，这些分子现象控制着RCP在表面上的动力学和平衡量，这是RCP中共聚单体分布的函数。

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