Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455, United States.
Department of Chemistry, San José State University, San José, California 95192, United States.
J Phys Chem B. 2020 Nov 12;124(45):10266-10275. doi: 10.1021/acs.jpcb.0c07543. Epub 2020 Nov 2.
Self-assembly of poly(styrene)--poly(isoprene)--poly(lactide)--poly(styrene) (PS-PI-PLA-PS' or SILS') tetrablock terpolymers, where the volume fractions of the first three blocks are nearly equivalent, was studied both experimentally and using the self-consistent field theory (SCFT). SCFT indicates that addition of the terminal PS' chain to a low-molecular-mass, hexagonally packed cylinders forming, SIL precursor can produce a disordered state due to preferential mixing of the polystyrene end-blocks with the PI and PLA midblocks in the SILS' tetrablock, alleviating the unfavorable contact between the highly incompatible PI and PLA segments. In contrast, SCFT predicts that higher-molar-mass triblock precursors will maintain an ordered morphology upon addition of the terminal PS' block due to stronger overall segregation strengths. These predictions were tested using three sets of SILS' polymers that were synthesized based on three precursor SIL triblock polymers differing in total molar mass (14, 30, and 47 kg mol) and varying the length of the terminal PS' chain. In the lowest-molar-mass set of tetrablock polymers, the shift from order to disorder was observed in the materials at ambient temperature as the molar mass of the terminal PS' block was increased, consistent with SCFT calculations. Disorder with longer S' chain lengths was not found in the two higher-molar-mass polymer sets; the medium-molar-mass set showed both microphase separation and long-range order based on transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS), while the largest of these block polymers microphase separated but showed limited long-range order. The combination of the experimental and theoretical results presented in this work provides insights into the self-assembly of ABCA'-type polymers and highlights potential complications that arise from frustration in accessing well-ordered materials.
聚（苯乙烯）-聚（异戊二烯）-聚（丙交酯）-聚（苯乙烯）（PS-PI-PLA-PS' 或 SILS'）四嵌段共聚物的自组装，其中前三个嵌段的体积分数几乎相等，通过实验和自洽场理论（SCFT）进行了研究。SCFT 表明，由于聚苯乙烯端基与 PI 和 PLA 中基在 SILS' 四嵌段中优先混合，将末端 PS'链添加到具有低分子量、六方堆积形成的圆柱状 SIL 前体中，可以产生无序状态，从而缓解 PI 和 PLA 段之间高度不相容的不利接触。相比之下，SCFT 预测，由于整体分离强度更强，较高摩尔质量的三嵌段前体在添加末端 PS' 嵌段后将保持有序形态。这些预测使用三种基于三种不同总摩尔质量（14、30 和 47 kg/mol）的 SIL 三嵌段聚合物合成的 SILS' 聚合物进行了测试，并改变了末端 PS'链的长度。在最低摩尔质量的四嵌段聚合物中，随着末端 PS' 嵌段摩尔质量的增加，观察到材料在环境温度下从有序到无序的转变，这与 SCFT 计算一致。在两个较高摩尔质量的聚合物系列中，没有发现具有较长 S'链长度的无序；中摩尔质量的聚合物系列基于透射电子显微镜（TEM）和小角 X 射线散射（SAXS）显示出微相分离和长程有序，而这些嵌段聚合物中最大的微相分离但显示出有限的长程有序。本工作中呈现的实验和理论结果的结合为 ABCA'型聚合物的自组装提供了深入的了解，并强调了在获得有序材料时出现的潜在复杂性。
