Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, USA.
J Am Chem Soc. 2012 Feb 29;134(8):3834-44. doi: 10.1021/ja210548e. Epub 2012 Feb 16.
Controlled/"living" polymerizations and tandem polymerization methodologies offer enticing opportunities to enchain a wide variety of monomers into new, functional block copolymer materials with unusual physical properties. However, the use of these synthetic methods often introduces nontrivial molecular weight polydispersities, a type of chain length heterogeneity, into one or more of the copolymer blocks. While the self-assembly behavior of monodisperse AB diblock and ABA triblock copolymers is both experimentally and theoretically well understood, the effects of broadening the copolymer molecular weight distribution on block copolymer phase behavior are less well-explored. We report the melt-phase self-assembly behavior of SBS triblock copolymers (S = poly(styrene) and B = poly(1,4-butadiene)) comprised of a broad polydispersity B block (M(w)/M(n) = 1.73-2.00) flanked by relatively narrow dispersity S blocks (M(w)/M(n) = 1.09-1.36), in order to identify the effects of chain length heterogeneity on block copolymer self-assembly. Based on synchrotron small-angle X-ray scattering and transmission electron microscopy analyses of seventeen SBS triblock copolymers with poly(1,4-butadiene) volume fractions 0.27 ≤ f(B) ≤ 0.82, we demonstrate that polydisperse SBS triblock copolymers self-assemble into periodic structures with unexpectedly enhanced stabilities that greatly exceed those of equivalent monodisperse copolymers. The unprecedented stabilities of these polydisperse microphase separated melts are discussed in the context of a complete morphology diagram for this system, which demonstrates that narrow dispersity copolymers are not required for periodic nanoscale assembly.
受控/“活性”聚合以及串联聚合方法为将各种单体链接到具有独特物理性质的新型功能嵌段共聚物材料中提供了诱人的机会。然而，这些合成方法的使用通常会在一个或多个共聚物链段中引入相当大的分子量多分散性，即链长不均一性。虽然单分散 AB 二嵌段和 ABA 三嵌段共聚物的自组装行为在实验和理论上都得到了很好的理解，但拓宽共聚物分子量分布对嵌段共聚物相行为的影响还没有得到很好的探索。我们报告了 SBS 三嵌段共聚物（S = 聚苯乙烯和 B = 聚 1,4-丁二烯）的熔体相自组装行为，该共聚物由较宽分子量分布的 B 嵌段（M(w)/M(n)=1.73-2.00）组成，两侧是相对较窄分子量分布的 S 嵌段（M(w)/M(n)=1.09-1.36），以便确定链长不均一性对嵌段共聚物自组装的影响。基于十七种 SBS 三嵌段共聚物的同步辐射小角 X 射线散射和透射电子显微镜分析，这些共聚物的聚 1,4-丁二烯体积分数为 0.27≤f(B)≤0.82，我们证明了多分散 SBS 三嵌段共聚物自组装成具有出乎意料的增强稳定性的周期性结构，这种稳定性远远超过了等效的单分散共聚物。在该体系的完整形态图的背景下讨论了这些多分散微相分离熔体的前所未有的稳定性，该图表明周期性纳米级组装不需要窄分散共聚物。
