Torres Vincent M, LaNasa Jacob A, Vogt Bryan D, Hickey Robert J
Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16801, USA.
Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16801, USA.
Soft Matter. 2021 Feb 19;17(6):1505-1512. doi: 10.1039/d0sm01661f.
Thermoplastic elastomers based on ABA triblock copolymers are typically limited in modulus and strength due to crack propagation within the brittle regions when the hard end-block composition favors morphologies that exhibit connected domains. Increasing the threshold end-block composition to achieve enhanced mechanical performance is possible by increasing the number of junctions or bridging points per chain, but these copolymer characteristics also tend to increase the complexity of the synthesis. Here, we report an in situ polymerization method to successfully increase the number of effective junctions per chain through grafting of poly(styrene) (PS) to a commercial thermoplastic elastomer, poly(styrene)-poly(butadiene)-poly(styrene) (SBS). The strategy described here transforms a linear SBS triblock copolymer-styrene mixture into a linear-comb-linear architecture in which poly(styrene) (PS) grafts from the mid-poly(butadiene) (PBD) block during the polymerization of styrene. Through systematic variation in the initial SBS/styrene content, nanostructural transitions from disordered spheres to lamellar through reaction-induced phase transitions (RIPT) were identified as the styrene content increased. Surprisingly, maximum mechanical performance (Young's modulus, tensile strength, and elongation at break) was obtained with samples exhibiting lamellar nanostructures, corresponding to overall PS contents of 61-77 wt% PS (including the original PS in SBS). The PS grafting from the PBD block increases the modulus and the strength of the thermoplastic elastomer while preventing brittle fracture due to the greater number of junctions afforded by the PS grafts. The work presented here demonstrates the use of RIPT to transform standard SBS materials into polymer systems with enhanced mechanical properties.
基于ABA三嵌段共聚物的热塑性弹性体，当硬端嵌段组成有利于形成具有连通域的形态时，由于在脆性区域内的裂纹扩展，其模量和强度通常受到限制。通过增加每条链的连接点或桥接点数量来提高阈值端嵌段组成以实现增强的机械性能是可行的，但这些共聚物特性也往往会增加合成的复杂性。在此，我们报道了一种原位聚合法，通过将聚苯乙烯（PS）接枝到商用热塑性弹性体聚苯乙烯-聚丁二烯-聚苯乙烯（SBS）上，成功增加了每条链的有效连接点数量。这里描述的策略将线性SBS三嵌段共聚物-苯乙烯混合物转变为线性-梳状-线性结构，其中在苯乙烯聚合过程中，聚苯乙烯（PS）从中间聚丁二烯（PBD）嵌段接枝。通过系统改变初始SBS/苯乙烯含量，随着苯乙烯含量增加，通过反应诱导相变（RIPT）确定了从无序球体到片层的纳米结构转变。令人惊讶的是，具有片层纳米结构的样品获得了最大机械性能（杨氏模量、拉伸强度和断裂伸长率），对应于PS总含量为61-77 wt%的PS（包括SBS中的原始PS）。从PBD嵌段接枝的PS增加了热塑性弹性体的模量和强度，同时由于PS接枝提供了更多的连接点而防止了脆性断裂。本文展示了利用RIPT将标准SBS材料转变为具有增强机械性能的聚合物体系。
