Domain Bridging in Thermoplastic Elastomers of Star Block Copolymer

Abstract

The performance of thermoplastic elastomers composed of block copolymers is dependent upon the molecular bridges linking together the discrete minority domains. Here we devise a strategy for calculating the bridging statistics for complex block copolymer architectures, using self-consistent field theory. The method is demonstrated on (AB) M stars with M identical diblock arms. The fraction of molecules forming bridges, νb, is found to increase rapidly with M to values well beyond that of conventional ABA triblock copolymers. Once M is of order 10, virtually all molecules form bridges, and furthermore their arms tend to be distributed equally among neighboring minority domains. These high bridging fractions combined with the tendency of single molecules to bridge multiple domains make diblock-arm stars an excellent candidate for improved thermoplastic elastomers.

Recent advances on the structure–properties relationship of multiblock copolymers

“…Since the late 90s, polymer-oriented SCFT coupled with numerical resolution methods have emerged as the state-of-the-art technique to predict the structure of multiphasic polymer-based systems, including MBCs. 78,80,81,103,104 In a paper published in 2016, Arora et al notably invite polymer physicists to utilize more SCFT to design their experiments, similarly as what is done in fluid mechanics or quantum chemistry with similar computational tools. 80 In the present context, SCFT consists of reducing the many-body problem describing the thermodynamics of a polymer melt into an easier problem of analyzing the conformation of a single chain in a potential field created by the other chains.…”

“…Also, it requires to compute interactions for the different couples of beads, that is, AA, AB and BB resulting in a minimum of five different potentials to be defined. Once fixed the model parameters and the chains topology (linear, 132,133 star, 81,134 ring, 135,136 …), the simulation box is equilibrated at high temperature. One can then focus on the phase separation occurring upon cooling, by following the variation of volume (or enthalpy).…”

“…"Lighter" computational methods such as SCFT-oriented simulations evoked in Section 2.1 appear therefore in this context as a great alternative. In Figure 6, we have adapted recent results from References [81,133,136] focusing on the link between the molecular topology and the resulting microphase separation for linear MBCs, star MBCs with diblock arms, and diblock ring polymers, respectively.…”

“…In other words, in spite of a growing number of available methods of characterization, a great part of the knowledge on MBCs remains empirical. A few exceptions are nevertheless worth to mention, starting from the analytical model proposed by Krause in the 70s 77 to the continuous development of the self-consistent field theory (SCFT) in the 90s 78,79 until its most recent advances 80,81 (see Section 2.1).…”

“Bridge” Makes Differences to the Self-assembly of Block Copolymers

“…我们之前已经提到: AB-型嵌段共聚物 也可以形成桥连, 如 ABA 三嵌段共聚物(如图 6); 但是 桥连构型的比率通常不够高, 在球状结构中是 75%～ 80%, 而在柱状结构中只有 60%～65% [39] . 我们提出: (AB) n 星型结构的"组合构象熵效应"可以大幅度提高 桥连的比率, 例如当臂数 n＝5 时, 球状结构的桥连比率 超过了 99%, 而柱状结构的也超过了 95% [44] . 实现了高 比率的桥连后, 我们需要解决的问题就是调节桥连的拉 伸程度.…”