Topological Frustration as a New Parameter to Tune Morphology Revealed through Exploring the Continuum between A-B-C 3-Arm Star and Linear Triblock Polymers

Abstract

Block polymers assemble into a variety of phase-separated morphologies based on volume fraction (φ) and interactions (χ) of the respective blocks. The arrangement of three different polymer blocks could either be a 3-arm star, with each block having one terminus attached to a common junction point or a linear A-B-C architecture. A versatile strategy is reported to synthesize a series of well-defined graft polymers that lie along the unexplored continuum between a 3-arm star and an A-B-C linear triblock polymer architecture. Using the technique of single-molecule insertion, precise control over the position of graft arm C along the B chain was achieved. A series of discrete graft polymers (PMMA-b-PS-g-PEO) with fixed φ and prescribed ω values that lie on the continuum between a 3-arm star (ω = 0) and linear triblock polymer (ω = 1) were synthesized. Morphological studies using small-angle X-ray scattering and conventional and energy-filtered transmission electron microscopy reveal the transition between lamellae, perforated lamellae, and cylindrical morphologies with systematic variation in the ω values, a trend attributed to the topological frustration and the associated χ values between the three blocks. Molecular dynamic simulations of coarse-grained models were found to predict phase diagrams that are consistent with the experimentally observed morphologies. Our results suggest that changes in ω lead to topological frustration which is an important additional new design parameter that can be used to tune the morphology of multiblock polymers in addition to φ and χ.

Cationic Single-Unit Monomer Insertion (cSUMI): From Discrete Oligomers to the α-/ω-End and In-Chain Sequence-Regulated Polymers

“…The incorporation of functional moieties within the polymer backbone or chain end demonstrated that even local simple structure changes can affect whole polymer behaviors . Several strategies were reported to prepare those chain-end and in-chain functionalized polymers, among which the method of precise insertion of a single-unit monomer in controlled/living polymerization has received increasing attention due to its atomic economy and ease of operation . For example, unhomopolymerizable 1,1-diphenylethylene derivatives are classical monomers that can be singly added to the growing-chain end of anionic and cationic polymerization. , Xia and co-workers reported single additions of cyclopropene derivatives to living ring-opening metathesis polymerization (ROMP) of norbornenes .…”

Universal Phase Identification of Block Copolymers from Physics-informed Machine Learning

“…The complexity of this approach is underscored by the need for rigorous peak indexing of each SAXS pattern to accurately determine a given structure, which is complicated by issues including poor long-range order, missing reflections (i.e., form-factor minima that suppress allowed reflections), limited peak resolution, sample purity, the presence of coexisting phases, and extraneous atmospheric scattering. [9][10][11][12][13] At best, analyzing SAXS datasets is time-consuming and slow; at worst, the aforementioned issues cause challenges that only an expert-level understanding of X-ray theory can help resolve. The considerable complexity, time, and effort required to accurately identify nanostructures formed by block copolymersand other materials-is compounded by an expansive parameter space, highlighting the potential utility of a workflow that accelerates the study of new materials, ideally in a fashion that is accessible to researchers from many different backgrounds.…”