Core–Shell Gyroid in ABC Bottlebrush Block Terpolymers

Abstract

Block polymer self-assembly provides a versatile platform for creating useful materials endowed with three-dimensional periodic network morphologies that support orthogonal physical properties such as high ionic conductivity and a high elastic modulus. However, coil configurations limit conventional linear block polymers to finite ordered network dimensions, which are further restricted by slow self-assembly kinetics at high molecular weights. A bottlebrush architecture can circumvent both shortcomings owing to extended backbone configurations due to side chain crowding and molecular dynamics substantially free of chain entanglements. However, until now, network morphologies have not been reported in AB bottlebrush block copolymers, notwithstanding favorable mean-field predictions. We explored the phase behavior by small-angle X-ray scattering of 133 poly(ethylene-alt-propylene)-b-polystyrene (PEP-PS) diblock and PEP-PS-PEO triblock bottlebrush copolymers prepared by ring-opening metathesis polymerization (ROMP) of norbornene-functionalized poly(ethylene-alt-propylene) (PEP), poly(styrene) (PS), and poly(ethylene oxide) (PEO) macromonomers with total backbone degrees of polymerization N bb between 20 and 40. The PEP-PS diblocks exhibited only cylindrical and lamellar morphologies over the composition range of ca. 30−70%. However, addition of variable-length bottlebrush PEO blocks to diblocks containing 30−50% PS led to the formation of a substantial core−shell double gyroid (GYR) phase window containing 20 bottlebrush triblock specimens, which is the focus of this report. Encouragingly, the GYR unit cell dimensions increased as d ∼ N bb 0.92 , portending the ability to access larger network dimensions than previously obtained with linear AB or ABC block polymers. This work highlights extraordinary opportunities associated with applying facile ROMP chemistry to multiblock bottlebrush polymers.

Structure and Phase Behavior of Bottlebrush Diblock Copolymer-Linear Homopolymer Ternary Blends

“…SEO BBCPs were synthesized using ring-opening metathesis polymerization of the corresponding macromonomers as described in the Supporting Information. Synthesis and characterization of S and EO macromonomers (1240 and 1090 g/mol, respectively) are described in a previous publication . The polymers were characterized by proton nuclear magnetic resonance ( 1 H NMR) spectroscopy and size exclusion chromatography (SEC), and their molecular weights, dispersities, and volume fraction are summarized in Table .…”

“…Chemical structure of the SEO BBCPs employed in this study, where a and b are 9.8 and 20.3, respectively. The molecular weights of S and EO macromonomers are 1240 and 1090 g/mol, respectively, as described in a previous publication …”

Self-Healable, Stretchable, and Super-Soft Bottlebrush Polyester Elastomers for Highly Sensitive Flexible Sensors

“…Bottlebrush polymers possess a unique architecture with dense and brush-like side chains, and their backbones are forced to take an extended conformation due to the repulsion effect. − Thus, the formation of entanglements is significantly suppressed in the dry networks of bottlebrush polymers, making the bottlebrush polymer an ideal candidate for the fabrication of super-soft elastomers free of solvents. − Ring-opening metathesis polymerization (ROMP) has been a powerful tool to produce well-defined bottlebrush polymers via the “grafting-through” synthesis of norbornenyl-terminated macromonomers. − Some prior works have reported the fabrication of super-soft solvent-free elastomers by cross-linking the side chains of the ROMP-derived polymers. , However, elastomers based on bottlebrush polymers are usually cross-linked via nondynamic covalent bonds, and these materials cannot repair themselves, thereby significantly shortening their service life and reducing their reliability. , Moreover, nearly all of the existing super-soft elastomers from bottlebrush polymers consist of nondegradable materials, which is not helpful to build a sustainable society. − Therefore, biodegradable elastomers integrated with super-softness and self-healing properties are highly desirable to meet the combination of different requirements. , …”

Hierarchical Self-Assembly of ABC-Type Bottlebrush Copolymers

“…One class of chain architectures that has recently emerged and attracted special research interest in experiments is the bottlebrush-like polymer. ,,,,,− The bottlebrush copolymer (BBCP) is composed of two or more types of chemically distinct blocks that are grafted to a backbone. − The conformations of the backbone can be influenced by the solvent quality − as well as grafting density . Usually, the backbone is densely grafted by side chains and tends to adopt extended conformations as a result of the strong excluded-volume effect between side chains, that is, effectively exhibiting a certain degree of rigidity.…”