Molecular Architecture Directs Linear–Bottlebrush–Linear Triblock Copolymers to Self-Assemble to Soft Reprocessable Elastomers

Abstract

Linear−bottlebrush−linear (LBBL) triblock copolymers represent an emerging system for creating multifunctional nanostructures. Their self-assembly depends on molecular architecture but remains poorly explored. We synthesize polystyrene-block-bottlebrush polydimethylsiloxane-block-polystyrene triblock copolymers with controlled molecular architecture and use them as a model system to study the self-assembly of LBBL polymers. Unlike classical stiff rodflexible linear block copolymers that are prone to form highly ordered nanostructures such as lamellae, at small weight fractions of the linear blocks, LBBL polymers self-assemble to a disordered sphere phase, regardless of the bottlebrush stiffness. Microscopically, characteristic lengths increase with the bottlebrush stiffness by a power of 2/3, which is captured by a scaling analysis. Macroscopically, the formed nanostructures are ultrasoft, reprocessable elastomers with shear moduli of about 1 kPa, two orders of magnitude lower than that of conventional polydimethylsiloxane elastomers. Our results provide insights on exploiting the self-assembly of LBBL polymers to create soft functional nanostructures.

Self-Assembly of Flexible Linear–Semiflexible Bottlebrush–Flexible Linear Triblock Copolymers

“…The observed anomalous self-assembly of architecturally semiflexible BCPs calls for further theoretical studies. It also cautions the use of the conventional definition of the bottlebrush contour length as that of the bottlebrush backbone, ,,, which often ignores the contribution of side chains. The side chains can rearrange to occupy the space near the ends of the bottlebrush backbone.…”

Microphase Segregation in the Melts of Bottlebrush Block Copolymers

“…A very recent study on poly(styrene)− poly(dimethylsiloxane)−poly(styrene) ABA block copolymer with PDMS bb block B demonstrated spherical morphology of PS domains at high contents of PDMS. 56 The data for samples with backbone length M B ≫ n B is collected in Table S6 in the SI. We mark the location of these samples in Figure 5 by violet diamonds, using the value of α B ≈ 0.50, evaluated for PDMS block from the data for PMMA−PDMS−PMMA block copolymer.…”

Applications of Hybrid Polymers Generated from Living Anionic Ring Opening Polymerization

“…Siloxane macromers appear to be of particular interest in creating these structures due to both the palette of functionality and the intrinsic flexibility of the siloxane structures, which allows the length-scale of the filaments to extend beyond the primary polymer backbone or nano-feature without imposing a “hard” structural domain. Siloxane macromers allow entry to classes of materials that possess an unusually low modulus while maintaining mechanical failure properties consistent with the main polymer backbone for both methacrylate [ 96 ] and norbornene [ 84 ] functional siloxane macromers.…”