Abstract The graft‐through synthesis of Janus graft block copolymers (GBCPs) from branched macromonomers composed of various combinations of homopolymers is presented. Self‐assembly of GBCPs resulted in ordered nanostructures with ultra‐small domain sizes down to 2.8 nm (half‐pitch). The grafted architecture introduces an additional parameter, the backbone length, which enables control over the thermomechanical properties and processability of the GBCPs independently of their self‐assembled nanostructures. The simple synthetic route to GBCPs and the possibility of using a variety of polymer combinations contribute to the universality of this technique.
Abstract The random copolymerization of norbornene‐functionalized macromonomers was explored as a method of synthesizing mixed‐graft block copolymers (mGBCPs). The copolymerization kinetics of a model system of polystyrene (PS) and poly(lactic acid) (PLA) macromonomers was first analyzed, revealing a gradient composition of side chains along the mGBCP backbone. The phase separation behavior of mGBCPs with PS and PLA side chains of various backbone lengths and side chain molar ratios was investigated, and increasing the backbone length was found to stabilize the phase‐separated nanostructures. The graft architecture was also demonstrated to improve the processability of the mGBCP, compared to a linear counterpart. Investigations of mGBCPs comprised of polydimethylsiloxane and poly(ethylene oxide) side chains exemplified the diverse self‐assembled morphologies, including a Frank‐Kasper A15 phase, that can be obtained with mGBCPs synthesized by random copolymerization of macromonomers. Lastly, a ternary mGBCP was synthesized by the copolymerization of three macromonomers.
Abstract Multicomponent nanostructured materials assembled from molecular building blocks received wide attention due to their precisely integrated multifunctionalities. However, discovery of these materials with desirable composition and morphology was limited by their low synthetic scalability and narrow structural tuning window with given building blocks. Here, we report a scalable and diversity‐oriented synthetic approach to hierarchically structured nanomaterials based on a few readily accessible building blocks. Mixed‐graft block copolymers containing sequence‐defined side chains were prepared through ring‐opening metathesis copolymerization of three or four types of macromonomers. Intramolecularly defined interfaces promoted the formation of ordered hierarchical structures with lattice sizes tunable across multiple length scales. The same set of macromonomers were arranged and combined in different ways, providing access to diverse morphologies in the resultant structures.
Abstract Multicomponent nanostructured materials assembled from molecular building blocks received wide attention due to their precisely integrated multifunctionalities. However, discovery of these materials with desirable composition and morphology was limited by their low synthetic scalability and narrow structural tuning window with given building blocks. Here, we report a scalable and diversity‐oriented synthetic approach to hierarchically structured nanomaterials based on a few readily accessible building blocks. Mixed‐graft block copolymers containing sequence‐defined side chains were prepared through ring‐opening metathesis copolymerization of three or four types of macromonomers. Intramolecularly defined interfaces promoted the formation of ordered hierarchical structures with lattice sizes tunable across multiple length scales. The same set of macromonomers were arranged and combined in different ways, providing access to diverse morphologies in the resultant structures.
Abstract Graft copolymers offer a versatile platform for the design of self-assembling materials; however, simple strategies for precisely and independently controlling the thermomechanical and morphological properties of graft copolymers over wide property windows remain elusive. Here, using a library of 92 systematically varied polynorbornene-graft-polydimethylsiloxane (PDMS) copolymers, we discover a versatile backbone-pendant sequence control strategy that overcomes this challenge. We find that small structural variations of aliphatic pendant groups, e.g., cyclohexyl versus n-hexyl, of small molecule comonomers have dramatic impacts on the order-to-disorder transitions, glass transitions, mechanical properties, and self-assembled morphologies of statistical and block silicone-based graft copolymers, providing an exceptionally broad palette of designable materials properties, e.g., elastic moduli that vary over 9 orders-of-magnitude. For example, statistical graft copolymers with very high PDMS volume fractions yielded unbridged body-centered cubic (BCC) morphologies that behaved as ultra-soft, shear-thinning, plastic crystals. By contrast, lamellae-forming statistical graft copolymers provided robust, stiff, yet reprocessable silicone thermoplastics (TPs) with transition temperatures spanning over 160 °C and elastic moduli as high as 150 MPa, which is much greater than commercial silicone thermosets. Altogether, this study reveals a new pendant-mediated assembly strategy that simplifies graft copolymer synthesis and enables access to a diverse family of silicone materials, setting the stage for the broader development of self-assembling materials with tailored performance specifications.
An atom transfer radical polymerization-mediated sequential “graft-from” approach was developed to synthesize molecular brush-on-brush (MBoB)-based hierarchically branched polymers with readily tunable structural parameters.
The graft-through synthesis of Janus graft block copolymers (GBCPs) from branched macromonomers composed of various combinations of homopolymers is presented. Self-assembly of GBCPs resulted in ordered nanostructures with ultra-small domain sizes down to 2.8 nm (half-pitch). The grafted architecture introduces an additional parameter, the backbone length, which enables control over the thermomechanical properties and processability of the GBCPs independently of their self-assembled nanostructures. The simple synthetic route to GBCPs and the possibility of using a variety of polymer combinations contribute to the universality of this technique.
Polymers with complex architectures, that is, non-linear ones, have been studied extensively, as the properties of the polymer, including thermal properties and mechanical properties, are highly dependent on the chain topology. The article provides an overview of the current literature on mixed-graft block copolymers, highlighting the control over grafting density and side chain sequence in each of the synthetic routes. The unique polymer architecture allows for encoding of multiple properties into the mixed-graft block copolymer material. For more details, see Concept by M. Zhong et al. on page 8177 ff.
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