Synthesis of bundle copolymers as an emergent class of copolymer architecture

Article https://doi.org/10.1038/s41467-026-73978-1 Synthesis of bundle copolymers as an emergent class of copolymer architecture Received: 2 October 2025 Accepted: 26 May 2026 1234567890():,; 1234567890():,; Check for updates Yuki Kametani 1,3, Rintaro Yamaguchi2, Yusuke Ando2, Yuta Kawasaki2 & Takashi Uemura 1,2 Copolymers play a central role in soft materials owing to their capacity for diverse molecular designs. While numerous combinations of composition and topology have been explored for the development of copolymers, only four types of basic architecture (random, sequence-controlled, block, and graft) have been synthetically and historically achievable. Herein, we introduce an emergent class of copolymers, bundle copolymers, comprising multiple different chains interlinked and aligned in a parallel configuration. To exemplify this concept, bundle copolymers are synthesised via nanoconfined polymerisation, in which radical polymerisation of vinyl monomers occurs alongside vinyl-functionalised polydimethylsiloxane within the one-dimensional channels of a metal–organic framework. Unlike conventional copolymers, bundle copolymers feature aligned lateral strands whose proximity can be modulated by the density of covalent junctions. This innovative approach for tying multiple chains opens an avenue for copolymer design, expanding the landscape of polymer chemistry. Copolymers, formed by combining different monomer units, are a central class of macromolecules with widespread importance in materials science and polymer chemistry. Their capacity to introduce molecular diversity often imparts properties inaccessible to homopolymers, rendering them indispensable in both fundamental research and industrial applications1–4. In 1994, the International Union of Pure and Applied Chemistry (IUPAC) formally classified copolymers into four primary categories based on the arrangement of monomer units: random (statistical), sequence-controlled (alternating, periodic), block, and graft (Fig. 1a)5. These established types and their combinations have provided an outline for the rational design of functional copolymer materials. Over the past decades, advances in polymer synthesis have enabled precise control over these architectures6–11, demonstrating that both chemical composition and structural design play a key role in dictating polymer properties12–16. Developing copolymer architectures beyond these conventional categories could expand accessible property spaces and enable a broader range of applications. Herein, we introduce a distinct class of copolymers, termed bundle copolymers (Fig. 1b), in which different polymer chains are aligned in parallel and covalently linked to form a multi-stranded architecture. This side-by-side arrangement contrasts with that in conventional copolymers, where monomer units are connected sequentially along a single backbone or at the chain termini. While each strand in a bundle copolymer preserves its intrinsic chemical identity, the bundled configuration is expected to profoundly influence chain dynamics and conformational behaviour, potentially giving rise to properties that are different from those of conventional copolymers. However, the realisation of this bundled architecture presents significant synthetic challenges. Unlike asymmetric rigid ladder motifs relying on specific monomer design17–22, the parallel alignment of distinct polymer chains remains difficult and unexplored23. To synthesise bundle copolymers, we developed a nanoconfined polymerisation approach employing the one-dimensional (1D) nanochannels of a metal-organic framework (MOF) as a spatially confined reaction environment. MOFs provide a highly versatile 1 Institute of Engineering Innovation, School of Engineering, The University of Tokyo, Bunkyo-ku, Japan. 2Department of Applied Chemistry, Graduate School of Engineering, The University of Tokyo, Bunkyo-ku, Japan. 3Present address: Department of Applied Chemistry, Faculty of Science and Technology, Keio e-mail: University, Yokohama, Japan. Nature Communications | (2026)17:4917 1 Article https://doi.org/10.1038/s41467-026-73978-1 Fig. 1 | Concept of bundle copolymers. a Schematic illustration of the four conventional types of copolymers categorised by the International Union of Pure and Applied Chemistry (IUPAC). b Schematic illustration of bundle copolymers introduced in this work. Bundle copolymers are polymers in which different polymer chains are covalently interconnected and aligned in a parallel configuration. Fig. 2 | Synthetic approach for bundle copolymers. a General schematic of bundle copolymer synthesis. The nanoconfined environment provided by metalorganic framework (MOF) nanochannels enables polymerisation of monomer B alongside polymer A, forming a bundled structure composed of commodity polymer strands (polyA-bundle-polyB). b Scheme for PDMS-bundle-vinyl polymer via MOF-templated polymerisation. c Hexagonal one-dimensional (1D) nanochannels of 1. The crystal structure is shown using a Corey–Pauling–Koltun (CPK) model (In, brown; O, red; C, grey; H, white). platform for designing nanopores, as their size and functionality can be precisely tailored by selecting from a wide variety of metal ions and organic linkers24–26. While MOFs are widely recognised for their applications in catalysis27,28, molecular capture29,30 and separation31,32, their use as nanoreactors for polymer synthesis has recently attracted attention33–35. Figure 2a presents the synthetic scheme for bundle copolymers, which capitalises on confinement within MOF nanopores. Both a polymer bearing pendant monomers (polyA) and free monomers (B) are infiltrated into 1D nanopores with diameters comparable to the thickness of the bundled polymer chains. Within these confined spaces, polyA adopts an axially extended conformation alongside B36,37. Under this spatial constraint, copolymerisation of the pendant monomers and B occurs, effectively tethering polyA and polyB chains into a bundled arrangement. Subsequent removal of the MOF scaffold yields the bundle copolymer, polyA-bundle-polyB. Importantly, this spatially guided strategy does not rely on the specific structure of the polymer species, allowing for a broad range of copolymer designs. We demonstrate the feasibility of this approach and provide structural characterisation for bundle copolymers to establish them as a category of copolymer architecture. Nature Communications | (2026)17:4917 Results In this work, bundle copolymers consisting of polydimethylsiloxane (PDMS, polyA)38 and vinyl polymers (polyB)39,40 were synthesised (Fig. 2b). This combination of commodity polymers demonstrates the generality and practical applicability of the MOF-templated approach. Methacrylate-functionalised PDMS (PDMS-MA; Supplementary Figs. 1 and 2) was introduced into the nanochannels of [In(bdc)(OH)]n (1, bdc = 1,4-benzenedicarboxylate; Fig. 2c)41, a MOF that features 1D hexagonal pores with diameters compar (...truncated)