Biopolymers such as proteins and nucleic acids are the key building blocks of life. Synthetic polymers have nevertheless revolutionized our everyday life through their robust synthetic accessibility. Combining the unmatched functionality of biopolymers with the robustness of tailorable synthetic polymers holds the promise to create materials that can be designed ad hoc for a wide array of applications. Radical polymerization is the most widely applied polymerization technique in both fundamental science and industrial polymer production. While this polymerization technique is robust and well controlled, it generally yields unfunctional all-carbon backbones. Combinations of natural polymers such as peptides, with synthetic polymers, are thus limited to tethering peptides onto the side chains or chain ends of the latter. This synthetic limitation is a critical restraint, considering that the function of biopolymers is programmed into the sequence of their main chain (i.e., primary structure). Here, we report the radical copolymerization of peptides and synthetic comonomers yielding synthetic polymers with defined peptide sequences embedded into their main chain. Key was the development of a solid-phase peptide synthesis (SPPS) approach to generate synthetic access to peptide conjugates containing allylic sulfides. Following cyclization, the obtained peptide monomers can be readily copolymerized with N,N-dimethylacrylamide (DMA)�controlled by reversible addition−fragmentation chain transfer (RAFT). Importantly, the developed synthetic strategy is compatible with all 20 standard amino acids and uses exclusively standard SPPS chemicals or chemicals accessible in one-step synthesis�prerequisite for widespread and universal application.

Highly efficient chemical ligations that operate in water under mild conditions are the foundation of bioorthogonal chemistry. However, the toolbox of suitable reactions is limited. Conventional approaches to expand this toolbox aim at altering the inherent reactivity of functional groups to design new reactions that meet the required benchmarks. Inspired by controlled reaction environments that enzymes provide, we report a fundamentally different approach that makes inefficient reactions highly efficient within defined local environments. Contrasting enzymatically catalyzed reactions, the reactivity controlling self-assembled environment is brought about by the ligation targets themselves�avoiding the use of a catalyst. Targeting [2 + 2] photocycloadditions, which are inefficient at low concentrations and readily quenched by oxygen, short β-sheet encoded peptide sequences are inserted between a hydrophobic photoreactive styrylpyrene unit and a hydrophilic polymer. In water, electrostatic repulsion of deprotonated amino acid residues governs the formation of small selfassembled structures, which enable a highly efficient photoligation of the polymer, reaching ∼90% ligation within 2 min (0.034 mM). Upon protonation at low pH, the self-assembly changes into 1D fibers, altering photophysical properties and shutting down the photocycloaddition reaction. Using the reversible morphology change, it is possible to switch the photoligation "ON" or "OFF" under constant irradiation simply by varying the pH. Importantly, in dimethylformamide, the photoligation reaction did not occur even at 10-fold higher concentrations (0.34 mM). The self-assembly into a specific architecture, encoded into the polymer ligation target, enables a highly efficient ligation that overcomes the concentration limitations and high oxygen sensitivity of [2 + 2] photocycloadditions.