Stepwise Light‐Induced Dual Compaction of Single‐Chain Nanoparticles

Abstract

A photochemical strategy for the sequential dual compaction of single polymer chains is introduced. Two photoreactive methacrylates, with side chains bearing either a phenacyl sulfide (PS) or an α-methylbenzaldehyde (photoenol, PE) moiety, are selectively incorporated by one-pot iterative reversible-addition fragmentation chain transfer copolymerization into the outer blocks of a well-defined poly(methyl methacrylate) based ABC triblock copolymer possessing a nonfunctional spacer block (M = 23 400 g mol , Đ = 1.2; ≈15 units of each photoreactive moieties of each type) as well as in model statistical copolymers bearing only one type of photoreactive unit. Upon UVA irradiation, PS and PE lead to highly reactive thioaldehydes and o-quinodimethanes, which rapidly react with dithiol and diacrylate linkers, respectively. The monomerfunctional copolymers are employed to establish the conditions for controlled intramolecular photo-crosslinking, which are subsequently applied to the bifunctional triblock copolymer. All compaction/folding experiments are monitored by size-exclusion chromatography and dynamic light scattering. The dual compaction consists of two events of dissimilar amplitude: the first folding step reveals a large reduction in hydrodynamic diameters, while the second compaction lead to a far less pronounced reduction of the single-chain nanoparticles size, consistent with the reduced degrees of freedom available after the first covalent compaction step.

Access to Photoreactive Core‐Shell Nanomaterials by Photoinitiated Polymerization‐Induced Self‐Assembly

“…The available set of photoinduced reactions constitutes an efficient, finely controllable, and environmentally friendly toolbox in chemistry for applications as varied as light‐induced deprotection reactions in organic synthesis, photopolymerization in dentistry, 3D printing, and photocatalysis . Importantly, the use of so‐called λ‐orthogonal reactions, which can be triggered independently by suitable choice of reaction partners and irradiation wavelengths, allows complex reaction schemes and new functions in materials The incorporation of photoreactive groups in polymeric materials enables a great variety of possibilities, e. g ., collapse of single‐chain nanoparticles, block copolymer synthesis by classic free‐radical polymerization, and crosslinking reactions . The usual mild reaction conditions also enable bioconjugation onto materials such as nanoparticles (NPs) .…”

Macromolecular Superstructures: A Future Beyond Single Chain Nanoparticles

“…Reactions using thermally reactive intermediates, which are photochemically generated, generally have lifetimes too long to effect the described selectivity. Reaction of such photo caged intermediates such as nitrile imines, thioaldehydes and o ‐quinodimethanes suffer from the previously noted ultra‐dilute conditions in the range of 0.01 mg mL −1 .…”

“…Due to the living character of polymerization, all particles continue to grow for the entire duration of the experiment, to yield particles each composed of a chain of identical length. As the growing chains are immediately deposited on the growing single‐crystal particle during this process, particle shape evolves uniformly over time during polymerization . Reproduced with permission from Nat Commun 10, 2592 (2019).…”

“…As the growing chains are immediately deposited on the growing single-crystal particle during this process, particle shape evolves uniformly over time during polymerization. [41] Reproduced with permission from Nat Commun 10, 2592 (2019). Copyright © 2019, Springer Nature.…”

Advances in Phototriggered Synthesis of Single-Chain Polymer Nanoparticles

“…Schematic illustration of the sequential photoactivated multifolding of a precursor containing phenacyl sulfide and protected α-methylbenzaldehyde units with a dithiol cross-linker (λ = 355 nm, 30 min) and a diacrylate cross-linker (λ = 320 nm, 30 min), respectively. Reprinted from [57] with permission.…”