Reversible Transformations of Polymer Topologies through Visible Light and Darkness

Abstract

A fundamentally important characteristic of a macromolecule is its shape. Herein, visible light and darkness are used as the only stimuli to reversibly alter the topology of welldefined polymers in a one-pot procedure. For this, linear naphthalene-containing polyacrylates are used as scaffolds for the visible light-induced cycloaddition with various substituted triazolinediones (i.e., butyl, stearyl, perfluoro, and polymeric), resulting in differently shaped graft polymers, including brushes and combs. The thus-formed cycloadduct linkages dissociate in the dark, resulting in the regeneration of the parent linear polymer at ambient temperature, establishing a dual-topology transformation by only switching green light on and off. By applying different temperatures during the cycloreversion process, the dissociation rate of the cycloadducts can be tuned in a facile manner, thus allowing for time control over the regeneration of the parent polymer. By engineering a polymer that consists of differently substituted naphthalenes at the chain ends and on the side chains, the inherently different cycloreversion rates of the formed cycloadducts are leveraged to achieve in situ multi-topology transformations without external stimuli. The shape transformations have been repeated up to 4 times sequentially in one pot without the need of any purification. The topological alterations are microscopically depicted through reversible self-assembly, with the polymers adopting different morphologies upon visible light or darkness. The versatile yet practical nature of this polymer "reshaping" strategy provides facile access to multifaceted polymer systems and, consequently, to a plethora of potential applications thereof.

The challenges of controlling polymer synthesis at the molecular and macromolecular level

“…167 There has also been research concerning how to install reversible bonds in the branching points of various architec-tures such as MPBs or polymer stars. [168][169][170] This is interesting because it serves as a rare case of discontinuous change in polymer structure at the molecular level.…”

Regioselective photocycloaddition for light-stabilised dynamic materials design

“…linear ⇌ brush co-polymers). 29 Very recently, we also explored the potential of LSDMs for additive manufacturing by 3D multiphoton laser printing, allowing for the fabrication of microstructures that can either be stabilised to remain structurally intact under LED light, or be made to self-erase over time to introduce post-printing material responsiveness such as motion or degradability. 30…”

“…linear ⇌ brush co-polymers). 29 Very recently, we also explored the potential of LSDMs Fig. 1 (a) Light-stabilised dynamic materials' concept based on the triazolinedione (TAD)/naphthalene crosslinking chemistry, yielding light-induced covalent network formation and stabilisation under continuous irradiation while covalent de-crosslinking spontaneously occurs in the dark at ambient temperature to regain a liquid polymer system.…”

Aggregation-Induced Emission Poly(meth)acrylates for Photopatterning via Wavelength-Dependent Visible-Light-Regulated Controlled Radical Polymerization in Batch and Flow Conditions

“…Reversible-deactivation radical polymerization (RDRP), or controlled/living radical polymerization, including nitroxide mediated polymerization (NMP), reversible addition-fragmentation chain transfer (RAFT), and atom transfer radical polymerization (ATRP) polymerization, has revolutionized polymer science, enabling good control over diverse molecular topology, molecular weight, and chain length distributions. ,, Other outstanding benefits of RDRP include the ability to perform chain extension with high tolerance to varying reaction conditions , and chemical functionalities, − collectively contributing to its robustness and versatility with respect to many vinyl monomers. ,,− In particular, a broad interest in light-mediated RDRP arises as it allows for spatial and temporal control over reaction kinetics, monomer sequences, and compositions via external regulation of the reversible activation–deactivation equilibrium using a renewable source of energy. − Photochemistry can also offer sustainable reaction conditions in a move to supply energy by either photons or electrons in chemical synthesis. As such, functional materials are accessible employing RDRP with applications including nanotechnology , and therapeutics. , …”