Depolymerization of supramolecular polymers by a covalent reaction; transforming an intercalator into a sequestrator.

Controlling the reciprocity between chemical reactivity and supramolecular structure is a topic of great interest in the emergence of molecular complexity. In this work, we investigate the effect of a covalent reaction as a trigger to depolymerize a supramolecular assembly. We focus on the impact of an in situ thiol-ene reaction on the (co)polymerization of three derivatives of benzene-1,3,5-tricarboxamide (BTA) monomers functionalized with cysteine, hexylcysteine, and alkyl side chains: Cys-BTA, HexCys-BTA, and a-BTA. Long supramolecular polymers of Cys-BTA can be depolymerized into short dimeric aggregates of HexCys-BTA via the in situ thiol-ene reaction. Analysis of the system by time-resolved spectroscopy and light scattering unravels the fast dynamicity of the structures and the mechanism of depolymerization. Moreover, by intercalating the reactive Cys-BTA monomer into an unreactive inert polymer, the in situ thiol-ene reaction transforms the intercalator into a sequestrator and induces the depolymerization of the unreactive polymer. This work shows that the implementation of reactivity into supramolecular assemblies enables temporal control of depolymerization processes, which can bring us one step closer to understanding the interplay between non-covalent and covalent chemistry.

Consequences of Molecular Architecture on the Supramolecular Assembly of Discrete Block Co-oligomers.

Supramolecular block copolymers composed of discrete blocks have promising properties for nanotechnology resulting from their ability to combine well-defined morphologies with good bulk material properties. Here, we present the impact of a well-defined siloxane block in either the main-chain or present as pendant grafts on the properties of supramolecular block copolymers that form ordered nanostructures with sub-5 nm domains. For this, two types of supramolecular block copolymers were synthesized based on the ureidopyrimidinone-urethane (UPy-UT) motif. In the first, oligodimethylsiloxanes (oDMS) of discrete length were end-capped with the UPy-UT motif, affording main-chain UPy-UT-Si n . In the second, the UPy-UT motif was grafted with discrete oDMS affording grafted UPy-UT- g -Si 7 . For the two systems, the compositions are similar; only the molecular architecture differs. In both cases, crystallization of the UPy-UT block is in synergy with phase segregation of the oDMS, resulting in the formation of lamellar morphologies. The grafted UPy-UT- g -Si 7 can form long-range ordered lamellae, resulting in the formation of micrometer-sized 2D sheets of supramolecular polymers which show brittle properties. In contrast, UPy-UT-Si n forms a ductile material. As the compositions of both BCOs are similar, the differences in morphology and mechanical properties are a direct consequence of the molecular architecture. These results showcase how molecular design of the building block capable of forming block copolymers translates into controlled nanostructures and material properties as a result of the supramolecular nature of the interactions.

Synthesis and Self-Assembly of ABn Miktoarm Star Polymers.

The stability of tetrahedrally close-packed (TCP) phases in block copolymer melts is predicted by theory to depend on molecular architecture, yet no experimental studies to date have probed its effect. Motivated by this open question, here we report an efficient synthesis of asymmetric ABn miktoarm star polymers using functionalized sugars as cores for orthogonal grafting-from block copolymerizations. A combination of ring-opening and atom transfer radical polymerization produced model low dispersity materials comprising a single A = poly(lactide) (L) and multiple B = poly(dodecyl acrylate) (D) arms that amplify "conformational asymmetry" through two concerted effects: the mikto architecture and disparate block statistical segment lengths. Analyzing the self-assembly of LD2 and LD3 samples resulted in the discovery of two TCP phases, σ and A15, that remained stable to significantly higher A-block volume fractions as the number of B arms increased. These results experimentally establish the importance of conformational asymmetry and molecular architecture as powerful design tools for the self-assembly of block copolymers into nonclassical phases.