Abstract
A library of copolymers with pendant, protected ureido-pyrimidinone (UPy) groups was prepared applying controlled polymerization techniques. The polymer backbones were based on polyacrylate, polymethacrylate, polystyrene and polynorbornene and differ in stiffness, molecular weight and the linking moiety between the backbone and the UPy group. In all cases, the percentage of protected UPy groups was kept constant. The effect of solvent on the behaviour of the polymers before and after removal of the protecting groups was evaluated in, among others, chloroform and tetrahydrofuran (THF). After deprotection of the UPy protecting group, the UPys dimerize via four-fold H-bonding in THF, inducing a collapse into single-chain polymeric nanoparticles (SCPNs), as evidenced by a combination of 1H-NMR spectroscopy, size-exclusion chromatography and dynamic light scattering. In chloroform, on the other hand, dimerization of the UPy groups is present but interchain interactions occur as well, resulting in less-defined SCPNs. Remarkably, the flexibility of the polymer backbone, the polymer molecular weight and the nature of the linker unit all do not affect SCPN formation. In contrast, the interaction between solvent and the UPy moiety is a critical parameter for SCPN formation. For example, strong intramolecular dimerization of the UPys is observed in THF while interparticle interactions are suppressed. From this investigation we conclude that a wide variety of polymer backbones are suitable for polymer collapse via supramolecular interactions and thus allow for the formation of SCPNs but that the solvent choice is crucial to enhance intramolecular H-bonding and, at the same time, to suppress interparticle interactions.
Highlights
The eld of supramolecular polymer chemistry has developed from the fusion of classic polymer science and supramolecular chemistry.[1,2] the creation of functional, highly ordered architectures that combine the excellent material properties of a classic polymer with the reversible and dynamic nature of non-covalent interactions is pursued.[1,3] In the past decade, a number of applications emerged from this interdisciplinary eld, ranging from innovative scaffolds for biomedical applications,[4] to electronic devices,[5] and self-healing materials.[6]
With the help of size exclusion chromatography (SEC) and dynamic light scattering (DLS), we evaluate the importance of solvent, polymer molecular weight, spacer length between UPy and polymer and the stiffness of the polymer in the folding behaviour of the single-chain polymeric nanoparticles (SCPNs)
In light of a recent report on issues with copolymerizing UPybased monomers, we opted for the post-functionalization strategy.14b Random copolymers with a degree of polymerization (DP) of around 200 and a loading of 10% of post-functionalizable groups were selected
Summary
The eld of supramolecular polymer chemistry has developed from the fusion of classic polymer science and supramolecular chemistry.[1,2] the creation of functional, highly ordered architectures that combine the excellent material properties of a classic polymer with the reversible and dynamic nature of non-covalent interactions is pursued.[1,3] In the past decade, a number of applications emerged from this interdisciplinary eld, ranging from innovative scaffolds for biomedical applications,[4] to electronic devices,[5] and self-healing materials.[6] The seminal work of Stadler[7] and Rotello[8] highlighted the potential of covalent polymers with pendant H-bonding groups, while advances in controlled polymerization techniques triggered renewed interest in the synthesis and application of such “sticky” polymers.[9,10] Recently, the tuneable, In a number of examples, secondary structures mimicking ahelices,[13,15] b-sheets14a,b or both14c have been observed within the SCPNs, sometimes even when the solvent is water. The quest for SCPNs that display a compartmentalised, de ned three-dimensional shape as a result of a tertiary structure, a feat currently only attainable by DNA and proteins, is a crucial theme.
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