Cationic polymers and DNA origami form electrostatic complexes for biotechnological applications.

This work explores the reactivity of a reversible superbase–CO ₂ zwitterion, which can be used as a stoichiometric source of CO ₂ .

We show ionically crosslinked, temperature responsive reversible or irreversible hydrogels of anionic cellulose nanocrystals (CNCs) and methacrylate terpolymers by mixing them homogeneously in the initially charge-neutral state of the polymer, which was subsequently switched to be cationic by cleaving side-groups by UV-irradiation. The polymer is a random terpolymer poly(di(ethylene glycol) methyl ether methacrylate)-rnd-poly(oligo(ethylene glycol) methyl ether methacrylate)-rnd-poly(2-((2-nitrobenzyl)oxycarbonyl)aminoethyl methacrylate), i.e., PDEGMA-rnd-POEGMA-rnd-PNBOCAEMA. The PDEGMA and POEGMA repeating units lead to Lower Critical Solution Temperature (LCST) behavior. Initially, homogeneous aqueous mixtures are obtained with CNCs and no gelation is observed even upon heating to 60 oC. However, upon UV-irradiation the NBOCAEMAs are transformed to cationic 2-aminoethyl methacrylate (AEMA) groups, as 2-nitrobenzaldehyde moieties are cleaved. The resulting mixtures of anionic CNC and cationic PDEGMA-rnd-POEGMA-rnd-PAEMA show gelation for sufficiently high polymer fractions upon heating to 60 oC due to the interplay of ionic interactions and LCST. For short heating times the gelation is thermoreversible whereas for long enough heating times irreversible gels can be obtained, indicating importance of kinetic aspects. The ionic nature of the crosslinking is directly shown by adding NaCl, which leads to gel melting. In conclusion, the optical triggering of ionic interaction allows a new way for ionic nanocellulose hydrogel assemblies.

Nanodiamonds (NDs) can considerably improve the mechanical and thermal properties of polymeric composites. However, the tendency of NDs to aggregate limits the potential of these non-toxic, mechanically- and chemically-robust nanofillers. In this work, tough, flexible, and stimuli-responsive polyelectrolyte films composed of cross-linked poly(butyl acrylate-co-dimethylaminoethyl methacrylate) (P(BA-co-DMAEMA)) were prepared by photopolymerization. The effects of the added carboxylate-functionalized NDs on their mechanical and stimuli-responsive properties were studied. When the negatively charged NDs were added to the polymerization media directly, the mechanical properties of the films changed only slightly, because of the uneven distribution of the aggregated NDs in the films. In order to disperse and distribute the NDs more evenly, a prepolymerized polycation block copolymer complexing agent was used during the photopolymerization process. This approach improved the mechanical properties of the films and enhanced their thermally-induced, reversible phase-transition behavior.