Multi-Responsive Polysiloxane/Poly(N-isopropylacrylamide) Interpenetrating Networks Containing Urea and Thiourea Groups

Hexakis-2-(β-carboxyethenylphenoxy)cyclotriphosphazene: Synthesis, Properties, Modeling Structure

Condensation of hexakis-2-(formylphenoxy)cyclotriphosphazene with malonic acid yielded hexakis-2-(β-carboxyethenylphenoxy)cyclotriphosphazene (2-CEPP), whose structure was confirmed by 31P, 1H, 13C NMR spectroscopy and MALDI-TOF mass spectrometry. A quantum-chemical calculation for the 2-CEPP molecule using the ab initio methods in the 6-311G** basis set and the DFT-PBE0/6-311g** method was performed with geometry optimization of all parameters by the standard gradient method. The acid strength of 2-CEPP was theoretically estimated. Using the small-angle X-ray scattering method, it was found that 2-CEPP is an amorphous substance, which, when heated, can transform into a crystalline state. However, when heated at 370 °C, 2-CEPP undergoes decarboxylation and polymerization to form an insoluble heat-resistant product. The occurrence of decarboxylation and polymerization reactions in the formed styrene fragments was confirmed by thermal (differential-scanning calorimetry) and spectral (solid-state 13C NMR spectroscopy) analysis.

Anion-Induced Reversible Actuation of Squaramide-Crosslinked Polymer Gels

Supramolecular anion binding to squaramide crosslinkers in poly(N,N-dimethylacrylamide) gel networks enhances swelling and allows reversible chemically driven actuation. The volume swelling ratio of the gels is shown to depend on both the type of anion and its concentration. ¹H NMR and UV-vis titrations with the squaramide crosslinkers reveal a relationship between anion binding affinity and the concentration-dependent swelling behavior. Gel swelling is shown to be reversible, and by embedding a solid support into rod-shaped gels, soft actuators are fabricated that undergo forward and backward bending motion in response to changing anion concentration. The swelling and bending process, which is accompanied by intense green coloration of the gel, is achieved by using only low amounts of crosslinker. This macroscopic actuation achieved by anion binding to specific molecular entities in the polymer network will open new opportunities in the field of chemically responsive materials.

Dual Temperature and Metal Salts-Responsive Interpenetrating Polymer Networks Composed of Poly (N-isopropylacrylamide) and Polyethylene Glycol

Novel interpenetrating polymer networks (IPNs) composed of poly(N-isopropylacrylamide) (poly-NIPAM) and polyethers—namely, polyethylene glycol (PEG) and poly(tetramethylene oxide)—were synthesized in the absence and presence of polysiloxane containing a silanol residue. Gelation was accomplished using end-capped polyethers with trimethoxysilyl moieties and proceeded through simultaneous radical gelation of NIPAM and condensation of the silyl groups to form siloxane linkages. Thus, a novel one-step method constructing an IPN structure was provided. The obtained IPNs showed a gentle temperature-responsive volume change in water owing to the constructed poly-NIPAM gel component. In addition, a specific color-change response to chemical stimuli, such as CuCl₂ and AgNO₃ in water, was observed only when both components of poly-NIPAM and PEG existed in a gel form. For example, a single network gel composed of poly-NIPAM or PEG was isolated as a pale blue hydrogel, whereas IPNs composed of poly-NIPAM and PEG components turned yellow after swelling in an aqueous CuCl₂ solution (0.1 M, pale blue). Dual-responsive functionalities of the synthesized hydrogels to temperature and metal salts, along with volume and color changes, were demonstrated.

Silicon-Containing Polymeric Materials

When thinking about a chemical element that has contributed to the technological progress over the last two centuries, carbon and all carbon-based materials immediately come to mind [...].