No abstract

With the deepening of research on high-strength hydrogels, the multi-functional study of hydrogels has become a hot spot. In this paper, a dual cross-linked physical high-strength hydrogels is prepared by a relatively simple method. 2-Vinyl- 4,6-Diamino-2-vinyl-1,3,5-triazine (VDT) induces the formation of the first cross-linking points through the interaction of hydrogen bonds with poly(acrylamide-co-acrylic acid) (PAm-co-Ac) chains, then the secondary physical cross-linkers Fe that introduce ionic coordinates between Fe and -COO groups. Due to the synergistic effect of hydrogen bonding and ionic coordination, hydrogels possess high tensile strength (approx. 4.34 MPa), large elongation (approx. 17.64 times), and good healing properties under alkali solution after cutting into two pieces. Meanwhile, VDT contains diaminotriazine functional groups that easily form hydrogen bonds so that the polymer of hydrogels could absorb 5-fluorouridine. In addition, the contribution of ionic polymer segments enables pH to be sensitive to hydrogels and facilitates the adsorption of a large number of ionic monomers to form ionic conductive networks, the prepared hydrogel capacitor device has very high sensitivity to pressure and deformation, and can detect the movement behavior of the human body. The dual-physical cross-linked hydrogels had a selective adsorption to biological small molecules and could be assembled into a flexible wearable device with high sensitivity.

N-vinylpyrrolidinone was polymerized in 3-methylbutan-2-one, which acted as both solvent and transfer agent. The main products of this reaction were poly(N-vinylpyrrolidinone)s with methyl ketone chain ends. These polymers were formed by transfer to solvent involving abstraction of hydrogen at either the isopropyl or 1-methyl position. MALDI-TOF mass spectrometry was used to fully characterize the polymers, and several other initiation and termination events were found to occur. Thus end groups associated with initiation by and combination with the primary radical were observed. Isopropyl end groups were formed as a result of fragmentation of 3-methylbutan-2-on-1-yl radical produced as a consequence of transfer to the 1-methyl group of 3-methylbutan-2-one. This fragmentation also yielded ketene, which underwent initial propagation followed by rapid extraction of a hydrogen atom from 3-methylbutan-2-one and yields aldehyde end groups that were observed in both NMR and MALDI-TOF spectra. Also, end groups associated with termination by combination between propagating and solvent radicals were observed.

The research on multiple hydrogen bonds (H‐bonds) hydrogels have gradually aroused wide interest. In this paper, a multiple H‐bonds‐reinforced poly(acrylamide‐co‐2‐vinyl‐4,6‐diamino‐2‐vinyl‐1,3,5‐triazine)/tannic acid (P(Am‐co‐VDT)/TA) hydrogels are prepared. The results suggest that the prepared hydrogel has two types of H‐bonds crosslinking regions: A “soft” region of H‐bonds between the diaminotriazine (DAT) moieties on the polymer chains and the TA pyrogallol/catechol groups, and a “hard” region of H‐bonds forming by DAT moieties with itself. The hard crosslinking region exhibits significantly higher activation energy than the soft region. Such soft and hard dual physically crosslinked networks dramatically enhance the mechanical properties of P(Am‐co‐VDT)/TA hydrogels in a synergistic manner (tensile strength is 2.34 MPa, elongation at break is 410%). Due to the multiple hydrogen bonds, the hydrogel has good pH sensitivity and rapid response to shape memory within a few minutes. In addition, the hydrogels have the capacity of physical adsorption of the anti‐inflammatory drug diclofenac sodium and other molecules with a specific spatially arranged chemical composition. These hydrogels with high mechanical strength, excellent shape memory behavior, and capacity of adsorption of anti‐inflammatory drug could be attractive candidates for applications in the fields of biomedicine, tissue engineering, and medical materials.

Dual-responsive (light and pH) yolk−shell structured drug delivery nanocapsules, each consisting of a movable upconversion nanoparticle (UCNP) core and a shrinkable poly(methacrylic acid) (PMAA) shell, were prepared by distillation precipitation polymerization. Monodispersed NaYF 4 : Yb 3+ /Tm 3+ UCNPs were synthesized and encapsulated in silica templates, followed by coating to form PMAA shells. Subsequently, the silica templates were dissolved to form nanocavities for drug loading. The PMAA shell contains pH and ultraviolet (UV) light sensing moieties, enabling a control release upon the exposure of nanocapsules to these stimuli. The near-infrared (NIR)-to-UV feature of UCNPs allows azobenzene isomerization to be light triggered remotely to control contraction and swelling of PMAA shells. The loading efficiency of the anticancer drug doxorubicin (DXR) was up to 17 wt % due to the unique nanoporous structure of PMAA shells. The values of the diffusion coefficient under different release conditions were determined using the Baker−Lonsdale model to facilitate the design of dual-responsive drug release devices or systems.