Volume 54 Issue 7, July 2022

This focus review describes a biosensing strategy called “chemical tongue”, which mimics the human taste system by employing fluorogenic materials containing various chemical structures in conjunction with statistical techniques. The focus is on the design of polymer-based chemical tongues and their applications with various complex biological samples. The chemical-tongue strategy is capable of recognizing biological samples in a unique manner that does not, in contrast to conventional approaches, rely on specific interactions, thereby potentially opening avenues for unexplored uses of polymers in a wide range of research areas.

Spherical hydrogels (ENTG-co-PSβCyD) were prepared by photocopolymerization of the polyethylene glycol macromonomer ENTG and the polysubstituted photocross-linkable β-cyclodextrin (β-CyD) macromonomer PSβCyD. The optimum composition ratio for use of this hydrogel as a microbe-immobilized support was examined, along with the phenol (PhOH)-removing capability of PhOH-decomposing bacteria immobilized on this hydrogel. The best microbe-immobilized support had a PhOH-removal rate of 0.76 mg (L h hydrogel g)⁻¹. This removal rate was 1.7 times faster, and the amount of free bacteria in the assay medium was 3.6 times lower than the corresponding data obtained using a microbe-immobilized hydrogel without PSβCyD.

Amine-containing polysilsesquioxane (PSQ) membranes were studied with regard to their CO₂ separation ability. PSQ membranes were prepared by using amine-containing monomers, bis(triethoxysilylpropyl)amine (BTESPA), (aminopropyl)triethoxysilane (APTES), and (aminoethylaminopropyl)triethoxysilane (AEAPTES). The CO₂ permeances of the membranes prepared by 1:1 copolymerization with bis(triethoxysilyl)ethane increased in the order of AEAPTES-derived membranes < APTES-derived membranes < BTESPA-derived membranes, and their CO₂/N₂ permselectivities decreased in the same order. Copolymerization under acidic conditions resulted in the formation of ammonium-containing membranes with improved CO₂ permeances and acceptable CO₂/N₂ permselectivities.

Silver(I) ions in nonpolar solvents were used to polymerize expanded l-lysine and l-ornithine derivatives. Introducing a bulky hydrophobic acyl group into the terminal amino group of the side chain increased the solubility of the amino acid in chloroform. Polymerization proceeded via the formation of head-to-head and tail-to-tail linkages, which resulted in chiral helical structures. Circular dichroism measurements and density functional theory calculations were used to estimate the overall secondary structures, which were significantly different from each other despite the small difference, namely, with or without the fourth CH₂ moiety.

Living radical polymerization was carried inside a liposome to prepare a deformable nanocapsule. The obtained nanocapsules showed good absorption of chemical substances depending on the binding ability to the incorporated polymers, and the absorption capacity could be controlled by the length and dissolved state of the polymer chains. Dynamic morphological changes in the capsules were observed when liposomes with high membrane fluidity were employed. Deformation of nanocapsules were induced by altering the pH value and ionic strength, resulting in the release of cargo in response to these environmental conditions.

Amphiphilic peptides bearing an alternating binary pattern of hydrophilic and hydrophobic repeating units were synthesized via polymerization exploiting Ugi’s four-component condensation reaction (Ugi’s 4CC) as the elemental polymerization reaction. We performed turbidity measurements on the aqueous polymer solutions at various temperatures. The results showed that the structural effects of the alternating peptides had the following impacts on thermoresponsiveness: (i) alternating peptides consisting of repeating hydrophilic and hydrophobic units tended to adopt upper critical solution temperature (UCST) behavior; and (ii) when the hydrophobes in the polymer were large enough for the intrachain hydrophobic interactions, the polymer displayed lower critical solution temperature (LCST) behavior. We also prepared thermoresponsive hydrogels comprising alternating peptide skeletons as the cross-linking points. Alternating peptides with LCST behavior may be useful for creating peptide-based smart materials in the future.

The shear-induced crystallization behavior of the blends of cyclic polyethylene (C-PE) and linear polyethylene (L-PE) was investigated. This figure shows the formation rate of shish-like fibril crystals (I) in the blend systems of C-PE(230k)/L-PE(42k) and C-PE(230k)/L-PE(104k) against the weight fraction of L-PE, Φ_L-PE. I reached a maximum at a certain Φ_L-PE. As Φ_L-PE increased, that is, as the entanglement density increased, the formation of the oriented melt was promoted. Crystallization was also suppressed by the entanglements. The maximum value of I was observed owing to these two competing factors.

PLA-pectin biocomposites were prepared at pectin contents from 2 to 8% w/w. The mechanical properties of PLA-pectin were considerably improved after the annealing process, especially at 4% w/w of pectin according to being the best dispersion indicated by SEM and synchrotron-based FT-IR mapping. Moreover, pectin aids in the crystallization of PLA confirmed by in situ SR-WAXS. The crystallization rate and crystallinity were maximum at 8% w/w pectin addition. Finally, the pectin dispersion is the main factor in determining the mechanical and thermal properties of biocomposites.

Synergistic effects of adding silica, as a secondary filler, to styrene-butadiene rubber composites highly filled with carbon black was investigated. It was shown that there is a critical concentration of silica at which improvements in the Payne effect, mechanical properties, abrasion resistance, and heat build-up were at extrema. This behavior was attributed to the filler networking in the hybrid filler systems, at which work of adhesion in a three-component system was considered as the driving force for flocculation of the primary filler and final morphology of fillers in hybrid composites.