Takayuki Nakahira

Salt-induced volume phase transition of poly(N-isopropylacrylamide) gel

The salt effect on the phase transition of N-isopropylacrylamide (NIPA) gel was studied. The swelling behavior of the NIPA gel strongly depends on the salt concentration and is well described as a function of the chemical potential difference of water molecules in solution from that at the transition. From the analysis of the OH stretching, Raman spectra in water and in various aqueous solutions in terms of collective proton motions reveals that the presence of salts tends to disrupt or distort the water molecules in hydrophobic hydration shell around the NIPA gel. This leads to inducing the growth of the cluster shell around the salts, which leads to gel collapse. The volume phase transitions due to the different types of perturbation (temperature, salt) are induced by the same mechanism, hydrophobic hydration and dehydration, and therefore can be described in a unified manner in terms of the chemical potential and the collective proton motions of water molecules.

An organic red-emitting diode with a water-soluble DNA–polyaniline complex containing Ru(bpy)32+

A Ru(bpy)32+-based red-emitting diode with a fast turn-on response was fabricated by employing a novel, processable and water-soluble DNA–photopolymerized PAn complex containing Ru(bpy)32+.

Surface modification of polymer latex particles by AGET ATRP of a styrene derivative bearing a lactose residue

Grafting of a styrene derivative bearing a lactose residue, i.e., N-2-4-(vinylbenzenesulfonamido)ethyl lactobionamide (VBSAELA), onto polymer latex particles was carried out in aqueous media by activator generated electron transfer atom transfer radical polymerization (AGET ATRP). The core polymer latex particles having alpha-chloroester groups as ATRP-initiating groups were prepared by miniemulsion polymerization of styrene and 2-chloropropionyloxyethyl methacrylate (CPEM) in the presence of a polymerizable surfactant, i.e., N,N-dimethyl-N-dodecyl-N-2-methacryloyloxyethylammonium bromide (C(12)Br). AGET ATRP was initiated with tris[(2-pyridylmethyl)amine] copper (II) dichloride and L-ascorbic acid. Dynamic light scattering (DLS) revealed that the P(St-CPEM)-g-P(VBSAELA) particles possess graft layers of 10 nm in thickness on the core particles of 91 nm in diameter. Critical coagulation concentration measurement revealed that the dispersion stability of the particles in water increased due to hydrated P(VBSAELA) shell layers. Adsorption of bovine serum albumin (BSA) onto the particles was considerably suppressed by the hydrated shell layers.

Preparation of organic/inorganic composites by deposition of silica onto shell layers of polystyrene (core)/poly[2-(N,N-dimethylamino)ethyl methacrylate] (shell) particles

Organic/inorganic composites were prepared by catalytic hydrolysis and subsequent condensation of tetraethoxysilane (TEOS) in a shell layer of core-shell polymer particles. First, core-shell particles were prepared by emulsifier-free emulsion polymerization of styrene (St) with 2-chloropropionyloxyethyl methacrylate (CPEM) using potassium persulfate as an initiator, followed by surface-initiated activator generated electron transfer-atom transfer radical polymerization (AGET-ATRP) of 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA). Dynamic light scattering revealed that hydrodynamic diameter of the particle increased from 482 to 931 nm after AGET-ATRP of DMAEMA. The amount of grafted DMAEMA was determined to be ca. 10 mol% with respect to (wrt) St by (1)H NMR. Second, the composite particles were prepared by adding TEOS into a water/methanol dispersion of the P(St-CPEM)-g-P(DMAEMA). The P(St-CPEM)-g-P(DMAEMA)-SiO(2) composite particles containing ca. 50 wt.% of silica wrt the total weight were obtained. Hollow silica shell particles were also obtained by extraction of polymer components from the composites with tetrahydrofuran.

Enzymatic miniemulsion polymerization of styrene with a polymerizable surfactant

Enzymatic polymerization is a powerful tool for synthesizing useful polymeric materials. However, the preparation of polymer particles by enzymatic polymerization has been reported only rarely. We demonstrated herein the preparation of polystyrene particles by enzyme-mediated miniemulsion polymerization with a polymerizable surfactant, i.e., N,N-dimethyl-N-n-dodecyl-N-2-methacryloyloxyethylammonium bromide (C12-DMAEMA), using a horseradish peroxidase (HRP)/H2O2/β-diketone system in water. Effects of various amounts of HRP, H2O2, and β-diketone on styrene conversion and particle size were investigated. The obtained polystyrene particles were characterized using DLS, GPC, and SEM measurements, and the polymerization kinetics was examined. Comparison of five β-diketones was also conducted: acetylacetone (ACAC), ethylacetoacetate (EAA), 1,3-cyclopentanedione (CP), tetronic acid (TA), and dibenzoylmethane (DM), for enzymatic miniemulsion polymerization.

Preparation, characterization, and optical properties of disulfide-comprising oligo(2,5-bis(thiomethyl)-1,4-dithiane) and its poly(S-alkylcarbamate)

Novel poly[S-alkylcarbamate]s were prepared by polyaddition of oligo [2,5-bis(thiomethyl)-1,4-dithiane] (oligo[BMMD]) with isocyanate for optical polymers having high refractive indices (nD) and Abbes numbers (νD). Oxidation of 2,5-bis(mercaptomethyl)-1,4-dithiane (BMMD) with ferric chloride or methylsulfoxide gave oligo[BMMD] in a mixture of n-mers (typically n = 1−6) by disulfide-forming propagation. The use of the former oxidant giving mainly BMMD dimer appeared to be preferable for the subsequent preparation of transparent poly[S-alkylcarbamate]. With 1,3-bis(isocyanatomethyl)cyclohexane, 1,6-diisocyanatohexane, or 1,3,5-tris(isocyanatomethyl)cyclohexane, nD:νD values of poly[S-alkylcarbamate]s ranging from 1.609:38.0 to 1.659:35.6 were comparable to those of flint glasses. Copoly[S-alkylcarbamate]s were prepared using 2-mercaptoethylsulfide or 2-mercaptoethylether for modification of nD and νD. Contribution of the disulfide bond and the 1,4-dithiane ring in oligo[BMMD] to increase nD is discussed in terms of molar refraction. Suppressed UV absorption of the polymer, which caused high νD, was attributed to the trans-gauche-trans conformation around the disulfide bond. This work shows that oligo[BMMD] serves as a useful material for the preparation of polymers having high nD and high νD and that poly[S-alkylcarbamate]s thus obtained are promising optical materials.

Surface-initiated enzymatic vinyl polymerization: synthesis of polymer-grafted silica particles using horseradish peroxidase as catalyst

A novel method of surface-initiated enzymatic vinyl polymerization was used to synthesize organic–inorganic hybrid core–shell particles comprising a silica core and a polyacrylamide shell covalently attached to the core surface.

Multinuclear NMR study on the sol-gel transition of gellan gum

A multinuclear NMR study was carried out to study the interaction between group I cations (Na+, K+, and Rb+) and gellan gum. It was found that the NMR parameters of 39K and 87Rb ions undergo an abrupt change in the vicinity of the sol-gel transition temperature. On the other hand, the NMR parameters of 23Na do not show any singular behavior. These results suggest that 39K and 87Rb ions (so-called gel-forming cations) selectively interact with gellan gum.

Preparation of organic/inorganic hybrid and hollow particles by catalytic deposition of silica onto core/shell heterocoagulates modified with poly[2-(N,N-dimethylamino)ethyl methacrylate]

The organic/inorganic hybrid particles PSt/P(St-CPEM)(θ)-g-PDMAEMA/SiO(2) were prepared by catalytic hydrolysis and subsequent polycondensation of tetraethoxysilane in the poly[2-(N,N-dimethylamino)ethyl methacrylate] (PDMAEMA) layers grafted on the PSt/P(St-CPEM)(θ) core/shell heterocoagulates. The micron-sized PSt core and the submicron-sized P(St-CPEM) shell particles bearing ATRP initiating groups were synthesized by dispersion polymerization of styrene (St) and emulsifier-free emulsion polymerization of St with 2-chloropropionyloxyethyl methacrylate (CPEM), respectively. The raspberry-shaped PSt/P(St-CPEM)(θ) heterocoagulates with a controlled surface coverage (θ=0.51, 0.81) were prepared by hydrophobic coagulation between the core and the shell particles in an aqueous NaCl solution near the T(g) of P(St-CPEM). Surface modification of heterocoagulates was carried out by ATRP of DMAEMA from the shell particles adsorbed on the core particles. Silica deposition was performed by simply adding tetraethoxysilane to a water/methanol dispersion of PSt/P(St-CPEM)(θ)-g-PDMAEMA. The SEM and TGA revealed that the resulting PSt/P(St-CPEM)(θ)-g-PDMAEMA/SiO(2) composites maintain a raspberry-like morphology after deposition of silica onto the PDMAEMA layer grafted on heterocoagulates. The micron-sized, raspberry-shaped or the submicron-sized, hole-structured silica hollow particles were obtained selectively by thermal decomposition of the PSt/P(St-CPEM)(θ)-g-PDMAEMA/SiO(2). The oriented particle array was fabricated by dropping anisotropically perforated silica particles onto a glass substrate settled at the bottom of a bottle filled with chloroform.

The gel that memorizes phases

A poly(4-acrylamidosalicylic acid) gel exhibits multiple phases as characterized by distinct degrees of swelling; the gel can take one of four different swelling values, but none of the intermediate values. The multiple phase behavior appears as a result of the combination of hydrogen bonding and hydrophobic interaction between polymer segments. The gel has remarkable memory: The phase behavior of the gel depends on whether the gel has experienced the most swollen phase or the most collapsed phase in the immediate past. The information is stored and reversibly erased in the form of a macroscopic phase transition behavior. These phenomena are explained by a mean field theory where the number of hydrogen bonds is added to the equation of the state of a gel.