Hiroyuki Aota

Polymer dependence of boson peak frequency studied by hole burning and Raman spectroscopies

Abstract Raman scattering spectra in polymers and phonon sideband spectra observed in hole burning experiments show that the peak frequency of the phonon sideband spectrum corresponds to the low-frequency fracton edge, the so-called boson peak in amorphous materials. The polymer dependence of the phonon sideband spectra indicates that the polymer which has hydrogen bonding has a higher boson peak frequency. The absence of a high-frequency fracton edge in the phonon sideband spectra, which has been observed in the Raman spectra, is attributed to the different frequency dependence of localized-electron-phonon coupling versus dielectric modulation in Raman scattering.

Free-radical crosslinking polymerization of unsymmetrical divinyl compounds, 1 Gelation in the polymerization of allyl methacrylate

As an extension of our continuing studies concerned with the free-radical crosslinking polymerization of multivinyl compounds, this article deals with the gelation in the polymerization of allyl methacrylate (AMA) as a typical unsymmetrical divinyl compound containing two types of vinyl groups such as methacryloyl and allyl ones having quite different reactivities. Thus, AMA was polymerized in bulk or in a 1,4-dioxane solution using an azo-initiator at 50°C in the presence of lauryl mercaptan as chain transfer agent. The actual gel point was compared with the calculated one according to Gordons equation by tentatively supposing equal reactivity of both vinyl groups. Tailed molecular-weight distribution curves were observed. The swelling ratios of the resulting gels obtained just beyond the gel point was very high. Thus, the intermolecular crosslinking occurred predominantly in the bulk polymerization. Even in the solution polymerization, the occurrence of intramolecular crosslinking was only a little. This was supported by the r.m.s. radii of gyration and second virial coefficients of resulting prepolymers.

Kinetics of emulsion crosslinking polymerization and copolymerization of allyl methacrylate

Abstract The emulsion polymerization and copolymerization of allyl methacrylate (AMA) initiated by potassium peroxodisulfate (KPS) using sodium dodecylsulfate (SDS) as an emulsifier were studied. Polymerization shows two distinct non-stationary rate regions with the maximum rate at ca. 50% conversion. The maximum rate of polymerization is found to be proportional to 0.68 and 0.25 power of KPS and SDS concentrations, while the number of particles is proportional to 0.54 and 0.67 power, respectively. The increased number of polymer particles as reactive crosslinked-polymer microspheres, the polymerization in the polymer particle surface area, the small monomer/polymer weight ratio, and the gel effect are assumed to be operative. The particle size decreased and the particle number increased with increasing the KPS and SDS concentrations. Moreover, the particle size continued to increase with conversion, up to a high conversion; this is due to the particle growth events by both agglomeration and propagation reactions, and the continued nucleation of particles to a high conversion region. The non-uniform particle morphology results from the agglomeration of microgels between themselves and with large stable particles. The polymerization accompanied by crosslinking mainly occurs in the surface area of the particles because of the restricted penetration of radicals into crosslinked particle cores. Where the Tg of the resulting polymer is much higher than the polymerization temperature, the particles become glassy during the polymerization, as is the typical case of AMA/methyl methacrylate (MMA) copolymerization; at a late stage of polymerization, the preferential polymerization in the surface area of polymer particles leads to the enhanced formation of network structure, resulting in the microgel-like polymers consisting of poly(MMA)-rich core and poly(MMA-co-AMA)-network shell.

Free-radical cross-linking polymerization of unsymmetrical divinyl compounds 2. Steric effect on gelation in the copolymerizations of allyl methacrylate with several alkyl methacrylates

As an extension of our continuing studies concerned with the free-radical cross-linking polymerization and copolymerization of multivinyl compounds, this article deals with the gelation in the copolymerization of allyl methacrylate (AMA), a typical unsymmetrical divinyl compound containing two types of vinyl groups such as methacryloyl and allyl ones having quite different reactivities, with several alkyl methacrylates, especially focusing on the steric effect of long-chain alkyl groups. Thus, AMA was copolymerized in bulk with methyl methacrylate (MMA), butyl methacrylate (BMA), lauryl methacrylate (LMA), and stearyl methacrylate (SMA) using azo-initiator at 50 °C in the presence of lauryl mercaptan as a chain transfer agent. The actual gel point was compared with the calculated one according to Stockmayers equation by tentatively supposing equal reactivity of both vinyl groups. In the copolymerizations with LMA and SMA, the suppressed occurrence of intermolecular cross-linking reaction caused by the steric effect of long-chain alkyl groups was clearly observed as a reflection of delayed gelation, whereas the copolymerizations with MMA and BMA were roughly governed by the predominant occurrence of intermolecular cross-linking. These were supported by the conversion dependencies of the molecular-weight distribution profiles, the correlation curve of molecular weight versus elution volume, and the correlation of intrinsic viscosity versus molecular weight of resulting precopolymers.

Free-radical crosslinking polymerization of neopentyl glycol dimethacrylate in the presence of lauryl mercaptan

Neopentyl glycol dimethacrylate was polymerized in bulk in the presence of lauryl mercaptan as a chain transfer agent, the primary chain length being reduced to a comparable order in allyl polymerization, and the gelation behavior was compared with diallyl terephthalate (DAT) polymerization as a typical example of multiallyl polymerizations. No Trommsdorff effect was observed, even beyond the gel point conversion, in spite of the polymerization of divinyl monomer, as were the cases of the bulk polymerization of multiallyl compounds. The variation of molecular weight distribution curves with conversion was quite similar to DAT polymerization. The deviation of actual gel point from the theoretical one was also similar. Moreover, the swelling ratio of the gel obtained just beyond the gel point was very high. Thus, no substantial difference was observed between allyl and vinyl polymerizations in the case where the primary chain lengths were adjusted to be comparable. In addition, no microgelation occurred up to the gel point.

Emulsion polymerization of lauryl methacrylate and its copolymerization with trimethylolpropane trimethacrylate

The emulsion polymerization of lauryl methacrylate and its copolymerization with trimethylolpropane trimethacrylate (TMPTMA) were investigated. The induction period (IP) for LMA polymerization was observed to be very long as compared to substantially no IP for methyl methacrylate polymerization. The addition of TMPTMA as a crosslinker clearly prolonged IP, owing to the reduced radical entry of oligomeric growing radical having rather hydrophilic and crosslinkable TMPTMA units into the polymer particle surface. Besides, no gelation was observed even above 90% conversion for LMA/TMPTMA(80/20) copolymerization. The initial abrupt increase in the conversion dependencies of weight-average molecular weight results from the compartmentalization of reaction loci and the gel effect.

Emulsion Crosslinking Polymerization of Allyl Methacrylate

Abstract In the emulsion polymerization of allyl methacrylate (AMA), no gelation occurred, whereas gelation occurred easily at about 4% conversion in the bulk polymerization. Thus, the reactive cross-linked-polymer microspheres as microgel-like polymers with abundant pendant allyl groups were easily obtained in the emulsion polymerization because AMA possesses two types of vinyl groups, methacrylic and allylic double bonds, having greatly different reactivities. The weight-average molecular weights, the r. m. s. radii of gyration, the second virial coefficients, the intrinsic viscosities, and 1H-NMR spectra of the resulting allyl-type reactive microspheres were characteristic of microgel-like polymers as compared with those of the branched-polymer-like prepolymers obtained in bulk. The precopolymers prepared from the emulsion copolymerization of AMA with methyl methacrylate and ethylene dimethacrylate in order to obtain the crosslinked-polymer microspheres having different crosslinking densities were also...

COMPARTMENTALIZATION OF ZINQII) TETRAPHENYLPORPHYRIN IN A HYDROPHOBIC MICRODOMAIN OF AN AMPHIPHILIC POLYELECTROLYTE: A PHYSICOCHEMICAL MODEL OF BIOLOGICAL METALLOPORPHYRIN SYSTEMS

Abstract— Small mole fractions of zinc(II) tetraphenylporphyrin (ZnTPP) moieties were covalently incorporated into amphiphilic polysulfonates having bulky hydrophobic groups such as lauryl, cyclododecyl, and (2‐naphthyi)methyl (Np) groups in their side chains. The ZnTPP moieties are “compartmentalized” in the hydrophobic domains of these amphiphilic polyelectrolytes in aqueous solution. For comparison, the ZnTPP moieties were covalently incorporated into a polysulfonate without hydrophobic groups. The ZnTPP moieties in this reference polymer are exposed to water in aqueous solution. The compartmentalized ZnTPP systems in aqueous fluid solution emitted phosphorescence and thermally activated delayed fluorescence at room temperature. This is due to an extremely long‐lived triplet excited state in the compartmentalized systems at room temperature in aqueous solution, e.g. 19 ms for ZnTPP compartmentalized in Np domains, compared with 3 ms for ZnTPP in the reference polymer. These remarkable compart‐mentalization effects may be attributed to a restriction of motional freedom of the ZnTPP moiety isolated in a rigid and hydrophobic microenvironment provided by the amphiphilic polyelectrolytes in aqueous solution.

In situ sensitive fluorescence imaging of neurons cultured on a plasmonic dish using fluorescence microscopy.

A plasmonic dish was fabricated as a novel cell-culture dish for in situ sensitive imaging applications, in which the cover glass of a glass-bottomed dish was replaced by a grating substrate coated with a film of silver. Neuronal cells were successfully cultured over a period of more than 2 weeks in the plasmonic dish. The fluorescence images of their cells including dendrites were simply observed in situ using a conventional fluorescence microscope. The fluorescence from neuronal cells growing along the dish surface was enhanced using the surface plasmon resonance field. Under an epi-fluorescence microscope and employing a donut-type pinhole, the fluorescence intensity of the neuron dendrites was found to be enhanced efficiently by an order of magnitude compared with that using a conventional glass-bottomed dish. In a transmitted-light fluorescence microscope, the surface-selective fluorescence image of a fine dendrite growing along the dish surface was observed; therefore, the spatial resolution was improved compared with the epi-fluorescence image of the identical dendrite.

Effect of hydrogen bonds on intermolecular crosslinking reaction by introduction of carboxyl groups in free-radical crosslinking monomethacrylate/dimethacrylate copolymerizations

The effect of physical interaction through hydrogen bonds on the intermolecular crosslinking reaction leading to the promoted gelation in free-radical crosslinking monovinyl/divinyl copolymerizations was discussed from the standpoint of the control of network formation. The solution copolymerizations of benzyl methacrylate (BzMA) with 2 mol% of 1,6-hexanediol dimethacrylate in t-butylbenzene were conducted in the absence and presence of different amounts of mono(2-methacryloyloxyethyl) succinate (MMOES). Gelation was promoted by the addition of MMOES and the ratio of the actual gel point to the theoretical one became smaller; this would be related to the formation of hydrogen bonds between carboxyl groups introduced into prepolymer and growing polymer radical. As an extension of the above discussion, we treated the effect of hydrogen bonds on the gelation in the crosslinking BzMA/triicosaethylene glycol dimethacrylate copolymerization. The addition of MMOES obviously promoted the gelation. The ratio of the actual gel point to the theoretical one calculated according to Stockmayers equation [J. Chem. Phys. 12 (1944) 125] was obtained as 1.9, very close to unity.