The treated scarred vocal folds showed persistent MSC. Injection of scarred rabbit vocal folds with MSC rendered improved viscoelastic parameters and less signs of scarring expressed as collagen content in comparison to the untreated scarred vocal folds.

Effect of free volume and temperature on the structural relaxation in polymethylphenylsiloxane: A positron lifetime and pressure-volume-temperature study Positron annihilation lifetime spectroscopy was used to study the free-volume size distribution and the o-Ps ͑ortho-positronium͒ formation in two amorphous polymers. We performed positron lifetime measurements on poly͑vinyl acetate͒ ͑PVAc͒ in the temperature range of 84-414 K and on poly͑methyl methacrylate͒ ͑PMMA͒ in the temperature range of 84-454 K and as a function of time (Ͻ200 h) at four temperatures ͑Tϭ84, 149, 224, and 249 K͒. The glass transition temperature T g and secondary transition temperature were determined from the average o-Ps lifetime 3 versus temperature. The width of the o-Ps lifetime distribution was evaluated using the maximum entropy method ͑MELT͒. Analysis by the MELT program on the spectra shows that ͑i͒ the standard deviation ( 3 ) of the o-Ps lifetime distribution in PVAc and PMMA increases slightly with temperature in the glassy state, and then increases significantly with temperature above the glass transition temperature T g ; ͑ii͒ the ( 3 ) in PMMA has no observable variation as a function of positron irradiation time, which suggests that the measured free-volume distribution is not influenced by the positron irradiation. The o-Ps formation probability shows large variations with temperature, thermal history, and measuring time. These effects are discussed in the framework of the spur model.

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Amino-functional benzoxazine monomers have been successfully prepared. Several routes have been applied to incorporate amino group into benzoxazine structure. These approaches include reduction of the corresponding nitro-functional benzoxazines and deprotection of protected aminofunctional benzoxazine monomers. Various approaches that allow primary amine groups to be prepared without damaging the existing benzoxazine groups have been evaluated. Tetrachlorophthalimide and trifluoroacetyl are found to be suitable protecting groups. In addition, a model compound of amidefunctional benzoxazines is prepared from primary amine-functional benzoxazine. Fourier transform infrared spectroscopy (FTIR) and 1 H and 13 C nuclear magnetic resonance spectroscopy (NMR) are used to characterize the structure of the monomers. The polymerization behavior of amino-functional monomers and model compound are studied by differential scanning calorimetry (DSC).

Most applications of positron beams require knowledge of the implantation characteristics for an appropriate interpretation of the experimental data. In this work, the median implantation depth as a function of implantation energy, z 1/2 (E), of 3-18 keV positrons and their implantation profile P(z,E) in a total of 13 thin films of atactic polystyrene, poly͑styrene-co-acrylonitrile͒, and polymethylmethacrylate spin coated onto a silicon substrate were determined from positron lifetime measurements using a pulsed, low-energy positron beam. z 1/2 (E) and P(z,E) were determined from the measurement of the ortho-positronium yield obtained from the intensity I 3 of the long lifetime. z 1/2 (E) was parametrized with the commonly used power-law fit z 1/2 (E) ϭ(A/)E n , with and E in units of g cm Ϫ3 and keV, respectively, yielding Aϭ2.81(Ϯ0.2) g cm Ϫ2 and n ϭ1.71(Ϯ0.05). Excellent agreement between amorphous polymer and literature data on Al and Cu suggests that the median implantation depth of positrons for low-to medium-Z materials in the studied energy range is independent of structure and only a function of mass density. Fitting of the Makhovian implantation profile to the experimental data suggested that the value of the parameter m varies between 1.7 and 2.3, systematically increasing with z at constant implantation energy, but is independent of the implantation energy. Using an equation proposed by Baker et al., the experimental data of 12 of the 13 studied polymer films could be described with a slightly better agreement than the Makhovian equation.

The free volume sizes and interstitial mesopore sizes in poly(1-trimethylsilyl-1-propyne) (PTMSP)/silica nanocomposites and the correlation between nitrogen permeability and cavity sizes were studied with positron annihilation lifetime spectroscopy (PALS) at filler concentrations between 0 and 50 wt %. A bimodal free volume distribution was observed for PTMSP, and the size of the larger free volume cavities was significantly increased upon addition of hydrophobic fumed silica. Nanometer-sized interstitial cavities in filler agglomerates were observed in all PTMSP/fumed silica nanocomposites and in neat hydrophobic fumed silica. The radius of these interstitial mesopores in the nanocomposites decreased with decreasing filler concentration. A strong correlation between nitrogen permeability and the volume of the interstitial mesopores in the nanocomposite membranes was observed.

We modified the sample cell of a commercial pressure-volume-temperature (PVT) apparatus to make glasses by pressure densification (0-200 MPa) in the equilibrium melt. The PVT data of the glasses and the melt were analyzed in terms of the Simha-Somcynsky equation-of-state (EOS) theory and the Tait EOS. Small macroscopic volume changes up to 1.2% were found to yield large microscopic volume changes in isotropic pressure-densified atactic poly(methyl methacrylate) glasses with densities in the range 1.1823-1.1963 g/cm 3 : the free-volume fraction h from the Simha-Somcynsky theory decreased by up to 19.2%, the orthopositronium (o-Ps) lifetime τ3 from positron annihilation lifetime spectroscopy (PALS) decreased by up to 8.4% whereas the o-Ps intensity I3 remained constant at 29 ( 0.5%, and the volume of the free-volume cavities V(τ3) decreased by up to 16.1%. Moreover, the microscopic volume quantities h and V(τ3) were found to correlate best. The radius of the free-volume cavities R(τ3) at zero h appears to approach the Bohr radius of the o-Ps species. The thermal expansivity R0 remains almost constant, the isothermal compressibility κ0 decreases by up to 10.3%, which corresponds to an 11.5% increase in bulk modulus, and the freezing fraction remains constant up to formation pressures of 200 MPa.