Macromolecules

The steady shear behavior of metallo-supramolecular polymer networks formed by bis-Pd(II) cross-linkers and semidilute entangled solutions of poly(4-vinylpyridine) (PVP) in dimethyl sulfoxide (DMSO) or N,N-dimethylformamide (DMF) is reported. The steady shear behavior of the ...

Водные растворы полиэтиленгликолей с различными молекулярными массами (600, 1000, 1500, 3000, 6000, 20000) исследованы рефрактометрическим методом и определены “конформационные” поляризуемости, среднеквадратичное расстояние между концами макромолекулярной цепи, длина сегмента и число сегментов Куна в макромолекуле с использованием уравнения Лоренца–Лоренца. Поляризуемость гидратированной макромолекулы представлена как сумма поляризуемостей не гидратированной макромолекулы с сохранением конформации и поляризуемостей молекул воды, участвующих в гидратации макромолекул. Установлено, что, начиная с определенной концентрации, размеры макромолекул стабилизируются. Сделан вывод, что начальная концентрация стабилизации сдвигается в сторону малых концентраций с ростом молекулярной массы полиэтиленгликоля. Показано, что зависимость среднеквадратичного расстояния между концами макромолекулярной цепи от числа сегментов Куна выражается степенной функцией с показателем, равным 0.3.

Photochromic compounds exhibit reversible transition between closed and open isomeric forms upon irradiation accompanied by change in their color. The two isomeric forms differ not only in absorption spectra, but also in various physical and chemical properties and find applications as optical switching and data storage materials. In this contribution we apply Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) to predict the equilibrium geometry and absorption spectra of a benchmark set of diarylethene based photochromic compounds in open and closed forms (before and after photocyclization). Comparison of the calculated Bond Length Alternation parameters with those available from the X-ray data indicates M05-2x functional to be the best method for geometry optimization when basis set includes polarization functions. We found M05 functional accurately predicts the maximum absorption wavelength when solvent is taken into account. We recommend combined theory level TD-M05/...

ABSTRACT Computer modeling of solvent-immersed polymeric brushes with anisotropic attraction and polyelectrolyte brushes shows extended microphase coexistence; i.e., a collapsed microphase coexists with a swollen outer layer in a wide range of temperatures. We present an analytical theory that serves as a basis for understanding this phenomenon. The theory clarifies the nature of the first-order transition initiating the ordering and predicts the effect of the chain length, N, on the transition point and on the size of the critical nucleus of the ordered phase. For bidisperse brushes composed of chains of two fractions differing in contour length, the theory explains two mechanisms of ordering observed by self-consistent-field computer modeling and gives predictions for certain important features of the ordering (character of transitions, shifts of the transition points, and parameter domains of ordering mechanisms). Predictions of the analytical theory are in good agreement with the results of SCF computer modeling.

The aim of this publication is to present a general strategy to engineer more efficient photoluminescent dendritic molecules based on polyhedral oligomeric silsesquioxane (POSS) cores. A series of chromophores were grafted
on POSS cores to form dendritic molecules for which steric hindrance was used as a trigger to tune their photophysical properties. For fluorescence in the blue/near-UV spectral ranges, 4-vinylbiphenyl molecules were chosen as model chromophores to present a general approach based on stable chemistry and bulky groups grafted to the chromophores to enhance photoluminescence efficiency of the dendritic molecules.
Photoluminescence quantum yields as well as steady-state and time-resolved solution spectroscopy along with molecular dynamics investigation and electronic structure calculations on a family of new materials are reported. We highlight an apparent contrast between free chromophore and dendritic molecules photophysical properties and show that chromophores’ engineering and confinement around an inorganic core allows the design of more efficient photoluminescent dendritic molecules relevant to sensors and hybrid light-emitting diodes.

ABSTRACT Despite a well-recognized clinical need for a material to replace missing or damaged vibratory connective tissue of the vocal fold, materials have yet to be engineered specifically for this purpose. Injectable hydrogels are particularly attractive because they would require a minimally invasive surgical procedure, could fill irregular defects, and could be designed to have viscoelastic properties similar to the normal tissue. We therefore synthesized a series of photo-cross-linkable hydrogels using hyaluronic acid (HA) as the starting material. The hydrogel precursors studied included HA modified with glycidyl methacrylate (HA/GMA), HA partially oxidized by sodium periodate (HAox) followed by GMA conjugation (HAox/GMA), and HA grafted with a synthetic polymer before introduction of GMA. The synthetic polymer employed was oligomeric poly(2-hydroxyethyl methacrylate) (P(HEMA)) with 31 mol % poly(N,N-dimethylacrylamide) (P(DMAM)), and the resulting hydrogel precursors were referred to as (HAox-g-Py)/GMA (y%:  grafting percent). The macromonomers were characterized by GPC and 1H NMR. Hydrogels were obtained by subjecting the aqueous macromonomer solutions to UV irradiation in the presence of a photoinitiator. Under physiological conditions HAox/GMA hydrogel exhibited the highest swelling ratio and degraded most readily, whereas (HAox-g-P1.9)/GMA hydrogel swelled to a lesser extent and was most resistant to enzymatic degradation. Mechanical tests using an acoustic shaker yielded viscoelastic properties from 20 to 180 Hz. HAox/GMA hydrogel showed the lowest viscoelastic modulus and viscosity while (HAox-g-P1.9)/GMA hydrogel exhibited the highest values. The interior structures of the fully swollen hydrogels examined by scanning electron microscopy (SEM) showed the presence of fibrous or porous morphology. The cell cytotoxicity study indicated that HAox/GMA macromonomer was cytocompatible at concentrations less than 0.2 mg/mL, and there was no loss of cells when encapsulated in (HAox-g-P1.9)/GMA photo-cross-linked network. These new hydrogels have potential as injectable formulations for regeneration of the vocal fold's mucosal layered microstructure.