Development of low‐shrinkage composites based on novel crosslinking vinylcyclopropanes

Polymerization shrinkage of methacrylate‐based dental composites remains a major concern in restorative dentistry. Cyclic monomers that undergo ring‐opening polymerization are known to exhibit reduced polymerization shrinkage compared to methacrylates. In this article, the synthesis of four crosslinking 1,1‐disubstituted 2‐vinylcyclopropanes bearing rigid spacers is described. These monomers were synthesized by esterification of 1‐ethoxycarbonyl‐2‐vinylcyclopropane‐1‐carboxylic acid with the corresponding diols. The photopolymerization kinetics of these monomers was investigated by photo‐differential scanning calorimeter using bis(4‐methoxybenzoyl)diethylgermane as the photoinitiator. The synthesized vinylcyclopropanes (VCPs) were shown to be more reactive than the frequently used reactive diluent triethylene glycol dimethacrylate. Composites based on these VCPs showed good mechanical properties and exhibited a significantly reduced volumetric shrinkage and shrinkage stress compared to a corresponding dimethacrylate‐based restorative material. This work highlights the excellent potential of VCPs as alternatives to methacrylates in the development of low‐shrinkage dental composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45577.     

Controlling Cellular Uptake and Toxicity of Polyphenylene Dendrimers by Chemical Functionalization

Polyphenylene dendrimers (PPDs) represent a unique class of macromolecules based on their monodisperse and shape‐persistent nature. These characteristics have enabled the synthesis of a new genre of “patched” surface dendrimers, where their exterior can be functionalized with a variety of polar and nonpolar substituents to yield lipophilic binding sites in a site‐specific way. Although such materials are capable of complexing biologically relevant molecules, show high cellular uptake in various cell lines, and low to no toxicity, there is minimal understanding of the driving forces to these characteristics. We investigated whether it is the specific chemical functionalities, relative quantities of each moiety, or the “patched” surface patterning on the dendrimers that more significantly influences their behavior in biological media.     

Measurement of Micro Kinetics of Hydrogenation in Liquid Phase Using Raman Spectroscopy

Hydrogenation of liquid organic hydrogen carriers is usually carried out in liquid phase. To measure the kinetics of this hydrogenation, an experimental setup using in situ Raman spectroscopy for analysis of the reaction mixture is proposed. With this setup it is possible to perform hydrogenation reactions at temperatures of up to 573 K and pressures up to 25 MPa. For validation of the experimental setup the hydrogenation of 1‐octene was measured in liquid phase. The reaction progress can be monitored in detail by Raman spectroscopy. To determine kinetic parameters from the experimental data, two modeling approaches were applied: a classic kinetic model and a thermodynamic kinetic model. The results were compared to literature data.     

Thermal behavior of mullite between 4 K and 1320 K

The evolution of metric parameters of 2:1 and 3:2 mullites have been measured between 4 K and 1320 K using neutron and X‐ray powder diffraction. Negative thermal expansion was observed at low temperature for the a‐cell parameter and consequently for the cell‐volume, which is more pronounced for 2:1 mullite than those for 3:2 mullite. Each parameter is simulated using Grüneisen first‐order approximation for the zero pressure equation of state at 0 K, where the vibrational energy was calculated using microscopic approach. While the b‐ and c‐cell parameters require only one Debye term, a second Debye spectrum with negative Grüneisen parameter was required to fit the a‐cell parameter as well as the cell volume. At 4 K, 300 K and 1320 K the model, respectively, calculates the volume thermal expansion coefficients of 0.09x10^?6 K^?1, 9x10^?6 K^?1, and 17.3x10^?6 K^?1 for 2:1 mullite, and 0.09x10^?6 K^?1, 8.7x10^?6 K^?1, and 17.3x10^?6 K^?1 for 3:2 mullite. Temperature‐dependent Raman spectra and phonon density of states hint for the possible microscopic sources of the cell contraction at low temperature. A simple polynomial approach is presented to calculate the elastic stiffness coefficients of the 3:2 mullite, which are not available from experiments.     

Production of Polyunsaturated Fatty Acids by Mortierella alpina Using Submerse and Solid State Fermentation

A new isolate of Mortierella alpina, > 98 % identical with M. alpina ATCC 16266, was cultivated in a defined glucose‐based medium with three organic nitrogen sources (glycine, urea and Na‐L‐glutamate) at three different concentrations in shaking flasks at 20 °C. The results were compared to the cultivation in complex medium with yeast extract as nitrogen source. In the defined media, high yields of polyunsaturated fatty acids (PUFAs) and arachidonic acid (ARA), respectively, were obtained with Na‐L‐glutamate. However, the absolute highest yields of PUFA and ARA were measured with the yeast extract medium. An optimized yeast extract complex medium was used for a submerse bioreactor cultivation in a 45‐L scale. Furthermore, M. alpina was cultivated in a solid state fermenter, using an oat bran water mixture as substrate.     

Monomers for Adhesive Polymers, 10‐Synthesis,Radical Photopolymerization and Adhesive Properties of Methacrylates Bearing Phosphonic Acid Groups

Syntheses of eight novel methacrylates bearing phosphonic acid groups were synthesized in three to five steps. The interaction of these monomers with hydroxyapatite was investigated using ¹³C‐NMR spectroscopy. Free radical homopolymerizations were carried out in a mixture ethanol/water (2.5/1, v/v) using 2,2′azo(2‐methylpropionamidine) dihydrochloride as initiator. The copolymerization of these monomers with a mixture HEMA/GDMA (5/3, mol/mol) was investigated by photo‐DSC. Dentin shear bond strength measurements showed that 2‐methacryloyloxy‐3‐(1,1,2,2‐tetrafluoroethoxy)propylphosphonic acid 4b , 2,3‐dimethacryloyloxypropylphosphonic acid 18 and 3‐(methacryloyloxy)‐2,2‐(di[(dihydroxyphosphoryl)methyl])propyl methacrylate 23 are promising candidates for dental adhesives.

     

Application of PSRK for Process Design

A survey about the current status and potential of the predictive Soave-Redlich-Kwong (PSRK) group contribution equation of state (EoS) is given. The PSRK method combines the SRK EoS with the UNIFAC group contribution model by the PSRK mixing rule. The availability of a large number of interaction parameters between UNIFAC and new PSRK main groups allows calculating the phase equilibrium behavior and other thermodynamic quantities for various kinds of systems even with strong electrolytes. Different fields of application are discussed: the prediction of gas solubilities in asymmetric systems, the air solubility calculated for mixed solvents, the removal of H₂S from natural gas by predicting the physical absorption, and the calculation of the enthalpy effects of absorption processes with pressure and temperature.     

Characterization of Soot Particles Produced in a Transparent Research CR DI Diesel Engine Operating with Conventional and Advanced Combustion Strategies

The effect of the combustion mode on particle emission was analyzed both in the cylinder and at the exhaust of a direct injection (DI) Common Rail (CR) transparent research diesel engine by means of spectroscopic and conventional methods. The engine was equipped with a flexible electronic control unit (ECU) capable of operating up to 5 injections per cycle with different start of injection and dwell time allowing performing different combustion modes. The conventional diesel combustion, the homogeneous charge compression ignition (HCCI), and the low temperature combustion (LTC) modes were analyzed. In-cylinder broadband UV–visible scattering and extinction measurements were carried out to follow the particle formation and oxidation processes as well as to have information about their chemical nature and size distribution. The characterization of the particulate emission at the exhaust was performed by means of an electrical low pressure impactor (ELPI), for the counting and the sizing of the particles, and an opacimeter, for measuring the smoke opacity. The in-cylinder measurements highlighted that particles ranged from 3 to 100 nm whatever was the combustion mode. Nevertheless, particles produced by a conventional diesel combustion process principally consist of soot. Whereas particles formed during HCCI and LTC modes are composed mainly of organic compounds. The exhaust particle emissions depend on the combustion mode both in terms of size and number. A larger amount of particles smaller than 100 nm was emitted during HCCI and LTC modes with respect to the conventional one. Moreover, HCCI mode showed a strong accumulation mode.

Copyright 2012 American Association for Aerosol Research     

Burn Rate Models for Gun Propellants

In the past, Vieille's law and minor modifications of it described sufficiently the linear burning rate of gun propellants which governs the design of charges by interior ballistic simulations. Recent developments to increase the performance led to new gun concepts and innovative propellants. These are the electrothermal‐chemical gun, porous and foamed charges as well as formulations exhibiting a temperature independent burning. Vieille's law cannot fully meet experimental results in these cases. Approaches based on the heat flow equation in the solid energetic material give simplified formulas to extend the validity. These burning rate models have the ability to describe the experimentally determined burning behavior at least in a simplified or qualitative way. More sophisticated methods consider complex geometrical structures in the solid or take into account the actual progress in phase behavior and reaction kinetics of heterogeneous combustion. The dependence of the burning rate on initial temperature, on phase transitions, porous structure and gaseous reactions can be described.