Interpenetrating polymer networks (IPNs) are unique alloys of crosslinked polymers. This article reviews the studies on kinetic effects involved in IPN formation. Several investigators have studied the effect of kinetics of curing reactions on the morphology and properties of IPNs. It was found, in general, that the faster the rates of the respective chain extension and crosslinking reactions are and the closer they are to simultaneity, the more homogeneous are the IPNs. Other investigations revealed that the individual components sometimes can polymerize more rapidly in the IPN than alone, due to a “solvent effect” of the IPN. Effects of changing reaction variables, such as NCO/OH ratio, composition activators and temperature were used to study reaction kinetics as well as phase morphology by the Fourier transform infrared technique. Thermochemical techniques have been utilized to study the kinetics of IPN formation which influence phase separation. Small‐angle X‐ray scattering and small‐angle neutron scattering techniques were used to estimate the extent of microheterogeneity of the phase domains in a study of the kinetics of phase separation in the IPNs.
SYNOPSISPolyurethane-urea anionomer dispersions with different stoichiometric DMPA/polyol and NCO/OH ratios were prepared from poly(oxypropylene)glycol, toluene diisocyanate (TDI), dimethylolpropionic acid (DMPA), and ethylenediamine (EDA). The dispersion-cast films were prepared and characterized by mechanical properties, dynamic mechanical analysis (DMA), and differential scanning calorimetry (DSC). Increasing the hard-segment content by either increasing the DMPA/polyol or the NCO/OH ratios affects the glass transition temperature (T,) of the soft segments.
SynopsisThe influence of mono and divalent nontransition and transition metals on the glass transition and mechanical properties of polyurethane anionomers have been investigated. NCO-terminated prepolymer prepared from 4,4'-methylene-bis(phenyl isocyanate) (MDI) and poly(capro1actone) glycol (PCL) was chain extended with dimethylolpropionic acid (DMPA), and the anionomers obtained by neutralization of the prepolymer. The glass transition temperatures of polyurethane anionomers have been studied as a function of the counterion. From simple electrostatic considerations, it is shown that a linear relationship exists between the glass transition temperature and ionic potential (+) for these particular materials. The relation is; T ' = A+ + B. The mechanical properties are greatly affected by the type of the counterion, and in some cases, such as monovalent and nontransition metals, the mechanical properties of the anionomers improved by increasing the ionic potential. On the other hand, transition metals containing anionomers exhibited good mechanical properties but no relationship was observed between the mechanical properties and the ionic potential. The extent of water absorption of PU anionomers follows the same relative trends as the tensile strengths of the transition metals with filled and partially filled d-orbitals.
A liquid chromatographic-mass spectrometric (LC-MS) method has been developed and validated for simultaneous determination of dehydroevodiamine and limonin from Evodia rutaecarpa in rat plasma. After addition of the internal standard, domperidone, plasma samples were extracted by liquid-liquid extraction with ethyl acetate and separated on an Apollo C(18) column (250 mm × 4.6 mm, 5 μm), with methanol-0.01% formic acid water (60:40, v/v) as mobile phase, within a runtime of 12.0 min. The analytes were detected without interference in the selected ion monitoring (SIM) mode with positive electrospray ionization. The linear range was 1.0-500 ng mL(-1) for dehydroevodiamine and 2.0-1,000 ng mL(-1) for limonin, with lower limits of quantitation of 1.0 and 2.0 ng mL(-1), respectively. Intra-day and inter-day precision were within 6.0% and 10.9%, respectively, for both analytes, and the accuracy (relative error, RE, %) was less than 4.8% and 6.5%, respectively. The validated method was successfully applied to a comparative pharmacokinetic study of dehydroevodiamine and limonin in rat plasma after oral administration of dehydroevodiamine, limonin, and an aqueous extract of Evodiae fructus. The results indicated there were obvious differences between the pharmacokinetic behavior after oral administration of an aqueous extract of Evodiae fructus compared with single substances.
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