Rate Of Network Formation Research Articles

Concurrent curing kinetics of an anhydride-cured epoxy resin and polydicyclopentadiene

The development of interpenetrating polymer networks provides a route to create tough materials that maintain high strength and stiffness, suitable for meeting the demands of an off-shore wind turbine environment. This work has focused on a system composed of diglycidyl ether of bisphenol A (DGEBA)-based epoxy resin, contributing high tensile strength and modulus, and polydicyclopentadiene (polyDCPD), which has a higher toughness and impact strength as compared to other thermoset polymers. In situ Fourier transform infrared spectroscopy was used to explore the reaction kinetics in neat, diluted and sequentially cured mixtures of epoxy resin and polyDCPD. There were significant differences in the rate of network formation in the two neat systems, as the rate of anhydride curing of the epoxy was extremely slow at the temperatures required for reasonably measurable dicyclopentadiene (DCPD) ring-opening metathesis polymerization. The dissimilar kinetics of these two systems were leveraged in the design of a sequential curing protocol in which the DCPD was first cured in the presence of the epoxy resin components, followed by curing of the epoxy resin at an elevated temperature. The curing kinetics of the macroscopically phase separated domains of the epoxy resin components in the presence of the polyDCPD network behaved as expected for a diluted epoxy resin. These results provide the kinetic basis for future studies to prepare interpenetrating polymer networks which employ thermodynamic control of phase separation such as through the addition of compatibilizing molecules.

Coumarin-Based Photodegradable Hydrogel: Design, Synthesis, Gelation, and Degradation Kinetics

The design, synthesis, and characterization of a new class of coumarin-based photodegradable hydrogels are reported. Hydrogel formation was achieved rapidly and efficiently under aqueous conditions using copper-catalyzed click chemistry, which afforded excellent control over the rate of network formation. Rapid photodegradation, to the point of reverse gelation, was observed using both 365 and 405 nm light, and micrometer-scale features were eroded using two-photon irradiation at wavelengths as long as 860 nm.

Reaction induced phase-separation controlled by molecular topology

Binary phase-separation driven by a difference in branch content of the two components has been widely reported in polyolefins. This concept is applied to polysiloxanes in an attempt to control morphology in chemically driven phase separation. It is shown that self-assembled, non-reversible spinodal morphologies (SD) as well as low-polydispersity nucleation and growth morphologies can be controlled through the rate of network formation in these systems. Time-resolved light scattering and optical microscopy were used to determine the character and kinetics of phase separation. The mechanism of phase separation in two similar systems was dictated by the rates of the crosslinking reactions. Both morphologies were ‘locked-in’ by network formation and late-stage phase-ripening was prevented by low surface energy associated with topologically driven phase-separation.

Polyurethane-polystyrene interpenetrating polymer networks synthesized in the presence of a common solvent

Interpenetrating polymer networks (IPN's) of polyurethane and polystyrene were synthesized by simultaneous polymerization. The effect of compositional variation and the presence of a common solvent in the reaction medium on the rate of polymerization, the onset of phase separation, and the morphology of product were investigated. 1,4-Dioxane was selected as a common solvent by the swelling experiment. The rate of network formation in the early stage of polymerization process increased with increasing the polyurethane composition. When 1,4-dioxane was present in the reaction medium, the extent of reaction of both components at the onset of phase separation was higher than that of IPN's by bulk preparation. The morphology of final product was influenced by the extent of reaction at the onset of phase separation. The density, glass transition behavior, and thermal stability were also studied.

Rheological Changes During Slow Acid Induced Gelation of Milk by D‐glucono‐δ‐lactone

ABSTRACTAlteration in the rheological behavior of milk during acidification were studied. Structure formation during gelling was monitored by a small strain rheological scanner. Dynamic viscoelastic properties were monitored as a function of time and temperature. Time of onset of gelation, rate of network formation and development of the elastic component during acidification were accelerated at higher temperatures (55°C). Addition of calcium (0–40 mM) facilitated gelation. Preheating milk at 90°C for 5 min prior to acidification enhanced gelation and induced protein‐protein network formation. The number or strength of elastically effective bonds between protein molecules were reduced and gels of lower firmness were obtained with preheated milk, compared to gels made from unhealed milk.

The surface properties of lung extract

The surface tension, surface potential, and surface flow characteristics of crude lung surfactant (LS) monolayers were studied as functions of surface compression and also as functions of age of extract solution. The surface tension characteristics show almost no change with age whereas the surface potential data have maxima at one to two weeks of age. The surface flow measurements, which show qualitative as well as quantitative changes with age, indicate that LS forms a two-dimensional network. The ability to form this network decreases with the age of the extract, and the variation correlates with the surface potential pattern. The rate of network formation is accelerated by compression and/or flow of the LS film. These results suggest that the nonlipid components of LS are probably involved in the formation of the network and that the LS network may be involved in the mechanism which stabilizes the alveoli.