Curing of mixtures of diane and aliphatic epoxy oligomers with different reactivities

Curing of diane and aliphatic epoxy oligomers and their blends is studied by DSC. The use of the traditional dynamic procedure and preliminary heating of the samples at a constant temperature are shown to be convenient for estimating the degree of conversion, glass-transition temperature, and activation energy of curing. Curing of diane, aliphatic epoxy oligomers, and blends with aliphatic amine is adequately described by the Kamal—Sourour equation, and the apparent activation energy of curing is 61.4–55.7 kJ/mol according to the Flynn—Wall—Ozawa model and 54.7–48.5 kJ/mol according to the Kissinger model. This value slightly changes with variation in the content of epoxy oligomers.     

Synthesis of urethane-containing epoxy oligomers

A procedure for preparing urethane-containing epoxy oligomers from reactive monourtheanes was developed.     

Kinetics and mechanism of epoxy oligomers curing

A review of new results concerning kinetics, thermodynamics and mechanism of epoxy oligomers curing with various nucleophilic agents (amines, phenols, carboxylic acids) has been made. The concept of the mechanism of such reactions is formulated on the basis of this study. Kinetic data obtained are interpreted within the framework of cyclic transition state. The addition of nucleophilic agent to epoxy ring is rather complicated. It results from preliminary formation of homo- and heteroassociates of reaction system components which finally form reactive cyclic heteroassociates. Reaction products are formed as a result of monomolecular rearrangement with synchronous transfer of electrons in the reactive cyclic heteroassociates.     

Single-stage synthesis of phosphazene-containing epoxy oligomers

A single-stage synthesis of phosphazene-containing epoxy oligomers via the direct interaction of hexachlorocyclotriphosphazene, diphenylolpropane and epichlorohydrin has been proposed. The resulting products are composed of a common epoxy-diane oligomer and an epoxyphosphazene component, with the content of the latter being up to 45 wt %. Oligomers with epoxy numbers up to 22 were characterized with the use of gel permeation chromatography, chromatography-mass spectrometry, laser mass spectrometry, ³¹P NMR spectroscopy, and ¹H NMR spectroscopy.     

Rheological and rheokinetic properties of phosphazene-containing epoxy oligomers

The rheological and rheokinetic properties of a two-component binder consisting of epoxy-diane oligomers and the oligoepoxyphosphazenes PEO-1 (30 wt %) and PEO-2 (40 wt %) are studied. The viscosities of the initial oligomers at 40°C are 130 (PEO-1) and 270 (PEO-2) Pa s; the activation energies of viscous flow in the range 40–70°C are from 122 to 128 kJ/mol. The addition of equivalent amounts of curing agents, such as triethylenetetramine or iso-methyltetrahydrophthalic anhydride, reduces the initial viscosity of a composition, most strongly in the presence of the second curing agent (by a factor of 50–100). The activation energies of the cure process with triethylenetetramine in the range 45–95°C are 89 (PEO-1) and 125 (PEO-2) kJ/mol, and the gelation time at 55°C is 6 min for both oligomers. The time of gelation for the system PEO–iso-methyltetrahydrophthalic anhydride at 90°C is 475 min, and the glass-transition temperatures of the cured compositions are 238 (PEO-1) and 250°C (PEO-2), as evidenced by thermomechanical studies.     

Eugenol derivatives of higher chlorocyclophosphazenes and related epoxy oligomers

The synthesis of eugenol derivatives of octachlorocyclotetraphosphazene and mixtures of oligomer chlorocyclophosphazenes [NPCl₂]_3–8 was performed. Not yet described octakis(4-allyl-2-methoxyphenoxy)cyclotetraphosphazene was isolated in the crystalline form and identified via ³¹P and ¹H NMR spectroscopy, laser mass spectrometry, DSC, and TGA. Oligomers with epoxy numbers of 15–16% and molecular masses from 1400 to 1800 were prepared via epoxidation of the synthesized eugenol derivatives with m-chloroperbenzoic acid. Some assumptions on the nature of side reactions occurring in the course of epoxidation were made.     

The structural organization of liquid low-molecular-weight epoxy oligomers

The possibility of the existence and the behavior of molecular aggregates in low-molecular-weight epoxy resins were studied. The globular morphology of all liquid resins was determined using transmission electron microscopy. The lamellar morphology of crystallized ED24 was established by additionally using atomic-force microscopy. The thermal behavior of oligomeric epoxides was studied over the temperature range ?100–100°C. The T _g and T _ll transitions were recorded for liquid resins by differential scanning calorimetry. For solid ED24, the T _m peak of resin melting situated between T _g and T _ll was observed. The existence of the T _ll transition was substantiated by positron annihilation measurements. The morphological picture was thermally unstable and became completely degenerate at T _ll. The morphology and thermophysical parameters of the resins changed substantially after their vibrational treatment. The morphology of oligomers was shown to be “hereditarily” (genetically) related to that of the corresponding network polymers.     

Modification of heat-resistant epoxy matrices with acryl-containing oligomers

With the aim to enhance the crack resistance and impact resilience of heat-resistant epoxy polymeric matrices for high-strength composites, modification of epoxy resins with new poly(ether acrylates) and their adducts with amines was studied.

     

Halogenated hydroxy-aryloxy phosphazenes and epoxy oligomers based on them

By partial substitution of the chlorine atoms in hexachlorocyclotriphosphazene for halophenols and subsequent reaction of the resulting halogenated phenoxy phosphazene and 2,2-di(4-hydroxyphenyl)propane monophenolate hydtoxy-aryloxy phosphazenes were synthesized with a molecular weight of 1100–1400 g mol^?1. Epoxide oligomers (epoxy number of 6–8%), which are cured with the formation of non-combustible compositions [PV-0 class of resistance to combustion according to State Standard (GOST 28157-89)], were obtained by reaction of these compounds with epichlorohydrin. Introduction of 5–50 wt% halogenated epoxyphophazene oligomers in industrial resin ED-20 can significantly improve the flame resistance of compositions based on these compounds.     

Controlling the softening temperature of epoxy oligomers and their mixtures

The possibility was shown of decreasing the temperature of softening of ED-8 brand high-molecular-weight solid epoxy oligomer by means of creation of mixtures with DER-332, DER-330, ED-22, and ED-20 low-viscosity epoxy oligomers. It was shown that the softening temperature of epoxy oligomers and their mixtures can be controlled by directional variation of molecular weight, molecular-weight distribution, and content of the low-molecular-weight fraction.     

Kinetics of curing of epoxy oligomers with adamantane diamines

The kinetics of curing of diglycidyl ester of diphenylolpropane (the first homolog of epoxy-diane oligomers) with diaminomethyladamantane is studied. It is shown that, at the initial stage, the autocatalytic polycondensation is developed which is characterized by an increase in viscosity, branching of a macromolecule, and increasing intermolecular interactions.     

Structural and spectroscopic studies of peptoid oligomers with alpha-chiral aliphatic side chains

Substantial progress has been made in the synthesis and characterization of various oligomeric molecules capable of autonomous folding to well-defined, repetitive secondary structures. It is now possible to investigate sequence-structure relationships and the driving forces for folding in these systems. Here, we present detailed analysis by X-ray crystallography, NMR, and circular dichroism (CD) of the helical structures formed by N-substituted glycine (or "peptoid") oligomers with alpha-chiral, aliphatic side chains. The X-ray crystal structure of a N-(1-cyclohexylethyl)glycine pentamer, the first reported for any peptoid, shows a helix with cis-amide bonds, approximately 3 residues per turn, and a pitch of approximately 6.7 A. The backbone dihedral angles of this pentamer are similar to those of a polyproline type I peptide helix, in agreement with prior modeling predictions. This crystal structure likely represents the major solution conformers, since the CD spectra of analogous peptoid hexamers, dodecamers, and pentadecamers, composed entirely of either (S)-N-(1-cyclohexylethyl)glycine or (S)-N-(sec-butyl)glycine monomers, also have features similar to those of the polyproline type I helix. Furthermore, this crystal structure is similar to a solution NMR structure previously described for a peptoid pentamer comprised of chiral, aromatic side chains, which suggests that peptoids containing either aromatic or aliphatic alpha-chiral side chains adopt fundamentally similar helical structures in solution, despite distinct CD spectra. The elucidation of detailed structural information for peptoid helices with alpha-chiral aliphatic side chains will facilitate the mimicry of biomolecules, such as transmembrane protein domains, in a distinctly stable form.     

Refractometry of melts

Journal of Structural Chemistry -     

Features of formation and viscoelastic properties of epoxyurethanes based on aliphatic cyclocarbonate oligomers

By the methods of dynamic mechanical analysis (DMA) and IR spectroscopy, the kinetics of curing and viscoelastic properties of epoxy urethanes of network structure based on epoxy diane resin and bifunctional oligocyclocarbonates (OCCs) are studied. The dependence of glass transition temperature and gel fraction of the obtained polymer on the amount of injected cyclocarbonate is established. It is shown that modification of epoxy diane oligomer by aliphatic OCCs results in an increase in its mechanical properties, particularly cohesive strength.     

The synthesis and cationic polymerization of multifunctional silicon-containing epoxy monomers and oligomers

Several series of multifunctional silicon-containing epoxide monomers and oligomers have been prepared using rhodium catalyzed hydrosilation reactions. Dialkyl and diarylsilanes can be condensed with vinyl epoxides to give high yields of the desired diepoxides while the hydrosilation of alkyl and aryl silanes yields a mixture of di and tri epoxy substituted products. The condensation of αω,? Si? H difunctional compounds with vinyl epoxides can be carried out regioselectively to give α-hydrogen-ω-epoxy intermediates, which can be further reacted with di and tri olefins bearing terminal double bonds to give a series of well characterized epoxy functional oligomers. An investigation of the photoinitiated cationic polymerization of the monomers and oligomers, which were prepared during the course of these studies, was carried out. © 1994 John Wiley & Sons, Inc.     

Peculiar features of curing epoxy oligomers in water-dispersible painting materials

The article discusses the properties of water emulsions/dispersions of epoxy resins, investigates peculiar features of their curing, and determines the physicochemical and structural parameters. In addition, the studied substances, which possess improved environmental properties and adhesion to fresh concrete, are characterized by significant vapor permeability.     

Curing of epoxy oligomers by the eutectic mixture of aromatic amines

Kinetics of curing of structurally different epoxy oligomers (ED-20 and PDI-3AK resins) in a mixture with other low-molecular-weight epoxy oligomers and plasticizers by the eutectic mixture of aromatic amines UP-0638/1 is studied by the DSC method. The activation energy and the heats of curing reactions are determined. It is established that crosslinked epoxy polymers cured at moderate temperatures (40–80°C) are strong moisture-resistant compositions with different mechanical characteristics. Plasicized elastomers based on PDI-3AK resin with glass transition temperatures of ?78 and ?95°C are freeze-and heat-resistant materials.     

Synthesis and properties of polymeric materials prepared by anionic polymerization of epoxy oligomers

The kinetics of anionic polymerization of epoxy oligomers of different functionalities in the presence of imidazoles was studied. Polymers based on the chosen systems, exhibiting high elastic and deformation characteristics at compression in a wide temperature range, and also resistance to heat and water, were synthesized. The epoxy compounds exhibit high adhesion to aluminum, preserved at elevated temperatures (150°C).     

Determination of residual stresses in adhesive materials based on epoxy oligomers

A method for calculating residual stresses in the adhesive layer is reported and results obtained are compared with experimental data. Theoretical calculations are performed under the assumptions that epoxy adhesive is an elastic material that obeys Hooke’s law. Residual stresses are measured by the console method.     

Rheological properties of epoxy oligomers and their mixtures in a wide temperature range

The rheological properties of a series of epoxy-diane and epoxy-novolac oligomers and active diluents were studied in a wide temperature range. The activation energies of their viscous flow in the regions of low and high temperatures were calculated. In a series of active diluents, the efficiency of decreasing viscosity of their mixtures with epoxy oligomers correlates with the glass transition temperature of the diluent.