Epoxy concentration

Instead of the familiar sequence of morphologies, a broad multiphase window centred at relatively high concentrations (ca. 50-70% block copolymer) truncates the ordered lamellar regime. At higher epoxy concentrations wormlike micelles and eventually vesicles at the lowest compositions are observed. Worm-like micelles are found over a broad composition range (Fig. 67). This morphology is rare in block copolymer/homopolymer blends [202] but is commonly encountered in the case of surfactant solutions [203] and mixtures of block copolymers with water and other low molecular weight diluents [204,205]. 

Polysulfide resins combine with epoxy resins to provide adhesives and sealants with excellent flexibility and chemical resistance. These adhesives bond well to many different substrates. Tensile shear strength and elevated-temperature properties are low. However, resistance to peel forces and low temperatures is very good. Epoxy polysulfides have good adhesive properties down to -100°C, and they stay flexible to -65°C. The maximum service temperature is about 50 to 85°C depending on the epoxy concentration in the formulation. Temperature resistance increases with the epoxy content of the system. Resistance to solvents, oil and grease, and exterior weathering and aging is superior to that of most thermoplastic elastomers. 

DSC Study. From the analysis of the total heats of reaction of the commercial and fractionated TGMDA resin/DDS formulations over a broad stoichiometric range, it is concluded that the total heat of reaction divided by the epoxy concentration has a constant value... 

Fig. 15. DMA of cured cyanate-epoxy neat resin blend. Epoxy concentration (mol %) (-) ...

In principle, this ratio can also affect the IP concentration profile in a quahta-tive sense. When considering a homogeneous epoxy-amine mixture just brought into contact with the surface of an adherend or a fiUer particle, preferential adsorption of the amine molecules will result in local variations of the amine/epoxy concentration ratio r (to be defined below). Assuming a comparably fast diffusion of the amine molecules, their quick enrichment at the interface will result in a near-interface zone of increased r values and an adjacent zone of amine depletion, i.e., with reduced r values. Similar concentration variations are dealt with in the field of surface-driven phase separation in polymer solutions and mixtures [8]. While the wetting layer is in local equihbrium with the depletion layer, the diffusion from the bulk down the concentration gradient into the latter feeds the growth of the former. 

The reaction mechanism indicates that the epoxy concentration decreases, and this is observed in the spectra as the decrease of the band centered at 4530 cm-i and also of the weak overtone of terminal CH2 at 6060 cm-i. The primary amine combination band decreases too ( = 4900 cm-i), and once it is exhausted it can be observed that there are still epoxy groups in the reaction media, which will react with the previously formed secondary amines up to vitrification or until the reaction is completed. The band correponding to O-H overtones ( 7000 cm-i) also increases during curing as a consequence of the oxirane ringopening, although this band is not suitable for quantification because of the low signal/noise ratio. The behavior of the band located at 6500 cm-i is more complex in this... 

Goddu and Delker [71] reported that terminal epoxides exhibit sharp absorbances relatively free of spectral interferences in the near IR at 2.2 pm and 1.65 pm (4532 cm and 6060 cm ). These absorptions result from overtones and/or combinations of fundamental vibrations found in the mid-IR. Using a dispersive infrared spectrometer, Dannenburg [72] conducted a study of epoxides in solution. Sensitivity was restricted by the capabilities of instrumentation available at that time. These investigations were limited to epoxide resins with an equivalent weight <1000 g resin/g-eq epoxy. Concentration levels for these resins were >1.0 eq/1. 

The 4532 cm combination tone is reasonably free of interferences, and can be employed to measure oxirane ring concentrations for epoxy-coating resin systems during synthesis and crosslinking. With the use of low S/N FTIR supported by computer data manipulation, chloroform solutions of five commercially available resins were analysed for epoxide-equivalent weight and correlated with results obtained by perchloric acid titrations. The near-IR technique displays linearity for epoxy concentrations of 3.6-20.7 meq/1. Similar results were obtained via a serial concentration study, indicating that the technique is not strongly affected by matrix effects. 

The most common preformed rubber particles used as a toughening agent for epoxy polymers are the so-called structured, core-shell latex particles (Figure 4). These particles typically have a polybutadiene-based core and an acrylate-based shell. Such additives can be purchased as powders from Rohm and Haas or Elf-Atochem and can be purchased as epoxy concentrates from the Dow Chemical Company. The key parameter for these modifiers is the composition of the shell polymer, since the shell chemistry plays a crucial role in the overall blend morphology. It should be noted that it is possible to obtain commercial core-shell latex particles with reactive groups in the shell for improved dispersion of the rubber particles. 

The objectives of this work are to investigate the cure behaviour and structure of bisphenol A dicyanate-novolac epoxy blends. The cure characteristics were investigated by gel time determination and dynamic DSC. To disclose the structural differences between cured cyanate-novolac epoxy blends and more traditional cyanate-diglycidyl ether systems, FTIR investigations were performed on the two kinds of blends, and in situ FTIR was used to examine the Bauer mechanism. The effects of epoxy concentration in the blend on the cure kinetics was investigated using two blends with different molar ratios, and in situ FTIR. 33 refs. 

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