Cyanate esters experimental

Experimentally a cyanate ester precursor mixture consisting of BPEC, 1 wt % BPE, and 100 ppm cobaltacetylacetonate was prepared and subsequently mixed with the cyclohexane phase separating solvent [86]. Essentially the same procedure as for the epoxy is used for sample preparation with the difference that the curing was done at 80 °C and post drying at 240 °C. 

Although a large variety of such experimental cyanate esters have been reported, few have achieved commercial success. Some of these have been listed in Table 2 along with their key properties. The properties are very much dependent on the backbone. Thus, the experimental CE resin XU.71787 developed by Dow... 

The model satisfactorily described the cure behavior for the entire range as experimentally monitored by FTIR, DSC, and torsional braid analysis (TBA). This model satisfactorily explained the cure behavior of both catalyzed and uncatalyzed systems over a wide range of temperature and throughout the curing process. The authors proposing the kinetic model considered the reaction to be triggered by the adventitious water and phenol impurities (whose reactions with the cyanate ester is considered as an equilibrium reaction). Catalysis by the added metal ions, which stabilizes the imino carbonate intermediates by complex-ing, is also considered. The model has considered all possible reaction paths and intermediates as detailed in Sect. 4 and depicted in Scheme 14. Considering the various reactions, expressions could be obtained for the individual apparent empirical rate constants of the second order auto catalytic model in terms of the actual rate constants and equilibrium constants. 

A model of the actual immobilization process with intact spherical catalyst particles was developed using the experimentally determined binding kinetics (48). The system was treated as a group of porous spheres suspended in a well-mixed solution of heparinase. The enzyme diffused through the porous network, where it reacted with the surface cyanate esters to produce the bound enzyme. 

Kp is a partition coefficient of the enzyme in agarose and kg is a mass transfer coefficient. Although predictions can be made about the bound-enzyme profile, it is not possible to directly verify them experimentally because of the protein impurities in heparinase. However, it is possible to measure the bulk heparinase concentration during the course of an immobilization and compare it to the model predictions. A series of immobilizations were conducted using intact agarose spheres with different cyanate ester concentrations and the bulk heparinase concentration monitored. 

Fig. 19. Experimental doud points and CPC and spinodal (S) cnrves calculated with the Hory-Huggins equation, assuming that the interaction parameter decreases with conversion according to Eq. (40). Curve A represents the CPC calculated using the initial value of the interaction parameter, assumed constant (Reprinted from Polymer, M, J. Borrajo, C.C. Riccardi, R.JJ. Williams, Z.Q. Cao, J.P. Pascault, Rubber-modified cyanate esters thermodynamic analysis of phase separation, 3541-3547, Copyright (1995), with kind permission from Butterworth-Hejnemarm Journals, Elsevier Science Ltd, The Boulevard, Lan ord Lane, Kidlington 0X5 1GB, UK)...

Properties of some new experimental cyanate esters are listed. 

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