Topological reaction limit

For some highly crosslinked thermosetting polymers with rigid backbones, topological restrictions limit the maximum attainable conversion. For the reaction between epoxidized novolacs and cresol-based novolacs, a maximum conversion, Xmax= 0.80 was reported (Hale et al., 1991). A similar value of x ,ax was reported for the cure of an epoxidized novolac with 4,4 -diaminodiphenylsulfone (DDS) (Oyanguren and WilKams, 1993a). In these cases, partially reacted networks may be modeled as a random solution of reacted functionalities with a concentration equal to x/x ax... 

Nevertheless, sometimes it is possible to point the reaction rate constant that is limiting for the relaxation in the following sense. For known topology of reaction network and given ordering of reaction rate constants we find such a constant (ergodicity boundary) that... 

It should be pointed out that the topological limit cannot be removed by a simple temperature rise as is the case in reactions controlled by glass transition. 

The reaction can be truly adiabatic for a wide range of experimental conditions. It initiates in the kinetic region and reaches a limit of 94-96 % conversion, which corresponds to the topological limit for these systems 5>14, l617-5169). The reaction kinetics is well described by the adopted mechanism 51,69 and the resulting experimental kinetic and thermodynamic reaction parameters are similar to those obtained in isothermal experiments. 

The rate-limiting step in the kinetic pathway of nucleotide incorporation is the conversion of the E p/t dNTP complex to the activated complex, E p/t dNTP (Step 3 in Fig. 1). This step is crucial in many respects. First, it is essential for the phosphoryl transfer reaction to occur. During the E p/t dNTP to E p/t dNTP transition, all the components of the active site are assembled and organized in a topological and geometrical arrangement that allows the enzyme to proceed with the chemical step (Step 4). Second, Step 3 plays a major role in the mechanism of discrimination between correct versus incorrect nucleotides. Interpretation of the kinetic measurements has led to the hypothesis that the E p/t dNTP... 

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