Molecular weight distributions reaction time

In order to rationalize these results, molecular weight distribution measurements were performed as a function of reaction time and the results are recorded in Figure 6. The variation in molecular weight distribution with time indicates that M, is initially... 

A factor in addition to the RTD and temperature distribution that affects the molecular weight distribution (MWD) is the nature of the chemical reaciion. If the period during which the molecule is growing is short compared with the residence time in the reactor, the MWD in a batch reactor is broader than in a CSTR. This situation holds for many free radical and ionic polymerization processes where the reaction intermediates are very short hved. In cases where the growth period is the same as the residence time in the reactor, the MWD is narrower in batch than in CSTR. Polymerizations that have no termination step—for instance, polycondensations—are of this type. This topic is treated by Denbigh (J. Applied Chem., 1, 227 [1951]). 

Mathematical models of the reaction system were developed which enabled prediction of the molecular weight distribution (MWD). Direct and indirect methods were used, but only distributions obtained from moments are described here. Due to the stiffness of the model equations an improved numerical integrator was developed, in order to solve the equations in a reasonable time scale. 

Using the above model improvements, Figiue 4 shows the variation of the predicted molecular weight distributions with reaction time for an initiator concentration and efficiency of 0.9 wt% and 0.18 respectively. The need for kinetic data to test these predictions again provides motivation for development of experimental techniques to obtain samples at lower reaction time. 

Good agreement between the experimental and model generated molecular weight distribution for an initiator concentration of 0.9 wt. % and a temperature of 200°C. However, under these conditions the degradation reactions were likely complete by the reaction time of 18.6 s. 

FIGURE 6.26 Oxidation of twin-tocopherol 33 by AgN03 in toluene at 25 °C molecular weight distributions of the resulting oligomers depend on the reaction time.73... 

At 0.06 millimole of uranium compound per 100 g of butadiene, conversions of more than 90 % were obtained after a reaction time of three hours. The rate of polymerization is of the first order in relation to both the monomer (Figure 1) and the catalyst concentration. The polymers have a cis content of about 98 to 99 % and a broad molecular weight distribution. 

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