Addition without chain termination

For addition polymerisation without chain termination or chain transfer, eqns. (73) and (77) may be used for a batch reactor when fe = fep. Here, the growing chains have similar histories and hence the final molecular weight distribution can be very narrow. Similar results would be expected from a plug-flow reactor. The mole fraction of A , 7 , is given by... 

Condensation Polymerization. As shown previously, condensation polymerization is characterized by polymer chains that combine both with each other and with monomer units to give larger chains capable of further reaction (Table VI). Like stepwise addition without termination,... 

Equation (32a) removes acyl radicals from the system without producing peroxy acid. This tends to reduce rates without increasing wasteful chain termination reactions. In this way, one can obtain an additional increment of efficiency [43, 87]. Equation (32a) produces acid anhydrides. Variations of this approach have been used to produce anhydrides commercially [88, 89]. 

FIGURE 150 Change in the MW distribution of polymer made with Cr/alumina when H2 is added to the reactor as a chain terminating agent. After activation at 700 °C, the catalyst was tested at 95 °C, with and without the addition of 0.34 MPa H2 in 3.8 MPa ethylene. 

H2 addition is different from other methods of chain termination. For example, when the reaction temperature is raised, the termination rate is multiplied by some factor, which is determined by the activation energy. If the responses of all the sites are approximately the same, the MW distribution is shifted intact to lower MW, without distortion. (To understand why, note that the GPC curve is plotted on a logarithmic MW scale, and the multiplication of the various termination rates by a constant factor amounts to an additive shift across the MW distribution.) However, when H2 is added to the reactor, a new termination pathway is opened, adding to the overall termination rate. If each site is affected equally, then a constant increment is added to the termination rate at each site, which means that the MW distribution should be distorted. High-MW sites should respond proportionately more than the others. 

The effective oxidizability parameter for oxygen uptake in the oxidation of 2-hydroxycyclo hexanone (RCH(0H)C(0)R) initiated by azobisisobutyronitrile in C6H5CI has been determined. The rate constants for chain propagation and termination and the equilibrium constant for addition of the hydroxyperoxyl radical to the keto alcohol are also reported. The ratio of the rate constants of quadratic-law peroxyl radical recombination reactions without and with chain termination increases with increasing [RCH(0H)C(0)R], passes through a maximum ([substrate] = 0.8 mol dm ) and then falls off this has been attributed to the variation of the proportions of the hydroper-oxyl and l-hydroxy-2-oxocyclohexylperoxyl or 1,2-dihydroxy-1-cyclo-hexylperoxyl radicals in the reaction medium." i... 

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