Chain length dependent determination radical polymerization kinetics

The discussion of the rate of bimolecular termination has, up to now, been mainly of a qualitative nature. The scaling of average or macroscopic kt values with viscosity, solvent effects and coil dimensions were discussed without much attention for the chain-length dependence of this process. This dependence originates from the simple fact that free-radical termination is a diffusion-controlled process. Consequently, the overall mobility of polymer chains and/or polymer chain ends determine the overall rate of radical loss in a polymerizing system. As small chains are known to be much more mobile than large ones, the chain length of radicals can be expected to have a profound effect on the termination kinetics. 

Also the group of Olaj have performed quite a number of simulation studies, mainly on the kinetics of PLP. In a recent series of papers [172-174, 230] they have used a simulation method based on an iterative procedure [239-241]. The time interval is divided in small, equal intervals, each of duration kp [M]. The radical profile is then converged until a pseudo-steady-state profile is obtained, from which relevant kinetic data can then be calculated such as the rate of polymerization and / or the MWD. Olaj et al. [172-174, 230] used these kinetic data to explore the possibilities of recovering chain-length dependent termination rate coefficients from PLP experiments. In their simulations they compared the exact value of (which can be calculated in a simulation, but is not experimentally accessible) with the value of that they obtained from analyzing output data of their simulations, which are experimentally accessible parameters. In the case of using MWD data [172], the second moment of this distribution, according to [242-244] ... 

In conclusion it can be said that the MWD method is capable of determining the chain-length dependence of kt model-independently. This method has been validated theoretically and, as long as the number MWD can be determined and scaled correctly, the method is robust and reliable. In this thesis, the first model-independent results have been reported for a set of three acrylates. These results will enable a better description of the overall kinetics of free-radical polymerizations and better predictions of the resulting MWDs and polymer properties. It is sincerely hoped that this method and lines of thought presented will find continuation in future scientific work by others in this field of great scientific interest and practical importance. 

In this thesis the chain-length dependence of termination reactions during free-radical polymerization has been investigated. After an extensive review of this field, provided in chapter 2, two novel kinetic analyses have been proposed in chapter 3, which should enable the direct and model-independent determination of the chain-length dependence of free-radical termination reactions. 

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