Polymeric nonuniform conditions

Phase Separation under Nonuniform Conditions in Polymeric Systems 1101... 

Precipitation chromatography, as proposed by Baker and Williams and improved in our laboratory, has a systematic error caused by the nonuniformity of the fractions. This error can be eliminated if the fraction nonuniformity is determined by a special kind of mixing experiment. Another interfering effect which is produced in anionic polymerizates by traces of impurities can be eliminated by testing the BW fractions by GPC. Exactly determined molecular weight distribution functions of samples which are synthesized under well defined kinetic conditions provide much information about elementary reactions of the polymerization process. This is demonstrated by some examples of the anionic polymerization of styrene and methyl methacrylate. 

For instance, by the described method one can determine the MWD of polymers which are produced under kinetic conditions for which a Poisson distribution is expected. That is the case in anionic polymerization when only contact on pairs are present and when the dissociation is suppressed by addition of counter ions. Moreover, the reaction time must be equal for all growing molecules. These conditions are realized for the polystyrene samples shown in Figure 9 (10, II, 12). The curves are calculated for the corresponding Poisson distributions, and the points are the experimental values. For a Poisson distribution, the nonuniformity is given by the equation... 

In one of the first bulk polymerizations of NVP [482 86], in which H2O2 was used as initiator, the resulting products of PVP were yellowish brown, nonuniform, and of low molecular weight. Initiation with benzoyl peroxide did not give satisfactory results either [482,483,485,486]. The initiator of choice is AIBN [487]. Breitenbach et al. [488,489] have polymerized NVP by heating it over 100 °C in the presence of AIBN. The same authors demonstrated that initiator-free polymerization is also possible. AIBN as initiator fulfilled the conditions of radical-induced vinyl polymerization (e.g., the rate of polymerization was found to be proportional to the square root of the initiator concentration). However, the average degree of polymerization is nearly independent of the AIBN concentration... 

Due to the widespread usa of alumimrm alkyls in olefin polymerization reactions (e.g., as water scavenger or for catalyst alkylation), it is often difficult to assess the influence of changes in the reaction conditions on a specific observance in the copolymetization behavior. The choice of an appropriate aluminum compound is cmcial for a satisfartory incorporation of polar monomers into polyolefins. MAO, often used for catalyst activation, is not always able to proted the catalyst from deactivation.This can be attributed to insufficient com-plexation " and a nonuniform composition of the commerdal MAO solutions. The contained trimethylalumi-num (TMA) can also lead to increased chain transfer from the catalyst to the present aluminum compoimds. Hence, isobutyl modified MAO, for example, exhibits better protective characteristics. Therefore, and due to the difficult examination of MAO containing reaction mixtures, the addition of further well-defined aluminum compounds like TMA, triethy-laluminum (TEAL), tri-n-butylaluminum (TNBA), TIBA, and tri-/i-octylaluminum (TOA) has been examined. 

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