Molecular-mass-distribution of oligomers in the products of tetrafluoroethylene telomerization in various solvents |
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Authors: | I P Kim |
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Institution: | 1.Institute of Problems of Chemical Physics,Russian Academy of Sciences,Chernogolovka, Moscow oblast,Russia |
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Abstract: | The possibility of using differential thermogravimetry (DTG) for determination of the molecularmass-distribution (MMD) of
oligomers in polymerization products has been experimentally and theoretically substantiated. The technique is based on the
assumptions that the increase in the boiling temperature of oligomers with the increasing chain length is described by the
additivity rule and the shape of DTG curves obeys the equation of mass transfer in the stationary convective flow created
by evaporation. The results have been confirmed by gel-permeation chromatography and 19F NMR data. It has been shown that the chain length of oligomers produced via tetrafluoroethylene (TFE) telomerization in
carbon tetrachloride, chloroform, acetone, and ethyl acetate reaches about 20–25 C2F4 units at an initial TFE concentration of C
0 ≈ 0.5 mol/l. The MMD includes a low-molecular-mass component (n ≤ 5) in an amount that decreases with increasing C
0 and a high-molecular-mass component, whose maximum shifts toward higher values of n with an increase in C
0. The bimodality of MMD is explained in terms of decrease in the propagation rate constant with the accumulation of long oligomers. |
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