Initial stage of the chlorination of natural rubber

Abstract Kinetics of the initial stage of the chlorination of natural rubber(NR), up to chlorine content ⩽1 Cl/C 5 , have been investigated using a stop-flow method in CCl 4 at room temperature. The chlorination is very fast and is accelerated by the product HCl. The first orders of the reaction rate relative to NR, Cl 2 , and HCl were established. A proposed mechanism includes formation of molecular complexes between polymer units, Cl 2 and HCl; the corresponding kinetic equation described satisfactorily the experimental data. Kinetic characteristics of the chlorination of the model compound 2-methylpentene-2(MP) are the same as for NR. The noncatalytic and autocatalytic rate constants for MP are close to those for NR. Compositional heterogeneity of chlorinated NR(CNR) containing 5 has been studied by cross-fractionation. The sample chlorinated by the routine procedure is markedly heterogeneous whereas the sample prepared in the stop-flow unit (where extremely fast mixing is realized) is quite homogeneous. These results lead to the conclusions: (1) high reaction rate is caused by high reactivity of “kinetically independent” NR units, not by a polymeric effect; (2) great compositional heterogeneity of CNR samples prepared by the routine procedure is caused by macrokinetic factors.