| Popis: |
The rates of initiation for the copolymerization of styrene and methyl methacrylate at 50°, in different reaction media (bulk, acetone, dimethylformamide and dioxane) have been determined by using the isotopic labelling technique (14C - azobisisobutyronitrile). For all mixtures, except dioxane, the experimental data do not support the linear interpolation of the initiation rates, which is usually adopted in literature. In the whole range of monomer feed compositions, any modification of the reaction medium causes a relevant change of the initiation rate, so that the overall pattern is markedly modified. The strongest solvent effect is given by dioxane, which reduces the initiation rates for all monomer mixtures. The radioactive tracer method also enables the determination of the modes of termination, which occur almost exclusively by combination for monomer feed compositions up to about 70 molar % of methyl methacrylate. The P w P n ratios obtained by g.p.c. confirm the general trend of the termination mechanisms as a function of monomer mixture and reaction medium. |
