Living cationic polymerization of styrene by the methanesulfonic acid/tin tetrachloride initiating system in the presence of tetra-n-butylammonium chloride

Summary

Living cationic polymerization of styrene was achieved by the methanesulfonic acid/tin tetrachloride (CH₃SO₃H/SnCl₄) initiating system in the presence of tetra-n-butylammonium chloride (nBu₄NCl) in methylene chloride solvent below 0 °C. The typical reagent concentrations of this initiating system were as follows: CH₃SO₃H/SnCl₄/nBu₄NCl=20/100/40 mM; [Styrene]₀=1.0 M. The number-average molecular weights of the product polymers increased in direct proportion to monomer conversion, and their molecular weight distributions (MWDs) were fairly narrow $\left( {\bar M_W /\bar M_n \leqslant {\text{1}}{\text{.2}}} \right)$throughout the reaction. On addition of a fresh feed of styrene at the end of the polymerization, the added feed was smoothly polymerized at the same rate as in the first stage; the polymer molecular weight further increased in direct proportion to monomer conversion; and their molecular weight distributions stayed narrow $\left( {\bar M_W /\bar M_n \leqslant {\text{1}}{\text{.2 - 1}}{\text{.3}}} \right)$. On the other hand, in the absence of nBu₄NCl, the polymerization initiated by CH₃SO₃H/SnCl₄ in CH₂Cl₂ at -15 °C led to non-living polymers with a broad molecular weight distribution. This indicates that nBu₄NCl is essential to this living system.