Cationic polymerization of 1,3,5,7 tetramethylcyclotetrasiloxane initiated by trifluoromethanesulphonic acid

Polymerization of 1,3,5,7 tetramethylcyclotetrasiloxane (D4H) by trifluoromethanesulphonic acid in CH2Cl2 solution at 20° has given high polymers (HP) with molecular weights > 105. For sufficiently high monomer concentrations (e.g. 1.9 mol · l−1), the HP yield may reach 60%. Small cycles are formed together with the high polymer by back-biting reactions as in the case of octamethylcyclotetrasiloxane (D4) but the polymerization rate is much higher than that of D4 and near that of D3. The kinetics are quite different and much simpler than those observed for the dimethylcyclosiloxanes: the reaction is still internally 1st order in monomer, but the apparent rate constants are 1st order in both acid and monomer concentrations. This effect may result from the much larger reactivities of silyltrifluoromethanesulphonates derived from this monomer.