CATIONIC POLYMERIZATION OF HEXAMETHYLCYCLOTRISILOXANE BY TRIFLUOROMETHANESULFONIC ACID AND ITS DERIVATIVES .1. INITIATION BY TRIFLUOROMETHANESULFONIC ACID

Polymerization of hexamethylcyclotrisiloxane (D3) initiated by trifluo romethanesulfonic acid (triflic acid TfOH) was carried out under vacuu m, in methylene chloride solution at 20-degrees-C. The reaction rate i s first order in [D3] and the constant active sites concentration [P] varies as [P] = k . [TfOH]0(3) . [D3]0(-1,8). The two main products of the reaction, both formed in similar amount from the beginning, are the dimer D6 and a high-molecular-weight polymer (HP). The other cycl ic products also formed are the multiples of D3 (D9, D12, ...), macroc ycles MC (number-average molecular weight M(n)BAR almost-equal-to 10(4 )) and small amounts of D4, D5 ... (with [D5] > [D4]). The concentrati on of HP, MC, D6, D9, D12, ... and the M(n)BAR of the high polymer gro w proportionally to conversion. The main reaction giving the high poly mer and D6 is interpreted as a chain reaction, the growing HP bearing at each end potentially reactive silyl triflates which may be activate d by the residual acid. D6 is mainly formed by a special type of back- biting reaction involving transitory tertiary siloxonium ions. The oth er cycles D3x and the macrocycles mainly result from cyclization react ions of a second population of growing macromolecules which bear a sil yl ester at one end and a nucleophilic silanol group at the other end.