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Mechanism of octamethylcyclotetrasiloxane polymerization in the presence of siloxanediols
Author(s) -
Bischoff Rémy,
Sigwalt Pierre
Publication year - 1996
Publication title -
polymer international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.592
H-Index - 105
eISSN - 1097-0126
pISSN - 0959-8103
DOI - 10.1002/(sici)1097-0126(199606)40:2<99::aid-pi540>3.0.co;2-3
Subject(s) - polymerization , triflic acid , octamethylcyclotetrasiloxane , silanol , chemistry , condensation polymer , polymer chemistry , chain transfer , bulk polymerization , living polymerization , polymer , organic chemistry , catalysis , radical polymerization
Polycondensation of tetramethyldisiloxanediol (HD 2 OH) by triflic acid (TfOH) in the presence of octamethylcyclotetrasiloxane (D 4 ) has been studied at 30°C in CH 2 Cl 2 solution and in bulk at 80°C. The condensation follows a similar pathway, at a similar rate, in the presence or in the absence of D 4 . Larger oligosiloxanediols and D 4 are formed first, and high polymer only after several hours. At 30°C, no polymerization of D 4 occurs, even 24 h after the total conversion of HD 2 OH. In bulk at 80°C, polymerization of D 4 takes place when silanol concentration becomes very low at the end of the polycondensation, and is assumed to result from a reaction of D 4 with ester end‐groups activated by hydrated acid at this temperature. Indeed, these results show that silanol groups activated by TfOH are not responsible for D 4 polymerization. Polymerization made in the presence of longer‐chain oligosiloxanes HD x OH (x ∼ 15) indicates that the presence of silyltriflates is a prerequisite of the propagation reaction. Polymerization of D 4 alone at 80°C also occurs in the presence of water in situ (0.9 mol litre −1 ) after addition of pure triflic acid, and water cocatalyses the propagation reaction. However, the initiation reaction is almost completely inhibited when triflic acid is prehydrated.