LIVING CATIONIC POLYMERIZATION OF INDENE .2. POLYMERIZATION INITIATED WITH CUMYL CHLORIDE TITANIUM TETRACHLORIDE AND CUMYL CHLORIDE N-BUTOXYTRICHLOROTITANIUM INITIATING SYSTEMS

The polymerization of indene in methylene chloride solution initiated with cumyl chloride and titanium tetrachloride has been investigated as a possibly ''living'' system. At-40-degrees-C, initiation is quantitative only in the presence of dimethyl sulfoxide (DMSO) as an electron-donating compound. Linear growth of the M(n)BAR with the amount of monomer converted can be observed for monomer to initiator ratios lower than 200, although transfer does take place (k(trM)/k(p,-40-degrees-C) = 6 x 10(-4)). At +5-degrees-C, linear growth is observed only up to M(n)BAR almost-equal-to 15 000, initiation is quantitative without DMSO, and this compound does not reduce transfer (k(trM)/k(p,+5-degrees-C) = 1.4 x 10(-3) in both cases). At -75-degrees-C, initiation is not quantitative, even in the presence of DMSO. Common ion salts have the same effect as DMSO on the molecular weight distribution and on the ''living'' character, and this is attributed to a shift of equilibria between dormant covalent species, ion pairs, and free ions, favoring the exchanges between active and dormant species. This implies the existence of a reversible termination, which is confirmed by initiation with a model of the chain end (1-chloroindan). Slow exchange between active and dormant species may explain the relatively broad molecular weight distributions observed (M(w)BAR/M(n)BAR almost-equal-to 2-3). Better results (M(w)BAR/M(n)BAR almost-equal-to 1.6-2) are obtained with n-butoxytrichlorotitanium as coinitiator at-40-degrees-C, without DMSO. The two parameters allowing the observation of a ''living'' polymerization are the propagation to initiation rate ratio, which must be low enough to allow quantitative initiation, and the monomer to initiator ratio, which must be low enough to yield low molecular weight polymers, for which transfer is undetectable. Besides, as could be expected, transfer is reduced at low temperatures. These results may be accounted for by classical carbocationic polymerization mechanisms.