. Can. J. Chem. 57,2355Chem. 57, (1979. The influence of 2,4-and 2,6-dimethylphenol, 2,3,6-and 2,4,6-trimethylphenol, 2,3,4,6-and 2,3,5,6-tetramethylphenol, 2,6-diisopropylphenol, 2-rert-butyl-4-methylphenol and 2,4-di-tert-butylphenol on the stannic chloride initiated polymerization of isobutene has been investigated. At -78.S°C and with 0.185 M stannic chloride, these phenols act as coinitiators.Rates of polymerizaiton reach maximum values at phenol concentrations which depend greatly on the number and positions of alkyl substituents; molecular weights decrease continuously with phenol concentration. Phenols without 4-substituents are incorporated in polyisobutenes as end groups and those with 4-substituents give rise largely to olefinic end groups. Termination of polymerization occurs mainly by attack at a free 4-position or at the O H group. The initial ferf-butyl carbenium ion is more readily terminated by 2,6-di-terr-butylphenol than the polymer carbenium ion.The rate and molecular weight results are interpreted in terms of a simplified reaction scheme in which termination occurs spontaneously or by reaction with uncomplexed phenol. Rate constants for termination by methyl-substituted phenols are of the order of one tenth of the propagation rate constant while those for 2-rerr-butyl-4-alkylphenols are about one hundredth of the propagation rate constant.On a etudik l'influence des dimCthyl-2,4 (et -2,6), des trimkthyl-2,3,6 (et -2,4,6), des tetramethyl-2,3,4,6 (et -2,3,5,6), du diisopropyl-2,6, du rerr-butyl-2 methyl-4 et du di-tert-butyl-2,4 phenols sur la polymerisation de l'isobutene catalysee par le chlorure stannique. A -78.0j0C et avec 0.18 M de chlorure stannique, ces phenols agissent comme coinitiateurs. Les taux de polymCrisation atteignent des valeurs maximales a des concentrations de phCnols qui dependent grandement du nombre et de la position des substituants alkyles; les poids moleculaires diminuent progressivement avec la concentration de phenol. Les phenols qui ne portent pas de substituants en position 4 sont incorpores dans les polyisobutylenes sous forme de groupes terminaux; ceux qui portent un substituant en position 4 donnent principalement lieu a des groupes terminaux portant des liaisons doubles. La terminaison de la polymerisation se produit principalement par une attaque au niveau de la position 4 vacante ou du groupe OH.Le carbocation rerr-butyle initial est plus facilenlent piegk par le di-re1.r-butyl-2,6 phCnol que le carbocation du polymere.On interprete la cinCtique et les poids moleculaires en termes d'un schCma reactionnel simplifiC dans lequel la terminaison se produit spontanement ou par reaction avec un phCnol qui n'est pas complexC. Les constantes de vitesse pour la terminaison par des phCnols porteurs de groupes mCthyles sont environ un dixieme de la constante de vitesse de propagation alors que celles des rerr-butyl-2 alkyl-4 phCnols sont Cgales a un centieme de la constante de vitesse de propagation.[Traduit par le journal]Introduction the influence of particular var...
The substance 2,6‐di‐tert‐butylphenol acts as a strong retarder for the cationic polymerization of isobutene. Spectroscopic studies show that the growing polymer cation attacks the phenol at the basic 4‐position. Analysis of the kinetic and degree of polymerization results yields estimates of the rates of initiation of the polymerization. The initiation reaction in the polymerization of isobutene in ethyl chloride at −78.5°C with stannic chloride and a coinitiator appears to be a first‐order process. Rate constants for the initiation reaction include 4 × 10−6sec−1 for water as coinitiator, 3.8 × 10−5sec−1 for 2,6‐dimethylphenol, 7.5 × 10−5sec−1 for 2,4,6‐trimethylphenol, 3.1 × 10−5sec−1 for 2,3,5,6‐tetramethylphenol, 7 × 10−5 sec−1 for 2,3,4,6‐tetramethylphenol, and 1.5 × 10−3sec−1 for acetic acid.
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