I n non-terminat ed anionic polymerization the propagating species may be a free anion or an ion-pair and the latter may dimerize to a relatively unreactive species1*2). VCi e wish t o report here some results of an attempt to study systematically the effects of the alkali metal cation and of the solvent on the ARRHENIW parameters in the propagation of ion-pairs involving (a) polystyryl anions and (b) poly-a-methylstyryl anions.X'hese resalts are given here in summary forni i n view of the current interest in these systems. A fuller account, with a more detailed discussion of the data, will be published shortly.The kinetics of polymerization were followed dilatometrically. a-Methylstyrene is a particularly convenient monomer since the polymerization can be reversed by an increase of temperature and a number of runs performed at different temperatures without recharging the dilatometer. Alkali salts of naphthalene, biphenyl or a-methylstyrene tetramer were used as initiators. Good &st-order decay curves were obtained with half-lives ranging from 20 seconds to 24 hours. Living-end concentrations, [LEI, were estimated either from optical density measurements or from the molecular weight of the polymer, using the SZWARC relation3).In tetrahydrofuran (THF) or tetrahydropyran (THP) it was necessary either to suppress ion-pair dissociation by the addition of excess alkali cations (in the form of alkali tetraphenylboron) or to extrapolate the apparent second-order rate constants to = 0. In the less polar solvents the proportionality between rate and [LEI, or the absence of a decrease of viscosity on killing the living ends, provides a check on the absence of ion-pair dimerization *--6).Our results t o date are summarized in Tables 1 and 2. The uncertainties in the values of log A, are commensurate with those in E,. Rather surprisingly it was possible t o obtain rate constants using cyclohexane as solvent; ion-pair dimerization is apparently not important for the larger counter-ions provided the living-end concentration is not too high. 257
The effect of a variety of phenols on the rate and degree of polymerization of styrene has been studied. With 1‐naphthol it is found that polystyryl radicals abstract the phenolic hydrogen atom, since 1‐naphthol has a far greater effect on the rate and degree of polymerization than 1‐deuteroxynaphthalene. Many phenols do not significantly retard the polymerization of styrene and transfer constants ranging up to 7.7 × 10−3 have been estimated for them. Other phenols, such as 1‐naphthol, 4‐methoxyphenol and 2,6‐diisopropylphenol, significantly decrease the rate and degree of polymerization. Transfer constants for these retarders have been calculated, both from the rate data alone by means of the treatment of Jenkins and from molecular weight data. The estimated values depend on the assumptions made concerning the mode of disappearance of the retarder radicals produced in the transfer reaction. Most of the retarders investigated give transfer constants in the range 10−2 to 10−1 but catechol, tert‐butylcatechol, and pyrogallol give larger values. An increased rate of polymerization observed in mixtures of styrene and some phenols is probably due to a higher rate of production of radicals by the initiator, azobisisobutyronitrile.
The effect of six deuterated phenols on the rate and degree of poly~nerization of styrene has been stlldied. The rate and degree of polymerization are decreased by deuterated phenols to a much less estent than by the corresponding phenols. Hpprosimate transfer constants are estimated, and it is found that the transfer constant for hydrogen abstraction from the deuterated phenol is less than 0 . 2 of the transfer cor~stant for the norrnal phenol. The rates of reaction of 2,2-diphenyl-1-picrylhydrazyl with three deuterated phenols have been determined. The rate constants for deuterated 2,6-di-t-butylphenol and 4-bro~nophenol are less than 0 . 1 5 of those for the correspondi~~g phenols, but the isotope effect appears t o be small with 4-nitrophenol.I n a recent study (1) it was shown that phenols lower both the rate and degree of polynlerization of styrene and t h a t the magnitude of the decrease depends oil the i l a t~~r e and position of substituents in the phenol. Tlle results are interpreted in terms of an attaclc by polystyryl radicals on the O H group of the phenol. Support for this suggestion comes from the observation t h a t certain 0-methg.1 phenols do not significantly alter the rate and degree of polymerization of styrene. In all attempt to obtain more positive evidence, the effect of six deuterated phenols on the polymerization of styrene has been determined, and the derivecl transfer constants compared with those estimated for the normal phenols.In a separate study (2) the rates of reaction of 5,2-diphenyl-1-picrylhydrazyl ( D P P H ) with a wide range of substituted phenols were obtained. T h e rate-determining step was considered to be the abstraction by DPPI-I of a hydrogen atom from the 01-1 group of the phenol since 0-methyl phenols are relatively weal; hg7drogen clonors, and deuteration of 2,6-di-t-butyl-4-methylphenol decreases the rate constant for hydrogen abstraction a t 20" by a factor of 1.95 (3). Strong supporting evidence has now been obtainecl using deuterated 2,6-di-t-butgllphe1101 and 4-brol~~ophenol a s donors. A surprisingly small isotope effect was observed with 4-nitrophenol.Styrene, a gift of Dow Chemical of Canada, Ltd., was distilled a t reduced pressure and then degassed and subjected to two distillations on the vacuum line. It was stored a t -78.5'. The phe!~ols were ~~o r m a l l y recrystallized twice and dried in a vacuum dcsiccator. Dcuteration was effected by adding about 4 g of heavy water or deuterated metha1101 to 1.5 g of the pher~ol and leaving overnight a t 60' or reflusing for 2 hours. The water and ~nethanol were removed on the vacuum line and the procedure \\.as twice repeated. The estent of deuteration was estimated by talcing infrared spectra of the deuterated phenols in chloroforln solution. The purified chloroform was dried over calcium chloride ancl the sodium chloride cells were filled in a dry bos. The general experimental procedure for studying the efiect of phc~lols on the polymerization of styrene a t 60' has been described elsewhere (1).For...
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