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 polymerization of isobutene in ethyl chloride solution at -78.5 "C has been studied using stannic chloride as catalyst and alkyl substituted phenols as cocatalysts. In preliminary experiments, the nature and extent of the complexing between phenols and stannic chloride was examined and it was shown that G-complexing occurs between the oxygen of the phenol and the stannic chloride. Equilibrium constants were determined over the temperature range 30 to -50 "C and were used, together with hydrogen bonding data, to estimate the concentrations of complex and free phenol in the polymerization mixtures at -78.5 "C. The active initiator in the polymerization is probably the G-complex but the free phenol acts as a chain terminating agent. This explains the ability of the cocatalyst to decrease the rate of polymerization under some experimental conditions. For isobutene concentrations up to 3 M and at constant dielectric constant the rate of polymerization and the molecular weight are proportional to the monomer concentration. A mechanism is proposed to account for the main features of the experimental results.

The article contains sections titled: 1. Synthesis by Anionic Polymerization 1.1. Solution 1,3‐Butadiene ‐ Styrene Rubber (S‐SBR) and Styrene ‐ Isoprene ‐ Butadiene Rubber (S‐SIBR) 1.1.1. Properties, Grades, and Applications 1.1.2. Basic Chemistry and Production Processes 1.1.3. Producers and Production Capacities 1.2. Lithium ‐ Butadiene (Li‐BR) and Lithium ‐ Isoprene (Li‐IR) Rubber 1.2.1. Properties, Grades, and Applications 1.2.2. Basic Chemistry and Production Processes 1.2.3. Producers and Production Capacities 2. Synthesis by Ziegler ‐ Natta Polymerization 2.1. Polybutadiene and Polyisoprene Rubber 2.1.1. Properties, Grades, and Applications 2.1.2. Basic Chemistry and Production Processes 2.1.3. Producers and Production Capacities 2.2. Ethylene ‐ Propene Elastomers (EPM, EPDM) 2.2.1. Properties, Grades, and Applications 2.2.2. Basic Chemistry and Production Processes 2.2.3. Producers and Production Capacities 3. Synthesis of Butyl Rubber by Cationic Polymerization 3.1. Properties, Grades, and Applications 3.1.1. Properties 3.1.2. Grades 3.1.3. Specialty Rubbers 3.1.4. Applications 3.2. Basic Chemistry and Production Processes 3.2.1. Basic Chemistry 3.2.2. Industrial Production 3.3. Producers and Production Capacities 3.4. Storage and Transportation 3.5. Legal Aspects 3.6. Toxicology and Occupational Health

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