SynopsisA theoretical and experimental study has been made of the polymerization of ethylene in a slurry reactor using a highly active Ziegler catalyst in the presence of hydrogen. A model of the polymerization system has been set up in which polymerization is assumed to proceed with encapsulation of catalyst subparticles. Allowance is made for an experimentally observed firsborder decay in intrinsic catalyst activity. The theoretical prediction of the model for the monomer absorption rate behavior and the molecular weight characteristics of the polymers formed are in agreement with experimental findings. Experimental evidence is presented that in the earliest moments of a polymerization significant amounts of polymer are formed with molecular weights 100 times those in the balance of the polymerization. It is concluded that in this system the polymerization is diffusion controlled throughout the major part of the catalyst lifetime. This diffusion phenomenon, together with the gradual loss of active sites, is of vital importance in determining the molecular weight and molecular weight distribution of the polyethylene product.

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Tetrachlorobenzyne and tetrafluorobenzyne react with styrene to yield predominantly or exclusively 1,2,3,4-tetrahalogeno-9,lO-di hydrophenanthrenes or 1.2.3.4-tetrahalogenophenanthrenes in good yield. Similar reactions are reported in which the arynes were generated in the presence of a-methyl-, trans-p-methyl-, 2-methyl-, 3-methyl-, 4-methyl-, and 2,4-dimethyl-styrene. Reactions were also carried out with trans-stilbene, 1 ,I -diphenylethylene, 1 -phenylcyclohexene, and 1 -vinylnaphthalene. The mechanism of formation of 1.2.3.4-tetrafluoro-9.1 O-dihydrophenanthrene has been studied by use of suitably deuteriated compounds. A discussion of the mechanism of formation of 1,2,3,4-tetrafluorophenanthrene, and of 9,1O-dihydro-9-phenylphenanthrene in the reaction of benzyne with styrene, is based on reactions with deuteriated styrenes.SEVERAL papers describing reactions of benzyne with substituted styrenes to give phenanthrene derivatives in low yield have appeared.2 However, no well defined product had been obtained with styrene i t ~e l f . ~ In view of the high yields obtained in cycloaddition reactions of tetrahalogenobenzynes,4 we have investigated the reactions of tetrachlorobenzyne and tetrafluorobenzyne with styrene and some derivatives. During these studies preliminary communications appeared which describe reactions of benzyne with styrene and with a-methylstyrene.6 The results of reactions of tetrafluorobenzyne with styrene have also been reported by

Tetrabromo-and tetraiodo-benzyne can be generated efficiently from the corresponding tetrahalogenoanthranilic acids, and undergo cycloaddition reactions in solution with aromatic substrates. Competition data have been compared with those obtained for tetrachloro-and tetrafluoro-benzyne. Certain substituted tetrabromobenzobarrelenes are converted into naphthalene derivatives in the presence of 3-methylbutyl nitrite. TETRACHLOROBENZYNE and tetrafluorobenzyne are more electrophilic than b e n ~y n e . ~ For example, high yields of benzobarrelene derivatives have been obtained in their reactions with carbocyclic aromatic compounds. In contrast, benzyne reacts with benzene to give low yields of cyclo-ad duct^,^ and shows a high propensity towards dimerisation, yielding biphenylene .5b3We report here some reactions of tetrabromo-and tetraiodobenzyne in solution.The pyrolysis of a number of phthalic anhydrides gives biphenylenes in reasonable yields, by aryne dimerisations.7 Both tetrachloro-7b-d and tetrafluorophthalic anhydride 7e undergo this reaction, but the pyrolysis of tetrabromophthalic anhydride affords hexabr~rnobenzene.~~The data obtained from reactions in which tetrafluorobenzyne % and tetrachlorobenzyne 2b were allowed to compete for an excess of equimolar amounts of benzene and 9-xylene cannot be rationalised in terms of simple inductive effect of the halogens, as reflected by their electronegativity valuess The inductive effect of substituents is normally thought to be of prime importance in affecting aryne reactions, since the two electrons of the ' third bond' are orthogonal to the aromatic x-electron system.*The ratio of bridgehead-substituted benzobarrelenes to the vinyl-substituted isomers produced in the reactions of tetrailuorobenzyne with monoalkylbenzenes did not reflect any steric effect in the transition state leading to the bridgehead-substituted product,3b even though severe hindrance to rotation was observed in an adduct formed between tetrafluorobenzyne and t-buty1benzene.QWe were unable to convert hexabromobenzene into pentabromophenyl-lithium in small scale reactions ; 2b 1