This review generalizes the data on the application of single site catalysts (SSCs) in the industrial production of polyethylene. The history of their industrial application, the basic types of SSCs, the main pro cesses of the production of polyethylene (PE) on the mentioned systems, the largest PE production plants using SSCs, and the application fields of polymers synthesized at these plants are described. The prospects for further development in this direction are discussed.

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The solid phase synthesis of zirconium carboxylates Zr(OOCR) 4 (R = Alk) by reactions of zirconium tetrachloride with metal carboxylates (isobutyrate, pivalate, and palmitate) (the molar ratio ZrCl 4 : RCOOM is 1 : (4-5)) under mechanical activation is developed. Further thermal treatment of the reaction mixture and extraction with an organic solvent afford zirconi um carboxylates.Key words: metal carboxylates, zirconium carboxylates, zirconium isobutyrate, zirconium pivalate, zirconium palmitate, mechanical activation, solid phase synthesis.Zirconium carboxylates 1-5 are of interest as both the starting compounds for the preparation of zirconium con taining materials possessing unique properties, which are very useful in new technologies and as components of catalysts for various chemical processes. In particular, zir conium tetracarboxylates have found wide application in industrial oligomerization of ethylene. 6,7 Carboxylates of various metals (including zirconium) are produced in an industrial scale by a number of large chemical com panies. 8,9 Various types of zirconium carboxylates are known 1-3 that differ in the structure of carboxylic substit uents, their number in the coordination sphere of the met al, and the nature of other substituents. Hetero ligand zirconium carboxylates containing water or hydroxyl groups are studied in most details. Zirconocene carboxyl ates (η 5 C 5 H 5 ) 2 Zr(OOCR) 2 are fairly well studied, while information on zirconium tetracarboxylates Zr(OOCR) 4 (R = Alk) is scarce.Reactions of zirconium derivatives with carboxylic ac ids are usually employed for the preparation of zirconium tetracarboxylates. 1-3 Of them, the reactions of zirconium tetrachloride with carboxylic acids in organic solvents are the most popular. 1-5 These reactions proceed stepwise (Scheme 1). Scheme 1 ZrCl 4 + HOCOR RCOOZrCl 3 + HCl RCOOZrCl 3 + HOCOR (RCOO) 2 ZrCl 2 + HCl (RCOO) 2 ZrCl 2 + HOCOR (RCOO) 3 ZrCl + HCl (RCOO) 3 ZrCl + HOCOR (RCOO) 4 Zr + HClThus zirconium acetate, propionate, n butyrate, and isobutyrate Zr(OOCR) 4 were prepared by heating zirconi um tetrachloride with an excess of the respective acid in xylene or using acid as a solvent; 1-3 zirconium stearate and palmitate were prepared by heating zirconium tetra chloride with an excess of the respective acid in benzene for 14 h. 10 No data on the possibility of preparation of zirconium tetrapivalate by the reaction of ZrCl 4 with piv alic acid or its salts are available. This approach has some major drawbacks: a low rate and long duration of the reaction; relatively high tempera tures (100-150 °C) required to end the process for the lower carboxylates; release of a large amount of corrosive hydrogen chloride; reversibility of the reaction.The aim of the present work is to study the possibility of application of the solid phase mechanochemical method for the preparation of zirconium tetracarboxylates, deriv atives of aliphatic carboxylic acids. We studied the possi bility of the application of the solid phase (solvent free) mechanochemical me...