“Polydentate phosphine oxides as new electron-donor components of titanium-magnesium catalysts for the synthesis of isotactic poly(1-butene)”

Abstract

Isotactic poly(1-butene) (PB-1) shows a number of very interesting properties, a unique combination of excellent creep resistance and high flexibility being the most important. The polymer has the lowest flexural modulus of all plastics used for tube manufacturing. Owing to the valuable properties of PB-1, its production is increasing in spite of technological difficulties [1]. The industrial synthesis of poly( α -olefins) utilizes mainly TiCl 4 –MgCl 2 catalysts (TMCs) modified with electron-donor compounds capable of forming chelate complexes to increase isospecificity. At present, alkylalkoxysilanes are mainly used as such compounds (external donors, EDs) introduced with the AlEt 3 cocatalyst [1, 2]. At the same time, a search for other types of electron-donor components providing the necessary combination of catalyst properties is in progress. In this work, we studied for the first time the possibility of using polydentate phosphine oxides as electron-donor components of TMCs for the synthesis of isotactic poly( α -olefins). Here, we report the results of study of the polymerization of 1-butene on TMCs with external donors of the type R n P(O)(CH 2 OR') 3 – n (where R = alkyl; R' = methyl, acyl; n = 1, 2). Phosphine oxides— Me 2 P(O)CH 2 OMe (ED-I) [3], Me 2 P(O)CH 2 OC(O)Me (ED-II) [4], Bu 2 P(O)CH 2 OMe (ED-III) [5], and iso - AmP(O)(CH 2 OMe) 2 (ED-IV) [6]—were obtained by known procedures; commercial tributylphosphine oxide (ED-V) was also used. The polymerization of 1-butene was carried out on the TiCl 4 ‐MgCl 2 ‐dibutyl phthalate catalyst (Ti content was 2.06%) in a 200-mL metallic reactor equipped with a stirrer in n -heptane (110 mL) at 323 K and at a constant monomer concentration during polymerization. The solid component of the TMC was introduced after saturation of the solvent with 1-butene, and then solutions of the AlEt 3 cocatalyst and external donor in n -heptane were added. The polymerization time was 1 h. The catalyst activity was assessed from the ratio of the polymer yield to the amount of Ti, monomer concentration, and process duration. The degree of polymer isotacticity was determined from the content of the fraction insoluble in boiling diethyl ether [7]. The viscosity-average molecular weight M v was determined by viscometry in decalin at 383 K and calculated by the formula [8]