The main special characteristics of anionic polymerization initiated by group II metals

Abstract

The results of the investigation of polymerization and copolymerization processes of hydrocarbon monomers initiated by compounds of alkaline-earth metals are summarized. Experimental data on the synthesis of initiators, stereospecifity, kinetics and mechanism of the processes are considered. The pecularities of the processes studied are discussed and compared with those of the polymerization initiated by alkali metals, the importance of bimetallic species in polymerization processes being emphasized.

Stereospecificity of Alkaline Earth Metal Compounds in the Anionic Polymerization of N,N-Dimethylacrylamide

“…[2] A similar situation was found earlier for anionic polymerization of butadiene, where the effect of the counterion size on polymer structure for alkaline earth initiators was also opposite to the effect observed with alkali metals. [5,6] …”

“…In THF, organobarium initiators produce polybutadiene with 75-80% 1,4-units, whereas polymers obtained with Ca and Mg in this solvent contain only 30% and 45% 1,4-units, respectively. [5,6] The aim of the present paper is to study whether the dependence described by Hogen-Esch et al is also valid for DMA polymerization with Group II metals or, similar to butadiene polymerization, the effect of the counterion size on poly(DMA) structure for alkaline earth initiators is opposite to the effect observed with alkali metals.…”

“…metals. [5,6] Here, the highest 1,4-stereoregulation occurs with the largest counterion, Ba, whereas the smaller counterions, Ca and Mg, are less stereospecific. Polybutadiene obtained with organobarium initiators in hydrocarbon solvents contains up to 80% cis-1,4-units, in comparison with ca.…”

Metal‐Containing Polymers: Cryochemical Synthesis, Structure, and Physicochemical Properties

“…This band lies between absorption bands of ionic organometallic compounds in the range 420-470 nm and those of organomagnesium derivatives with predominantly covalent Mg-C bonds in the range 280-300 nm [38,39]. Thus, the bonds in complexes of PX with a magnesium atom (or cluster Mg n ) are neither purely ionic not covalent, but have intermediate structure.…”

Retarded Anionic Polymerization: Copolymerization of Butadiene and Styrene in the Presence of Alkyllithium and n,s‐Dibutylmagnesium or Triisobutylaluminium Derivatives

“…Conversely, in polar media or in the presence of polar additives or complexing agents, as well as with alkali metal counter-ions other than lithium, a much higher styrene incorporation rate is observed: copolymers exhibit a tapered distribution of styrene and butadiene units with a higher amount of 1,2-vinyl structure. [3][4][5][6][7][8] Although numerous studies have focused on the influence of Lewis bases, only a limited number of works have dealt with the influence of Lewis acids on the stereochemistry of buta-1,3-diene polymerization and on the styrene/buta-1,3-diene copolymerization initiated by alkyllithium in hydrocarbons. Hsieh and Wang have studied the effect of small amounts of n,s-dibutylmagnesium (n,sBu 2 Mg) on s-butyllithium (s-BuLi)-initiated polymerization and copolymerization of styrene and butadiene.…”