Stereospecific Polymerization of Methacrylates with Ethylmagnesium Alkoxides

Abstract

ABSTRACT:Ethylmagnesium alkoxides (EtMgOR) resulting from an equimolar reaction of diethylmagnesium (Et2Mg) with a variety of alcohols were employed as catalysts for the stereospecific polymerization of methyl methacrylate (MMA) in toluene at -78°C. The catalysts obtained from normal alcohols did not show a clear stereospecific tendency, but the alkoxides of 2-monosubstituted primary alcohols such as 2-methyl-1-propanol (iso-BuOH), 2-butanol, cyclohexylmethanol, and ( -)-cis-myrtanol, worked as isospecific catalysts. Secondary and tertiary alkoxides formed syndiotactic polymers. In the polymerization with Et2Mg-isoBuOH system, the activity of the catalyst and the isotacticity of the obtained polymer were highest at [iso-BuOH]/[Et2Mg] = 1; the isotacticity decreased with an increase in temperature. The stereospecificity of Et2Mg-2-methyl-2-propanol (t-BuOH) system did not depend on the [t-BuOH]/[Et2Mg] ratio; the temperature effect was not pronounced. The stereospecific polymerization of ethyl, tert-butyl, a-methylbenzyl, and a, a-dimethylbenzyl methacrylates was also investigated with iso-BuOMgEt and t-BuOMgEt in toluene at -78°C. The structure of the catalysts was investigated by means of the 1 H NMR method.KEY WORDS Stereospecific Polymerization / Diethylmagnesium / Ethylmagnesium Alkoxide / Methyl Methacrylate / Methacrylate / Tacticity / Anionic Polymerization / Many organomagnesium compounds such as dialkylmagnesium (RMgR), 1 ' 2 alkylmagnesium amide (RMgNR'R"), 3 and Grignard reagent (RMgX) 1 ' 2 have been used as stereospecific catalysts for the polymerization of methacrylic esters. These compounds possess Mg-carbon, Mgnitrogen, and Mg-halide bonds, respectively, in addition to the Mg-carbon bond. However alkylmagnesium alkoxide (RMgOR') has scarcely been used for the polymerization of methacrylates. Coates and Ridley have reported that alkylmagnesium alkoxide can be prepared from dialkylmagnesium and alcohol, and forms dimer, trimer, and higher oligomers in benzene depending on both the alkyl group and alkoxy group. 4Such an association of alkylmagnesium alkoxides has also been observed even in diethyl ether.5 group bound to a magnesium cation always stays at a position close to a polymer-chain anion and the structure of the alkoxy group may have an influence on the stereoregulation of the polymerization.The polymerization of methacrylates catalyzed by alkylmagnesium alkoxides is initiated by an insertion reaction of a monomer molecule into the Mg-carbon bond. Consequently, the alkoxy In order to ascertain this point, we undertook the polymerization of methyl (MMA), ethyl (EtMA), tert-butyl (t-BuMA), a-methylbenzyl (MBMA), and a, a-dimethylbenzyl (DMBMA) methacrylates by using various ethylmagnesium alkoxides (EtMgOR) obtained from equimolar reaction of diethylmagnesium and alcohols in toluene. In particular, the polymerization of MMA with Et2Mg-2-methyl-l-propanol (isoBuOH) and Et2Mg-2-methyl-2-propanol (tBuOH) systems was investigated in detail. EXPERIMENTAL MaterialsCommercial MMA, EtMA, and t-BuMA we...

Asymmetric-Selective Polymerization of (RS)-α-Methylbenzyl Methacrylate with the Cyclohexylmagnesium Chloride-(---)- Sparteine System in Toluene at -78 °C

“…HexMgBr)-( -) -sparteine systems initiated the polymerization of (BS)-MBMA to form a highly isotactic (S) polymer having about 90% optical purity in the early stage of the polymerization, while the unreacted monomer was enriched in (R)-antipode whose optical purity was more than 90% at about 60% yield. [1][2][3] The catalyst systems also polymerized 2,3-epoxypropyl methacrylate (glycidyl methacrylate) stereoelectively to give a highly isotactic polymer.2 This monomer has an asymmetric carbon at a further remote position from the carbon-carbon double bond in comparison with (fiS)-MBMA.…”