Asymmetric-Selective Polymerization of (RS)-α-Methylbenzyl Methacrylate

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...

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“…Actually, we found that the stereoelective polymerization of MBMA was possible with some of the chiral systems. 12 …”

Section: Discussionmentioning

confidence: 99%

Stereospecific Polymerization of Methacrylates with Ethylmagnesium Alkoxides

Urakawa

Yuki

1978

Polym J

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“…The Sp complexes with phenylmagnesium bromide 14 and tert-butylmagnesium chloride (t-BuMgCl) produced no polymer, and all the other examined Sp complexes with anionic initiators, including n-butyllithium (nBuLi), calcium zinc tetraethyl (CaZnEt 4 ), and diethylaluminum diphenylamide (Et 2 AlNPh 2 ), showed no enantiomer selectivity. 15 Before our discovery, the Sp-triethylaluminum (AlEt 3 ) complex had been used for the polymerization of PEMA.…”

Section: Enantiomer-selective Polymerization (Esp) Of Racemic Methacrmentioning

confidence: 99%

(−)‐Sparteine: The compound that most significantly influenced my research

Okamoto

2004

J. Polym. Sci. A Polym. Chem.

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A chiral diamine alkaloid, (−)‐sparteine (Sp), has been found to be very effective as a ligand for Grignard reagents when used for the enantiomer‐selective polymerization of racemic RS‐1‐phenylethyl methacrylate. The enantiomeric excess of the initially polymerized monomer is 93%, and at about a 60% conversion, nearly optically pure R‐monomer is recovered. This enantiomer selectivity is today the highest in polymer chemistry. Triphenylmethyl methacrylate (TrMA) is a unique monomer that gives a highly isotactic polymer even during radical polymerization. When TrMA is polymerized with the Sp complex with n‐butyllithium in toluene at −78 °C, an optically active, isotactic polymer [poly(triphenylmethyl methacrylate) (PTrMA)] with a one‐handed helical conformation is obtained. The helical structure is maintained even at room temperature in solution. Analogous helical polymethacrylates that show various conformational changes have also been found. One‐handed helical PTrMA exhibits high chiral recognition to a variety of racemates as a chiral stationary phase (CSP) for high‐performance liquid chromatography. This finding has led to the development of very powerful CSPs based on polysaccharides, such as cellulose and amylose. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4480–4491, 2004

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“…Although the peak of the main chain methylene protons overlaps with that of the amino proton around 2.2 ppm, the spectral pattern is simple. Figure 2 shows the 13 reaction) from the growing polymer chain end to the reactive unprotected amino group thus hardly occurs. The 13 C NMR spectra of the carbonyl carbon in the poly(3) obtained with n-BuLi (Table I, entry 7) and the Ph2 NLi-TMEDA complex in toluene (Table I, A sharp singlet at the same chemical shift is observed in Figure 3(a) and 3(b), indicating that the polymers obtained from 3 in toluene are highly stereoregular vinyl polymers.…”

Section: Polymerization Of R:t-(n-alkylaminomethyl)acrylatesmentioning

confidence: 99%

“…HPLC analysis of unreacted monomer indicated that enantiomer-selective polymerization 12 -14 hardly took place under these conditions. 1 H and 13 NMR spectra of the obtained polymers were very broad ( Figure 4), because 2 is a mixture of enantiomeric monomers with a chiral center on the amino group 15 in addition to the H-transfer from the amino proton occurred in polymerization process. The anionic polymerization of 4 bearing the most bulky amino group in toluene at -78°C did not proceed (Table I, entries 10 and 11), probably due to the bulkiness of a-substituent which may prevent polymerization as reported previously for the anionic polymerization of a-(trityloxymethyl)acrylate having a bulky alkoxy group.…”

Section: Polymerization Of R:t-(n-alkylaminomethyl)acrylatesmentioning

confidence: 99%

Stereospecific Anionic Polymerization and Novel Hydrogen-Transfer Polymerization of α-(Aminomethyl)acrylates Having Unprotected Amino Group

Baraki

Habaue

1999

Polym J

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ABSTRACT:Anionic polymerization of 1)(-(aminomethyl)acrylates (2-8) having an unprotected amino proton was carried out using lithium reagents at -78°C. Acrylates except for 4 and 8 afforded the polymers in good yields. The polymerization of ethyl 1)(-[N-(diphenylmethyl)aminomethyl]acrylate (3) with n-BuLi or the Ph2NLi-N,N,N',N'-tetramethylethylenediamine (TMEDA) complex in toluene afforded a polymer with a normal vinyl polymer structure and high isotacticity. Hydrogentransfer of the amino proton hardly occurred in the polymerization process. The anionic polymerizations of ethyl 1)(-[N-(1-phenylethyl)aminomethyl]acrylate (2) using lithium reagents in toluene and tetrahydrofuran (THF) proceeded with hydrogen-transfer reaction. CH carbon generated by hydrogen-transfer in the main chain was detected by DEPT NMR measurement of poly(2). The CH -containing unit in the polymer increased up to nearly 40% when THF was used as a solvent. Monomers 4 and 8 showed low polymerizability.

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Asymmetric-Selective Polymerization of (RS)-α-Methylbenzyl Methacrylate

Cited by 36 publications

References 6 publications

Stereospecific Polymerization of Methacrylates with Ethylmagnesium Alkoxides

Stereospecific Polymerization of Methacrylates with Ethylmagnesium Alkoxides

(−)‐Sparteine: The compound that most significantly influenced my research

Stereospecific Anionic Polymerization and Novel Hydrogen-Transfer Polymerization of α-(Aminomethyl)acrylates Having Unprotected Amino Group

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