Polymer Journal, Vol. 19, No.9, pp 1047-1065 (1987)
Highly Asymmetric-selective and Stereoselective Polymerization of (RS)-rx-Methylbenzyl Methacrylate with Cyclohexyl magnesium Bromide-Axially Dissymmetric 2,2' Diamino-6,6' -dimethylbiphenyl System
Shigeyoshi KANOH, Sakae GOKA, Nobutsugu MUROSE, Hideo KUBO, Masao KONDO, Tomoaki SUGINO, Masatoshi MOTOI, and Hiroshi SUDA
Department of Chemistry and Chemical Engineering, Faculty of Engineering, Kanazawa University, 2-40-20 Kodatsuno, Kanazawa 920, Japan
(Received February 13, 1987)
ABSTRACT: Enantiomer-selective polymerization of (RS)-IX-methylbenzyl methacrylate [(RS)-MBMA] was investigated in toluene at -30oc. Reaction products between cyclohexylmag nesium bromide (cHexMgBr) and axially dissymmetric 2,2 '-diamino-6,6' -dimethylbiphenyl (AMB) in the mole ratio of 1.5: I were used as a chiral initiating system. The polymer produced a biphenyl group from the catalyst fragment. The polymerization proceeded in an anionic coordi nation mechanism and the racemic monomer was kinetically resolved during the course of the reaction. The enantiomer selectivity ratio when using (R)-AMB was estimated to be r Since binaphthyl-substituted crowns by recognized as "chiral seeds" possessing the Cram1 and BINAL-H reagents by NoyorF salient chiral discrimination ability for asym appeared, axially dissymmetric biaryl units metric polymerization.3 -s have now become very common in the design Optically pure 2,2 '-diamino-6,6 '-dimethyl and synthesis of chiral auxiliaries for many biphenyl (AMB) or 2,2'-diamino-1,1'-bi asymmetric reactions. 3 Recently special atten naphthyl (ABN) has been used for the for tion is drawn increasingly to the construction mation of a chiral LiAlH4 complex.9 •10 Each of chiral polymerization initiators by the use of reagent provided moderate or rather low selec such compounds. These compounds have been tivity in the enantioface-differentiating reduc- 1047 S. KANOH et a/. tion of phenyl alkyl ketones. We have found showed the highest selectivity. On the other recently that products of reactions between hand, the same polymerization was success Grignard reagent and each of the two diamines fully achieved by· Okamoto's catalyst, are excellent catalysts for the enantiomer Grignard reagent-(-)-sparteine system. 11 selective polymerization of racemic oc-methyl This polymerization system may be regarded benzyl methacrylate [(RS)-(MBMA)]. 3•4 as the so-called asymmetric-selective or Among these catalysts, the cyclohexylmag stereoelective polymerization according to the nesium bromide (cHexMgBr)-AMB system classification by Tsuruta.12 CH H C=C I ·J 2 ) C=O 0 "6'"'I* (R)-AMB (R)-ABN (RS)-MBMA In this paper, we wish to describe a detailed [methy/-14C]toluidine hydrochloride were investigation on the enantiomer-selective available from The Radiochemical Center, polymerization of (RS)-MBMA with the Amersham. cHexMgBr-optically pure AMB system in toluene at - 30°C. In addition, the reaction Grignard Reagents between cHexMgBr and AMB is described After the dilution of [1- 14C]ethanol with also. ordinary ethanol, this was converted into the corresponding bromide with PBr3 •14 An EXPERIMENTAL ethereal solution of the ethyl bromide (0.13 J.LCi mmol- 1) was refluxed with mag Materiah nesium turnings for 0.5 h to afford [1- 14C] Diethyl ether and tetrahydrofuran (THF) as ethylmagnesium bromide ([1- 14C]EtMgBr). polymerization media were distilled over Ethylmagnesium bromide (EtMgBr) and LiAlH4 in vacuo just before use. Toluene was cHexMgBr were prepared according to the refluxed and distilled over CaH2 , and then method described previously.4 All the Grig redistilled under vacuum from butyllithium nard reagents were used as ethereal solutions just before use. Methacrylic esters of methyl after determining the concentrations. (MMA) and benzyl alcohol (BzMA) were obtained from commercial sources. (RS) Axially Dissymmetric Biphenyl Diamines MBMA and oc,oc-dimethylbenzyl methacrylate AMB was prepared according to Scheme 1, (DMBMA) and diphenylmethyl methacrylate with some modification of the procedures de (DPMMA) were prepared from methacryloyl scribed in the literature. 15 - 19 The synthetic chloride and the corresponding alcohols in routes of the brominated derivatives of AMB benzene or diethyl ether in the presence of are also shown in Scheme 1. triethylamineY The monomers were dried 2,2'-Diamino-6,6'-dimethylbiphenyl (AMB) over CaH2 , and distilled repeatedly over 2-Amino-3-nitrotoluene (2). To acetic an Cu2Cl2 in vacuo. [1-14C]ehtanol and o- hydride (1.21) was added a-toluidine (214 g, 1048 Polymer J., Vol. 19, No. 9, 1987 Enantiomer-selective Polymerization of (RS)-MBMA 11 Ac 20 21 cHN03 Cu 31 cHCI DMF cV NBS --DM_F_.._ Br 2 NaOAc Scheme 1. Synthetic routes of AMB, AMBBr, and AMB2Br. 2 mol) with stirring at 50°C. After 0.5 h, the amount of Na2 S03 . After the solvent was solution was cooled to 10°C. Concentrated removed, the residue was recrystallized from HN03 (61%, 220ml) was added dropwise ethanol to afford 318 g (91 %) of 3: mp 66- over a period of 2 h with maintaining the tem 6rC (lit. 16 67-68°C). perature exactly at 11 ± 1oc, and the reaction 2,2'-Dimethyl-6,6'-dinitrobiphenyl (4). A so was continued for an additional 30 min lution of 3 (320 g, 1.2 mol) in N,N-di utes at this temperature. The reaction mix methylformamide (DMF) (200 ml) was warm ture was poured onto ice water (3 1). The re ed at 140°C. Copper powder (150 g) that was sulting precipitates were separated, added to treated with iodine in acetone17 was added by cHCl (500 ml), and refluxed for 2 h. The hot portions with caution against exothermic re solution was poured into water (750 ml). The action. Stirring and gentle reflux were con dark red precipitates were separated, and tinued for 1 h. The copper was separated and recrystallized from ethanol (130 ml). The first thoroughly washed with hot benzene. The crop obtained was 84 g (55%) of practically filtrate was washed with water and then with pure 2: mp 94-96°C (lit. 15 95-96°C). dil. HCI. After the removal of the solvent, the 2-Iodo-3-nitrotoluene (3). Powdered 2 (228 g, residue was recrystallized from ethanol to yield 1.5 mol) was added portion by portion to 150g (91%) of 4: mp 109-ll0°C (lit. 18 107- cH2 S04 (500ml) with stirring below 50°C. To 1080C). this were added crushed ice ( 500 g) and then 2,2' -Diamino-6,6'-dimethylbiphenyl (AMB). water (500ml) with cooling. The finely sus The reduction of 4 (30 g, 0.11 mol) was carried pended precipitates were diazotized with a out using hydrazine hydrate (50 ml) and a saturated aqueous solution of NaN02 (120 g, catalytic amount of W-2 Raney nickel in 1.9 mol) at 5-10°C. After excess nitrite was ethanol (11). 19 After the color of the inter decomposed with urea, a saturated aqueous mediates disappeared, the catalyst was sepa solution of KI (257 g, 1.55 mol) was added at rated through celite. The filtrate was con 15°C. The mixture was allowed to stand over centrated to give quantitatively colorless crys night at room temperature. The brownish pre tals of AMB (23 g): mp 135-136°C (lit. 20 cipitates were separated, dissolved in benzene, 136°C); IR (KBr) 3440, 3420, 3340, 1620, 1300, 1 1 and washed with water containing a small 790, and 745cm- ; H NMR (CDC13) fJ 1.97 Polymer J., Vol. 19, No. 9, 1987 1049 S. KANOH et a/. (s, 6H, CH3), 3.37 (br s, 4H, NH2), and 6.6- Similarly (S)-AMB was converted to (S) 7.3 ppm (m, 6H, ArH); 13C NMR [CDC13- AMB2Br: mp 200-201 oc; [a]55 -54.4° (c, 1.0 dimethylsulfoxide-d6 2: 1 (vjv)] b 19.4 (q), g dl-1, ethanol). 112.4 (d), 119.0 (d), 121.7 (s), 127.9 (d), 137.1 3-Bromo-6 ,2' -Diamino-2 ,6' -Dimethyl (s), and 144.7 ppm (s). Found: C, 79.16%; H, biphenyl (AMBEr) 7.63%; N, 13.60%. Calcd for C14H16 N2: C, 2-Nitro-2' -amino-6,6' -dimethylbiphenyl (5). 79.20%; H, 7.60%; N, 13.20%. The partial reduction of 4 was carried out Resolution of (RS)-AMB. The optical re using Na2S in ethanol in the presence of ethyl solution of AMB via D 5 -( +)-tartrate was acetate according to the reported method. 23 achieved following the method of Mislow et Dilution of the reaction mixture with water a/. 21 (R)-( + )-AMB: yield, 33%; mp 160- gave yellow crystals of5: yield, 87%; mp 122- 1610C (lit. 21 156-158°C); [a]55 + 50.SO (c, 1.0 1230C (lit. 23 100-101°C). gdl-1, ethanol) (lit. 21 +48° (c, 2.5gdl-\ 2-Nitro-2'-acetoamino-6,6' -dime thy/biphenyl abs. ethanol)). (S)-(-)-AMB: yield, 17%; mp (6). A solution of 5 (20 g, 83 mmol) in acetic 160-161°C(lit.21 156-158°C);[a]55 -49.SO(c, anhydride (47 ml) was warmed with stirring l.Ogdl-1, ethanol) (lit. 21 [a]56 -47o (c, 3.3 for 1.5 h at 50°C, and then poured onto ice g dl-1, abs. ethanol)). water. The precipitates were separated and (R)-[methyl- 14 qAMB. The preparation fol recrystallized from benzene-petroleum ether lowed a similar procedure to that mentioned to yeild 22g (94%) of 6: mp 103-104°C. above, except for using isotope-diluted a 2-Nitro-3 '-bromo-6 '-acetoamino-6 ,2' toluidine (0.20 .uCi mmol-1): overall yield, 7%; dimethylbiphenyl (7). A solution of bromine mp 161-162°C; specific radioactivity, 0.40 (3.4 g, 21 mmol) in acetic acid (25 ml) was .uCi mmol-1 ; [a]55 + 49.SO (c, 1.0 g dl-1, added with stirring to a solution of 6 (5.0 g, ethanol). 18 mmol) and sodium acetate (2.9 g, 35 mmol) 3,3 '-D ibromo-6 ,6 '-D iamino-2 ,2 '-Di in acetic. acid (25 ml) at room temperature, and methylbiphenyl (AMB2Br) the reaction was continued for 1 hat 60°C. The A solution of N-bromosuccinimide (NBS) mixture was then poured into water (1 00 ml) (1.54g, 9.0mmol) in DMF (15ml) was added containing a small amount of sodium hy dropwise to a solution of AMB (0.95 g, drosulfite. The precipitates were collected, and 4.5mmol) in DMF (15ml) at room tempera recrystallization from ethanol-petroleum ether ture. 22 The reaction mixture was stirred for 5 h afforded 4.5 g (70%) of 7: mp 129.5-130.SOC. at room temperature, and then poured into 3-Bromo-6,2' -diamino-2,6 '-dimethylbiphenyl water (lOOml). The precipitates were collected, (AMBEr). A solution of cHCl (6.6ml) and and purified by recrystallization from ethanol (2.2 ml) was added with stirring to a benzene-petroleum ether to yeild AMB2Br: mixture of 7 (2 g, 4.6 mmol) and tin powder yield, 89%; mp 195.2-195.8°C; IR (KBr) (1.52 g, 12.8 mmol) in ethanol (10 ml) at 60°C, 3430, 3350, 1625, 1310, and 810cm-1; 1H and the reaction was continued for 1.5 h. After NMR (CDC13) b 2.03 (s, 6H, CH3), 3.14 (br s, volatile materials were removed, the residue 4H, NH2), and 6.5-7.4 ppm (m, 4H, ArH); was made strongly basic with aqueous NaOH 13C NMR [CDCk-dimethylsulfoxide-d6, 2: 1 (30%) and extracted with ether. After evap (v/v)] b 19.5 (q), 111.8 (s), 114.2 (d), 122.9 (s), orating the ether, the crude AMBBr was pu 131.9 (d), 136.1 (s), and 144.3 ppm (s); MS rified via its acetamide. Thus, the residual oil (20eV) mjz (%) 368 (100), 370 (196),-and 372 was dissolved in acetic anhydride and warmed (96). Found: C, 45.73%; H, 3.73%; Br, with stirring for 1 h at 50°C. The solution was 43.02%; N, 7.52%. Calcd for C14H14Br2N2: C, poured onto ice water, and the precipitates 45.44%; H, 3.81%; Br, 43.18%; N, 7.57%. were collected. Recrystallization from 1050 Polymer J., Vol. 19, No. 9, 1987 Enantiomer-selective Polymerization of (RS)-MBMA ethanol-petroleum ether afforded the acet cooled at - 30°C and then the monomer (5.34 amide of AMBBr: mp 187.5-188SC. The mmol) was added. The reaction was termi amide was refluxed in 6 N HCl (9 ml) for 1 h. nated by the addition of a small amount of After diluting with water, the solution was methanol. The polymer was precipitated in decolorized with charcoal and basified with 100 ml of methanol containing a few drops of ammonia water. The precipitates were sepa cHCl and separated by filtration. Unreacted rated, and recrystallized from aqueous ethanol monomer was recovered by distillation after to give AMBBr in 78% overall yield: mp the removal of inorganic materials and sol 117.5-118°C; IR (KBr) 3450, 3350, 1610, vents from the filtrate. The methanol-soluble 1300, 805, 775, and 745cm- 1; 1H-NMR oligomeric part was less than 2% yield. (CDC13) b 1.95, 2.05 (ss, 6H, CH3), 3.30 (br s, The copolymerizations of (RS)-MBMA 4H, NH2), and 6.5-7.4 ppm (m, 5H, ArH); with achiral methacrylates were carried out in MS (20eV), mjz (%) 290 (100), and 292 (97). a similar way. Equimolar amounts of two Found: C, 57.84%; H, 5.12%; Br, 27.73%; N, monomers were mixed in toluene. The catalyst 9.57%. Calcd for C14H15BrN2 : C, 57. 75%; H, solution in toluene was added to the co 5.19%; Br, 27.44%; N, 9.62%. monomer solution cooled at - 30°C. The co Resolution of AMBEr. (RS)-AMBBr was polymer was precipitated in methanol. The resolved in a similar manner to that described compositions of the copolymer and recovered for the resolution of AMB. After repeated comonomer were determined from the 1 H recrystallization of the diastereomeric tartrates NMR spectra.3 Monomer reactivity ratios, r1 from ethanol, a less soluble tartrate was ob and r 2 , were computed by the method of tained: mp 154.5-155SC; [ocJ55 +22.4° (c, nonlinear least square fitting24 by the Mayo 0.1 g dl- 1 , ethanol). The pure salt was decom Lewis equation. 25 posed with ammonia water. The precipitates The triad tacticity ofpoly(methacrylate) was were collected and purified by recrystallization determined from 1 H or 13C NMR spectrum of from aqueous ethanol to give (R)-( + ) poly(MMA) derived from an original poly AMBBr in 33% yield: mp 120.5-121SC; (methacrylate).3 [oc]l,5 +82.0° (c, 1.0 gdl- 1 , ethanol). The polymerization in an NMR sample tube ( + )-AMBBr was further brominated with (5-mm diameter) was carried out under dry NBS in DMF, as described before. The nitrogen according to the method of product was confirmed to be AMB2Br from Okamoto.26 As the polymerization medium, the mixed melting point and spectral data. we used toluene-d8 containing a small amount This AMB2Br showed [ocJ55 + 56.2° (c, 1.0 of toluene as an intensity standard. The g dl- 1, ethanol), whose sign indicated ( + ) monomer (0.05 ml) and solvent (0.3 ml) were AMBBr to belong to the R-series. mixed in the degassed tube and cooled at - 78°C. The catalyst solution (0.25 ml, Polymerization mol%) in toluene-d8 The polymerization of (RS)-MBMA was was added to this at - 78°C. It has been carried out in a glass ampule under nitrogen shown that polymerization does not take purified by being passed through molecular place at this temperature.4 The tube sealed sieves 4A as described previously.4 To a tol under dry nitrogen was inserted into an uene solution (10ml) of AMB (38mg, NMR probe thermostated at - 78°C. The 0.18 mmol) was added cHexMgBr (0.27 mmol) temperature was rapidly raised to - 30°C to in diethyl ether, and the reaction was allowed initiate the polymerization, and the con to proceed for 30 minutes at room tempera sumption of the monomer was followed by ture. The homogeneous catalyst solution was a 1 H NMR spectrometer at - 30°C. Polymer J., Vol. 19, No. 9, 1987 1051 S. KANOH et a/. Determination of Optical Purities of the a Wescan model-231 membrane osmometer in Unreacted MBMA and Polymer THF at 20oc using Schleicher & Snell RC51 The preparations of optically pure (S) (0.05Jlm) as a membrane. Optical rotations MBMA and the isotactic polymer were de were measured on a Union PM101 automatic scribed previously.3 (S)-MBMA: -52.9° digital polarimeter at 25°C; the reading pre (neat) (lit. 26 - 53.0°). 100% Isotactic cision was ± 0.002°. The rotation of polymer poly[(S)-MBMA]: -125.0° (c, 1.0 g was measured in toluene or chloroform using a dl- 1 , toluene) (lit. 26 - 125.0° (c, 2 g 2-cm quartz cell, and that of the monomer was dl- 1 )), -94.7° (c, 1.0 g dl- 1 , chloro done with 0.1-0.5 em cells in undilution. Gel form). The optical purities of the polymer permeation chromatograms were obtained and unreacted MBMA obtained in the po using a Waters M-45 pump assembled with lymerization of (RS)-MBMA were deter UV (Jasco UVIDEC-100-11) and RI (Jasco mined from their optical rotations on the RID-300) detectors, using a prepacked basis of the maximum values described above. polystyrene-gel column of Hitachi GL In the case of the copolymerization, A100M. The eluent was THF and the flow rate based on MBMA residue of copolymer was was l.Oml min- 1 at room temperature. A calculated by dividing the observed rotation liquid scintillation system, Beckman LS9000, of the copolymer by the weight fraction of was used to measure the radioactivity of 14C the MBMA residues contained in the copoly labeled compounds in toluene ( 5 ml) contain mer. 3 In the copolymerization with BzMA or ing 1,4-bis[2-( 5-phenyloxazoyl)]benzene (0.0 1 DMBMA, the recovered monomer was a wt%) and 2,5-diphenyloxazole (0.4 wt%). mixture of MBMA and an achiral comono mer. Thus, the observed rotation of the re RESULTS AND DISCUSSION covered monomer mixture was calibrated by the content of MBMA, according to the Polymerization of(RS)-MBMA method described previously. 3 In the other In the reaction between cHexMgBr and copolymerizations, the monomer recovered AMB in the mole ratio of 1.5: 1.0, almost by distillation consisted of MBMA having quantitative conversion of cHexMgBr into a GLPC purity of more than 98%. cyclohexane was observed. Up to the [cHexMgBr]/[AMB] ratio of 2.0, an equimolar Measurement amount of cyclohexane to that of the Grignard 1 H NMR spectra were taken on a Jeol reagent was produced. When more than two JNM-PS-100 (lOOMHz) or a JNM-FX-100S molar amounts of cHexMgBr were used, the (100 MHz) spectrometer. 13C NMR measure excess remained unreacted. The details for this ments were performed using the latter at have been described in a previous paper.4 25MHz or a Jeol JNM-GX-400 at 100MHz. From these results, the most probable reaction The thermocouples at low temperature were may be expressed as Scheme 2. The reaction of calibrated by comparison of differences in cHexMgBr with the two primary amino chemical shifts in the spectra of methanol. 27 groups of AMB gives the corresponding IR spectra were recorded on a Jasco A-202 mono- and bis-bromomagnesium amides infrared spectrophotometer. Mass spectra (Amides A and B, respectively, in Scheme 2), were recorded on a Hitachi mass spectrometer and any duplicated metalation onto the single M-80 at 20eV. Absorption spectra were ob amino group does not take place even in the tained on a Shimadzu UV-204S in THF so presence of more than two molar amounts of lutions at 25oC. The number-average mole cHexMgBr with respect to AMB. This is con cular weight of the polymer was determined on trary to the formation of phenyliminodimag- 1052 Polymer J., Vol. 19, No. 9, 1987 Enantiomer-selective Polymerization of (RS)-MBMA (AMB2Br) (Scheme 1). It was found that in the enantiomer-selective polymerization of (RS)-MBMA, the cHexMgBr-(R)-AMBBr AMB-COCH 3 nesium dibromide from aniline and two r--n equivalents of ethylmagnesium bromide with * ** AMBBr-COCH3 ease.28 Although the isolation of labile Amides A IIIJ and B failed, they were caught as acetylation derivatives. Upon addition of a large excess of p-nitrophenyl acetate (pNPA) to a toluene solution of the catalyst in the ratio of 1.5 at * room temperature, the rapid development of a yellow color was observed, whereas no re action between AMB and pNPA occurred under the same conditions. The preparatory thin layer chromatographic separation of the reaction products gave the mono- and sym * metric bis-acetamides of AMB, the yields of which were 28 and 4%, respectively. These compounds were identified by IR, 1 H NMR, and mass spectroscopic data. The remaining AMB was recovered in an intact form in 63% yield. The formation of the two acetylation products strongly suggests that the ionic spe cies being contained in the catalyst solution are 2.2 2.0 1.8 the axially chiral Amides A and B. [) (ppm) The (R)-configuration of ( + )-3-bromo-6,2' Figure 1. 1 H NMR spectrum of the methyl region of diamino-2,6' -dimethyl biphenyl (AMBBr) was the monoacetylation products obtained by the addition determined by chemical correlation with the of pNPA to the ternary cHexMgBr-AMB-AMBBr sys known (R)-( + )-AMB/9 through ( + )-3,3' tem in toluene: Initial ratio, (cHexMgBr]/[AMB] =2.0; dibromo-6,6 '-diamino-2,2 '-dimethylbiphenyl final ratio, [cHexMgBr]/[AMB + AMBBr] = 1.0. + IRJ-AMB c Hex H Amide A Amide B Scheme 2. Reactions between cHexMgBr and AMB. Polymer J., Vol. 19, No. 9, 1987 1053 S. KANOH et a/. (1.5: 1) system showed (S)-monomer selec The subsequent addition of pNPA gave not tivity comparable to that of the corre only the monoacetamide of AMB but also the sponding AMB system. 30 We prepared a ter acetylation products of AMBBr, together nary catalyst system consisting of cHex with a trace amount of the bisamide of MgBr, AMB, and AMBBr. When AMB AMB. Figure 1 shows the 1 H NMR spectrum was mixed with two equivalents of cHex of the methyl region of the monoacetylated MgBr, the resulting catalyst solution con diamine mixture. Although the spectrum was tained probably Amide B alone. By the ad rather complicated because of the isomers of dition of AMBBr to the above solution, the monoacetylated AMBBr, all the resonances final mole ratio of the total biphenyl di were assigned completely to the monoacet amines to cHexMgBr was adjusted to unity. amides of AMB and AMBBr by comparison CHr (AMB) y X ArH (AMB) ,-..., y L Jj ..__ _I B =C(CH3 I Ph- X H3C'C/ II -CH 0- c 2 H/ 'H (ether) I \ A 8 6 5 4 3 2 1 0 5 (ppm) Figure 2. 1 H NMR spectra of the cHexMgBr-(R)-AMB (1.5: I) system in the presence of (RS)-MBMA in toluene-d8 at - 30oC: [Mg]/[monomer] :d.O. (A) Measured before quenching. (B) Measured after the addition of a small amount of methanol-d4 • (X and Y represent signals due to remaining protons in deuterated toluene and methanol, respectively.) 1054 Polymer J., Vol. 19, No. 9, 1987 Enantiomer-selective Polymerization of (RS)-MBMA with the resonances of the authentic samples. of the magnesium ion at - 30°C. In Figure 2, This result indicates that the transmetalation the 1 H NMR spectrum of the system thus occurred from Amide B to AMBBr added obtained is shown together with the spectrum later. It is therefore considered that the re measured after adding a small amount of action products of cHexMgBr and AMB methanol-d4 . It was found from the spectrum (1.5: 1) are a statistical mixture of Amides A before quenching that the catalyst still con and B, that is, an equimolar mixture of the tained a small amount of the ether. Also clear two, and unreacted AMB does not exist. It signals due to the AMB moiety were not should be emphasized that there is no differ observed at all. The assumed low mobility of ence in the enantiomer selectivity between the AMB moiety would mean that the amides Amides A and B, since the polymerization of AMB exist in an aggregate state in toluene. with the cHexMgBr-AMB systems prepared However, it remains obscure whether such a in the ratios between 1.0 and 2.0 brought consideration can apply to the case of the about quite similar selections.4 polymerization system or not, since the prep The 1 H NMR spectrum of the cHexMgBr aration conditions of this NMR sample were (R)-AMB system prepared in toluene-d8 was different from those of the polymerization in measured. Although one singlet of cyclo some points, such as the solvent composition hexane produced through the reaction between and the monomer concentration. After the Grignard reagent and AMB was detectable quenching, the expected peaks at 6. 7 and 2.0 at 1.4 ppm, no peaks due to the reaction ppm appeared, which should be assigned to products containing the AMB moiety were the aromatic and methyl protons of AMB, observed. In order to be free from the strong respectively. Noticeable initiation reaction did resonances of the diethyl ether used as the not occur during the NMR measurement for solvent of the Grignard reagent, the solvents of about 10min. the catalyst system were replaced by toluene-d8 The ethylmagnesium bromide (EtMgBr) on a vacuum line. The resulting heterogeneous AMB (1.5: 1) system4 has been found to show mixture became almost clear by the addition of a quite similar selectivity to that of the an equimolar amount of the monomer to that cHexMgBr-AMB (1.5: 1) system regardless of Table I. Polymerization of (RS)-MBMA with 14C-labeled EtMgBr-(R)-AMB systems• in toluene at - 30ocb Catalyst Polymer [EtMgBr]/[monomer] Yield [AMB]/[EtMgBr] DPM' A 1.3 5.4 59 712 A 2.9 5.4 98 762 B 6.0 90 1664 B 1.3 6.2 88 B 3.0 6.1 72 106 B 3.0 8.9 8.6 332 a A, (R)-[methyl-14C]AMB was used; B, [l-14C]EtMgBr was used. b Toluene !Oml, (RS)-MBMA 5.34mmol. ' Disintegrations per minute (DPM) of I 00 mg of polymer. Polymer J., Vol. 19, No. 9, 1987 1055 S. KANOH et a/. Table II. AMB and its derivatives obtained in the DPM value. These results may be well ex polymerization of (RS)-MBMA with the plained according to Scheme 2. At the ratio of cHexMgBr-AMB system• 1.3, EtMgBr is consumed completely through Isolated yield the reaction with AMB to release inactive Derivative ethane, and the resulting Amides A and B g %b initiate the polymerization. Therefore, the AMB moiety is introduced into the initiating Recovered AMB 0.123 65 Monomethacrylamide 0.016 6 end (o:-end) of the polymer chain as an initiator Bismethacrylamide 0.003c fragment. In contrast, the catalyst system pre Methanol-soluble oligomer 0.121 n.d. pared at the ratio of 3.0 contains the unreacted 2d Methanol-insoluble polymer 2.370 Grignard reagent, which polymerize the • Polymerization conditions were similar to those of 2 in monomer concurrently, though without any Table III. selectivity. This is in agreement with the b Percentage based on the AMB used ( 188 mg). previous work;4 when the catalyst was pre c Containing impurities. pared from AMB and more than two equi d Calculated from the M. of polymer (1.43 x 105 ). valents of cHexMgBr, both the isotacticity and optical purity of the produced polymer the difference of the Grignard reagents: the decreased in comparison with those obtained same bromomagnesium amides of AMB were by the catalyst in the ratio of 1.5. probably produced in both systems, according When (RS)-MBMA was polymerized with to Scheme 2. Thus, the polymerization of the cHexMgBr-(R)-AMB (1.5: 1) system in (RS)-MBMA was carried out in toluene at toluene at - 30°C, the number-average mo - 30°C with the carbon-fourteen-labeled lecular weight (Mn) of the polymer obtained EtMgBr-(R)-AMB systems, which were pre at 46.7% polymer yield was estimated to pared by using either [l-14C]EtMgBr or (R)• be 1.43 x 105 (osmometric pressure measure [methyl-14C]AMB as one of the two com ment). This means that only about 2% of the ponents. After the polymers obtained were total AMB molecules used participate in the purified by repeated reprecipitation from process of forming polymeric products, if each CHC1 3-methanol system, the radioactivity was polymer molecule is assumed to contain one counted. The results are summarized in Table AMB moiety. In order to see the fate of the I. Each of the polymers produced by using (R)• other AMB, the filtrate obtained in the pre [methyl-14C]AMB showed radioactivity, in cipitation of the above polymer was analyzed. dicating that the polymer contains the AMB The results are summarized in Table II. More moiety. This may arise from the bromomag than half the amount of the .AMB used was nesium amides probably operating as ini recovered from diluted hydrochloric acid tiators. On the other hand, when [l-14C] extracts of the evaporated residue. Distillation EtMgBr was employed, the values of the in vacuo of the remaining oil afforded almost disintegration per minute (DPM) counted for quantitatively the unreacted monomer. The the resulting polymers varied by changing the residual mixture was separated into three com [EtMgBr]/[AMB] ratio. In these cases, the ponents through column and preparatory thin radioactivity of the polymers must be caused layer chromatographies on silica gel. One was by the labeled ethyl group of the Grignard oligo(MBMA), whose 1H NMR spectrum was reagent. The polymers produced with [l- rather similar to that of atactic poly(MBMA). 14C]EtMgBr alone as well as with the catalysts The other two were mono- and bis in the ratio of 3.0 were radioactive, while at the methacrylamides of AMB. Although the latter ratio of 1.3, the polymer showed a negligible was not pure, their structures were strongly 1056 Polymer J., Vol. 19, No. 9, 1987 Enantiomer-selective Polymerization of (RS)-MBMA supported by 1 H NMR and mass spectra. isopropenyl group forms the initiating species. From the results summarized in Table II, it is The further addition of the monomers results concluded that in the polymerization with the in the formation of polymer possessing a AMB cHexMgBr-AMB system, bromomagnesium moiety. In contrast to this, attack on the amides of AMB attack both the isopropenyl carbonyl group forms a tertiary alkoxide, as and carbonyl groups of MBMA. Attack on the shown in eq 1. CH 3 I H N CH C=CH2 2 3 I ?H3 H3C0 NH-y- OMg Br H N CH C=CH2 2 3 I (1) 0 .. H C NH-C=O 3 0 I "6'"' In the case of the bis-bromomagnesium amide, bromide or on termination with methanol. the carbonyl attack sometimes takes place on Although about 25% of the AMB used cannot each of two monomer molecules, leading to be accounted for at the present time, the another dialkoxide. Both alkoxides are con product population in Table II suggests that verted to the methacrylamides of AMB by the most of the initiator remains unreacted during release of tx-methylbenzyloxy magnesium- the process of polymerization. More infor- Table III. Polymerization of (RS)-MBMA with the cHexMgBr-(R)-AMB (1.5: I) system at - 30oC" Time Yield Polymer Monomer Tacticity/% Solvent of Polymerization Entry cHexMgBrh medium (v/v) o; 5 5 min 10 [a]5 '/deg. (O.P.)d [a]5 •;deg. (O.P.)d I H s lf Ether Toluene 60 30.2 -107.3 (86) + 19.8 (37) 100 2"·h Ether Toluene 80 46.8 +97.7 (78) -36.8 (69) 100 3 Ehter Toluene 270 72.9 - 34.4' (36) + 52.6 (99) 100 4•·h Ether Toluene 480 94.5 +5.0' (5) 100 5" Etheri Toluene 60 10.8 +I 10.5 (88) -5.7(11) 100 6 Ether Toluene-ether 45 16.2k -106.0 (85) +8.9(17) 97 2 (3: I) 7 THF1 Toluene 30 12.4 -37.0 (30) +2.2 (4) 37 25 38 8 THF1 THF 20 23.1 + 11.5 (9) -2.1 (4) 8 30 62 • (RS)-MBMA, 5.34mmol; polymerization medium, !Om!. b [cHexMgBr] = 1.3 moll- 1 iQ diethyl ether. ' In toluene, optically pure isotactic poly[(S)-MBMA]: [a]55 -125° (toluene) and -94.7° (chloroform). d Optical purity. • Neat, optically pure (S)-MBMA: [aJ55 -53°. r Data from ref 4. • (S)-AMB was used. h Five-fold reaction scale. ' The polymer was appreciably insoluble in toluene. The rotation was measured in chloroform. i After preparation of the catalyst, the solvents were removed. k The polymer was precipitated during the reaction. 1 [cHexMgBr] = 1.0 moll- 1 in THF. Polymer J., Vol. 19, No.9, 1987 1057 S. KANOH et a/. mation on the oligomer is necessary to clarify MBMA was carried out using the cHexMgBr definitely the fate of the AMB. (R)-AMB system in toluene at - 30°C. The In order to see the effect of diethyl ether optical purities of the polymer and unreacted used as the solvent of the Grignard reagent, monomer were plotted against the polymer the cHexMgBr-(R)-AMB (1.5: 1) system pre yield in Figure 3. The catalyst system con pared in toluene was evaporated to dryness sumed preferentially (S)-monomer over (R)• under dry nitrogen. Although the residual monomer. Although the polymer formed in solids did not dissolved appreciably in toluene, the very early stage of the polymerization had upon the addition of the monomer the mixture an optical purity of only 73%, the optical immediately became almost homogeneous and purities of the polymers obtained in 6 to 30% polymerization occurred. In Table III, the yields were greater than 85%. These polymers solvent effects on the polymerization are sum were soluble in toluene, THF, and chloroform. marized. It is clear that the effects of diethyl Then, the optical purity of the polymer de ether on the selectivity of the catalyst were not creased gradually. After the polymer yield important. However, the ether seems to be exceeded 73%, the resulting polymer became necessary to dissolve the catalyst. On the con appreciably insoluble in toluene or THF at trary, the selectivity greatly decreased in the room temperature after being thoroughly presence of THF. Interestingly, when the po dried in vacuo. But it was still soluble in lymerization was carried out in THF, the chloroform. The optical measurement of such catalyst showed selectivity opposite to that polymers was carried out in chloroform in observed in toluene. The reasons for this are place of toluene (see Entries 3 and 4 in Table not clear at the present time, however. III). The optical purity of the monomer in A series of the polymerization of (RS)- creased as the reaction progressed. Almost optically pure (R)-MBMA was obtained at a polymer yield of 66%. From these results, it follows that the racemic monomer in the feed can be kinetically resolved during the course of the polymerization with this catalyst. The 80 0 curves in Figure 3 were obtained by calcula tion using the enantiomer selectivity ratio ....t' 60 (r 1058 Polymer J., Vol. 19, No.9, 1987 Enantiomer-selective Polymerization of (RS)-MBMA MBMA] and poly[(S)-MBMA] forms the ra present polymerization were almost fully iso cemate insoluble in toluene, but soluble in tactic (B in Figure 4). The polymer obtained chloroform. All the polymers obtained in the at a later stage of the polymerization show ed a close similarity in the solubility property to the polymer racemate. Similar solubility behavior was also observed with the optical ly inactive and isotactic polymers prepared by using racemic AMB. These results c strongly suggest that the present polymer is composed of a mixture of the (R)- and (S) 1 polymers, which form a toluene-insoluble CHr complex at high polymer yields. CH 0- 1 3 -CH2- The H NMR spectra of poly(MBMA)s are illustrated in Figure 4. Polymer A was ob B I tained in the polymerization of the racemic !Ph- C_!! 3?H monomer, while polymer C was obtained in the polymerization of partially resolved I CH3?!! monomer (O.P. = 35. 7%) by cHexMgBr A alone in toluene at - 30oC. Both polymers were isotactic, and had quite similar op 7 6 5 4 3 5 (ppm) tical purities. However, the spectral patterns Figure 4. 1 H NMR spectra of poly(MBMA)s (A and greatly differed from each other. Except for C) and poly(MMA) (B) in CDC13 at 60°C: (A) 3 in Table the peak due to the phenyl groups, the other III (O.P. of polymer= (B) derived from A; (C) peaks of polymer C are much broader com obtained in the polymerization of partially resolved MBMA + 18.9°) by cHexMgBr alone in toluene at pared with those of polymer A. The arrange -30oc (O.P. ofpolymer=36%, /:H:S=92:5:3). ment of the two enantiomeric monomer 80 -- 60 § ..... k "'111 40 0 u 100 200 300 Time I min Figure 5. Time-conversion curves in the polymerization of MBMA (0.26mmol) with the cHexMgBr (0.02 mmol)-AMB (1.5: I) system in toluene-d8 at - 30°C: (A) polymerization of the racemic monomer with the (RS)-catalyst; (B) polymerization of the racemic monomer with the (R)-catalyst; (C) polymeri zation of the (R)-enriched monomer (O.P. = 34.3%) with the (R)-catalyst. Polymer J., Vol. 19, No. 9, 1987 1059 S. KANOH et a/. units in polymer C seems to be more or less optical punhes shown in Figure 3. At the random, because of the achiral initiator. initial part, the (S)-monomer was polymer This may be the reason why the peaks of ized preferentially, leading to the (-)-poly polymer C are broad. Actually, when the mer. After 60% conversion, where the (S) optical purity of the monomer used in the monomer was almost completely consumed, polymerization by cHexMgBr alone was close the remaining (R)-monomer was polymer to 100%, the signals of the resulting poly ized slowly up to high conversion. The ini mer became sharper, as observed for poly tial rate was estimated to be 6 times greater mer A. Therefore, the clearly resolved NMR than that of the latter. A partially resolved (R)• resonances of polymer A suggest the possi monomer (O.P. = 34.3%) was also polymerized bility of a mixture of the (R)- and (S) in place of the racemic one. The reaction polymers. The relative contents of both pattern (curve C) was analogous to that of polymers will correspond to the optical pu curve B. The deflection point, however, ap rity. peared at a lower conversion of 40%, as ex The rate of consumption of the monomer pected from the low content of the (S)- was investigated according to Okamoto's NMR method. 26 The polymerization was car ried out on a small reaction scale by using the (R)- or (RS)-catalyst in toluene-d8 at - 30°C. The procedure was varied slightly from that of the ordinary polymerization mentioned above (see EXPERIMENTAL). The spectrum ob tained at the initial stage of the polymerization was similar to that of A shown in Figure 2, except for the existence of the peaks due to cyclohexane and ordinary toluene which was OP = OP = 38% added as an intensity standard. 26 The inten I = sities of the peaks due to the monomer de creased along the reaction, whereas the poly mer formed showed no clear peaks owing to the slow mobility.26 The time-conversion curves thus obtained are represented in Fig ure 5. For the polymerization with the (RS)• catalyst, the straight plots up to high conver sion were obtained (curve A). When the con version reached nearly 90%, the reaction rate began to decrease gradually, perhaps owing to the effect of viscosity. The consump tion rate seemed to be independent on the monomer concentration over the wide range. 50 10 5_4 1 This suggests that the polymerization pro Mol. weight x 10 (polystyrene) ceeds with a coordination nature. 11 On the 10 12 14 16 18 other hand, when the (R)-catalyst of the (S) Elution volume I ml monomer choice was used, the reaction rate Figure 6. GPC curves of poly(MBMA)s obtained with slowed down at about 60% conversion (curve the cHexMgBr-{S)-AMB (1.5: I) system: A and B, 2 B). This is consistent with the change in and 4 in Table III, respectively. 1060 Polymer J., Vol. 19, No.9, 1987 Enantiomer-selective Polymerization of (RS)-MBMA monomer to be polymerized preferentially. Typical gel permeation chromatograms (GPC) of the poly(MBMA)s produced by using the cHexMgBr-(S)-AMB (1.5: 1) system are shown in Figure 6. The sample polymers A and B are Entries 2 and 4, respectively, in Table III. Polymer A showed a rather com plicated distribution that contained a small amount of low-molecular-weight polymers. Interestingly, inspection of the UV- and RI detected chromatograms revealed that the rel ative heights of the low-molecular-weight peaks are not identical; the low-molecular weight part gives a rather weaker response in I I I I I I I I I I I an RI detector than in a UV one. The differ I I I I I ' ence in the shapes between both chromato 180 179 178 177 176 I) (ppm) grams may arise from the AMB moiety in corporated at the tX-end of each polymer mol Figure 7. 13C NMR signa.! of the carbonyl carbon in ecule as the initiator fragment. The molar ab the poly(MMA) derived from the high-molecular-weight 3 sorptivity of AMB (e254 =6.2 x 10 in THF) poly(MBMA) (sample: the fractionated Polymer A in was found to be much greater than that of Figure 6). Nitrobenzene-d5, ll0°C, 100 MHz. poly(MBMA) having a cyclohexyl-end (e254 based on the MBMA residue= 1.2 x 102). Therefore, the contribution of the AMB moi molecular-weight part were found to be lower ety to the absorbance of polymer at 254 nm than those of the original polymer. These re will become greater as the molecular weight sults indicate that there exist other initiating of polymer decreases. A similar GPC pattern species which form different types of poly was also observed with polymer B, which was mers from the isotactic polymer produced by obtained in higher yield. (Since polymer B was the main species. The content of the low practically insoluble in THF, its GPC sample molecular-weight polymer, however, seemed was prepared by dilution of a highly concen to be a few percent of the total polymer. trated chloroform solution with THF.) From the GPC analysis of the polymers ob Polymer A was separated into two portions tained in various yields, it was found that at an elution volume of about 14 ml, as shown such a polymer was formed at the initial in Figure 6. Most of the original polymer was stage of the polymerization and the rela included in the high-molecular-weight part, tive content gradually decreased with an in which had a slightly higher optical purity of crease of the polymer yield. This may be the 80% than that of the original polymer. The reason why the optical purity of the polymer tacticity of poly(MMA) derived from the formed initially was slightly lower than those polymer in this part was analyzed by means formed at the subsequent steps, as shown in of a 13C NMR spectroscopy in detail. Fig Figure 3. ure 7 shows the partial spectrum for the es During the course of a similar fractionation ter carbonyl region. Only a single peak of polymer B, we were able to gain interesting was observed, which was ascribed to an iso findings that the head and tail fractions of the tactic pentad (mmmm). 33 On the contrary, high-molecular-weight polymer showed opti the isotacticity and optical purity of the low- cal rotations opposed in sign to each other 'Polymer J., Vol. 19, No.9, 1987 1061 S. KANOH et a/. (Curve B in Figure 6). Polymer B showed only Although we cannot directly determine the a small rotation, + 5.0° (chloroform), concentrations of the active centers, there is because of near completion of the polymer the possibility that ["' S-Cs *]/["' R-CR *] is ization. This result strongly suggests that there close to unity; this will be explained later. The is the possibility of forming both (R)- and (S) above equation, assuming r to be constant, polymers during the process of polymer could be mathematically regarded as an in ization. The (+)-polymer in the head fraction tegrated composition equation for an "ideal" might be produced through the preferential copolymerization of (R)- and (S)-monomers, consumption of the (R)-monomer by the (S) although the interpretation of r differs. 34 By catalyst at the early stage of the polymer introduction of the data derived from Figure 3 ization, while the (-)-polymer in the tail frac the most probable enantiomer selectivity ratio, tion might be still growing at the later stage. r 1062 Polymer J., Vol. 19, No. 9, 1987 Enantiomer-selective Polymerization of (RS)-MBMA Qj 0 0 .., ············-(). 0 ······-. 0 ...... 80 ··-9•• 100 >...... 0 0. 0 0 20 40 60 80 100 Conversion of MBMA I % Figure 8. Change in the optical purities of the unreacted MBMA and the MBMA residue in the copolymer obtained in the copolymerizations of (RS)-MBMA and achiral methacrylates in I : I feed with the cHexMgBr--(R)-AMB (1.5: I) system in toluene at - 30oC: (e/O) with MMA; (+I<>) with BzMA; ("'f/\1) with DMBMA; (•/D) with DPMMA; (-/---)the change in the homopolymerization of (RS)• MBMA. copoly(MMA-MAA)s (Figure 9), peaks 3 and the upfield with increasing MBMA content. 6 are assigned to the isotactic triads of the These facts indicate that the distribution of MMA sequence and of the MAA one, re the monomer units in the BzMA copoly spectively, according to Klesper et a/?5 The mers was more or less random. 13 spectra reveal that the intensities of peak 3 are From the above results, it was found that very low, especially in the copolymer formed the enantiomer selection was not affected by initially, compared with those of peak 6. This the incorporation of each of the three M2 result is responsible for the average sequence comonomers, even by a rather bulky monomer length of the monomer units expected from the such as DPMMA, and the distribution pattern monomer reactivity ratios (Table IV). 36 of MBMA unit and M2 one in a polymer chain Therefore, it is considered that the oc-end sides was not important with respect to this point. of the MMA copolymers are composed of the These result suggest that the ratio of the rather long MBMA sequences interconnected concentrations of (S)- and (R)-type active sites by the MMA unit, and the length of the do not vary in these copolymerizations, and MBMA sequence is gradually shortened with both sites form a mixture of an (S)-MBMA an increase of the polymer yield. M2 copolymer and an (R)-MBMA-M2 co On the other hand, an ideal copolymeri polymer in a highly isotactic manner. It is ex zation is expected in the MBMA-BzMA sys pected that the catalyst reacts not only with tem, because the product r1 • r2 is nearly equal MBMA but also M2 monomer in the ini to unity (Table IV). From inspection of the 1 H tiations of the copolymerizations. The later NMR spectra of the BzMA copolymers, the reaction will result in the formation of both of peaks due to two kinds of methyl groups (S)- and (R)-centers, because each M2 is attached to the main chain shifted gradually to achiral.26 However, if the ratios of both active Polymer J., Vol. 19, No.9, 1987 1063 S. KANOH et a/. possible explanation may be that the ratios of (R)- and (S)-centers are close to unity in all the X polymerizations. Of course, the rates of the polymerization at both sites are different from each other. The optical rotations based on the MBMA residues in these copolymers were estimated from the observed rotations of the copolymers and the contents of the MBMA residues. In most cases, however, these optical rotations differed from the values expected from the optical purities of the unreacted MBMA (a broken curve in Figure 8). The reasons are not clear at the present time, although the calculation seems to be oversimplified. In contrast with the cases of the above copolymerizations, the enantiomer selection greatly decreased in the copolymerization with DMBMA, and the copolymer formed was less isotactic (I: H: S = 70: 21 : 9 at 30 wt% poly 3 2 1 mer yield) compared with the other copoly 6 (ppm) mers. DMBMA has no hydrogen on the ex Figure 9. 1 H NMR spectra of copoly(MAA-MMA) carbon of the ester group, whereas the other derived from copoly(MBMA-MMA). Copolymer yield: three comonomers and also MBMA have one (A) 30 wt%, (B) 42 (C) 58 wt%. Peak 3, isotactic (MMA-MMA-MMA); peak 6, isotactic (MAA-MAA or more than one hydrogen on each ex-carbon. MAA); X, signal due to acetone. Pyridine-d5 , 100°C, The positioning of the hydrogen may be quite HMDS, IOOMHz. important in order to avoid steric hindrance in approaching the active center in an isotactic manner. In DMBMA, the coordination fol Table IV. Monomer reactivity ratios, r 1 .and r2 , in the copolymerizations of (RS)-MBMA (M1) lowed by the addition to the anionic end in a and achiral methacrylates (M2)a different way perhaps alters the chiral environ ment of the active center. This may be the Comonomer (M ) r2 2 't reason for the lower selectivity. MMA 12.6 0.20 In conclusion, the enantiomer-selective BzMA 1.53 0.68 polymerization of (RS)-MBMA with the DPMMA 0.36 1.29 cHexMgBr-optically pure AMB system could DMBMA 13.0 0.45 be regarded as an asymmetric-selective a Catalyst cHexMgBr--(R)-AMB, (1.5: I); [Mg)/ (stereoelective) and streoselective polymer ([M 1)0 + [M2)0 ) = 5 toluene, 10 ml; temperature, ization.12 On the other hand, Okamoto et a/. -30°C. have demonstrated that the asymmetric selective polymerization of (RS)-MBMA with centers change depending upon the structures the cHexMgBr-(-)-sparteine (1 : 1.2) system of the monomers participating in the ini can be treated as a copolymerization of (S) tiation, the compatibility of the enantiomer and (R)-monomers.U They have evaluated the selectivity would not be observed for the enantiomer selectivity ratios, rs = 33.7 and rR = homo- and the three co-polymerizations. One 0.27, which correspond to the monomer re- 1064 Polymer J., Vol. 19, No.9, 1987 Enantiomer-selective Polymerization of (RS)-MBMA activity ratios in a usual copolymerization. 12. T. Tsuruta, J. Polym. Sci., D, 6, 179 (1972). Enantiomer selection has been shown to 13. H. Yuki, Y. Okamoto, K. Ohta, and K. Hatada, J. strongly decrease in the copolymerization Polym. Sci., Polym. Chern. Ed., 13, 1162 (1975). 14. R. H. Goshorn and T. Boyd, "Organic Syntheses," 26 with MMA, that is in contrast to our case. Coil. Vol. I, Wiley, New Yotk, 1932, p 36. 15. J. C. Howard, "Organic Syntheses," Coli. Vol. VI, Acknowledgements. Support of this work Wiley, New York, 1963, p 42. by Grants-in-Aid for Scientific Research (Nos. 16. L. Wheeler and L. M. Liddle, Am. Chern. J., 43, 441 (1910). 56470084 and 59750717) from the Ministry of 17. R. C. Fuson and E. A. Cleveland, "Organic Education, Science, and Culture of Japan is Syntheses," Coil. Vol. III, Wiley, New York, 1955, p gratefully appreciated. We thank Prof. Dr. 339. Koichi Hatada and Dr. Yoshio Okamoto of 18. G. Wittig and 0. Stichnoch, Chern. Ber., 68, 928 (1935). Osaka University for their helpful discussion 19. R. E. Moore and A. Furst, J. Org. Chern., 23, 1504 during this work, and Prof. Dr. Tadashi (1958). Nakajima and Dr. Hideki Kinoshita of 20. J. Kenner and W. V. Stubbings, J. Chern. Soc., 119, Kanazawa University for the measurements of 593 (1921). 21. F. A. McGinn, A. K. Lazarus, M. Siegel, J. E. Ricci, NMR spectra. and K. Mislow, J. Am. Chern. Soc., 80, 476 (1958). 22. R. H. Mitchell, Y.-H. Lai, and R. V. Williams, J. Org. Chern., 44, 4733 (1979). REFERENCES 23. S. Sako, Bull. Chern. Soc. Jpn., 9, 393 (1934). 24. T. Nakagawa and Y. Oyanagi,. "SALS User's I. E. B. Kyba, K. Koga, L. R. Sousa, M. G. Siegel, and Manual," Computer Center of Tokyo University, D. J. Cram, J. Am. Chern. Soc., 95, 2692 (1973). 1979. 2. R. Noyori, I. Tomino, and Y. Tanimoto, J. Am. 25. F. R. Mayo and F. M. Lewis, J. Am. Chern. Soc., 66, Chern. Soc., 101, 3129 (1979). 1594 (1944). 3. S. Kanoh, N. Kawaguchi, and H. Suda, Makromol. 26. Y. Okamoto, K. Ohta, and H. Yuki, Macro Chern., 188, 463 (1987) and references cited therein. molecules, 11, 724 (1978). 4. H. Suda, S. Kanoh, N. Murose, S. Goka, and M. 27. A. L. Van Geet, Anal. Chern., 42, 679 (1970). Motoi, Polym. Bull., 10, 162 (1983). 28. M. Okubo, M. Yoshida, K. Horinouchi, H. Nishida, 5. S. Kanoh, H. Suda, N. Kawaguchi, and M. Motoi, andY. Fukuyama, Bull. Chern. Soc. Jpn.; 56, 1196 Makromol. Chern., 187, 53 (1986). (1983). 6. S. Kanoh, N. Kawaguchi, T. Sumino, Y. Hongoh, 29. L. H. Pignolet, R. P. Taylor, and W. D. Horrocks, and H. Suda, J. Polym. Sci. Part A, Polym. Chern., Jr., J. Chern. Soc., Chern. Commun., 1443 (1968). 25, 1603 (1987). 30. H. Suda, S. Kanoh, and S. Goka, unpublished data. 7. M. Sepulchre, N. Spassky, C. Mark, and V. Schurig, 31. H. Yuki, K. Ohta, K. Uno, and S. Murahashi, J. Makromol. Chern. Rapid Commun., 2, 261 (1981). Polym. Sci., 6, 829 (1968). 8. D. J. Cram and G. D. Y. Sogah, J. Am. Chern. Soc., 32. K. Hatada, S. Shimizu, Y. Terawaki, K. Ohta, and 107, 8301 (1985). H. Yuki, Polym. J., 13, 811 (1981). 9. H. Suda, M. Motoi, M. Fujii, S. Kanoh, and H. 33. K. Hatada, K. Ute, K. Tanaka, Y. Okamoto, and T. Yoshida, Tetrahedron Lett., 20, 4565 (1979). Kitayama, Polym. J., 18, 1037 (1986). 10. K. Kabuto, T. Yoshida, S. Yamaguchi,.S. Miyano, 34. H. G. Biihrer and H. G. Elias, Makromol. Chern., and H. Hashimoto, J. Org. Chern., 50, 3013 (1985). 169, 145 (1973). II. Y. Okamoto, K. Suzuki, T. Kitayama, H. Yuki, H. 35. E. Klesper and W. Gronski, J. Polym. Sci., Polym. Kageyama, K. Miki, N. Tanaka, and N. Kasai, J. Lett. Ed., 7, 727 (1969). Am. Chern. Soc., 104, 4618 (1982) and references 36. V. E. Meyer and G. G. Lowry, J. Polym. Sci., A, 3, cited therein. 2843 ( 1965). Polymer J., Vol. 19, No. 9, 1987 1065 • was computed to be 18.0. The curves From the results mentioned in the preceding shown in Figure 3 were theoretically obtained sections, it is concluded that a catalyst control on the basis of this value. The curves follow mechanism probably operates in the present the change in the optical purities of both the polymerization,12 that is, the propagation is polymer and unreacted monomer. independent of the structure of the terminal monomeric unit at the growing chain end (w• Copolymerizations of (RS)-MBMA with Achi end), and cross-propagations are absent. Such ral Methacrylates kinetic features are quite similar to those ob The cHexMgBr-AMB (1.5: 1) system was served previously in the enantiomer-selective possible to copolymerize (RS)-MBMA (M1) polymerization of (RS)-MBMA with the with achiral methacrylates (M2), such as cHexMgBr-(R)-ABN (1.5: 1) system? Taking methyl (MMA), benzyl (BzMA), oc,oc-di into account the fact that the polymerization methylbenzyl (DMBMA), and diphenyl proceeds in an anionic coordination me methyl (DPMMA) methacrylates, in toluene chanism, the propagation reactions may be at - 30°C. The selectivity of the catalyst sys expressed analogously as follows: tem toward (RS)-MBMA was investigated Ks k in the copolymerizations with equimolar -s-cs*+S -s-cs* amounts of M 1 and M2 . The (R)-catalyst also KR k showed high (S)-MBMA selectivity in these -R-CR*+R -R-CR* copolymerizations as shown in Figure 8. All plots for the unreacted MBMA obtained by where C * and CR* are S-type and R-type 8 each copolymerization with MMA, BzMA active centers, respectively, and "'S- and or DPMMA are well fitted to a solid curve, - R- represent the w-ends of (S)- and (R)• which shows the change in the optical purity polymers, respectively. The (S)-monomer is of the unreacted MBMA in the case of the preferentially consumed if the (R)-catalyst is homopolymerization mentioned before. This used. Thus the enantiomer selectivity ratio, r• means that the selectivity did not decrease is given by: at all. The copolymers formed were found to be highly coisotactic. The distribution of monomer units in the copolymers was investigated by a 1 H NMR where method. The MMA copolymers were treated with hydrogen bromide to hydrolyze only the MBMA residues to the methacrylic acid ones (MAA).26 In the spectra of the resulting