Asymmetric anionic polymerization of 2,6-dimethyl-7-phenyl-1,4-benzoquinone methide

Asymmetric anionic polymerizations of 2,6-dimethyl-7-phenyl-1,4-benzoquinone methide ( 1 ) were performed with various chiral anionic initiators, and the specific rotations of the obtained polymers were investigated. Optically active poly( 1 )s with configurational chirality were obtained with all the initiators, and a complex of fluorenyllithium (FlLi) with (−)-sparteine [(−)-Sp] produced poly( 1 ) with the largest negative specific rotation ([α]₄₃₅ = −26.8°). The specific rotations of poly( 1 )s obtained with FlLi/(−)-Sp depended on the initiator concentration and the solvent polarity. The maximum specific rotations were obtained at an almost constant initiator concentration (ca. 0.03 mol/L), regardless of the monomer concentration, in toluene, whereas a higher initiator concentration was required in more polar solvents. These results suggested that the aggregation state of the propagating chain end significantly affected the specific rotation of poly( 1 ). © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4548–4555, 2004     

Asymmetric anionic polymerizations of 7‐cyano‐7‐alkoxycarbonyl‐1,4‐benzoquinone methides

Asymmetric anionic polymerizations of 7‐cyano‐7‐alkoxycarbonyl‐1,4‐benzoquinone methides ( 1 ) with various alkoxy groups were performed using chiral initiators such as lithium isopropylphenoxide (ⁱPrPhOLi)/(S)‐(–)‐2,2′‐isopropylidene‐bis(4‐phenyl‐2‐oxazoline) ((–)‐PhBox) and lithium isopropylphenoxide (ⁱPrPhOLi)/(–)‐sparteine ((–)‐Sp) to investigate the effect of the alkoxy groups of alkoxycarbonyl substituent in the monomers 1 and chiral ligands of chiral initiators on the control of chiral center in the formation of polymers. Molar optical rotation values of the polymers were significantly dependent upon alkoxy groups, and the polymers with higher molar optical rotation were obtained in monomers with primary alkoxy groups. The asymmetric anionic oligomerizations of the quinone methides having methoxy( 1a ), ethoxy( 1b ), and n‐propoxy( 1c ) groups with chiral initiators were carried out. Both 1‐mers and 2‐mers were isolated and their optical resolutions were performed to determine the extent of stereocontrol. High stereoselectivity was observed at the propagation reaction, but not at the initiation reaction. The effect of the counterion on the control of chiral center in the formation of the polymer was investigated in the asymmetric anionic polymerizations of 1b with ⁱPrPhOM(M = Li, Na, K)/(–)‐Sp and ⁱPrPhOM(M = Li, Na, K)/(–)‐PhBox initiators and discussed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Asymmetric polymerization of the mixture of TrMA and MMA initiated by chiral complexes

A mixture of triphenylmethyl methacrylate (TrMA) and methyl methacrylate (MMA) was polymerized with chiral anionic initiator, such as fluorenyl lithium(−)-sparteine [FlLi-(−)-Sp] and fluorenyl lithium-(+)-2S,3S-dimethoxy-1,4-bis(dimethylamino)butane [FlLi-(+)-DDB] in toluene at −78°C. The results show that after the stable helix formed, when FlLi-(+)-DDB was used as the initiator, TrMA and MMA could be copolymerized, whereas when FlLi-(−)-Sp was used, the two monomers tended to be selectively polymerized into two polymers. This phenomenon has been explained by the existence of helix-selective polymerization. © John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 1925–1931, 1997     

Anionic polymerization of N-substituted maleimide. II. Polymerization of N-ethylmaleimide

Anionic polymerization of N-ethylmaleimide (N-EMI) was carried out with potassium t-butoxide, lithium t-butoxide, n-butyllithium, and ethylmagnesium bromide as initiators in THF and in toluene. An almost quantitative yield of poly(N-EMI) was obtained with potassium t-butoxide as initiator in THF in a wide range of polymerization temperatures. Initiators possessing lithium as counter cation produced poly(N-EMI) in slightly lower yields and ethylmagnesium bromide gave the polymer only in less than 35% yield in THF. As a polymerization reaction solvent, THF was preferable for the polymerization of N-EMI compared with toluene with respect to polymer yields. Poly(N-EMI) obtained with anionic initiators exerted unimodal molecular weight distribution. From ¹H- and ¹³C-NMR spectra of poly(N-EMI) anionic polymerization of N-EMI with potassium t-butoxide was revealed to proceed at carbon–carbon double bond. t-Butoxide system was found to have a “living” polymerization character, i.e., the observed average degree of polymerization was in good agreement with the one calculated from the initial molar ratio of N-EMI/initiator and the yield of polymer.     

Asymmetric polymerization of aromatic isocyanates with optically active anionic initiators

The asymmetric anionic polymerization of o-, m-, and p-methylphenyl isocyanates, p-methoxyphenyl isocyanate, p-chlorophenyl isocyanate, 2,6- and 3,4-dimethylphenyl isocyanates, and 1-naphthyl isocyanate was carried out using chiral anionic initiators such as the lithium salts of (?) -menthol, (?) -(2-methoxymethyl) pyrrolidine, and (+) -1-(2-pyrrolidinylmethyl) pyrrolidine. Although o-methylphenyl isocyanate gave an insoluble polymer and 2,6-dimethylphenyl isocyanate afforded no polymer, the other monomers gave soluble polymers, which showed optical activity due to the prevailing helicity of the polymer chain induced by chiral initiator residues attached to the α-end of the polymer chain. The molecular mechanics conformational calculation for a tetramer of m-methylphenyl isocyanate supported the helical conformation of the main chain. The optical rotation of the polymers depended significantly on temperature. © 1994 John Wiley & Sons, Inc.     

Highly effective, easily accessible screw-sense-determining end group in the asymmetric polymerization of 1,2-diisocyanobenzenes

Enantiopure helical poly(quinoxaline-2,3-diyl) was formed stereoselectively in the polymerization of 1,2-diisocyanobenzene using a new organopalladium initiator bearing the (4S,5S)-N-acyl-4,5-dihydro-4,5-diphenyl-1H-imidazol-2-yl group as the polymer-end screw-sense-determinant.     

N-乙烯基咔唑与卤代烃引发甲基丙烯酸甲酯聚合的研究

<正> N-乙烯基咔唑(NVC)具有大的共轭结构和中间有一个杂原子氮,而容易与其它试剂反应,形成自由基、阳离子和电荷转移络合物,故是一种活性较高的单体,1970年有人发现NVC与N-C_4H_9NCl_2一起可以引发甲基丙烯酸甲酯(MMA)聚合,此外,文献报道了电子给体如胺与CCl_4体系在二甲亚砜(DMSO)中引发MMA聚合,本文研究了NVC与几种卤代烃所组成的双组分体系对MMA的引发聚合反应;该体系的引发活性和组成与分子量及分子量分布的关系;并探讨了反应机理。     

Asymmetric Polymerization of Menthyl Methacrylate by Anionic Catalysts

In this paper,(-) menthyl methacrylate(-) MnMA) was polymerized at -78℃ in toluene with three types of anionic catalysts, which were complexes of fluorenyllithium with (-) sparteine-((-)-Sp),(S,S)-( )-2,3-dimethoxy-1,4-bis(dimethylamino) butane( )DDB) and N,N,N,N′-tetra-methylethylenediamine(TMEDA), and the chiral optical property of the obtained polymer was studied. The circular dichroism (CD) spectrum of the polymer showed negative Cotton effect.     

Vinyl polymerization by lithium organocuprates

Vinyl polymerizations initiated by lithium organocuprates under several conditions were investigated. It was observed that this catalyst was effective in the polymerization of specific monomers such as α,β-unsaturated nitrile and carbonyl analogues. The rate of polymerization was rapid but retarded by the addition of pyridine, nitrobenzene, or hydroquinone. Polymerization of methyl methacrylate (MMA) with lithium di-n-butylcuprate as initiator produces predominantly isotactic poly(methyl methacrylate) (PMMA) in toluene. The overall activation energy was estimated as 3.5 kcal/mol deg. Lithium di-n-butylcuprate exerts a higher stereoregulating effect on the addition of monomers than other organolithium initiators. It is proposed that polymerization proceeds via a coordinated anionic mechanism.     

Anionic Polymerization of Chiral Isocyanate and Influence of the Initiator on Changes in the Optical Activity

A chiral polyisocyanate, poly[6‐{1‐[(S)‐(–)‐2‐methylbutyl]oxycarbonylamino}hexyl isocyanate], was synthesized using sodium diphenylmethanide and sodium naphthalenide as unidirectional and bidirectional initiators, respectively, via anionic polymerization in THF at –98°C. NaBPh₄ as a common ion salt was used to produce the polymer in quantitative yield and with narrow molecular‐weight distribution. The polymer showed different optical activity depending on the nature of the initiator.     

Preparation of functional polymers by living anionic polymerization: Polymerization of allyl methacrylate

The anionic polymerization of allyl methacrylate was carried out in tetrahydrofuran, both in the presence and in the absence of LiCl, with a variety of initiators, at various temperatures. It was found that (1,1-diphenylhexyl)lithium and the living oligomers of methyl methacrylate and tert-butyl methacrylate are suitable initiators for the anionic polymerization of this monomer. The temperature should be below −30°C, even in the presence of LiCl, for the living polymerization to occur. When the polymerization proceeded at −60°C, in the presence of LiCl, with (1,1-diphenylhexyl)-lithium as initiator, the number-average molecular weight of the polymer was directly proportional to the monomer conversion and monodisperse poly(allyl methacrylate)s with high molecular weights were obtained. ¹H-NMR and FT-IR indicated that the α CC double bond of the monomer was selectively polymerized and that the allyl group remained unreacted. The prepared poly(allyl methacrylate) is a functional polymer since it contains a reactive CC double bond on each repeating unit. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2901–2906, 1997     

几种手性原子转移自由基聚合引发剂的合成及其在螺旋选择性聚合中的应用

合成了(S)-2,2'-二(溴甲基)-1,1'-联萘, (S)-2'-甲基-2-溴甲基-1,1'-联萘, α-溴代苯乙酸薄荷酯, N-薄荷基-α-溴代苯乙酰胺和α-溴代苯乙酸胆甾烷醇酯5种旋光的溴代烷并将其用作非手性单体甲基丙烯酸-1-苯基二苯并环庚醇酯 (PDBSMA)的原子转移自由基聚合(ATRP)的手性引发剂. 为了使这些手性引发剂在引发一步生成的初级自由基不发生消旋化, 引发剂中的手性中心都不直接与溴原子相连. 用这5种手性溴代烷做引发剂引发PDBSMA的ATRP所得聚合物可分成四氢呋喃(THF)可溶部分和THF不溶部分. THF可溶部分具有较大的比旋光度. 对THF可溶部分的手性光学性质研究以及比较该部分聚合物和在同样引发条件下得到的甲基丙烯酸甲酯聚合物的比旋光度, 我们得出聚合物大的比旋光度是由聚合物单手性螺旋过量引起的结论, 即合成的手性引发剂对PDBSMA的ATRP均有一定的螺旋选择性, 其中(S)-2,2'-二(溴甲基)-1,1'-联萘、(S)-2'-甲基-2-溴甲基-1,1'-联萘螺旋选择性最好. 引发剂的螺旋诱导能力跟聚合反应的温度有很大关系, 聚合温度上限为70 ℃, 在0～70 ℃之间, 随着温度的升高引发剂的螺旋选择性逐渐增强.     

旋光性聚{(+)-甲基丙烯酸-2,5-二[4′-((S)-2-甲基丁氧基)苯基]苄酯}的合成与表征

设计、合成了一个带有横挂三联苯侧基的手性乙烯基单体——(+)-甲基丙烯酸-2,5-二[4′-((S)-2-甲基丁氧基)苯基]苄酯,进行了普通自由基和原子转移自由基聚合反应.所得聚合物具有比单体低30°左右的比旋光度,且在侧基的紫外吸收处呈现明显不同于单体的Cotton效应,说明其主链可能形成了具有相反旋光方向的螺旋构象.在所研究范围内,聚合条件对聚合物的旋光度没有明显的影响.在分子量较小时,聚合物的比旋光度随着分子量的增加而降低,说明主链螺旋构象的贡献在增大,而当分子量达到一定值后,聚合物的比旋光度不再随分子量的增加而显著变化.     

SYNTHESIS OF OPTICALLY ACTIVE POLY (N-VINYLCARBAZOLE)S

The organic salts as initiators [A~+B~-:Ph_3C~+ClO_4~-, Ph_3C~+SbCl_6~-, (-)Sp~+ClO_4~- and(-)(Sp)_2~(+3)(ClO_4)_3] and catalysts [A~+B~-:(+)CSA, A~+B~-:Ph_3C~+(+)CSA~- and(-)Sp~+(+)CSA] are prepared and characterized by specific rotation. The asymme-trically stereoselective induction of the initiators and catalysts in the polymerization ofN-vinylcarbazole is in an order of A~+B~->A~+B~->A~+B~-. The specific rotations ofobtained poly (N-vinylcarbazole ) (PVCZ) generally are in accordance with mentioned order.     

Copper(II) complexes containing chiral substituted 2-(4-isopropyl-4-methyl-4,5-dihydro-1H-imidazol-5-one-2-yl)pyridine ligands: Synthesis, X-ray structural studies and asymmetric catalysis

New chiral N,N-bidentate ligands derived from substituted 2-(4-isopropyl-4-methyl-4,5-dihydro-1H-imidazol-5-one-2-yl)pyridines have been prepared and characterised by means of ¹H, ¹³C NMR spectroscopy and optical rotation. Their Cu(II) complexes were characterized by means of elemental analysis, ¹H NMR spectroscopy and MS. By means of X-ray diffraction, molecular geometry of the complex of 2-(1-methyl-4-isopropyl-4-methyl-4,5-dihydro-1H-imidazol-5-one-2-yl)pyridine with copper(II) chloride was determined. The complex exhibits heterochiral dimeric arrangement of two square pyramids with one terminal and one bridge-forming chlorine atoms and two nitrogen atoms in the bases of the pyramids. The tops of these pyramids are formed by the remaining chlorine atoms. The complexes prepared catalyse the Henry reaction with the overall yields of 41-97% and with the maximum enantioselective excess of 19%.     

Mono- and dinuclear bioxazoline-palladium complexes for the stereocontrolled synthesis of CO/styrene polyketones

The coordination chemistry of the chiral bioxazoline ligand (4S,4'S)-2,2'-bis(4-isopropyl-4,5-dihydrooxazole) to Pd(II) provides evidence that the ligand bonding can occur either through chelation of one Pd(II) ion leading to a mononuclear species with the expected cis geometry, or by double bridging of two Pd(II) ions giving a dinuclear complex with trans geometry. The species in solution are identified by 1H NMR spectroscopy. Both the mononuclear and the dinuclear complexes promote the CO/styrene copolymerization, yielding the corresponding polyketone with a fully or a predominantly isotactic microstructure, depending on the reaction medium. The nature of the anion present in the palladium precatalysts affects the polyketone stereochemistry. MALDI-TOF analysis of the copolymers synthesized reveals the presence of p-hydroxyphenolic end-groups, thus confirming and explaining the role of 1,4-hydroquinone as a molecular weight regulator.     

Mixed complexes formed by lithioacetonitrile and chiral lithium amides: observation of (6)li,(15)N and (6)Li,(13)C couplings due to both C-Li and N-Li contacts

NMR spectroscopic studies have been performed on the mixed complexes formed by the lithium salt of acetonitrile (LiCH(2)CN) and the chiral lithium amides Li-(S)-N-(2-methoxybenzyl)-1-amino-1-phenyl-2-ethoxyethane (Li-1) and Li-(S)-N-isopropyl-2-amino-1-phenyl-3-methoxypropane (Li-2) in diethyl ether and tetrahydrofuran solvent. In diethyl ether Li-1 and LiCH(2)CN form a mixed dimeric (1:1) complex, while Li-2 and LiCH(2)CN form a mixed trimeric (2:1) complex. The dimer undergoes fast exchange between ketenimine and bridged structures. Both (1)J((15)N,(6)Li) and (1)J((13)C,(6)Li) couplings were observed for the respectively isotopically labeled compounds. In the trimeric complex the CH(2)CN anion also undergoes fast degenerate exchange between ketenimine and bridged structures, and the complex appears C(2)-symmetric on the NMR spectroscopy time scale. Both the dimer and trimer complexes have the bridged acetonitrile anion in common, as indicated by the highly shielded alpha-carbon (13)C NMR shifts (delta -6.1 and -7.4, respectively). In tetrahydrofuran only N-metalated mixed LiCH(2)CN dimers were observed for both Li-1 and Li-2 with the less shielded (13)C NMR shifts of delta -2.5 and -2.2 for the alpha-carbon of LiCH(2)CN of the complexes.     

Synthesis of optically active polymers using P-chiral bisphosphines as anionic initiators

Anionic polymerization of triphenylmethyl methacrylate was performed by using P-chiral bisphosphine initiators. According to the optical rotation analysis and circular dichroism measurements, the polymer obtained by using the initiator (S,S)-1,2-bis(boranato(tert-butyl)methylphosphino) ethane exhibited one-handed helical conformation induced by the chirality of phosphorus atoms in the polymer terminal. The enantiomer (R,R)-1,2-bis(boranato(tert-butyl)methylphosphino) ethane gave the opposite one-handed helical polymer. Optically active bisphosphine (S,S)-1,2-bis(boranatomethylphenylphosphino) ethane was employed for the helix-sense-selective polymerization of triphenylmethyl methacrylate in order to obtain the polymer with the same helix sense as the polymer obtained from the initiator (S,S)-1,2-ethane bis(t-butylm-ethylphosphineborane). Further, removal of the coordinated boranes and complexation with platinum(II) on the chiral phosphorus atoms were carried out in order to yield the corresponding polymer-platinum(II) complex without loss of its chiral higher-ordered structure.     

Chiral arylnickel complexes as highly active initiators for screw‐sense selective living polymerization of 1,2‐diisocyanobenzenes

Optically active chiral organonickel complexes served as efficient chiral initiators for living aromatizing polymerization of 1,2‐diisocyanobenzene derivatives, which afford optically active helical poly(quinoxaline‐2,3‐diyl)s up to 84% s.e. (screw‐sense excess). In comparison with asymmetric polymerization with the corresponding organopalladium initiators, the nickel initiators show a much greater polymerization rate, while the selectivity remains high. The organonickel initiators can be generated in situ from nickel(0) precursors with the corresponding enantiopure (S,S)‐2‐(4,5‐diphenylimidazolin‐2‐yl)phenyl chloride, leading to the convenient synthesis of highly stereo‐controlled poly(quinoxaline‐2,3‐diyl)s. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 898–904, 2010     

Screw-sense-selective polymerization of aryl isocyanides initiated by a Pd-Pt mu-ethynediyl dinuclear complex: a novel method for the synthesis of single-handed helical poly(isocyanide)s with the block copolymerization technique

Living polymerization of chiral aryl isocyanides, such as m- and p-menthoxycarbonylphenyl isocyanides 2 and 5, initiated by the Pd-Pt mu-ethynediyl dinuclear complex 1, proceeds with a high screw-sense selectivity to give the poly(isocyanide)s 3 and 6, which exhibit a large specific rotation and an intense CD band at lambda = 364 nm as a consequence of a helical chirality. The molar optical rotation and molar circular dichroism of the resulting polymers 3 and 6 reach a constant value at a degree of polymerization (Pn) of more than 30. Screw-sense-selective polymerization of achiral aryl isocyanides that bear very bulky substituents, such as 3,5-di(propoxycarbonyl)phenyl isocyanide (11), 3,5-di(butoxycarbonyl)phenyl isocyanide (13), and 3,5-di(cyclohexyloxycarbonyl)phenyl isocyanide (15), is achieved by the use of chiral oligomer complexes 3(30) and 6(30), prepared from the reaction of 1 with 30 equivalents of 2 or 5, as an initiator to give predominantly single-handed helical polymers. In contrast, smaller aryl isocyanides are also polymerized by 3(30) and 6(30) with screw-sense selectivity in the initial stage of the reaction, but the single-handed helix is not preserved up to high molecular weight. Kinetic studies of the polymerization of (L)- and (D)-2, or (L)- and (D)-5 with chiral oligomer complexes (L)-3(50) or (L)-6(100) suggests that the screw sense of the polymer backbone is not controlled kinetically, but rather that the thermodynamically stable screw sense is produced.