Tamaki Nakano

Free-radical copolymerization of vinyl esters using fluoroalcohols as solvents: The solvent effect on the monomer reactivity ratio

Free-radical copolymerizations of vinyl acetate (VAc = M1) and other vinyl esters (= M2) including vinyl pivalate (VPi), vinyl 2,2-bis(trifluoromethyl)propionate (VF6Pi), and vinyl benzoate (VBz) with fluoroalcohols and tetrahydrofuran (THF) as the solvents were investigated. The fluoroalcohols affected not only the stereochemistry but also the polymerization rate. The polymerization rate was higher in the fluoroalcohols than in THF. The accelerating effect of the fluoroalcohols on the polymerization was probably due to the interaction of the solvents with the ester side groups of the monomers and growing radical species. The difference in the monomer reactivity ratios (r1, r2) in THF and 2,2,2-trifluoroethanol was relatively small for all reaction conditions and for the monomers tested in this work, whereas r1 increased in the VAc-VF6Pi copolymerization and r2 decreased in the VAc-VPi copolymerization when perfluoro-tert-butyl alcohol was used as the solvent. These results were ascribed to steric and monomer-activating effects due to the hydrogen bonding between the monomers and solvents.

Free‐radical polymerization of vinyl esters using fluoroalcohols as solvents: Effect of monomer structure on stereochemistry

Free-radical polymerization of vinyl esters including vinyl propionate (VPr), vinyl isobutylate (ViBu), vinyl 2,2-dimethylbutylate (VDMB), vinyl 2,2-dimethylvalerate (VDMV), vinyl 2,2-bis(trifluoromethyl)propionate (VF6Pi), and vinyl benzoate (VBz) was carried out using fluoroalcohols as solvents, and the tacticity of the obtained polymers was determined by NMR analysis of the produced poly(vinyl alcohol) (PVA). The polymerization of VPr, ViBu, VDMB, and VDMV, which are bulkier than VAc, in fluoroalcohols afforded polymers rich in heterotacticity (up to mr = 61%) similar to that of vinyl pivalate (VPi) whereas VAc is known to give a syndiotactic polymer under the reaction conditions used here. The polymerization of VF6Pi, which is the bulkiest among the monomers used in this study, gave a polymer rich in syndiotacticity in bulk and in fluoroalcohols regardless of the structure of the solvents. On the other hand, the polymerization of VBz in fluoroalcohols gave polymers with a higher isotacticity (up to mm = 33%) than bulk polymerization. Thus the monomer structure strongly affected the stereochemistry of the free-radical polymerization of vinyl esters in fluoroalcohols.

Synthesis and Chiral Recognition of Helical Polymers

Abstract Asymmetric syntheses of optically active polymethacrylate, polyacrylate, polyacrylamide, and polyisocyanate with helical conformation and their chiral recognition abilities are described. 1-Phenyldibenzosuberyl methacrylate (PDBSMA) gave a purely onehanded-helical, optically active polymer ([α]365 +1670 ∼ +1780o) with almost perfectly isotactic structure by anionic polymerization using optically active initiators. Radical polymerizations of PDBSMA using chiral initiators, chain transfer agents, and additives also afforded optically active polymers with a prevailing onehanded helicity. Triphenylmethyl acrylate yielded an optically active, helical polymer ([α]365 +102o) having a dyad isotacticity of 70% using an optically active anionic initiator. Although the polyacrylate demonstrated chiral recognition ability as a chiral stationary phase for HPLC, the ability was low mainly because of the low degree of one-handedness. N-(3-Chlorophenyl)-N-phenylacrylamide gave an optically active, helical polyme...

Polymerization of t-butyl acrylate using organoaluminum complexes and correlation between main-chain tacticity and glass transition temperature of the obtained polymers

Abstract The polymerization of tert -butyl acrylate ( t BA) was performed with triethylaluminum-(−)-sparteine, triethylaluminum–tertiary phosphine, triethylaluminum– n -BuLi and bis(2,6-di- tert -butyl-4-methylphenoxide)methylaluminum– t -BuLi complexes in toluene. The poly( t BA)s obtained with these initiators were rich in syndiotactic diad as observed by 1 H NMR analysis. On the basis of the triad and tetrad stereochemical information of the poly( t BA)s obtained using triethylaluminum-(−)-sparteine and triethylaluminum– n -BuLi, the polymerization reactions were found to obey Bernoullian statistics. Glass transition temperatures of the poly( t BA)s were measured by differential scanning calorimetry (DSC). A syndiotactic poly( t BA) (racemo (r) diad content: 65%) and an isotactic one (r=19%) exhibited higher glass transition temperature (50 and 43°C, respectively) than an atactic one ( r =50%, T g =21° C ).

Polymerization of optically active 2-fluorophenyl-4-fluorophenyl-2-pyridylmethyl methacrylate with anionic and radical initiators: Stereospecificity and helix-sense selection

Almost optically pure (+)- and (−)-2-fluorophenyl-4-fluorophenyl-2-pyridylmethyl methacrylate (2F4F2PyMA) monomers were obtained by HPLC resolution of the racemic monomer and polymerized with the use of anionic and free-radical initiators. Helix-sense selectivity during the polymerization seemed to be governed mainly by the chirality of the monomer itself, and the polymers obtained by using the complex of N,N′-diphenylethylenediamine monolithium amide with (S)-(+)-1-(2-pyrrolidinylmethyl)pyrrolidine (PMP) in toluene at −78°C appeared to possess single-handed helical conformation (+)-poly[(−)-2F4F2PyMA], [α]365 + 1510°; (−)-poly[(+)-2F4F2PyMA], [α]365 − 1610°]. The single-handed helical (+)-poly[(−)-2F4F2PyMA] and (−)-poly[(+)-2F4F2PyMA] obtained with the PMP complex exhibited better chiral recognition ability toward trans-stilbene oxide compared with the single-handed helical poly(rac-2F4F2PyMA) prepared previously.

Asymmetric anionic polymerization of (2‐fluorophenyl)(4‐fluorophenyl)(2‐pyridyl)methyl methacrylate leading to a helical polymer

A novel racemic methacrylate, (2-fluorophenyl)( 4-fluorophenyl)( 2-pyridyl)-methyl methacrylate (2F4F2PyMA), was synthesized and polymerized with chiral complexes of N,N-diphenylethylenediamine monolithium amide (DPEDA-Li) with (-)-sparteine (Sp), (2S, 3S)-(+)-2,3.-dimethoxy-1,4-bis (dimethylamino)butane (DDB), and (S)-(+)-1-( 2-pyrrolidinylmethyl )pyrrolidine ( PMP ) in toluene at -78°C. The monomer showed higher resistance against methanolysis compared with triphenylmethyl methacrylate (TrMA) and several other analogues. In the asymmetric anionic polymerization of 2F4F2PyMA, PMP was found to be a more effective chiral ligand than DDB and Sp and gave quantitatively an optically active polymer with nearly perfect isotacticity. Enantiomer selection was observed in the polymerization of racemic 2F4F2PyMA with the chiral lithium complexes. Chiral recognition ability of the optically active poly( 2F4F2PyMA) was examined by an enantioselective adsorption experiment.

Quaternary salt formation of optically active helical polymethacrylates having pyridyl group in the side chain

Abstract The reaction of diphenyl-3-pyridylmethyl and 1-(3-pyridyl)dibenzosuberyl methacrylates with CH 3 I in CHCl 3 at 35°C for 24 h lead to quantitative quaternization of pyridyl group while the reaction using diphenyl-2-pyridylmethyl and 1-(2-pyridyl)dibenzosuberyl methacrylates gave only low degree of quaternization. Single-handed helical poly(diphenyl-3-pyridylmethyl) and poly[1-(3-pyridyl)dibenzosuberyl methacrylate] were also quantitatively quaternized with CH 3 I under the above reaction conditions: the former polymer appeared to lose its helical conformation and the chiroptical properties through the reaction while the conformation of the latter polymer seems to survive the quaternization process. The latter polymer quantitatively reacted with decyl and octadecyl iodides in a CHCl 3 –DMSO mixture at 55°C to give hairy rod molecules.

Asymmetric polymerization of cyclopropyldiphenylmethyl and cyclohexyldiphenylmethyl methacrylates and stereomutation of the polymers

SummaryCyclopropyldiphenylmethyl and cyclohexyldiphenylmethyl methacrylates were polymerized with chiral anionic initiators in toluene at low temperature. The former monomer gave an atactic polymer and the latter monomer a highly isotactic, optically active polymer of one-handed helical conformation. The optically active polymer underwent a helix-helix transition in chloroform at 60°C.

Poly(2,7-di-n-pentyldibenzofulvene) showing chiroptical properties in the solid state based purely on a chiral conformation

Poly(2,7-di-n-pentyldibenzofulvene)s with no stereocenters, obtained by anionic polymerization using chiral 9-fluorenyllithium ligand complexes, showed intense circular dichroism in film form due purely to the chiral conformation of the main chain, while no chiroptical properties were detectable in solution.

Helical Polymers: Synthesis, Conformation, and Function

Asymmetric polymerization of acrylic monomers and an isocyanate derivative leading to a helical conformation is described. 1-Phenyldibenzosuberyl methacrylate, triphenylmethyl acrylate, and N,N-diphenylacrylamide were polymerized using the complexes of diphenylethylenediamine monolithium amide with (-)-sparteine, (S,S)-(+)-2,3-dimethoxy-1,4-bis(dimethylamino)butane, and (S)-(+)-1-(2-pyrrolidinylmethyl)pyrrolidine. The methacrylate gave a purely one-handed helical, optically active polymer ([α]365 +1670° ~ +1780°) having a perfect isotactic structure; the polymer exhibited chiral recognition ability to some racemic compounds. This monomer gave optically active polymers also by radical mechanism. The acrylate also gave an optically active, helical polymer ([α]365 +102°) having a dyad isotacticity of 70% using the pyrrolidine complex. The poly(methyl acrylate) derived from the polyacrylate showed a specific rotation which appears to be based on configurational chirality of the main chain. The acrylamide gave an optically active polymer ([α]365-429°) which may have a helical structure by asymmetric anionic polymerization; the polymer had a dyad isotacticity of 86%. m-Methylphenyl isocyanate was polymerized using optically active lithium alkoxides and amides to produce a polymer having a chiral group at the α-end. A prevailing one-handed helical structure was induced for the main chain due to the chiral end group.