Asymmetric Polymerization Research Articles

Synthesis of polystyrene-based Y-shaped asymmetric star by the combination of ATRP/RAFT and its thermal and rheological properties

A2A′-type asymmetric stars and A2B-type miktoarm star polymers were prepared by the combination of atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer polymerization (RAFT) using the designed initiator.

Micelle-provided microenvironment facilitating the formation of single-handed helical polymer-based nanoparticles

Micelles provide microenvironment effects for asymmetric polymerization: an unprecedented methodology for controlling the preferential helicity of synthetic helical polymers.

Fluorinated poly(arylene ether ketone)s for high temperature dielectrics

There is a need for polymeric capacitors with improved energy storage density and thermal stability. In this work, the effect of polymer molecular structure and symmetry on Tg, breakdown strength, and relative permittivity were investigated. A systematic series of four amorphous poly(arylene ether ketone)s were compared. Two of the polymers had symmetric bisphenols while the remaining two had asymmetric bisphenols. Two contained trifluoromethyl groups while the other two had methyl groups. The symmetric polymers had Tg's of approximately 160 °C while the asymmetric polymers showed higher Tg's near 180 °C. The symmetric polymers had breakdown strengths near 380 kV/mm at 150 °C. The asymmetric counterparts had breakdown strengths near 520 kV/mm even at 175 °C, with the fluorinated polymers performing slightly better in both cases. The non-fluorinated polymers had higher relative permittivities than the fluorinated materials, with the asymmetric polymers being better in both cases.

Asymmetric polymerization of N-vinylcarbazole with optically active anionic initiators

The anionic polymerization of N-vinylcarbazole (NVC) by using optically active anionic initiators such as the lithium salts of (S)-1-(9H-fluoren-2-yl)-4-isopropyl-4,5-dihydrooxazole ((S)-1-FIDH) and (S)-2-(9H-fluoren-2-yl)-4- isopropyl-4,5-dihydrooxazole ((S)-2-FIDH) and complexes of (-)-Sparteine with n-butylithium (n-BuLi-(-)-Sp) or fluorenyl lithium (FILi-(-)-Sp) was achieved. The yield and specific rotation of poly(N-vinylcarbazole)s (poly(NVC)s) were considerably affected by the molar ratio of (S)-FIDH to NVC. The highest yield and specific rotation were obtained with Li- (S)-1-FIDH as an initiator, with a molar ratio of monomer and initiator [M]/[I] = 10/1. The effects of the chiral initiators, type of solvent and the polymerization temperature were investigated. The obtained optical activity of polymers was attributed to asymmetric induction of the chiral initiators.

Asymmetric AB3 Miktoarm Star Polymers: Synthesis, Self-Assembly, and Study of Micelle Stability Using AF4 for Efficient Drug Delivery.

A simple and versatile methodology, which employs a combination of ring-opening polymerization and alkyne-azide click chemistry to synthesize amphiphilic AB3 miktoarm stars, is reported. Their aqueous self-assembly behavior was studied using dynamic light scattering, fluorescence, and asymmetrical flow field-flow fractionation (AF4). AB3 miktoarm stars form micelles which incorporate curcumin with high efficiency, and significantly reduce the viability of glioblastoma cells in spheroids. We demonstrate that AF4 is an effective technique to determine the size distribution of self-assembled structures exposed to a biological medium. The ease, with which asymmetric AB3 miktoarm polymers are constructed, provides a platform that can be widely employed to deliver a variety of lipophilic drugs.

Helical Network Polymers Exhibiting Circularly Polarized Luminescence with Thermal Stability. Synthesis via Photo-Cross-Link Polymerizations of Methacrylate Derivatives in a Chiral Nematic Liquid Crystal

We synthesized helical network polymers with chiroptical properties through photo-cross-link polymerizations of functionalized methacrylate derivatives in chiral nematic liquid crystals (N*-LCs) used as asymmetric polymerization solvents. Two types of novel methacrylate monomers that contain either a phenylcyclohexyl mesogen-based liquid crystalline moiety or a bis(1,1′-biphenyl)fluorene-luminescent moiety were synthesized. The N*-LCs were prepared by adding axially chiral di- or tetra-substituted (R)/(S)-binaphthyl derivatives into a host nematic LC (N-LC) mixture containing alkyloxyphenylcyclohexyl and alkylbiphenylcyclohexyl derivatives. Photo-cross-link polymerizations for the mixture of the methacrylate monomers were achieved using a photoinitiator and an additional triacrylate-based cross-linker in the N*-LCs. The helical network polymers showed fingerprint morphologies and even spiral morphologies similar to those of the N*-LCs. Helicities of the helical network polymers were strictly controlled by...

Erratum to: Asymmetric polymers in bicontinuous microemulsions and their accretion to the bending of the membrane

After linear hydrophilic polymers with a short hydrophobic sticker have been proven to be highly suitable as efficiency boosters in microemulsions, a whole set of asymmetric polymers was studied in more detail. Sticker polymers with two hydrophilic polymeric arms, hydrophobic polymers with ionic stickers, and a Y-shaped tri-arm-polymer were studied for their high surface activity. While low asymmetry of the Y-shaped polymer resulted in very similar dependence as a diblock copolymer, the highly asymmetric polymers showed a renormalized behavior of the bending rigidity coming from preferential accretion of the polymer at the membrane. The experimental evidence for the accretion of the polymer according to the preferential membrane bending is reported here for the first time. Furthermore, the isolated, diffuse counter ion clouds of the ionic sticker polymers act in a way similar to that of a polymer anchored at the membrane. All asymmetric polymers are highly suitable as efficiency boosters in microemulsions.

Synthesis and Characterization of ABC-Type Asymmetric Star Polymers Comprised of Poly(3-hexylthiophene), Polystyrene, and Poly(2-vinylpyridine) Segments

ABC-type asymmetric star polymers containing a P3HT segment were successfully synthesized by polymer coupling/linking reactions by combining the Kumada catalyst-transfer polymerization and living anionic polymerization for the first time. The synthetic methodology involves the following three stage reactions: (a) the anionic linking reaction between ω-chain-end-functionalized P3HT with a bromobutyl moiety (P3HT-C4-Br) and living anionic PS end-capped with 1-(3-tert-butyldimethylsilyloxymethylphenyl)-1-phenylethylene (1), (b) the transformation reaction of the 3-tert-butyldimethylsilyloxymethylphenyl (TBDMS) moiety at the junction between the P3HT and PS segments into the α-phenyl acrylate (PA) moiety through the hydroxymethylphenyl moiety, and (c) the anionic linking reaction between PA-in-chain-functionalized P3HT-b-PS and living anionic P2VP. Indeed, the well-defined ABC star polymers in which A, B and C are poly(3-hexylthiophene) (P3HT), polystyrene (PS), and poly(2-vinylpyridine) (P2VP), respectively,...

Asymmetric polymers in bicontinuous microemulsions and their accretion to the bending of the membrane

Asymmetric polymers in bicontinuous microemulsions and their accretion to the bending of the membrane

Textile‐surface interfacial asymmetric polymerization

ABSTRACTThis research demonstrated that polymerization of aniline on cellulose produces chiroptically active composites. Polymerization of aniline in the presence of cotton fibers consisting of chiral cellulose are performed to prepare a polyaniline (PANI)/cotton composite. The polymerization is conducted at the cotton interface. The resultant PANI/cotton composite shows chiroptical activity elucidated with diffuse reflectance circular dichroism. In this reaction, textile‐surface interfacial asymmetric polymerization is performed with imprinting of chiral structure from the cotton as a natural chiroptically active polymer to the PANI. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41118.

New Method for Asymmetric Polymerization: Asymmetric Allylic Substitution Catalyzed by a Planar-Chiral Ruthenium Complex

A new type of asymmetric polymerization reaction by asymmetric allylic substitution catalyzed by planar-chiral cyclopentadienyl-ruthenium (Cp′Ru) complexes is described. Achiral AB-type monomers, which feature both the allylic chloride and N-alkoxyamide moieties in a single molecule, are smoothly polymerized by the catalysis of chiral ruthenium complexes with quantitative monomer conversion to afford optically active polyamides in good yields. The resulting polymers are characterized by optical rotation, circular dichroism, and 1H NMR analyses, which clearly show that the polymerization system works in a highly stereoselective manner to afford optically active polyamides with high regio- and enantioselectivities. The results revealed that the planar-chiral Cp′Ru complexes work as a highly efficient catalyst to control the stereochemistry even in the polymerization reaction.

Morphology and optical properties of chiral polymer films containing hetero-atoms prepared by electrochemical polymerisation in a cholesteric liquid crystal

Synthesis of chiral films in chiral liquid crystal is reported. The monomers (3, 3′-hexylsilane-2, 2′-bithiophene and 3,6-bis(3, 4-ethylenedioxythienyl)pyridazine) in cholesteric liquid crystal (CLC) electrolyte solution were elecropolymerised by the application of voltage to yield a thin film. Circular dichroism measurements display the Cotton effect for the films. The polymers show a fingerprint texture very similar to that of the CLC. The structure developed during polymerisation was preserved even after washing. Note that no chiral molecule reacted chemically with the monomer during polymerisation. The electrolyte functioned as a chiral matrix. This simple method can be defined as asymmetric polymerisation in chiral environment.

Asymmetric polymerisation in liquid crystals and resultant electro-chiroptical effect: Structure organising polymerisation and chiral charge carrier "chiralion"

Electrochemical synthesis in liquid crystal (LC) affords conducting polymers having LC molecular order and electro-activity. The polymerisation method can be referred to as structure organising polymerisation (SOP). The optical textures of the polymers thus prepared appear very similar to that of the LC electrolyte solution used for the polymerisation. Especially, polymers prepared in cholesteric LC (chiral LC) having structural chirality show doping-dedoping (redox) driven change in chiroptical activity (controllable circular dichroism and optical rotation), as "electro-chiroptical effect". The polymer films exhibit interference colour and electrochemically driven refractive index modulations. The chiroptical activity of the polymer prepared in cholesteric LC comes from axial chirality of the helical structure.

Catalysis direction selective asymmetric polymerization in chiral liquid crystal medium

A series of optically inactive aryl isocyanide derivatives were polymerized with an achiral nickel catalyst (Ni(II)Cl2) in a cholesteric liquid crystal (CLC) medium. The polymers synthesized from ortho-substituted phenyl isocyanide monomers in CLC phase show optical activity even though they have no chiral carbons. The Cotton effects of these polymers suggest that main chains of the polymers formed predominantly one-handed helical conformation. One-handed chiral environment in reaction state provided by CLC medium allows the formation of the polymers. The helical sense of the polymers is controllable by choice of (R)- or (S)-CLC as reaction solvent, though the monomer is same.

Synthesis, structural features and biological activities of three asymmetric pyridazine–triazole coordination polymers

The complexes [CuL2Cl2]n (1), [CoL2Cl2(H2O)2]·L (2) and [MnL2Cl2(H2O)2]·L (3) (L = 3-chloro-6-(1H-1,2,4-triazol-1-yl) pyridazine) were synthesized and characterized by physicochemical and spectroscopic methods. X-ray crystallographic analysis reveals that the Cu(II) center of complex 1 is located in a slightly distorted tetragonal pyramidal environment and bridged by chlorine atoms to generate infinite 1D chains, which are further connected into 2D supramolecular structures by C–H…Cl hydrogen bonds. The Co(II) and Mn(II) atoms in complexes 2 and 3 both have a distorted octahedral coordination sphere, and the crystal lattices include hydrogen bonds and π–π stacking interactions to yield 3D supramolecular frameworks. The antioxidant activities (influence on O2•− and •OH) and antibacterial activities of the ligand L and its three complexes were also investigated.

In vivo formation of double-stranded T-DNA molecules by T-strand priming

During plant genetic transformation, Agrobacterium transfers a single-stranded DNA (T-strand) into the host cell. Increasing evidence suggests that double-stranded (ds) T-DNA, converted from T-strands, are potent substrates for integration. Nevertheless, the molecular mechanism governing T-strand conversion to dsT-DNA is unknown. Integrated T-DNA molecules typically exhibit deletions at their 3' end as compared with their 5' end. We hypothesize that this may result from asymmetric polymerization of T-DNA's ends. Here we show that β-glucuronidase (GUS) expression from sense T-strands is more efficient than from antisense T-strands, supporting asymmetric conversion. Co-transfection with two partially complementary, truncated GUS-encoding T-strands results in GUS expression, which suggests functional hybridization of the T-strands via complementary annealing and supports the notion that T-strands can anneal with primers. Indeed, red fluorescent protein (RFP) expression from mutated T-strand can be restored by delivery of synthetic DNA and RNA oligonucleotides with partial wild-type RFP sequence, implying the involvement of plant DNA repair machinery.

Optically Active Conjugated Polymer from Solvent Chirality Transfer Polymerization in Monoterpenes

Disubstituted acetylene monomers [1,2-diphenylacetylenes (DPAs: DPA-pC1, DPA-mC1, DPA-pC8); 1-phenyl-2-hexylacetylene (PHA-pC1)] are tested for asymmetric polymerization in chiral monoterpenes used as solvents and compared with the corresponding monosubstituted acetylene monomer [1-phenylacetylene (PA-pC1)]. DPA-pC1 containing a trimethylsilyl group in the para-position of the phenyl ring produces an optically active polymer with a large Cotton effect, despite the absence of a stereogenic center. The polymer sample obtained by polymerization in 87% ee (-)-α-pinene shows the strongest CD signal (gCD value at 385 nm: ∼3.2 × 10⁻³). The Cotton bands of the polymers obtained in (-)- and (+)-α-pinenes show the opposite sign in the CD signals. Theoretical calculations show that only the cis-cisoid model adopts a helical conformation. A time-correlated single photon counting experiment shows that the emission of the chiral polymer originates from a virtually single excited species with a 98% component fraction. This polymer solution does not show any significant decrease in gCD value over a wide temperature range of 20 to 80 °C. No noticeable decrease in the gCD value is detected when the polymer solution is kept at relatively low temperatures for a prolonged period (35 d). In contrast, the other polymers show no CD signal.

Synthesis and temperature gradient interaction chromatography of model asymmetric star polymers by the “macromonomer” approach

We describe herein the synthesis and characterisation of a series of asymmetric three arm polystyrene stars via the “macromonomer” approach. The stars have been designed as model polymers to probe branched polymer dynamics and in particular to establish the chain-length of side-arm which precipitates a change in the rheological properties of the resulting polymers from “linear-like” to “star-like”. Thus, a homologous series of three arm stars have been prepared in which the molar mass of two (long) arms are fixed at 90,000gmol−1 and the molar mass of the remaining (short) arm is varied from below the entanglement molecular weight (Me) to above Me. The arms were prepared by living anionic polymerisation, resulting in well-defined chain lengths with narrow molecular weight distribution. In contrast to the usual chlorosilane coupling approach, the macromonomer approach involves the introduction of reactive chain-end functionalities on each of the arms, either through the use of a functionalised (protected) initiator or a functional end-capping agent, which allows the stars to be constructed by a simple condensation coupling reaction. In this study we will compare the relative efficiency of a Williamson and ‘click’ coupling reaction in producing the stars. Most significantly, although this approach maybe a little more time-consuming than the more common silane coupling reaction, in the present study the “long” arm may be produced in sufficient quantity such that all of the asymmetric stars are produced with long arms of identical molecular weight – the only remaining variable being the molecular weight of the short arm. This will allow for a far more robust interpretation of the resulting characterisation of the dynamic properties. Temperature gradient interaction chromatography was used alongside size exclusion chromatography to characterise the structural dispersity of the resulting stars and establish the degree of structural homogeneity.

Facile preparation of gold nanoparticles using the self-assembled ABC non-amphiphilic fluorosilicone triblock copolymer template

Gold nanoparticles “AuNPs” with improved stability against aggregation were prepared using a self-assembled ABC non-amphiphilic poly(dimethylsiloxane)-b-poly(methyl methacrylate)-b-poly(2,2,3,3,4,4,4-heptafluorobutylmethacrylate) (PDMS-b-PMMA-b-PHFBMA) triblock copolymer as a template. The polymer-stabilized AuNPs were characterized by UV–visible spectrophotometry and transmission electron microscopy (TEM). Depending on the self-assembled templates, the relatively monodispersed and stable AuNPs with an average diameter of 30 nm were obtained. Therefore the triblock copolymer was demonstrated to be an effective stabilizer for the synthesis of AuNPs. The PDMS-b-PMMA-b-PHFBMA copolymer used in the study contains siloxane and fluorinated segments and belongs to ABC non-amphiphilic triblock copolymers, which proves that the asymmetric ABC non-amphiphilic triblock copolymers can also self-assemble in a dilute solution to serve as a template, or “nanoreactors”. To the best of our knowledge, this work is the first example of facile preparation of metal nanoparticles using self-assembled ABC non-amphiphilic fluorosilicone triblock copolymer as a template. Our present work broadens the range of polymer templates that can be used to synthesize and stabilize metal nanoparticles from amphiphilic block polymers (or symmetric ABA non-amphiphilic block polymers) to asymmetric ABC non-amphiphilic block polymers. In addition, this work also broadens the application of fluorinated ABC triblock copolymers.

Research and Progress in Chiral Binuclear Catalyst of First Row Transition Metal and Corresponding Nonlinear Effect

The study on chiral binuclear complexes of first row transition metal has been expended to correlated fields such as asymmetric catalysis, biomimetic, functional supramolecular material and medicine, and reaches a research hot point of vast attraction and potential. Contrasting with other traditional organic-metal catalysts, the chiral binuclear complexes which com- bine several chiral centers and cooperated binuclear often play preferable catalysis behavior in enantioselective reaction. This review covers the recent progress in chiral binuclear complexes of V, Ti, Mn, Fe, Co, Ni, Cu, Zn applied in asymmetric reac- tions involving asymmetric addition, kinetic resolution, selective oxidation, asymmetric polymerization, as well as the mecha- nistic investigations. Some studies on the nonlinear effect along with the dimer catalysts are also discussed. The challenges and perspectives are given at the end of this article. Keywords chiral binuclear complexes; first row transition metal; asymmetric catalysis; nonlinear effect