A novel strategy for synthesis of multiblock copolymers

Multi-block copolymers with well-controlled numbers of blocks and block chain length are synthesized for the first time using a 'polyinitiator'.     

Comb-shaped liquid crystalline ionogenic copolymers

 A series of new ionogenic liquid crystalline (LC) copolymers (A4CB-AA) was prepared by radical copolymerization of 4-(4-cyanobiphenyl-4′-yloxy) butyl acrylate (A4CB) and acrylic acid (AA). The presence of the AA units do not prevent the development of the nematic phase, which is typical of the initial cyanobiphenyl homopolymer. At a content of AA of 42–52 mol%, the copolymers produce the S _Ad type of mesophase, and this phenomenon is explained by an increased rigidity of the main chain due to the development of intramolecular hydrogen bonds. By increasing the concentration of AA units higher than 55 mol%, the development of mesophase is prevented, and the as-received copolymers are amorphous. A crucial role of intramolecular hydrogen bonds for the development of the S _A phase in the copolymers is proved by synthesizing and studying the copolymers, in which the same type of the mesogenic group A4CB is preserved but the second component is provided by methyl ether of acrylic acid; such copolymers are able to produce only a nematic phase. Studying orientation of LC A4CB-AA copolymers in the magnetic field by the method of wide-line ¹H NMR spectroscopy allows one to calculate the temperature dependences of order parameter S and to advance a correct interpretation of experimental data. Received: 8 January 1998 Accepted: 14 April 1998     

Epoxy ketones as versatile building blocks in organic synthesis

The major advances made in the functionalisation of racemic and optically active epoxy ketones where one or several stereogenic centres are either preserved or modified are reviewed. Some relevant applications to the synthesis of natural products and biologically active compounds are also described.     

Block copolymers with liquid crystalline segments

This paper describes the synthesis and characterization of polystyrene-block-poly(2,2'-dimethyl-4,4'-biphenylene phenylterephthalate)-block-polystyrene and of poly(ethylene glycol)-black-poly(2,2'-dimethyl-4,4'-biphenylene phenylterephthalate)-block-poly (ethylene glycol) block copolymers. The ABA-triblock copolymers were synthesized by condensation reaction of telechelic poly(2,2'-dimethyl-4,4'-biphenylene phenylterephthalate) with ω-hydroxy polystyrene and ω-hydroxy poly(ethylene glycol) methyl ether of different molecular weights prepared by anionic polymerization. Some aspects of the liquid crystalline behavior and the phase transitions with respect to the block copolymer composition will be discussed.     

Glycosyl thioimidates as versatile building blocks for organic synthesis

This review discusses the synthesis and application of glycosyl thioimidates in chemical glycosylation and oligosaccharide assembly. Although glycosyl thioimidates include a broad range of compounds, the discussion herein centers on S-benzothiazolyl (SBaz), S-benzoxazolyl (SBox), S-thiazolinyl (STaz), and S-benzimidazolyl (SBiz) glycosides. These heterocyclic moieties have recently emerged as excellent anomeric leaving groups that express unique characteristics for highly diastereoselective glycosylation and help to provide a streamlined access to oligosaccharides.     

Cyclic ureas as novel building blocks for bent-core liquid crystals

Cyclic ureas represent a new class of bent-core liquid crystals which, depending on the ring size and other structural parameters, can form a series of polar (ferroelectric and antiferroelectric), as well as non-polar, tilted and non-tilted smectic and undulated smectic phases.     

Synthesis of 5-aminothiazoles as building blocks for library synthesis

A convenient route to 4-phenyl-5-aminothiazoles is described, which offers control over substitution at the 2-position. 2-N-Acylglycinamides were dithionated and a subsequent TFAA-mediated cyclisation step was followed by removal of the 5-N-trifluoroacetyl group providing the free amines. Though applicable generally the method was found to be most effective when introducing aromatic substituents at the 2-position, whereupon moderate overall yields of the 5-amino compounds were obtained.     

Amino acids as building blocks for the synthesis of substituted 1,2,4-triazoles

We report on the synthesis of 1,2,4-triazoles substituted with 2 or 3 amino acid side chains, using silver benzoate as a key reagent for the cyclization step. A complete study of the optical purity retention during the synthetic process leading to these compounds is described. In addition an improved work-up after the addition-cyclization step was also established leading to better yields and metal-free products.     

Precision synthesis of acrylate multiblock copolymers from consecutive microreactor RAFT polymerizations

Well‐defined acrylate RAFT polymers and multiblock‐copolymers have been synthesized via the use of a continuous‐flow microreactor, in which polymerizations could be executed in 5?20 min reaction time. First, Poly(n‐butyl acrylate) (PnBuA) was synthesized in the micro‐flowreactor by using two different trithiocarbonate RAFT agents. Reaction time and reaction temperature were optimized and collected samples were directly studied with NMR, SEC and ESI‐MS to determine conversion, molar mass and end group fidelity. Using the continuous flow technique, highly reproducible and fast polymerizations yielded quantitatively functionalized PnBuA in a very facile and efficient manner. One batch of RAFT acrylate polymer with a molar mass of 1100 g mol^?1 and excellent end group fidelity was employed as a macro‐RAFT agent for the subsequent copolymerization with different acrylate monomers (2‐ethylhexyl acrylate, t‐butyl acrylate, n‐butyl acrylate). Using this procedure, a sequential multiblock‐copolymer (M_n = 31,200 g mol^?1, PDI = 1.46) consisting of five consecutive acrylate blocks was synthesized. This study clearly demonstrates the potential of using a continuous‐flow microreactor for subsequent RAFT polymerizations towards well‐defined multiblock‐copolymers. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013, 51, 2366–2374     

New uses of amino acids as chiral building blocks in organic synthesis

[reaction: see text] N,N-Dibenzylamino aldehydes have emerged as a highly useful class of chiral building blocks in synthetic organic chemistry. We envisioned the transformation of the N,N -dibenzylamino aldehydes to the corresponding aldimines followed by diastereoselective methylene transfer with a sulfonium ylide to obtain alpha-amino aziridines in high yields.     

Design and preparation of liquid crystalline block copolymers

The design and preparation of liquid crystalline (LC) block copolymers by use of azo-macroinitiators are outlined. This approach is very versatile and makes it possible to realize diverse architectures of block copolymers, including non-LC/side-chain, non-LC/main-chain and side-chain/main-chain block copolymers. The different blocks were phase separated and underwent their individual phase transitions. In side-chain/main-chain block copolymers different LC mesophases coexisted in equilibrium.     

Synthesis of polystyrene-polysiloxane side-chain liquid crystalline block copolymers

The synthesis of a new liquid crystalline block copolymer consisting of a polystyrene block and a side-chain liquid crystalline siloxane block is reported. The synthetic approach described is based on the anionic polymerization of styrene and cyclic trimethyltrivinyltrisiloxane monomers, followed by functionalization of the siloxane block with side chain mesogens. The siloxane block has a T_g well below 25°C and is designed to exhibit a chiral smectic C^* phase at room temperature. These block copolymers are the first side-chain liquid crystalline block copolymers which contain both a high T_g glassy block and a low T_g liquid crystalline block.     

Beta-hydroxy-gamma-lactones as chiral building blocks for the enantioselective synthesis of marine natural products

The enantioselective synthesis of trans-(+)-laurediol, (2S,3S,5R)-5-[(1R)-1-hydroxy-9-decenyl]-2-pentyltetrahydro-3-furanol, and (2S,3S,5S)-5-[(1S)-1-hydroxy-9-decenyl]-2-pentyltetrahydro-3-furanol are described. In addition, a formal synthesis of trans-(-)-kumausyne is also developed. All the synthetic procedures have in common the use of enantiomerically enriched beta-hydroxy-gamma-lactones, easily available by Sharpless asymmetric dihydroxylation (AD) from the suitable beta,gamma-unsaturated ester. The use of Katsuki-Sharpless asymmetric epoxidation (AE) as an additional enantioselective reaction provides cyclic compounds of high enantiomeric purity.     

Morphology and physical properties of triblock copolymers with crystalline end blocks

The morphology of crystalline end-block copolymers of poly(thiacyclobutane-b-isoprene-b-thiacyclobutane) (TCB–I–TCB) was studied by optical microscopy, electron microscopy, and small-angle x-ray scattering (SAXS). A spherulitic texture was observed for both the TCB homopolymer and the TCB–I–TCB block copolymers. Well-defined phases arranged in an ordered structure exist when the films are cast above the melting temperature of the crystalline end blocks. The dimensions and the arrangements of the domains have been derived from both SAXS and electron microscope measurements. The deformation mechanism of the 41% end-block copolymer sample was also examined by a combination of SAXS and stress–strain studies. It was found that the interdomain spacing increased along the stretching direction as the extension ratio was increased. The morphology changes from hexagonally packed cylinders to rowtype cylinders upon the application of stress.     

Block copolymers and liquid crystalline block copolymers: A bird's-eye view

Block copolymers and liquid crystals are separately known to order at different length scales. Various types of molecular interactions in liquid crystalline block copolymers determine complex phase behaviors and states of order, and thereby can provide a way of tailoring the material properties. Examples of liquid crystalline block copolymers will be discussed as they may offer unique opportunities for both theoretical and experimental research.     

Binuclear ladder-type complexes as building blocks for the synthesis of novel polynuclear systems

Summarized are reactivity studies of binuclear ladder complexes in the metallation reaction that has been applied to prepare novel homo- and heteropolynuclear transition metal complexes. The electron transfer through π-ligand-metal-σ,π-ligand-metal chain has been studied by IR spectroscopy and cyclic voltammetry techniques.     

Multiple length scale self-organization in liquid crystalline block copolymers

A series of block copolymers were prepared consisting of a block of poly(styrene) and a block in which a mesogenic group was attached by polymer analogous chemistry to a flexible backbone. Two types of mesogenic groups which produced a range of mesophases were investigated: (i) an azobenzene mesogenic group and (ii) a semifluorinated group. Organization caused by liquid crystallinity and phase separation leads to simultaneous organization on a variety of length scales. Comparison of the ordering behavior of these two types of mesogenic groups and more conventional flexible chain diblocks are made.