Block Oligomers Research Articles

Electrochemical comparison of several cross-linked polyethers

Several unsaturated polyethers have been prepared by a polycondensation route, from α, ω dihydroxy oligoethers, and cross-linked by free-radical initiation. The ionic conductivities and thermal behavior of LiTFSI/network electrolytes have been investigated and show that conductivities depend on the nature of the solvating oligomeric blocks, the maxima corresponding to poly(oxyethylene) based networks. Oligomeric poly(oxypropylene) and poly(oxytetramethylene) blocks however provide a quite satisfactory conductivity level.

Solid-phase synthesis of oligoribonucleotides using T4 RNA ligase and T4 polynucleotide kinase

The concept of solid-phase synthesis of oligoribonucleotide using T4 RNA l ipase and T4 polynucleotide kinase has been proposed and tested with model homo-oligoribonucleotides. The method consists of the immobilization of the first oligomer block at the 3′-terminus on a solid support followed by a chain elongation in the 5′-direction with trinucleoside diphosphates using T4 RNA-ligase and phosphorylation using polynucleotide kinase. Hydrazides of Biogel P-300, Sepharose 4B and cellulose were tested as solid supports for immobilization of initial oligomers. The properties of supports were rated on reactivities of immobilized 5′-phosphorylated oligomers as phosphate donors in the solid phase reactions, hydrodynamical properties and capacity to eliminate donor molecules spontaneously during reactions. Hydrazide of Sepharose 4B appeared to be a more suitable support because of better hydrodynamic properties and highest reactivities of immobilized donors. Saturated concentrations of RNA ligase and polynucleotide kinase and optimal time of joining reaction were determined. In a model experiment ApApA was twice attached to the immobilized hydrazide of Sepharose 4B donor (pA) 6pA ox. The yield of (Ap) 12 was 25%.

Hoogsteen‐Duplex DNA: Synthesis and base pairing of oligonucleotides containing 1‐deaza‐2′‐deoxyadenosine

AbstractOligodeoxyribonucleotides containing 1‐deaza‐2′‐deoxyadenosine ( = 7‐amino‐3‐(2‐deoxy‐β‐D‐erythro‐pentofuranosyl)‐3H‐imidazo[4, 5‐b]pyridine; 1b) form Hoogsteen duplexes. Watson‐Crick base pairs cannot be built up due to the absence of N(1). For these studies, oligonucleotide building blocks – the phosphonate 3a and the phosphoramidite 3b – were prepared from 1b via 4a and 5, as well as the Fractosil‐linked 6b, and used in solid‐phase synthesis. The applicability of various N‐protecting groups (see 4a–c) was also studied. The Hoogsteen duplex d[(c1A)20] · d(T20) (11 · 13; Tm 15°) is less stable than d(A20) · d(T20) (12 · 13; Tm 60°). The block oligomers d([c1A)10–;T10] (14) and d[T10–(c1A)10] (15) containing purine and pyrimidine bases in the same strand are also able to form duplexes with each other. The chain polarity was found to be parallel.

The Influence of Mesomorphic State on the Durability of Polymer Coatings

Abstract The laws governing the destruction of polymer coatings during their use are partly defined by the fact that the rate and other specific features of their destruction are influenced by internal stresses occurring as a result of incomplete relaxation processes due to peculiarities of structure formation.1 This paper deals with an investigation carried out with the help of the NMR method of higher resolution, electron microscopy and physicochemical methods to study the effect of the oligomeric block structure, length and flexibility of a number of oligoester acrylates on peculiarities of oligomer structure formation as well as coatings structure and properties and their durability in the conditions of aging under ultraviolet radiation. It's been shown that coatings set through the intermediacy of mesomorphic structure formation have increased durability of 2-2.5 times, during aging under ultraviolet light radiation. Of all the studied systems those with a globular structure tend to have the lowest d...

Protecting groups in oligonucleotide synthesis.

A biopolymer is synthesized by assembling monomeric or oligomeric blocks. Each block features at least a nucleophilic and an electrophilic function, i.e., the α-amino and the carboxylic functions for peptides, the 5′-OH and the 3′-function (phosphate, phosphoramidite, or phosphonate), for nucleotides. The nucleophilic and electrophilic sites are linked together at the coupling step. Protection is a necessity. It guarantees the chemoselectivity of coupling and the solubility of synthons in organic solvents.

Coionomeric mixtures of polyhydroxyethers and ethylene methacrylic acid copolymers. I. Effects of cation concentration and ABA oligomeric miscibilisers on morphology and properties

AbstractMixtures of a phenoxy polymer (polyhydroxyether of bis‐phenol A) and a polyolefin ionomer (sodium ionomer of ethylene methacrylic acid copolymer) were compatibilized by the addition of small amounts of sodium ethoxide and/or by the incorporation of varying amounts of A‐B‐A block oligomers. The latter were produced by reacting several bis‐phenol A epoxy resins, varying in molecular weight, with montanic acid in order to provide segments soluble in each of the two polymer components of the blend. Chemical miscibilization by the addition of sodium ethoxide changed the morphology into one containing larger amounts of cocontinuous phases, while the incorporation of substantial amounts of A‐B‐A oligomer brought about primarily the formation of irregular and highly elongated particles. The mixtures were found to exhibit the typical properties of ionomers which were enhanced by the addition of sodium ethoxide. Furthermore sufficient evidence was gathered to establish that the ionomeric aggregates are shared by both polymer components of the blend, from which the term coionomeric mixture is derived. © 1993 John Wiley & Sons, Inc.

Coionomeric mixtures of polyhydroxyethers and ethylene methacrylic acid copolymers. II. Compatibilizers for blends of polybutylene terephthalate and ethylene butyl acrylate copolymers

AbstractBlends of polybutylene terephthalate and ethylene butyl acrylate copolymers were studied at two extreme concentration levels so that each polymer would form, in turn, a particulate dispersed phase. The blends contained 5% by weight of a coionomeric compatibilizer, which was produced from 1 : 1 mixtures of a polyhydroxy ether of bisphenol A and the sodium ionomer of an ethylene methacrylic acid copolymer, using sodium ethoxide to enhance the formation of ionomeric clusters together with an A‐B‐A block oligomer to assist the solubilization of the two ionomeric polymers. In all cases the addition of the coionomeric compatibilizer mixture to the blend was found to decrease the size of the dispersed particles with a concomitant reduction in the interphase gap. It was also observed that the dispersed polymer exhibited a lower level of crystallinity and a slightly lower melting point than when it was present as a matrix, particularly for the case of the ethylene butylacrylate copolymer. The inability of the compatibilizer to completely prevent the formation of an interfacial gap which did not allow the blends to achieve more substantial improvements in mechanical properties, was attributed to the vast difference in crystallization temperature between the two polymers. © 1993 John Wiley & Sons, Inc.

The stepwise synthesis of oligo(glycosyl phosphates) via glycosyl hydrogenphosphonates. The chemical synthesis of oligomeric fragments from Hansenula capsulata Y-1842 exophosphomannan and from Escherichia coli K51 capsular antigen

A stepwise approach has been used in the syntheses of pentamannosyl tetraphosphate HO-[-6Man(α)-PO 4-] 4-6Man(α)-OMe and tetra( N-acetylglucosaminyl) triphosphate HO-[-3GlcNAc(α)-PO 4] 3-3GlcNAc(β)-OC 6H 4NO 2, which are fragments of the yeast and bacteria extracellular phosphoglycans. Elongation of the chain was performed with the use of suitably protected glycosyl hydrogenphosphonate derivatives for successive introduction of glycosyl phosphate residues. Partially protected monosaccharide derivatives and oligomeric blocks served as hydroxylic components.

Low temperature transmission electron microscopy and differential scanning calorimetry characterization of latexes stabilized with surface active block oligomers

The spatial distribution of a short-chain amphiphilic diblock copolymer (i.e. block oligomer), used as an emulsifier during the preparation of a latex, is determined by low temperature transmission electron microscopy and differential scanning calorimetry (d.s.c.). The main question is whether intermixing of the amphiphilic block oligomer and latex core materials actually takes place to a significant extent. Electron microscopy gives a clear indication that a surfactant-rich layer exists in all latex samples examined. At very high surfactant concentration (>6%, not typically used in commercial latexes), electron beam radiation damage reveals the presence of a surfactant gradient from the particle surface to its core. These results are in good agreement with our d.s.c. data.

A comparative study of sorption of water vapor by oligomeric triblock copolymers of ethylene and propylene oxides

AbstractEquilibrium sorption of water vapor by oligomeric block copolymers (PEP) of ethylene and propylene oxides was measured at 23°C at five values of the relative vapor pressure, 0.32 ≦ p/p0 ≦ 0.90. Sorption isotherms were described by a simple empirical two‐parameter equation. The effect of the copolymer composition on the parameters was established. The Lundberg‐Zimm clustering function, the mean size of clusters of water molecules, and the Flory‐Huggins interaction parameters were estimated. Their dependencies on copolymer composition and water content in the system are discussed.

Microheterogeneous oligoester urethane semicarbazide acrylates and polymers based on them

A series of oligoester urethane semicarbazide acrylates has been synthesized in which the strongly interacting urethane semicarbazide blocks and acrylate groups are located at the ends of the chain. Differential scanning calorimetry, IR spectroscopy and small-angle X-ray techniques have been used to investigate the structure of the oligomers and polymers based on them as compared with polymers based on oligourethane acrylates of similar chemical structure. It is shown that the thermodynamic incompatibility of the blocks promotes the formation of a microheterogeneous structure in the oligomers. On polymerization of the block oligomers in the condensed state the microheterogeneous structure transfers to the polymer. Polymerization of the oligomers in the homogeneous state gives microheterogeneous polymers with a lower degree of microphase separation of the blocks. The synthesized polymers posses far higher strength properties than polymeric materials based on oligourethane acrylates.

Aspects of molecular mobility in the three dimensional polymer diallyl terephthalate and its copolymers with the allyl ester of benzoic acid

The wide line NMR method has revealed in the product of three-dimensional polymerization of diallyl terephthalate two regions of nuclear magnetic relaxation due to the molecular motion of the oligomeric block the main contribution to which is made by the mobility of the phenyl groups and the process of vitrification. With increase in the diallyl terephthalate fraction in its copolymer with allyl benzoate the glass transition point of the latter moves from 325 to 385 K with rise in the degree of crosslinking of the sample and the activation energy. Separation of the two-component resonance absorption spectra into narrow and wide components yields the quantitative characteristics of the samples studied at different temperatures.

Preparation and morphology of a silicone‐acrylate copolymer system

AbstractThis paper presents the synthesis and analysis of a new series of silicone acrylate (SiAc) copolymers. The building block oligomers are linear polydimethylsiloxanes with alkylene urethane methacrylate end groups (Mn 1000–3000). A variety of analyses were performed in order to elucidate the morphology of these copolymers. Data are presented from differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), permeability testing, small angle x‐ray scattering (SAXS), and electron microscopy. These data indicate that these co‐polymers possess a two‐phase morphology in the range of compositions studied. Conclusions are drawn about the continuity, shape, and size of the domains. Some comparisons are made between data for these “ladder” polymers and data for siloxane‐containing alternating block copolymers reported in the literature.

Crystallinity of methylene-oxyethylene-methylene triblock oligomers. A study of the C 4, C 15 and C 30 di- n-alkyl ethers of pentacosaethylene glycol

Block oligomers of general formula H(CH 2) n (OCH 2CH 2) 25O(CH 2) n H where n = 4, 15 or 30 have been prepared. All blocks are homogeneous. Examination of their crystallinity (by differential scanning calorimetry, X-ray scattering, infra-red and Raman spectroscopy) reveals characteristic layer structures: n = 4, structure I, crystalline oxyethylene blocks and liquid crystalline n-alkyl blocks; n = 15, structure II, completely crystalline; n = 30, structure III, crystalline n-alkyl blocks and liquid crystalline oxyethylene blocks. The chains are either unfolded ( n = 4, 15) or once-folded ( n = 30).

Influence of reactions of cyclization and aminolysis on the dynamic mechanical properties of network epoxy polymers

A study has been made of the role of monocyclization and aminolysis reactions in the formation of network polymers and in determination of their dynamic mechanical properties. Dynamic investigations were carried out on a number of the synthesized epoxyamine networks, whose oligomeric blocks had differing degrees of proneness to amoncyclization and aminolysis reactions. Values of the molecular packing coefficient k, and densities of the network junctions have been computed. It was found that k is only slightly dependent on the occurrence of the above mentioned reactions, and the dynamic shear modulus in the glasslike state is consequently insensitive to the connectivity of the networks. In the high elastic region the determining factor is the topological structure of the network polymer and the effect of reactions of monocyclization and aminolysis on this structure.

Crystallinity of methylene‐oxyethylene‐methylene triblock oligomers derived from pentadeca(ethylene glycol)

AbstractBlock oligomers of the general formula CH3(CH2)nO[CH2CH2O]15(CH2)nCH3 where n + 1 = nc = 1 to 18 and 21 have been prepared. Both the oxyethylene and the methylene blocks are monodisperse. Examination of their crystallinity (by differential scanning calorimetry (DSC); X‐ray scattering; IR, Raman, and 1H NMR spectroscopy) shows two important structures I and II.I: 3 ⩽ nc ⩽ 6: oxyethylene blocks crystalline, methylene blocks non‐crystalline;II: 13 ⩽ nc ⩽ 18: oxyethylene and methylene blocks crystalline.Samples with nc = 1 or 2 crystallise essentially as poly(oxyethylene). Samples with 7 ⩽ nc ⩽ 12 are intermediate in structure between I and II. Structure II has 7/2 helical oxyethylene blocks in high density crystalline layers, with a structure closely related to that of monoclinic poly(oxyethylene), and planar zig‐zag methylene blocks in low density crystalline layers. The oxyethylene helices are normal to the lamella end‐planes, or almost so, and the methylene planar zig‐zags are tilted. The enthalpies of fusion of the type II block oligomers show an even‐odd effect. There is evidence of chain folding in the block oligomer with nc = 21.

Crystallinity of methylene‐oxyethylene‐methylene triblock oligomers derived from nonaethylene glycol

AbstractBlock oligomers of general formula CH3(CH2)nO[CH2CH2O]9(CH2)nCH3 where n = 0 to 25 have been prepared. All blocks are monodisperse. Examination of their crystallinity (by differential scanning calorimetry, X‐ray scattering, infra‐red and Raman spectroscopy) shows that, within defined limits (n > 9, crystallisation temperature high), the block oligomers can crystallise completely. A likely structure is 7/2 helical monoclinic oxyethylene blocks and planar zigzag low density methylene blocks, with the oxyethylene helices normal to the lamella end‐planes and the methylene chains titled.

Influence of the structural ordering of liquid oligomers on the kinetics of radiation-induced polymerization

Temperature dependences of viscosity have been measured for η-ethylene glycol dimethacrylates (η⩾1) and the average degrees of association have been calculated on the basis of these dependences. The kinetics of the radiation-induced polymerization have been analyzed by infrared spectroscopy. Linear dependences were obtained for the maximum rate of radiation polymerization versus average degrees of association, and for maximum degrees of conversion versus MW of the oligomer block.

Radiation hardening of oligoester acrylate and oligocarbonate methacrylate systems

Oligocarbonate methacrylates (OCM) have been used in mixtures with oligoester methacrylates (MDPh) to reduce the irradiation dose with 60Co sources and electron accelerators. Experimental results show that the decisive factor influencing the polymerization rate of the systems is the length of the OCM oligomeric block, as well as its concentration. Given particular amounts of MDPh mixed with the oligocarbonate methacrylate, the microhardness index for coatings exceeds the corresponding index for films based on OCM.

Preparation of triple-block DNA polymers using recombinant DNA techniques.

The construction of several recombinant plasmid derivatives containing novel triple-block DNA sequence insertions is described. The protocol for these constructions involves synthesis of a heterogenous mixture of block oligomer duplexes, : formula: (see text), using pancreatic deoxyribonuclease and terminal transferase. The synthetic duplexes were mixed with linearized and dG-tailed vectors and the DNA mixture used to transform E. coli. Triple-block sequences of the type dGidAjdCk.dGkdTjdCi, characterized by DNA sequencing, were inserted into the Bam HI site of pBR322 and next to the lac wild-type and UV5 promoter regions in pRW26 and pRW28. Similarly, sequences were inserted into the Sma I site of pACYC189 and could be excised by cleavage with Sma I since the procudure regenerates the recognition site. The approach provides a technique for the synthesis of a large family of defined sequence triple-block polymers in essentially unlimited amounts. Although these inserts contain sequences which have the potential for forming stable hairpin structures, the recombinant plasmids are stable and appear to replicate normally.