Synthesis and calorimetric curing study of amino-terminated PEEK oligomers

Amino-terminated polyetheretherketone (PEEK) oligomers were prepared by the condensation of 4,4′-difluorobenzophenone and hydroquinone in the presence of a calculated excess of m-aminophenol endblocker. The molecular weight of the oligomer was controlled by the manipulation of the ratio of difluoride to hydroquinone with the appropriate stoichiometric amount of m-aminophenol ensuring amino termination. The thermally induced self-crosslinking of these oligomers was studied by differential scanning calorimetry (DSC). Curing was found to be quite slow, taking up to 1 h to reach completion at 668 K. Cured materials were all completely amorphous in contrast to the semi-crystalline starting material. The limiting T_g reached on curing was found to be proportional to the percentage of reactive terminal groups, as would be expected.     

Dimerization of methylstyrenes by acetyl perchlorate and trifluoromethanesulfonic acid

Ring-substituted methylstyrenes (p-, m-, and o-methylstyrenes) in conjunction with acetyl perchlorate (AcClO₄) or trifluoromethanesulfonic acid as catalysts gave their linear unsaturated dimer in high yield in benzene at temperatures from 50 to 70°C. In particular, the yield of o-methylstyrene dimer was as high as 90% in the AcClO₄ catalysis at 50°C. The dimer yield depended on solvent and catalyst. The terminal structures of the dimers and higher oligomers were analyzed by NMR spectroscopy. Oligomers with a cyclic terminal structure increased in the products at higher temperature. The dimer yield was improved by codimerizing p-methylstyrene with less reactive m-methylstyrene or styrene with AcClO₄ catalyst. The dimers obtained partly consisted of linear unsaturated codimers.     

Raman scattering from the longitudinal acoustic mode of oligo-oxyethylene

Low-frequency Raman spectra are reported for monodisperse oligo-oxyethylenes with hydroxy and alkoxy end groups. Assignments are made to the longitudinal acoustic modes. The results are modeled by a rod with a longitudinal modulus E ≥ 2.2 × 10¹⁰ N m^?2 and perturbing forces as large as (alkoxy-ended oligomers) or larger than (hydroxy-ended oligomers) those suggested for the n-alkanes.     

Synthesis of telehelic oligodimethylsiloxanes with 4-carboxypyrrolidone fragments: rheological and thermal properties

Telehelic oligodimethylsiloxanes containing 4-carboxypyrrolidone fragments were synthesized by the reactions of oligodimethylsiloxanes bearing terminal 3-aminopropyl groups with itaconic acid. The thermal and rheological properties of the obtained polymers were studied. The activation energies of viscous flow of the oligomers obtained and the previously synthesized oligodimethylsiloxanes containing terminal fragments of undecenoic or benzoic acid are compared.

     

Kinetic studies on the formation of cyclic oligomers in poly(ethylene terephthalate)

The mechanism of cyclic oligomer formation has been kinetically studied by determining the rate of the formation of cyclic oligomers during melt of poly(ethylene terephthalate) (PET) at several levels of average molecular weight, which were obtained by fractionation and did not initially contain oligomers. The experimental rate equation of cyclic oligomer formation was introduced and then compared with the rate equation derived theoretically. The close agreement between the two equations suggested that the cyclic oligomer formation takes place according to cyclodepolymerization by the action of hydroxyl end groups in PET. The relation is represented as [C] = m·[OH]₀·t^1–n, where [C] is the concentration of cyclic oligomers, [OH]₀ is the initial concentration of hydroxyl end groups, m and n are constants, and t is melting time. A method has also been developed for separating cyclic oligomers from PET using dimethylformamide (DMF) as a solvent.     

Preparation of telechelic oligomers by controlled thermal degradation of isotactic poly(1-butene) and poly(propylene-ran-1-butene)

It was found that telechelic isotactic oligo(1-butene) and telechelic oligo(propylene-ran-1-butene) could be isolated as nonvolatile oligomers from polymer residues resulting from the thermal degradation of isotactic poly(1-butene) and poly(propylene-ran-1-butene), respectively. Their structures were determined by ¹H and ¹³C NMR with attention being paid to their reactive end groups. The maximum average number of terminal vinylidene groups per molecule (f_TVD) was 1.8, indicating that about 80 mol% were α,ω-diene oligomers having two terminal vinylidene groups. This useful new telechelic oligomer had a lower polydispersity than the original polymer, in spite of its lower molecular weight and T_m. The composition of end groups of nonvolatile oligomers obtained by thermal degradation of poly(propylene-ran-1-butene) could be explained by the differences in bond dissociation energy and activation energy of elementary reactions during thermal degradation, based on the monomer composition of the original polymer.     

Novel Synthesis of a Macromonomer Having Organosilyl and Amino Groups

Abstract

Reaction between dimethyldivinylsilane (1) and N,N′-diethyl-N-lithio-ethylenediamine (2a) in the presence of N,N′-diethylethylenediamine (3a) in THF at 20°C gave a monoadduct, 3,3-dimethyl-6-ethyl-3-sila-6,9-diaza-1-undecene (4a). An anionic self-polyaddition reaction of 4a in the presence of lithium diisopropylamide (LDA) proceeded to form oligomers. Each of the oligomers thus obtained was found to carry a polymerizable vinylsilane moiety at the oligomer chain terminal. As a result, a new type of macromonomer having alternating repeating units of ethylenediamine and organosilyl groups was synthesized. Acid-base titration showed the macromonomer to have unique characteristics on protonation of diamine moieties. Anionic polyaddition reactions between 1 and N-lithio-piperazine (2b) in the presence of piperazine (3b) also gave a macromonomer consisting of alternating repeating units of piperazine and organosilyl groups (4b). Radical copolymerizations of styrene with 5b gave comblike graft copolymers.     

Electronic and optical properties of pyrrole and thiophene oligomers: A density functional theory study

The conductive mechanism of pyrrole (Py) and thiophene (Th) oligomers is investigated in the framework of density functional theory. Geometric constructions and electronic structures of neutral n‐Py/n‐Th and oxidized n‐Py^m+/n‐Th^m+ oligomers (6 ≤ n ≤ 48, 2 ≤ m ≤ 18) are reported as a function of oligomer length. The charges in the oxidized oligomers have a localized distribution along the oxidized n‐Py^m+/n‐Th^m+ oligomers, and each set of two positive charges is localized in one area. Therefore, the charge carriers in oxidized n‐Py^m+/n‐Th^m+ oligomers are bipolarons. Furthermore, the nonlinear optical properties of the n‐Py/n‐Th oligomers are investigated, for which the static polarizability α, the first polarizability β, and the second polarizability γ are calculated. When the ratio of m/n is 1/3, the static polarizability <α> and the polarizability anisotropy Δα are maximized. In addition, neutral n‐Py/n‐Th oligomers have maximum <γ> values. The values of β were determined mainly by the dipole of the molecule, while the values of γ were closely related to the aromaticity of the oligomer. The stronger the aromaticity, the bigger the γ value. All calculations indicate that the polarizability and absorption spectrum can be tuned by controlling the oxidation level, making these oligomers applicable as good nonlinear optical materials.     

Selective preparation of poly(p‐oxybenzoyl) by using fractional polycondensation

Selective preparation of poly(p‐oxybenzoyl) (POB) in the copolymerization system of p‐acetoxybenzoic acid (p‐ABA) and m‐acetoxybenzoic acid (m‐ABA) was examined by using reaction‐induced crystallization of oligomers. Polymer crystals mainly composed of p‐oxybenzoyl moiety were precipitated when the content of m‐ABA in the feed was 30 mol %. The formation of the polymer crystals was attributed to both the reactivity of monomer and the phase‐separation behavior of oligomer. Reactivity of p‐ABA was twice higher than that of m‐ABA, and thereby, the homo‐oligomers of p‐oxybenzoyl moiety were more rapidly formed in solution than do co‐oligomers at the early stage in polymerization. They were selectively precipitated by crystallization to form crystals because of low miscibility. Co‐oligomers containing m‐oxybenzoyl moiety were also formed in solution, but they were unable to be phase‐separated because of higher miscibility. Further polycondensation occurred between oligomers in the precipitated crystals, leading to the formation of POB. This polymerization proceeded with selecting certain monomers by crystallization and afforded a new methodology for fractional polycondensation. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2732–2743, 2006     

Application of infrared spectroscopy to investigation of the structure of tetrafluoroethylene telomers in acetone and their intermolecular interaction

Measured FTIR spectra of the products of the radiation-chemical telomerization of tetrafluoroethylene in acetone have been compared with the spectra calculated by density functional theory for oligomers with the structural formula H(C₂F₄) _n CH₂COCH₃, n ≥ 3, and the dimer of the latter. Inhomogeneous broadening, splittings, and shifts of the CH, CC, and CO vibration bands in the terminal groups on the oligomers relative to the associates of acetone molecules confirm the structural formula of the oligomers and show that strong hydrogen bonds are formed between their end groups.     

Effect of blending ratio and oligomer structure on the thermal transitions of stereocomplexes consisting of a D‐lactic acid oligomer and poly(L‐lactide)

Poly(lactic acid) (PLA) stereocomplexes have high potential as renewable materials for advanced polymer applications, mainly due to their high melting temperature (T_m, typically 230–240°C). The properties of PLA stereocomplexes consisting of linear high molar mass homopolymers have been studied extensively in the past, but the available information about the possibilities to affect the thermal properties of the stereocomplex by varying the structure of the blend components has not been sufficient. Novel stereocomplexes containing linear or star‐shaped D ‐lactic acid (D ‐LA) oligomers and high molar mass poly(L ‐lactide) (L‐ PLA) were thus prepared. The T_m and melting enthalpy (ΔH_m) of the racemic crystallites were found to depend strongly on both the blending ratio and the arm‐length of the D ‐lactic acid oligomer. The preparation method of the oligomers, i.e. step‐growth polymerization or ring‐opening polymerization (ROP), did not affect the T_m or ΔH_m of the blends significantly. Slightly higher ΔH_m values were, however, obtained, when linear oligomers were used. The results thus indicated that the T_m and ΔH_m of PLA stereocomplexes could be optimized, simply by selecting a D ‐LA oligomer having a suitable arm‐length and structure as the other blend component. The possibility to adjust the melting behavior of the stereocomplex blend is a significant advantage and could make PLA suitable for a wider range of products used at elevated temperatures. Copyright © 2010 John Wiley & Sons, Ltd.     

Sulfone/ester polymers containing pendent ethynyl groups

Sulfone/ester polymers containing pendent ethynyl groups were prepared by multistep and direct routes. Hydroxy-terminated sulfone oligomers(M _n = 2650 and 8890 g/mol) were reacted with diacid chlorides to yield high-molecular-weight polymers. In the multistep route, a pendent bromo group on the polymer was converted to an ethynyl group. In the direct route, the hydroxy-terminated sulfone oligomers were reacted with a stoichiometric amount of 5-(4-ethynylphenoxy)isophthaloyl chloride to yield high polymers. The pendent ethynyl groups on the sulfone/ester polymers were reacted in the 200 to 300°C range to provide branching and crosslinking. The resultant polymers exhibited higher T_gs and better resistance to chloroform than comparable polymers void of ethynyl groups. Films of the cured polymers displayed good mechanical properties. The synthesis and characterization of the monomer, oligomers, and polymers are discussed.     

Structural study of the smectic phases of several 4-cyanoalkoxybenzylidene-4'-alkylanilines

Abstract

A series of 4-cyanoalkoxybenzylidene-4'-alkylanilines (CN-nO. m; n = 3, 4, 6 and m = 4, 5, 8) have been synthesized. Their thermotropic liquid-crystalline polymorphism has been investigated using optical microscopy, differential scanning calorimetry and dilatometry. Nematic, smectic A and smectic B mesophases have been identified. The structure of the smectic phases has been studied with X-ray diffraction. Depending upon the compound and the temperature, the smectic layers have been found to be either single (A₁) or double (A₂) layers of molecules. Unexpected from a simple comparison with the well-known behaviour of the very similar nO. m smectogens, which belong to the class of the so-called symmetric and therefore exhibit single-layered smectics only, this structural behaviour has been interpreted to mean the importance of the dipole interactions of the terminal cyano groups. For CN-60.8, a transition has been detected at 64°C between the single and double layered structure.     

Aqueous solution self-assembly of polystyrene-b-poly(l-lysine) diblock oligomers

This paper reports on the dilute, aqueous solution self-assembly of two asymmetric polystyrene-b-poly(l-lysine) (PS_nPK_m) diblock oligomers with PS and PK number-average degrees of polymerization of eight, respectively, 40 and 60. The self-assembly of these diblock oligomers was investigated using static and dynamic light scattering in combination with analytical ultracentrifugation. Direct dissolution of the diblock oligomers in water generates a mixture of solution assemblies, part of which is cylindrical or rod-like in nature according to the light scattering experiments. This is surprising given the highly asymmetric nature of the diblock oligomers. Additional experiments in which the sample preparation conditions were varied and sample solutions subjected to a thermal treatment or prepared via dialysis from an organic/aqueous solution, however, suggest that direct dissolution results in kinetically trapped assemblies, which are (partially) converted into thermodynamically more favored assemblies upon varying the sample preparation conditions.     

Synthesis,characterization of Mannich base oligomers used with epoxy resin for glass fibre-reinforced laminates

This article aims to modify conventional epoxy resin by blending with four different Mannich base oligomers. These oligomers are similar to phenolic resin matrix and simultaneously function as amino curing agent for epoxy matrix. In this context, Mannich base oligomers were prepared, respectively, by Mannich polycondensation reaction of four phenols namely phenol, m-cresol, resorcinol and 1,5-dihydroxy naphthalene, respectively, with formaldehyde and piperazine in presence of acid catalyst. The resulting oligomers were characterized by elemental analysis, spectral studies (IR and NMR), number average molecular mass [`(M)]_n {\bar{M}}_{\rm n} estimated by non-aqueous conductometric titration and thermal stability by thermogravimetric analysis (TG). Each of these oligomers was used in resin matrix as a blending component for the modification of commercial epoxy resin for fabricating glass fibre reinforced laminates. Finally, these laminates were evaluated for their synergetic thermal stability, mechanical properties and chemical resistance to different reagents.     

Branching by reactive end groups. III. Synthesis,branching, and analysis of m‐ethynylphenol/p‐t‐butylphenol‐coterminated bisphenol a polycarbonates

The use of m‐ethynylphenol (m‐EP) and p‐t‐butylphenol (PTBP) as coterminators for bisphenol A polycarbonates (BA PCs) provided long‐chain‐branched PCs, partially crosslinked PCs, or both after the thermal reaction of the terminal m‐EP groups, depending on the molar ratio of the chain terminators. Linear m‐EP/PTBP PCs were prepared by solution phosgenation of BA and the two coterminators. Differential scanning calorimetry showed the onset of the m‐EP‐end‐group reaction at about 250 °C by the appearance of a reaction exotherm. The enthalpy (ΔH) of this reaction was roughly proportional to the amount of m‐EP in the PC and to an extent could be used to monitor the progress of the reaction and estimate its kinetics. A complete m‐EP‐end‐group reaction was evident from gel permeation chromatography analysis upon heating under N₂ to 380 °C for 10 min or 360 °C for 60 min. The amount, if any, of gel formed after the m‐EP‐end‐group reaction depended on X_EP; those PCs with a X_EP value less than or equal to 0.33 had little or no gel. The maximum X_EP that precluded the formation of gels after branching was estimated to be about 0.45–0.48. The molecular weight of m‐EP/PTBP PCs increased after branching, as evidenced by gel permeation chromatography analysis. Assuming that the terminal m‐EP groups had a statistical distribution on the polymer chain ends and that they underwent only homopolymerization, the average reacted m‐EP‐group functionality according to estimated gel‐point composition was about 2.8–3.0. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2352–2358, 2000     

Quantitative analysis of specific target DNA oligomers using a DNA-immobilized packed-column system

Although a DNA-immobilized packed-column (DNA-packed column), which relies on sequence-dependent interactions of target DNA or mRNA (in the mobile phase) with DNA probes (on the silica particle) in a continuous flow process, could be considered as an alternative platform for quantitative analysis of specific DNA to DNA chip methodology, the performance in practice has not been satisfactory. In this study, we set up a more efficient quantitative analysis system based on a DNA-packed column by employing a temperature-gradient strategy and DMSO-containing mobile phase. Using a temperature-gradient strategy based on T _m values of probe/target DNA hybridizations and DMSO (5%)-containing mobile phase, we succeeded in the quantitative analysis of a specific complementary target distinguishable from non-complementary DNA oligomers or other similar DNA samples. In addition, two different target DNA oligomers even with similar T _m values were separated and detected quantitatively by using a packed column carrying two different DNA probes.     

Dimer effect on fractional polycondensation of poly(p‐oxybenzoyl)

Selective preparation of poly(p‐oxybenzoyl) (POB) crystals was examined from the viewpoint of a dimer effect on fractional polycondensation. Four different copolymerization systems were chosen as the combinations of p‐acetoxybenzoic acid (p‐ABA), m‐acetoxybenzoic acid (m‐ABA), and their dimers. The crystals obtained from the copolymerization of the dimer of p‐ABA (p‐ABAD) and m‐ABA contained only 3.1 mol % of m‐oxybenzoyl moiety even at high content of m‐oxybenzoyl moiety in feed (χ_f) of 40 mol %. p‐Oxybenzoyl homo‐oligomers were more rapidly formed from p‐ABAD in the solution than from p‐ABA, and they were crystallized to form the crystals with segregating co‐oligomers. While co‐oligomers containing more m‐oxybenzoyl moiety were formed in the solution, afterward they were unable to be phase‐separated because of higher miscibility. The further polycondensation proceeded in the precipitated crystal, and finally the POB crystal was selectively formed. Lower polymerization temperature and concentration enhanced the fractionability, and the POB crystals containing less than 1 mol % m‐oxybenzoyl moiety were prepared at χ_f of 30 mol %, 270 °C, and a concentration of 0.5%. The dimer effect on the fractional polycondensation was clearly observed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1598–1606, 2008     

Polyarylates. IV. Synthesis of block copolymers via two-step interfacial polycondensation

A new method for preparing block copolyarylates via two-step interfacial polycondensation is proposed. First, oligomers with acid chloride end groups were obtained from interfacial polycondensation with a mole ratio of bisphenol A to diacid chloride(s) less than I. In the second step, two reaction systems containing various oligomers were mixed thoroughly and more bisphenolate was charged into this mixture. The synthesis of the block copolyarylates was justified from the viewpoint of statistics, and of differences in molecular weight between oligomers and block copolymers. These block copolyarylates could be differentiated from polyarylates through crystal-line behavior and solubility in m-cresol analyses.     

Synthesis,conformation and cytotoxicity of new,branched polymeric polypeptides containing hydrophobic amino acid or arginine moiety

In this paper we report on the synthesis and solution conformation of a new set of structurally related polycationic branched chain polypeptides (poly[Lys(X _i -dl-Ala _m )]) with hydrophobic (Ile, Nle, Val) or cationic (Arg) amino acids at the N-terminal end of the side chains as well as their cytotoxic effect on murine bone marrow derived macrophages. Solution conformation of the polypeptides was studied with circular dichroism spectroscopy under different conditions (pH, ionic strength). The results of these comparative studies indicate that a) polypeptides could adopt an ordered (mainly helical) conformation at physiological pH and salt concentration (pH 7.4, 0.2 M NaCl); b) the nature of side chain terminal amino acid (X) could determine under which conditions the ordered structure was formed. Thus, the solution conformation of branched polypeptides could be modulated by the selection of amino acid X under physiological conditions. All polypeptides with hydrophobic amino acid at the terminal position were essentially non-toxic on macrophages, whereas the polypeptide with terminal Arg proved to be markedly cytotoxic.