Synthesis and characterization of phenolic hydroxyl terminated phenylquinoxaline oligomers

The synthesis of phenylquinoxaline oligomers of predictable molecular weight and with phenolic hydroxyl functional end groups is reported. The synthetic procedure utilizes 4-hydroxybenzil as a substituted monofunctional monomer in a conventional PPQ synthesis to both control molecular weight and introduce the functional end groups. The molecular weights of the oligomers were determined by derivatization of the hydroxyl end groups with 3-(trimethylsilyl)propionyl chloride, followed by ¹H-NMR analysis. Comparison of the integration of the trimethylsilyl resonance to the aromatic resonances allowed calculation of the number average molecular weight. A plot of log(η) vs. log(M_n) correlated well with that reported for high molecular weight PPQ. The end groups influenced the solubility behavior of the oligomers in chlorinated solvents, possibly due to hydrogen bonding. The oligomers were chain-extendable to high molecular weight, confirming their suitability for utilization in copolymerizations to prepare phenylquinoxaline-based block copolymers.     

A facile and controllable synthesis of dual‐crosslinked elastomers based on linear bifunctional polydimethylsiloxane oligomers

Dual‐crosslinked supramolecular elastomers with the hybrid network consisting of hydrogen bonds and covalent bonds combine the reversibility of hydrogen bond and mechanical properties of covalent crosslinking network. In this article, isocyanate mixture is used as curing agent to prepare dual‐crosslinked elastomer based on bifunctional polydimethylsiloxane under mild condition. This method can effectively build up a hybrid network with the designed structure. A series of elastomers with same hydrogen bond density and variable covalent crosslinking degree are obtained. Swelling measurements and ¹H‐NMR spectra confirm the feasibility and controllability of curing method, the increasing of bifunctional isocyanate give rise to higher covalent crosslinking degree, improving the solvent resistance. The studies on viscoelastic property show that the introduction of an irreversible covalent crosslinking network stabilize the hybrid network, restrain the chain movement. The mechanical and self‐healing property studies reveal that the covalent crosslink significantly reinforce the whole network, while the reparable strength seems to mainly depend on the hydrogen bond density. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3760–3768     

The mixed-aldehyde synthesis of difunctional tetraarylporphyrins

The synthesis is reported of nine unsymmetrical, meso-substituted porphyrins. Among the compounds prepared are the following 5-(R)-10,15,20-tri-p-tolylporphyrins; R = 2,6-dinitrophenyl, 4-hydroxy-3-ethoxy-phenyl, 4-hydroxy-3-methoxy-5-nitrophenyl, 5-hydroxy-2-nitrophenyl and 4-hydroxy-3-nitrophenyl. Other porphyrins reported include 5-(2-(1-butoxy)phenyl)-15-(2-nitrophenyl)-10-15-di-p-tolylporphyrin and the two 5-(R)-10-15,20-tripropylporphyrins in which R = 2-nitrophenyl and 2-hydroxyphenyl. The disubstituted porphyrins offer a rational route to the synthesis of difunctional “tailed-porphyrins”.     

Curing chemistry of phenylethynyl‐terminated imide oligomers: Synthesis of 13C‐labeled oligomers and solid‐state NMR studies

4‐(Phenylethynyl‐α,β‐¹³C)phthalic anhydride (PEPA) and ¹³C‐labeled phenylethynyl‐terminated imide (PETI) oligomers were synthesized, and solid‐state ¹³C nuclear magnetic resonance (NMR) spectroscopy was used to determine the structure of cured oligomers. Solid‐state ¹³C NMR spectra were collected before and after thermal curing. Using solid‐state ¹³C NMR difference spectroscopy, several cure products were identified. The observed ¹³C NMR resonances were assigned to four different classes of cure products: aromatics, products from backbone addition (substituted stilbenes and tetraphenylethanes), polyenes, and cyclobutadiene cyclodimers. The effects of postcuring and oligomer chain length on the structure of the cured resins were examined. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3486–3497, 2000     

Effect of Buchwald-type ligands on platinum catalyzed hydrosilylation of vinyl terminated polydimethylsiloxane

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Kinetics and mechanism of epoxy oligomers curing

A review of new results concerning kinetics, thermodynamics and mechanism of epoxy oligomers curing with various nucleophilic agents (amines, phenols, carboxylic acids) has been made. The concept of the mechanism of such reactions is formulated on the basis of this study. Kinetic data obtained are interpreted within the framework of cyclic transition state. The addition of nucleophilic agent to epoxy ring is rather complicated. It results from preliminary formation of homo- and heteroassociates of reaction system components which finally form reactive cyclic heteroassociates. Reaction products are formed as a result of monomolecular rearrangement with synchronous transfer of electrons in the reactive cyclic heteroassociates.     

Synthesis of new polydimethylsiloxane-polyamide copolymers from phenylene-bis-5-oxazolones and aminopropyl-terminated polydimethylsiloxane oligomers

Alternating polydimethylsiloxane-polyamide block copolymers were prepared in dichloromethane or chloroform solution at room temperature from 3-amino-n-propyl-terminated polydimethylsiloxane oligomers and 2,2′-p-phenylenebis(4,4-dimethyl-5-oxazolone). Solution and thermal properties of the polymers were characterized.     

Condensation synthesis of high molecular polydimethylsiloxane

Synthesis approach to high molecular organosilicon polymers by condensation way merely starting from low molecular α,ω-dihydroxyoligomers was developed.     

Total synthesis of the aminopropyl functionalized ganglioside GM1

GM1 is a common ganglioside pentasaccharide present on mammalian cell surface.It has been shown to play important roles in cellular communications and initiation of β-amyloid aggregation.In order to synthesize GM1,an efficient synthetic route was developed via a [3+2] strategy.The GM3 trisaccharide acceptor bearing an azido propyl group at the reducing end was prepared using the traditional acetamide protected sialyl thioglycosyl donor,which gave better stereoselectivity than sialyl donors protected with trichloroacetamide or oxazolidinone.The glycosylation of the axial 4-hydroxyl group of GM3 by the disaccharide donor was found to be highly dependent on donor protective groups.Donor bearing the more rigid benzylidene group gave low glycosylation yield.Replacing the benzylidene with acetates led to productive coupling and formation of the fully protected GM1 pentasaccharide.Deprotection of the pentasaccharide produced GM1 functionalized with the aminopropyl side chain,which will be a valuable probe for biological studies.     

Silicon‐terminated telechelic oligomers by ADMET chemistry: Synthesis and copolymerization

Methoxydimethylsilane and chlorodimethylsilane‐terminated telechelic polyoctenomer oligomers (POCT) have been prepared by acyclic diene metathesis (ADMET) chemistry using Grubbs' ruthenium Ru(Cl₂)(CHPh)(PCy₃)₂ [Ru] or Schrock's molybdenum Mo(CH CMe₂Ph)(N 2,6 C₆H₃ i Pr₂)(OCMe(CF₃)₂)₂ [Mo] catalysts. These macromolecules have been characterized by FTIR, ¹H‐, ¹³C‐, and ²⁹Si‐NMR spectroscopy. The molecular weight distributions of these polymers have been determined by GPC and vapor pressure osmometry (VPO). The number‐average molecular weight (M_n) values of the telechelomers are dictated by the initial ratio of the monomer to the chain limiter. The termini of these oligomers (M_n = 2000) can undergo a condensation reaction with hydroxy‐terminated poly(dimethylsiloxane) (PDMS) macromonomer (M_n = 3300) [HO Si(CH₃)₂ O { Si(CH₃)₂O }_x  Si(CH₃)₃], producing an ABA‐type block copolymer, as follows: (CH₃)₃SiO [ Si(CH₃)₂O ]_x [ CHCH (CH₂)₆ ]_y [ OSi(CH₃)₂ ]_x OSi(CH₃)₃. The block copolymers were characterized by ¹H‐ and ¹³C‐NMR spectroscopy, VPO, and GPC, as well as elemental analysis, and were determined by VPO to have a M_n of 8600. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 849–856, 1999     

One-step continuous flow synthesis of aminopropyl silica-coated magnetite nanoparticles

One-step continuous flow synthesis was developed and applied for the preparation of amino propyl silica-coated nanoparticles (APSMNPs). This was accomplished in one step through continuous flow synthesis and amino propyl silica coating. Magnetite nanoparticles (MNPs) are generated in situ using a continuous flow synthesis system before being coated with amino propyl silica using tetraethyl orthosilicate (TEOS) condensation process and 3-aminopropyl triethoxysilane (APTES) condensation process in different ratios. The effect of the molar ratio of TEOS to APTES on the structure and physicochemical properties of the corresponding APSMNPs was examined by N₂ adsorption–desorption isotherm, transmission electron microscope (TEM), vibrating sample magnetometer (VSM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscope energy dispersive X-ray (SEM-EDX). This continuous flow process has advantages such as easy scalability, convenient production, easy control, an economical method with less time and reagents than traditional synthetic methods. It is a good choice for industrial production of APSMNPs.     

Control synthesis of isocyanate and alkoxy-silane terminated macromers

The kinetics of the reactions in bulk of 4,4′-dicyclohexyl methane diisocyanate (H₁₂ MDI) and 5-isocyanato-1,3,3-trimethylcyclohexylmethyl isocyanate or isophorone diisocyanate (IPDI) with benzylic alcohol (BZA) and α-hydroxy-ω-methyl ether-terminated polyethylene oxide PEO (M?_w = 350) were studied by size exclusion chromatography (SEC) and ¹³C nuclear magnetic resonance (¹³C-NMR). The substitution effect is exhibited in the case of H₁₂ MDI reactivity. The kinetic constants were calculated by a numerical method. The second-order kinetic mechanism was shown to be valid. In the IPDI case, the cycloaliphatic isocyanate group is shown to be more reactive than the aliphatic group in our conditions, without catalysis, in agreement with previous results from the literature, in our obtained by ¹H-and ¹³C-NMR without any catalyst. The reactivity ratio is found to be on the order of 3. This difference in reactivity of the two isocyanate groups is used for the control synthesis of isocyanate and alkoxy-silane-terminated macromers.     

Kinetics studies of nano-structured iron catalyst in Fischer-Tropsch synthesis

Kinetic parameters of nano-structured iron catalyst in Fischer-Tropsch synthesis (FTS) were studied in a wide range of synthesis gas conversions and compared with conventional catalyst. The conventional Fe/Cu/La catalyst was prepared by co-precipitation of Fe and Cu nitrates in aqueous media and Fe/Cu/La nanostructure catalyst was prepared by co-precipitation in a water-in-oil micro-emulsion. Nano-structured iron catalyst shows higher FTS activity. Kinetic results indicated that in FTS rate expression, the rate constant (k) increased and adsorption parameter (b) decreased by decreasing the catalyst particle size from conventional to nano-structured. Since increasing in the rate constant and decreasing in the adsorption parameter affected the FTS rate in parallel direction, the particle size of catalyst showed complicated effects on kinetic parameters of FTS reaction.     

Kinetics of thermal depolymerization of trimethylsiloxy end-blocked polydimethylsiloxane and polydimethylsiloxane-N-phenylsilazane copolymer

The thermal degradation of Me₃SiO end-blocked polydimethylsiloxane (eb-PDMS) and polydimethylsiloxane-N-phenylsilazane (eb-PDMS–NPhSz) copolymer was studied. For both polymers relative degree of polymerization (DP /DP ₀) as a function of conversion (1 – W/W₀) data were obtained. For eb-PDMS the results were consistent with a mechanism involving a rate determining random siloxane bond cleavage initiation step followed by a rapid and complete depropagation of the active fragments evolving volatile cyclic oligomers. Rate constants (k) for initiation were obtained at four temperatures from plots of DP ^?1 vs. time. An Arrhenius activation energy of approximately 80 kcal/mol was determined and is consistent with a SiOSi scission transition state. The degradation of eb-PDMS–NPhSz appears to follow the same depolymerization process evolving cyclic oligomers. Although DP /DP ₀ vs. C data suggest a random cleavage–complete depolymerization mechanism, an Arrhenius plot suggests a more complex degradation mechanism. The role of impurities as degradation catalysts is discussed.     

Efficient synthesis of thioamide terminated molecular wires

Bis-thioamide terminated ‘molecular wires’ are formed in a high yield under mild conditions from readily synthesised bis-nitrile terminated molecules and aqueous ammonium sulfide in DMF.     

Kinetics of polymeric network synthesis via free-radical mechanisms - polymerization and polymer modification

The kinetics of polymeric network formation via free radical mechanisms is an attractive research area because there are many phenomena which are not well understood and in addition, the commercial potential for crosslinked systems is great. Recently, a large research/development program was initiated at the McMaster Institute for Polymer Production Technology (MIPPT) to investigate the fundamentals and applications of polymeric network, in particular, the kinetics of synthesis via free-radical mechanisms and network characterization. The research on crosslinking involved both theoretical developments and experimentation. Herein is provided a comprehensive summary of this work. In the experimental polymerization, two comonomers, methyl methacrylate (MMA) / ethylene glycol dimethacrylate (EGDMA) and acrylamide (AAm) / N,N-methylene bisacrylamide (Bis), as model systems were studied in considerable detail. Measurements included: monomer conversions, radical concentrations, sol/gel fractions, crosslink densities (equilibrium swelling and swollen-state ¹³C-NMR) over the entire range of divinyl monomer levels as a function of polymerization time. In the polymer modification, high density polyethylenes were crosslinked using peroxides and γ-radiation. For this system, crosslinking and chain scission occur simultaneously. In the theoretical studies, it was shown that in general, network formation by free-radical mechanisms is highly irreversible requiring that the classical equilibrium gelation theories after Flory/Stockmayer be generalized. The general model which was developed using the pseudo-kinetic rate constant method predicts the existence of a crosslink density distribution (crosslink density of a primary polymer chain depends on its birth time) with a variance which can vary widely depending on network synthesis conditions.     

Organochromiumoxane yttriumoxane alumoxane oligomers: synthesis,properties, pyrolysis

Russian Chemical Bulletin - Ceramic-forming organochromiumoxane yttriumoxane alumoxane oligomers with a given molar ratio of Al: Cr and Al: Y, hydrolytically stable in air, have been synthesized....     

Synthesis and properties of multiblock copolymers based on polydimethylsiloxane and polyamides from dicarboxylic acid and diisocyanate terminated functionalities

Polydimethylsiloxane (PDMS)–polyamide multiblock copolymers were successfully synthesized via diisocyanate route by two different procedures, i.e., the one-step and two-step methods, In the two-step method, α, ω-diisocyanate-terminated polyamide oligomers, which were prepared in situ from a mixture of isophthalic acid (IPA) and azelaic acid (AZA) with 4,4′-methylenedi (phenyl isocyanate) (MDI) in 1,3-dimethyl-2-imidazolidone (DMI) in the presence of 3-methyl-1-phenyl-2-phosopholene 1-oxide catalyst, were reacted with α, ω-bis (10-carboxydecyl) polydimethylsiloxane (PDMS-diacid) leading to the formation of multiblock copolymers. In the one-step method, the reaction components, MDI, IPA, AZA, and PDMS-diacid were reacted all together in DMI in the presence of the catalyst. These polymerizations gave multiblock copolymers having inherent viscosities in the range of 0.36–1.12 dL/g in N,N-dimethylacetamide (DMAc). These multiblock copolymers were soluble in amide-type solvents, and transparent (or translucent) and ductile films could be cast from the solutions in a mixture of DMAc and bis(2-ethoxyethyl) ether. The multiblock copolymers prepared by the two-step method had better-defined, microphase-separated morphology than those obtained by the one-step method. The mechanical properties of PDMS–polyamide multiblock copolymer films were found to be highly dependent on the PDMS content; the tensile strength and modulus of the films decreased with increasing the PDMS content.