Acetyl End Groups Research Articles

Modification of Molecular Conductance by in Situ Deprotection of Thiol-Based Porphyrin.

Acetylthio-protected free base porphyrins are used to form scanning tunneling microscope-molecular break junctions. The porphyrin molecules are deprotected in situ, before the self-assembly. Two types of molecular junctions are formed in the junctions: Au-S-Por-SAc-Au and Au-S-Por-S-Au. Lower conductance values and higher conductance values are observed. Computational modeling attributes the lower conductance to the Au-S-Por-SAc-Au junctions and the higher conductance to the Au-S-Por-S-Au junctions. First-principles calculation suggests that the reduced conductance in the protected porphyrin originates from the presence of the acetyl end groups (-COCH3), rather than from the elongation of the sulfur-gold (S-Au) bonds at the tip-molecule interface.

Effect of a Scaffold Fabricated Thermally from Acetylated PLGA on the Formation of Engineered Cartilage

A MHDS has been employed to fabricate 3D scaffolds from PLGA with acetyl endgroups to achieve in vivo regeneration of cartilage tissue. The fabricated acetylated-PLGA scaffold showed open pores and interconnected structures. Rabbit chondrocytes were seeded on the PLGA scaffolds and transplanted immediately into subcutaneous sites of athymic mice. Chondrocytes transplantation with untreated PLGA scaffolds served as a control. Histological analysis of the implants at 4 weeks with H&E staining and alcian blue staining revealed higher extracellular matrix and GAG expression at the neocartilage in the PLGA-6Ac scaffolds than that of the PLGA-6OH scaffold group. This endgroup-modified scaffold may be useful for successful cartilage tissue engineering in orthopedic applications.

Levocetirizinium dipicrate.

There are two cation–dianion pairs in the asymmetric unit of the title compound, C21H27ClN2O3 2+·2C6H2N3O7 − {systematic name: 1-[2-(carb­oxy­meth­oxy)eth­yl]-4-[(R)-(4-chloro­phen­yl)phenyl­meth­yl]piperazine-1,4-diium bis­(2,4,6-trinitro­phenol­ate)}. The piperazine group in the levocetirizinium cation is protonated at both N atoms. The acetyl end groups form R 2 2(8) hydrogen-bonded motifs with adjacent cations. Each picrate anion inter­acts with the proponated N atom in the cation through a bifurcated N—H⋯O hydrogen bond, forming R 1 2(6) ring motifs. Strong and weak inter­molecular N—H⋯O and strong O—H⋯O hydrogen bonds, and weak π–ring and π–π stacking inter­actions [centroid–centroid distance = 3.7419 (14) Å] dominate the crystal packing, creating a three-dimensional supra­molecular structure.

Group Contribution Theory for the Gibbs Energy of Solutions of Polyethers

The Gibbs energies of different oligoethers (oligomers of tetrahydrofuran and ethylene oxide and a block cooligomer of these ethers) with hydroxyl and acetyl end groups in tri- and tetrachloromethane are obtained by vapour pressure measurements. A group contribution theory, based on a quasichemical equilibrium between contacting segment surfaces, which was used so far only for calculating mixing enthalpies, is extended to Gibbs energies. The Gibbs energies predicted with this theoretical approach show a good agreement with the measured data of the tested polymer solutions. With this theory it is not only possible to describe but even to predict gaps in the mixing behaviour of polymer solutions.

Matrix-assisted laser desorption/ionization, fast atom bombardment and plasma desorption mass spectrometry of polyethylene glycol esters of (2-benzothiazolon-3-yl)acetic acid

Fast atom bombardment (FAB), matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) and plasma desorption (PD) mass spectra of newly synthesized polyethylene glycols (PEGs), (M(w) 600-4000 Da) chemically modified with biologically active (2-benzothiazolon-3-yl)acetyl end-groups are described (products 1-6). The spectra were also used for the determination of the molecular mass characteristics (number average (M(n)) and weight average (M(w)) molecular masses) of the initial and modified PEGs. As expected, M(n) and M(w) of the modified samples are higher than those of the non-modified samples. However, it is shown that molecular mass dispersity (determined by the comparison of the polydispersity indices (PDI = M(w)/M(n)) of both types of PEGs) essentially do not change during this modification. The FAB mass spectra, together with molecular species, show the presence of abundant [M + Na](+) ions of product 1 and [M + Na + H](+) species of 2 and 3, and [M + Na + 2H](+) of product 4. Two main series of fragment ions, derived from the cleavage of the ether bonds, are observed. The number fractions of the molecular adduct ions and fragment adduct ions, determined from the FAB and PD mass spectra of the modified PEGs, are compared. The MALDI-TOF mass spectra of compounds 1-6 show the presence of two series of polymers. The most abundant peaks are due to [M + Na](+) and [M + K](+) ions originating from the polymers, in which the two terminal hydroxyl groups of PEGs are esterified with (2-benzothiazolon-3-yl)acetic acid. The less abundant peaks are due to the monosubstituted polymers.

Determination of End Groups of Synthetic Polymers by Matrix-Assisted Laser Desorption/Ionization: High-Energy Collision-Induced Dissociation

Matrix-assisted laser desorption/ionization has been combined with high-energy collision-induced dissociation for the analysis of poly(ethylene glycols) with butanoyl, benzoyl and acetyl end groups, using novel technology comprising a magnetic-sector mass spectrometer and ion buncher with an in-line quadratic-field ion mirror. High-energy (>8 keV) collision-induced dissociation facilitated unambiguous end-group determination of these polymers, providing masses of end groups and structural information. The high-energy collision-induced dissociation also provided information regarding repeat units.

A morphological investigation of thermosets toughened with novel thermoplastics. I. Bismaleimide modified with hyperbranched polyester

The morphology of a bismaleimide (BMI) toughened with a thermoplastic hyperbranched aliphatic polyester (HBP) was studied by scanning electron microscopy (SEM). The effect of thermoplastic architecture, molecular weight, and end group on the size and arrangement of the dispersed phase was investigated and compared with the thermoset fracture toughness. SEM micrographs showed that higher molecular weight HBP formed roughly spherical dispersed domains of up to ∼ 60 μm, which contained BMI inclusions. Lower molecular weight HBP formed spherical dispersed thermoplastic domains, with diameters up to ∼ 10 μm with no BMI inclusions. A low molecular weight linear polyester with a repeat unit structure, which was similar to that of the HBP, was prepared and used as a control. Within error, BMI toughened with the linear control yielded the same fracture toughness as the best values obtained with HBP-modified BMI, but the morphology differed. The linear polyester phase separated into particles with a larger average diameter and also possessed some phase-inverted regions. End group effects were studied by modifying the hydroxy-terminated HBP to unreactive nitrophenyl, phenyl, and acetyl end groups. The nitrophenyl-terminated HBP did not phase separate from the thermoset, whereas the nonpolar phenyl- and acetyl-terminated HBP phase separated to form small (≤1 μm and ∼ 2 μm, respectively) spherical domains. Some comparisons were made to other results with HBP thermoplastics in BMI and epoxy thermosets. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1065–1076, 1999

Mixing enthalpies of polyethers in solvents of various polarity treated with a group contribution theory

The mixing enthalpies of different oligoethers (oligomers of tetrahydrofuran and ethylene oxide and a block cooligomer of these ethers) with hydroxyl and acetyl end groups in various solvents (2-propanol, tri- and tetrachloromethane) are obtained by microcalorimetry. An extended group contribution theory, based on a quasichemical equilibrium between contacting segment surfaces, is applied successfully for the description and prediction of the mixing enthalpies. The theory can be used for every kind of molecular interaction, for polar and non-polar interactions as well as for hydrogen bridges. In addition, it is possible to apply the theory to mixing enthalpies of polymer blends.

Synthesis and Characterization of Poly(Oxyethylene)S with (2-Benzoxazolon-3-yl)Acetyl End-Groups. Complex Formation with Polycarboxylic Acids

Chemical modification of poly(oxyethylene)s (MW from 600 Da to 3000 Da), leading to the obtaining of poly(oxyethylene)s with (2-benzoxazolon-3-yl)acetyl endgroups, is described. The corresponding diesters were synthesized in high yields-70—84% and degree of esterification-82—92% under mild conditions in the presence of dicyclohexylcarbodiimide and 4-dimethylaminopyridine as catalyst. The diesters were characterized by 1H-NMR, 13C-NMR and IR spectra, and SEC analysis. The relatively narrow molecular weight distribution was retained in the process of chemical modification. The complex formation between polyacrylic or polymeth-acrylic acids and (2-benzoxazolon-3-yl)acetyl derivatives of poly -(oxyethylene)s was studied in dilute aqueous solutions by potentio-metric titration and viscometry. The presence of (2-benzoxazolon-3-yl)acetyl end groups attached to the poly(oxyethylene)s chains results in a significant decrease of the critical poly(oxyethylene) chain length necessary for the formation of stable polymer-polymer complexes.

Heterogenized polymetallic catalysts. Part I. Catalytic air oxidation of 3,5-di- t-butylphenol by Cu(II) and Fe(III) complexed to a polyphenylene polymer containing β-di-and tri-ketone surface ligands

Catalysis preparation involves the cyclic trimerization polymerization of acetylated aromatics. The polymer is coated on a high surface area support, Celite, and cured to give insoluble high molecular weight polymer. Reaction of the remaining acetyl end groups with base and methyl acetate gave β-diketone groups on the surface of the polymer. A second reaction with base and methyl acetate places β-triketones on the surface. The β-triketones can bind two metal ions in a known geometry. The chemically modified surfaces containing β-diketone and β-triketone surface ligands were reacted with Cu(OAc) 2 and FeCl 3 to give mono- and bi-metallic surface complexes. The oxidation of 3,5-di- t-butylcatechol was studied with all the surfaces. The monometallic catalysts gave only the ortho-quinone as product. The bimetallic catalysts absorbed about twice as much dioxygen as the monometallic catalysts and gave ring cleaved products. Both gave induction periods before dioxygen uptake began. With the bimetallic catalysts the dioxygen uptake stopped at about the ratio: 2 O 2 1 catechol . This is twice as much dioxygen as that required for ring cleavage so H 2O 2 may be the dioxygen reduction product rather than water. The monomeric Cu(OAc) 2 dioxygen uptake curve reached a maximum and then released gas. This could result from Cu(II) catalyzed decomposition of H 2O 2.

Effect of IR-laser radiation on crosslinking and some physical and mechanical properties of a composition surface

A study was made of three-dimensional structures formed in surface layers of polymers obtained from a phenylene type oligomer with acetyl end groups by the action of IR laser radiation. As a result of treating the surface of the composition surface in the field of laser radiation the content of sol fraction decreased; parameters of the network structure of the binder were calculated. The effect of network density variation on physical and mechanical properties of the surface was examined.

Synthesis of oligophenylenes based on ketals of acetyl aromatic compounds and some methods leading to crosslinking of the oligomers

“Blocked” oligophenylnenes without ketal or acetyl endgroups have been synthesized by polycyclocondensation of ethyl ketals of mono- and diacetyl aromatic compounds, using an excess of the ketal of acetophenone. These products were then hardened by p-xylylene glycol telomer. Oligophenyleness containing biphenylene groups were prepared, using as monomers ketals of 2-acetyl- and 2,6-diacetylbiphenylene. Hardening of these oligomers takes place without liberation of any volatile products, and results in polymers that have high heat resistance and thermal stability.

Study of the high-temperature moulding of the polyphenylene prepolymer based on 4,4′-diacetyldiphenyl oxide

A study has been made of the press moulding of a polyphenylene prepolymer based on 4,4′-diacetyldiphenyl oxide. It was found that two main processes take place during formation of the phenylene type polymer structure. The reaction taking place at 250–300° results in transformation of ketal and acetyl endgroups into dypnone fragments leading to formation of polymer with a partially crosslinked structure. Further transformations of acetyl and dypnone groups take place during high temperature moulding (450°) through cyclopolycondensation, as well as dehydration and diphenylation processes resulting in the formation of polyphenylene type three-dimensional structures.

Haloaldehyde polymers, 15. Stabilization of polychloral by posttreatment

AbstractPolychloral prepared by anionic polymerization has primarily alkoxide endgroups as the living terminal ends. The initial endgroups depend on the type of nucleophile used for the initiation. Alkoxide‐terminated polychloral degrades to monomer on heating to slightly above 100°C or on extraction with methanol or acetone. Programmed DTG shows a degradation rate maximum (MDT) near 150°C. Terminations of the polymer endgroups were observed when the polymer was allowed to stand for long periods of time before workup. The type and amount of stabilization depends on the cation and residual monomer. With HCI the alkoxide ends can be protonated to give hydroxyl terminated polychloral, which is stable to extraction and has an MDT of 220°C. Acylation or alkylation as posttreatments could not be shown to produce the expected acyl‐ or alkyl endcapped polychloral, but posttreatment with acetyl chloride produced partially stable polymer (one MDT higher than 300°C) without detectable acetyl endgroups. The most effective posttreatment is with PCl5/CCl4 which gives highly stabilized polychloral with an MDT near 350°C. The treatment was only effective in thin sections of polymer and appeared to have introduced a chlorine endgroup.

Polyphenylenes from diacetylarylenes or their ketals, containing reactive cyanomethylcinnamate and dicyanopropylidene groups

In order to modify the crosslinking of polyphenylene prepolymers, obtained by copolycondensation of di- and monoacetyl aromatic compounds or their ketals, the residual acetyl end groups were replaced by cyanomethylcinnamate or dicyanopropylidene groups, of the general formula −C(CH 3)=C(CN)R (where R=CN or COOC 2H 5). This was achieved by reacting the prepolymers with ethyl cyanoacetate or malonodinitrile. The structure of the resulting polymers was confirmed by IR-spectroscopic and elementary analysis. The ability of ethyl 2-cyano-3-methylcinnamate, taken as a model of the prepolymer end groups, to polymerize through the CN group or the substituted double bond, was examined.

Chemical transformations of polyphenylenes based on acetyl-aromatic compounds (acephenes)

Chemical analysis of polyphenylenes synthesized by polycyclocondensation of p-diacetylbenzene and 4,4-diacetyldiphenyl oxide with acetophenone (acephenes) has revealed the presence in polymer of defective diphnone fragments and end ketal and acetyl groups. In acephenes oxidized by KMnO4, diphnone fragments and end ketal groups are oxidized to carboxyl groups. Oxidized acephene (Mn = 6000) contains about 6 carboxyl and 6 acetyl endgroups. The thermal and thermomechanical characteristics of the acephenes before and after oxidation have been investigated and the influence of defective structures on these characteristics has been demonstrated.

Molecular weight distribution in anionic polycaprolactam

We examined the molecular weight distribution in polycaprolactam obtained at 180 with sodium hydride and acetylcaprolactam. The polymer was fractionated in a continuous procedure with phenol/water system at 70. Titration of acetyl end groups in the various polymer fractions led to values of M n. At all stages of the polymerization, the molecular weight distribution seems very narrow in agreement with the step-addition process of the lactam molecules. Fractionations of samples, made with the same catalyst system but above the polymer melting point (220°), were also carried out. In this case, the method just mentioned could not be used to find M n because of the presence of free amino end groups. According to recent theories, this could indicate the presence of branched products together with smaller linear molecules. Indirect measurements suggested a progressive broadening of the distribution. This effect suggests the occurrence of transamidation reactions in the molten state.

The effect of stabilizing additives in the degradation of polyformaldehyde

2137 (2) It is shown that the thermal-oxidative decomposition of both types of PFA is an apparent first-order reaction with respect to oxygen over a wide range of oxygen concentrations (up to 809/0 [O2] ). (3) The suggestion is made that the polymeric active centres are of two types. (4) It is noted that there is a relationship between the degree of oxidative degradation and the extent of random rupture of the polymer chain for the acetylated polymer for any method of initiation of degradation. (5) Differences were found in the rates of formation of formic acid during the degradation of PFA with hydroxyl and acetyl end groups, in complete agreement with theoretical concepts of the mechallism of formation of this product.