Mechanism of Rubber Coagent Peroxide Cure System

1970 ◽  
Vol 43 (3) ◽  
pp. 613-623 ◽  
Author(s):  
J. A. Cornell ◽  
A. J. Winters ◽  
L. Halterman
Keyword(s):  
Methyl Ester ◽  
Hydrogen Abstraction ◽  
Addition Product ◽  
Side Chain ◽  
Dicumyl Peroxide ◽  
Experimental Conditions ◽  
Branched Hydrocarbons ◽  
Similar Product ◽  
Ethylene Dimethacrylate ◽  
Single Addition

Abstract Peroxide vulcanization mechanisms of curing natural and synthetic rubbers have been extensively investigated. Little work has been reported on the use of polyfunctional monomers as coagents. Utilizing a model hydrocarbon, decane, with dicumyl peroxide and a methacrylate ester monomer, the mechanism for vulcanization in polyethylene is postulated. In the absence of the monomer, the dicumyl peroxide has been shown to abstract a hydrogen from the backbone —CH2— to form a radical. This radical terminates with another radical similarly formed to produce a crosslink. With n-decane, C20 dimers are formed. On the addition of a methacrylate ester, the hydrogen abstraction appears to still take place, but the methacrylate is added to the radical. This is not a typical polymerization initiation since the chain length of the methacrylate side chain is extremely short. Depending on the concentration, it may be limited to a single addition product. Using methyl methacrylate, infrared and nuclear magnetic resolution spectra confirm this addition product under experimental conditions. A similar product was also obtained when ethylene dimethacrylate was reacted, hydrolyzed, and re-esterified to the methyl ester. Comparative products using branched hydrocarbons indicated that tertiary hydrogens were also abstracted. Comparison of IR spectra obtained in a peroxide coagent vulcanization of polyethylene indicated the lack of polymethacrylate absorption. This curve is similar to that obtained with the decane, but quite different from that obtained with a mixed polymer of polyethylene and polymethyl methacrylate or polyethylene dimethacrylate.

A Reinvestigation of the Deceptively Simple Reaction of Toluene with ●OH, and the Fate of the Benzyl Radical. I. a Combined Thermodynamic and Kinetic Study on the Competition Between ●OH Addition and Hydrogen Abstraction Reactions.

2019 ◽  
Author(s):  
Zoi Salta ◽  
Agnie M. Kosmas ◽  
Marc E. Segovia ◽  
Martina Kieninger ◽  
Oscar Ventura ◽  
...  
Keyword(s):  
Density Functional ◽  
Room Temperature ◽  
Hydrogen Abstraction ◽  
Reaction Rates ◽  
Composite Model ◽  
Alternative Mechanism ◽  
Radical Intermediate ◽  
Experimental Conditions ◽  
Methyl Group ◽  
Benzyl Radical

This work reports density functional and composite model chemistry calculations performed on the reactions of toluene with the hydroxyl radical. Both experimentally observed H-abstraction from the methyl group and possible additions to the phenyl ring were investigated. Reaction enthalpies and heights of the barriers suggest that H-abstraction is more favorable than ●OH addition to the ring. The calculated reaction rates at room temperature and the radical-intermediate product fractions support this view. This is somehow contradictory with the fact that, under most experimental conditions, cresols are observed in a larger concentration than benzaldehyde. Since the accepted mechanism for benzaldehyde formation involves H-abstraction, a contradiction arises that begs for an explanation. In this first part of our work we give the evidences that support the preference of hydrogen abstraction over ●OH addition and suggest an alternative mechanism which shows that cresols can actually arise also from the former reaction and not only from the latter.

A Reinvestigation of the Deceptively Simple Reaction of Toluene with ●OH, and the Fate of the Benzyl Radical. I. a Combined Thermodynamic and Kinetic Study on the Competition Between ●OH Addition and Hydrogen Abstraction Reactions.

2019 ◽  
Author(s):  
Zoi Salta ◽  
Agnie M. Kosmas ◽  
Marc E. Segovia ◽  
Martina Kieninger ◽  
Oscar Ventura ◽  
...  
Keyword(s):  
Density Functional ◽  
Room Temperature ◽  
Hydrogen Abstraction ◽  
Reaction Rates ◽  
Composite Model ◽  
Alternative Mechanism ◽  
Radical Intermediate ◽  
Experimental Conditions ◽  
Methyl Group ◽  
Benzyl Radical

This work reports density functional and composite model chemistry calculations performed on the reactions of toluene with the hydroxyl radical. Both experimentally observed H-abstraction from the methyl group and possible additions to the phenyl ring were investigated. Reaction enthalpies and heights of the barriers suggest that H-abstraction is more favorable than ●OH addition to the ring. The calculated reaction rates at room temperature and the radical-intermediate product fractions support this view. This is somehow contradictory with the fact that, under most experimental conditions, cresols are observed in a larger concentration than benzaldehyde. Since the accepted mechanism for benzaldehyde formation involves H-abstraction, a contradiction arises that begs for an explanation. In this first part of our work we give the evidences that support the preference of hydrogen abstraction over ●OH addition and suggest an alternative mechanism which shows that cresols can actually arise also from the former reaction and not only from the latter.

Synthesis of oxytocin analogues modified in the tripeptide side-chain by condensation of aminoterminal linear hexapeptide with the carboxyterminal tripeptide

1979 ◽  
Vol 44 (1) ◽  
pp. 275-287 ◽  
Author(s):  
Jan Hlaváček ◽  
Tomislav Barth ◽  
Karel Bláha ◽  
Karel Jošt
Keyword(s):  
Methyl Ester ◽  
Side Chain ◽  
Glycine Methyl Ester

For the synthesis of oxytocin (Ia) analogues modified in the carboxyterminal part of the molecule, a method based on the condensation of protected aminoterminal hexapeptide with tripeptides by the action of dicyclohexylcarbodiimide and pentafluorophenol in the presence of 1-hydroxybenzotriazole was devised. Using this method [7-[U-13C]proline]oxytocin (Ib), des-9-glycine-oxytocin (Ic) and methyl ester of oxytocinoic acid ([9-glycine methyl ester]oxytocin) (Id) were prepared.

scholarly journals Unusual Structural Features in the Adduct of Dirhodium Tetraacetate with Lysozyme

2021 ◽  
Vol 22 (3) ◽  
pp. 1496
Author(s):  
Domenico Loreto ◽  
Giarita Ferraro ◽  
Antonello Merlino
Keyword(s):  
Anticancer Agents ◽  
Structural Features ◽  
Side Chain ◽  
Side Chains ◽  
Valuable Insight ◽  
Experimental Conditions ◽  
Egg White Lysozyme ◽  
Potential Applications ◽  
Model Protein ◽  
Hen Egg White

The structures of the adducts formed upon reaction of the cytotoxic paddlewheel dirhodium complex [Rh2(μ-O2CCH3)4] with the model protein hen egg white lysozyme (HEWL) under different experimental conditions are reported. Results indicate that [Rh2(μ-O2CCH3)4] extensively reacts with HEWL:it in part breaks down, at variance with what happens in reactions with other proteins. A Rh center coordinates the side chains of Arg14 and His15. Dimeric Rh–Rh units with Rh–Rh distances between 2.3 and 2.5 Å are bound to the side chains of Asp18, Asp101, Asn93, and Lys96, while a dirhodium unit with a Rh–Rh distance of 3.2–3.4 Å binds the C-terminal carboxylate and the side chain of Lys13 at the interface between two symmetry-related molecules. An additional monometallic fragment binds the side chain of Lys33. These data, which are supported by replicated structural determinations, shed light on the reactivity of dirhodium tetracarboxylates with proteins, providing useful information for the design of new Rh-containing biomaterials with an array of potential applications in the field of catalysis or of medicinal chemistry and valuable insight into the mechanism of action of these potential anticancer agents.

FREE RADICALS OF BIOLOGICAL INTEREST: PART II. ELECTRON SPIN RESONANCE (ESR) SPECTRA OF 2537 A IRRADIATED AMINO ACIDS

1967 ◽  
Vol 45 (12) ◽  
pp. 1831-1839 ◽  
Author(s):  
W. F. Forbes ◽  
P. D. Sullivan
Keyword(s):  
Amino Acids ◽  
Electron Spin Resonance ◽  
Electron Spin ◽  
Hydrogen Abstraction ◽  
Esr Spectra ◽  
Side Chain ◽  
Biological Interest ◽  
Spin Resonance ◽  
Cyclohexadienyl Radical ◽  
Secondary Radical

Polycrystalline amino acids, when irradiated with 2537 Å light, afford a variety of electron spin resonance signals. These signals are generally stable at room temperature for relatively long periods of time. For a number of the spectra obtained, there is evidence that more than one radical species contributes to the observed spectra. The signals obtained frequently differ from those obtained on exposure to ionizing radiation. The postulated species formed can often be visualized as being formed by effective hydrogen abstraction from the alkyl-substituted tertiary carbon atom or from the —OH, —SH or —NH group contained in the side chain. For L-phenylalanine a secondary radical is obtained, which is ascribed to a cyclohexadienyl radical.

scholarly journals On active chlorine

1934 ◽  
Vol 147 (861) ◽  
pp. 309-332
Keyword(s):  
Acetic Acid ◽  
Electric Discharge ◽  
Closed System ◽  
Surface Characteristics ◽  
Chemical Activity ◽  
Active Chlorine ◽  
Side Chain ◽  
Experimental Conditions ◽  
Electrically Charged ◽  
Atomic Chlorine

Evidence has long been available that a modification of chlorine of abnormal chemical activity is produced by an electric discharge in this gas. The greater part of the earlier work was conducted under very badly defined experimental conditions which render the various researches difficult to correlate, but the properties of this “active chlorine” may be summarized as follows:— ( a ) It possesses abnormal bleaching powers, and can react in the cold and the dark with acetic acid to form the monochlor derivative; with benzene it gives the hexachloride, while with toluene the combination occurs mainly in the side chain. ( b ) They yield of active gas is enhanced by irradiation of the discharge, by cooling, and by the presence of moisture. ( c ) It has a life period of at least 75 secs, but is destroyed by heating, passage through water, and the action of another discharge; it is not electrically charged and does not possess as abnormal density.§ ( d ) Since only very small changes in pressure follow passage of a discharge in a closed system containing chlorine, the active modification does not presumably represent an associated molecule such as Cl 3 .‖ Reference may also be made to papers by Venkataramaiah¶ who gives a number of chemical reactions of chlorine activated in various ways but his results must be treated with reserve (see Germann, idem ., p. 951). In the present experiments we have endeavoured to repeat and extend the earlier studies under better defined conditions, and conclude that the phenomena are very probably due to a trace of atomic chlorine whose behaviour is markedly dependent upon the surface characteristics of the apparatus.

Amidation of methyl ester side chain bearing poly(2-oxazoline)s with tyramine: a quest for a selective and quantitative approach

2019 ◽  
Vol 10 (8) ◽  
pp. 954-962 ◽  
Author(s):  
Joachim F. R. Van Guyse ◽  
Maarten A. Mees ◽  
Maarten Vergaelen ◽  
Mathijs Baert ◽  
Bart Verbraeken ◽  
...  
Keyword(s):  
Methyl Ester ◽  
Quantitative Approach ◽  
Side Chain

Three new amidation approaches are evaluated to incorporate tyramine on methyl ester functional poly(2-oxazolines).

Influence of the structure of new poly(amide-imide)s on their optical properties

e-Polymers ◽  
2004 ◽  
Vol 4 (1) ◽  
Author(s):  
Danuta Sęk ◽  
Eugenia Grabiec ◽  
Anna Sobolewska ◽  
Andrzej Miniewicz
Keyword(s):  
Laser Light ◽  
Side Chain ◽  
Intersection Angle ◽  
Experimental Conditions ◽  
Time Constants ◽  
Polarized Beams ◽  
Azo Group ◽  
Linearly Polarized ◽  
One Step ◽  
Kinetics Of

Abstract Two classes of poly(amide-imide)s with mono- and bisazoaromatic chromophores in the side chain have been synthesized using one-step hightemperature polycondensation. The influence of the structures of the macromolecules on their properties was investigated. Preliminary results of the kinetics of holographic grating recording using 514.5 nm Ar+ laser light for chosen poly(amideimide) films are presented. The gratings were recorded using two linearly polarized beams with s-s or s-p configurations. For comparative purposes all experimental conditions (light intensity, two-beams intersection angle) were kept unchanged. It was found that time constants of grating build-up were significantly larger for polymers containing a chromophore with two azo groups when compared with the same polymers having a single azo group. On the other hand diffraction efficiencies were lower for polymers containing a chromophore with two azo groups than with a single azo group.

Volume phase transition induced by temperature sensitive DL-amino acid methyl ester side chain based copolymer gels

2000 ◽  
Vol 3 (3) ◽  
pp. 381-387 ◽  
Author(s):  
Akihiro Hiroki ◽  
Hideaki Iwakami ◽  
Masaru Yoshida ◽  
Takeshi Suwa ◽  
Masaharu Asano ◽  
...  
Keyword(s):  
Phase Transition ◽  
Amino Acid ◽  
Methyl Ester ◽  
Acid Methyl Ester ◽  
Side Chain ◽  
Temperature Sensitive ◽  
Volume Phase Transition ◽  
Volume Phase ◽  
Acid Methyl ◽  
Amino Acid Methyl Ester

The Inactivation of Penicillopepsin with l,2-Epoxy-3-(p-nitrophenoxy)propane, an Active-Site Directed Reagent

1974 ◽  
Vol 52 (11) ◽  
pp. 1018-1023 ◽  
Author(s):  
G. Mains ◽  
T. Hofmann
Keyword(s):  
Methyl Ester ◽  
Aspartic Acid ◽  
Active Site ◽  
Side Chain ◽  
Porcine Pepsin ◽  
Protein Inactivation ◽  
Pepsin Inhibitor

Penicillopepsin was fully inactivated by the pepsin inhibitor 1,2-epoxy-3-(p-nitrophenoxy) propane, and 1.3 ± 0.3 mol of reagent became associated with each mole of protein. Inactivation was more rapid at pH 3.0 than at pH 6.0. Approximately 1 equivalent of the bound reagent was esterified to an aspartic acid side chain. Enzyme previously inactivated with diazoacetylnorleucine methyl ester did not react with the epoxide; and enzyme that was first inactivated with the epoxide did not react with the diazo inhibitor. The results add further evidence for the enzymatic similarity of porcine pepsin and penicillopepsin.

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