Main-chain Bonds Research Articles

A Study of Wool Carbonizing

During the time delay in rapid carbonizing, the distribution of sulfuric acid between surface acid and total acid inside the wool changes. At zero time delay there is 2.3% owf surface acid and 2.1% owf total acid inside the wool, while after 15 minutes delay the surface acid has dropped to 0.7% owf and the total acid inside the fiber has increased to 3.7% owf. Within the wool, the bound acid increases from 1.2% owf to 3.0% owf, leaving only 0.7% owf free acid inside the wool. Thus the amount of concentrated acid formed during drying and baking is minimized and less chemical attack occurs to wool in rapid carbonizing. The reduced chemical attack is indicated by a lower amino group content and a significantly higher disulphide bond content for rapidly carbonized wool compared with conventionally carbonized wool. These results show that there is both a reduced main chain and disulphide bond breakdown in rapidly carbonized wool. In the time range examined in this work, 10 minutes seems to be the optimum delay time. For delay times greater than 10 minutes, the delay is neither industrially practicable nor is the quality of the carbonized wool optimized.

Protein structural homology: a metric approach.

The flexibility of the polypeptide fold of proteins is essentially due to the rotational freedom about the main chain bonds involving C alpha atoms. The polypeptide fold can therefore be represented by virtual bonds joining consecutive C alpha atoms. The ordered sequence of virtual torsion and bond angles involving these bonds can be used to specify the fold. Such representations can then be compared to reveal structural similarities using the Needleman & Wünsch algorithm, which has been developed for comparison of amino acid sequences. Such an approach is presented and illustrated with examples. The method is suitable for detecting structural similarities that extend over 7 or more residues.

Mechanism of Bond Alternation and Solitons in Polydihalogenoacetylene

Br or I, are studied using the HUckel model in approximations beyond the weak coupling limit (WCLl. A four component spinor representation is derived for the HUckel equation of (CX)x from which a continuum version can be obtained. The solution of the spinor HUckel equation is obtained for the bond alternated regular lattice using the perturbation method. Beyond the WCL, the Fermi velocity becomes distortion dependent and the dispersive stabilization of 7f electrons alters the effective elastic force constants. The leading correction due to these effects is a renormalization of the effective dimensionless electron· lattice coupling constants in the main chain C-C and side chain C-X bonds. The renormalization is essential in realizing the side chain bond alternated ground state in (CF)x. Approximate analytic expressions for solitons are obtained in the approximation to take into account the renormalization of the coupling constants. In the case of (CX)x with the main chain bond alternated lattice ground state but with negligibly small side chain bond alternation, solitons are nearly pure amplitude solitons. In the case of (CF)x with a significantly large side chain bond alternation, solitons are nearly pure phase solitons obeying a sine·Gordon equation. The case of (CF)x with the nearly continuously degenerate ground state with coexistence of both kinds of bond alternation is realized in a very small range of the C-F bond force constant. The coexistence case arises from the second order correction due to the distortion dependence of the Fermi velocity.

Short‐branch formation via the roedel mechanism in copolymers of ethylene and vinyl acetate

AbstractA realistic rotational isomeric state model has been used to estimate the relative probabilities of the formation of various types of short branches in ethylene–vinyl acetate copolymers that are rich in ethylene. Butyl is predicted to be the most common short branch in all of the copolymers examined, although it is less common in the copolymers than in low‐density polyethylene. The major factor responsible for the suppression of the R04 backbiting intrachain radical transfer is the increased preference for trans states at the mainchain bonds flanking the attachment site for an isolated acetoxy side chain.

A functionalized fine powder made by high-energy irradiation of polytetrafluoroethylene

High energy radiation produced by electron accelerators and gamma sources transform emulsion and suspension polymerizates of PTFE in the presence of the oxygen of the air into finely grained powders of PTFE functionalized with carboxyl acid groups. With increasing dose of irradiation rises the concentration of these groups and the free surface energy, too. The G-value for the splitting of the main chain bonds lies in dependence of the dose of irradiation in the range of 1.5 to 41.2 in the case of the electron accelerator and 0.64 to 12.8 using a gamma source. The specific surface of PTFE polymerizates and of finely grained powders produced thereof is approximately of the same magnitude. It amounts to about 2 m 2 per g in the case of finely grained powder from suspension polymerizate and to 14 m 2 per g and more from emulsion polymerizate. A change of the size of the primary particles takes not place. The grain size of the particles has been determined to about 2/um or less than 0.2/um, respectively. As successfully investigated finely grained powders of PTFE are applicable as dry lubricants, form separating agents, in aqueous and organic dispersions and as additive to formstable diaphragms for the electrolysis of alkali-metal chlorides and maintenance-free materials for slider bearings.

Effect of main-chain double bond on dynamics of polystyrene: an ESR study of macromolecules spin labeled by copolymerization

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEffect of main-chain double bond on dynamics of polystyrene: an ESR study of macromolecules spin labeled by copolymerizationP. Simon, L. Suemegi, A. Rockenbauer, F. Tuedos, J. Cseko, and K. HidegCite this: Macromolecules 1985, 18, 6, 1137–1139Publication Date (Print):June 1, 1985Publication History Published online1 May 2002Published inissue 1 June 1985https://doi.org/10.1021/ma00148a015RIGHTS & PERMISSIONSArticle Views37Altmetric-Citations4LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (362 KB) Get e-Alerts Get e-Alerts

The stress relaxation of the 1,2‐syndiotactic polybutadiene thermoplastic elastomer

Abstract The stress relaxation of a low‐crystallinity type thermoplastic elastomer (TPR), 1,2‐syndiotactic polybutadiene, was studied. By using the continuous and intermittent stress relaxation method, the Co60 r‐ray irradiated samples were tested from 30°C to 106°C under air, nitrogen or oxygen atmosphere. The relative stress relaxation curve of this low crystallinity kind of elastomer can be expressed by two Maxwellian decay terms. f(t)/f(0)=o 1 exp (‐k 1 t) + o 2 exp (‐k 2 t) Since there are only a few C=C double bonds in the polymer main chain, the oxidation of C=C in the side chain does not influence the strength of the stress relaxation. Thus the chemical relaxation can be ignored in this kind of thermoplastic elastomer. These two Maxwellian terms are both of physical stress relaxation, namely, flexible chain slippage and crystalline domain disintegration (breaking), respectively:

ジアミンとジアルデヒドの縮合によるＣＨ＝Ｎ結合を持ったポリマー（ポリイミン）の合成

In this paper, syntheses and characterizations of polymers containing CH=N bond in main chain (polyimine) will be described. Polyimines could be synthesized by the condensation of primary diamines and dialdehydes. The polymers were prepared first by Krässig and Greber in 1953. However, numerous polymerization techniques (solution, melt, Schiff-base exchange and others) and conditions tried have not given high molecular weight polyimines because of the insolubility and the high melting point. But, the discovery of m-cresol method by Suematsu and solid state polymerization by Morgan made high molecular weight polyimine formation possible. m-Cresol accelerated CH=N bond formation keeping a homogeneous solution. The reaction rate in m-cresol was as fast as that of acid chloride and primary amine in benzene, though top limit of degree of polymerization was not very high because of the presence of an equilibrium between polymerization and depolymerization. However, exclusion of reaction-water produced higher molecular weight polymers. The reaction rate in m-cresol was found to obey the reversible second order equation, defined as v=k [CHO] [NH2] -k* [C=N] [H2O], where k is the rate constant in polymerization and k* in depolymerization. The condensation in dilute solution resulted in the formation of macrocyclic imines in high yield. This could be explained not in terms of cyclization theory by Stockmayer et al., but favourable conformational changes and an equilibrium shift accompanied by the separation of products. Chain length of most aromatic polyimines is calculated according to the equation Pn=1/2 [3.6 (AυC=N/AυC=O) +1], where AυC=N and AυC=O are the absorbance of υC=N and υC=O respectively. An equation [η] =1.9×10-3M1.20 by Millaud holds in poly- (p-xylidene-2-methyl-p-phenylenediamine).

Structural information from degradation studies

Abstract

Micro- and macroconformation of macromolecules

The first results are reported about the conformational analysis of an amorphous polymer in the glassy state by means of proton enhanced variabletemperature magic angle spinning 13C NMR experiments. In amorphous threodiisotactic poly(1,2-dimethyltetramethylene) at 220 K different conformational diads could be resolved and assigned. From the spectrum of the glassy polymer the shift increment associated with a conformational change of main chain bonds from anti to gauche is determined. In addition the populations of the conformations of CH-CH bonds and of CH-CH-CH 2 bond pairs of poly(l,2dimethyltetramethylene)s are determined in the glassy state and energy differences between these conformations are estimated.

Determination of crosslink density by end group analysis after partial degradation: 1. Theory

A method is derived for estimating the intermolecular crosslink density of any polymeric gel, provided it can be partially solubilized by main-chain degradative procedures to yield a soluble fraction that can be analysed for end groups. Predicted end group concentration for a given solubilization is derived from a model that assumes uniform initial chain lengths before crosslinking, random crosslink sites, and random attack on main chain bonds. Results are almost invariant with respect to chain length, so that simpler expressions can be used that are derived for infinite chain length, and which have the advantage of being applicable to gels in which the initial chain molecular weight or its distribution is unknown.

ChemInform Abstract: RELATION BETWEEN CONFORMATIONAL STRUCTURE, VIBRATIONAL SPECTRA AND INTRAMOLECULAR EXCIMER FORMATION IN 2,4‐DIMETHYL‐2,4‐DIPHENYLPENTANE

Abstract Conformational energy calculations on 2,4-dimethyl-2,4-diphenylpentane have been performed with explicit allowance for methylene bond-angle flexibility. The value of this angle which minimizes the energy is close to 126°, whatever the conformation. The energy contours are given versus main chain bond rotations. An intramolecular mobility study reveals that two kinds of motions are expected: the first includes motions with low activation energies while motions of the second group require a much higher activation energy and involve a large rotation around C-C skeleton bonds. In all cases the phenyl ring rotations are rather strongly coupled with the chain rotations. IR analysis and intramolecular excimer formation indicate that 2,4-dimethyl-2,4-diphenylpentane exists in one of the most stable conformations in the crystalline state. In the liquid state higher-energy conformers are present. Fluorescence emission studies show that 2,4-dimethyl-2,4-diphenylpentane exhibits a higher efficiency of excimer formation than 2,4-diphenylpentane, because of the rather small energy barrier between the excimer and the ground-state conformations.

Relation between conformational structure, vibrational spectra and intramolecular excimer formation in 2,4-dimethyl-2,4-diphenylpentane

Conformational energy calculations on 2,4-dimethyl-2,4-diphenylpentane have been performed with explicit allowance for methylene bond-angle flexibility. The value of this angle which minimizes the energy is close to 126°, whatever the conformation. The energy contours are given versus main chain bond rotations. An intramolecular mobility study reveals that two kinds of motions are expected: the first includes motions with low activation energies while motions of the second group require a much higher activation energy and involve a large rotation around C-C skeleton bonds. In all cases the phenyl ring rotations are rather strongly coupled with the chain rotations. IR analysis and intramolecular excimer formation indicate that 2,4-dimethyl-2,4-diphenylpentane exists in one of the most stable conformations in the crystalline state. In the liquid state higher-energy conformers are present. Fluorescence emission studies show that 2,4-dimethyl-2,4-diphenylpentane exhibits a higher efficiency of excimer formation than 2,4-diphenylpentane, because of the rather small energy barrier between the excimer and the ground-state conformations.

Conformational entropy of liquid polyethylene

Abstract In previous work [I], the relationship between the conformational entropy Sc, associated with rotational isomerization about main-chain bonds, and T0, the constant in the Vogel equation for polymer liquid mobility, was derived for a three-state rotational model with independent bond rotations. The present study takes into account the exclusion of transitions between gauche states of opposite sign (the “pentane interference”).

Rotational energetics in vinyl polymer liquids: 2. Other polymers

The procedures described for poly(vinyl acetate) in the preceding paper are applied to compute the effects of pressure on the Vogel T 0 and B between P∗ = −b ( Tait) and P = 2000 bars for polystyrene, linear polyethylene, polyisobutylene, and polydimethylsiloxane. From these are derived the pressure dependences of the rotational energies U and V, where U is the energy difference between the rotational states and V is a rotational barrier. The U∗ for the ‘isolated’ chain is corrected by the factor Z∗, which appears to be an intramolecular cooperative unit, to yield U∗∗, the energy difference between the rotational states for a single main-chain bond in the ‘isolated’ chain. A major conclusion of this work is that statistical mechanical calculations of the conformational (i.e. rotational) properties using ‘isolated’ chain values for U will give erroneous results when applied to the real polymer liquid. The same conclusion based on a different approach has been reported previously.

The sensitized photo-oxidation of aliphatic polyamides

The sensitized photo-oxidation (SPO) of aliphatic polyamides (PA) has been studied on the basis of comparing the kinetic curves of oxygen absorption, the accumulation of peroxides, main chain bond fractures and the comsumption of sensitizers. The quantitative characteristics of the SPO have been determined. The photo-sensitization was carried out by non-chain oxidation with the following compounds: peroxides, aromatic ketones, quinones, phenolic-type anti-oxidants, variable valence metal salts, and xanthene dyes; all these had the same mechanism of photo-degradation of the polymer, and the kinetic curves for bond fracture showed the existance of an induction period. The results have been explained as due to the sensitization of the photo-oxidation by there compounds, which consists of a photo-initiation of the central marco-radical, i.e. ∼CH 2CONHCHCH 2∼ (P 1); this cannot result main chain bond fracture of the PA. The decomposition of the macromolecules is explained by the features of the recombination mechanism of the P 1O 2 peroxide radicals.

Thermal degradation of polymers. Part XIX. The thermal cyclization and characterization of quinazolone pre‐polymers

AbstractA series of pre‐polymers prepared from 4,4′‐diaminodiphenyl‐3,3′dicarboxylic acid and aromatic diacetamido compounds have been thermally cyclized and their structures have been investigated using infrared spectroscopy, combustion analysis, and weight loss techniques. The structures obtained on cyclization are discussed in terms of concurrent cyclization and decarboxylation reactions resulting in incomplete cyclization. Specific structural features due to the lability of main chain bonds at the cyclization temperatures are also discussed. Dynamic thermogravimetry and isothermal weight loss studies have been used to evaluate thermal stability and kinetic parameters. The results are discussed in terms of the overall complexity of the polymer structure and the complexity of the degradation process. It is concluded that in such systems, where the structural variations are large, it is not possible to define a meaningful stability sequence because like systems are not under comparison.

Synthesis and Characterization of Poly(N-cyanoethylglycine)

N-Cyanoethylglycine was synthesized from glycine and acrylonitrile, and converted into its N-carboxyanhydride (NCA) by Leuch’s method. The NCA was polymerized in a HCONMe2 solution using an amine as the initiator to give, for the first time, a white, powderic, amorphous polymer having Pn=15–16. The rate of polymerization was much smaller than that of N-n-butylglycine NCA under the same conditions, and the low basicity of the amino group at the growing end, which is a result of an electron-withdrawing effect of cyanoethyl group, was found to be responsible for the slow polymerization. Poly(N-cyanoethylglycine) is soluble in aprotic solvents such as HCONMe2, Me2SO, and Me2CO, and its main-chain peptide bonds comprise ca. 70% of cis form and ca. 30% of trans form in Me2SO. Poly(N-cyanoethylglycine) is therefore flexible and compact in organic solvents. A part of the side chains of poly(N-cyanoethylglycine) was reduced into 3-aminopropyl groups by the hydro genation.

Stress-optical behaviour oftrans-1,5-polypentenamer

The stress-optical behaviour of crosslinked trans-1,5-polypentenamer (TPR) in the unswollen and the swollen state was investigated and the results were compared with the data for other elastomers. The optical anisotropy of the statistical segment was found to be 5.6 × 10−24 cm3 at 50°C. The number of chemical bonds in the main chain per statistical segment, a measure of the chain stiffness, was 5.6. From the comparison of the data in the unswollen and swollen state an estimate for the short range orientational order in the bulk polymer was made. The mean aggregate size of 1.6 at 50°C is relatively high compared to natural rubber.

Photodegradation of polyacetaldehyde in solution. I. Direct photolysis

The quantum yields measured for the random scission of main-chain bonds of polyacetaldehyde in benzene solution by 254 nm irradiation at 298°K are on the order of 10−3–10−4 scissions per quantum absorbed by the polymer. The quantum yields are unaffected by oxygen but are dependent upon initial polymer concentration and upon the inverse square root of absorbed light intensity. The direct photochemistry involves excitation of carbonyl chromophores in their 1nπ* bands, and a Norrish type I process is believed to be responsible for subsequent free-radical random-chain scissions. It has been established that direct photoexcitation processes do not lead to sequential depolymerization of polyacetaldehyde to monomer.