Irreversibility of stretching-induced local conformational changes as verified through an FTIR dichroism study for PVC

Guarrotxena, Nekane; Millán, J.

doi:10.1002/(sici)1097-0126(199911)48:11<1108::aid-pi276>3.0.co;2-0

Cited by 3 publications

(4 citation statements)

References 18 publications

(6 reference statements)

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“…In a series of recent publications1–14 we have experimentally demonstrated the straight relation between the physical properties and the stereochemical microstructure of poly(vinyl chloride) (PVC) as induced by the tacticity. This microstructure refers to the tactic sequences whether isotactic or syndiotactic, and especially the local configurations, which occur necessarily whenever a tactic sequence breaks off, namely the mmr and rrm tetrads, respectively, and the conformations, which are likely in them 1, 2.…”

Section: Introductionmentioning

confidence: 99%

“…This microstructure refers to the tactic sequences whether isotactic or syndiotactic, and especially the local configurations, which occur necessarily whenever a tactic sequence breaks off, namely the mmr and rrm tetrads, respectively, and the conformations, which are likely in them 1, 2. It depends on the polymerization conditions, which are suitable for every monomer, and can be modeled through stereoespecific chemical reactions3–5 or physical treatments like stretching6 or annealing 7…”

Section: Introductionmentioning

confidence: 99%

“…These correlations were all obtained by accurately changing the specific microstructures through controlled substitution reaction in cyclohexanone solution. A preliminary attempt to extend these correlations to the dielectric molecular motions was made for, first, a PVC sample prepared at 70 °C and the same polymer after substitution reaction to various molar percents with sodium benzenethiolate in the melt state,5 and, second, a film of the same polymers prior to and after drawing at 90 °C to an elongation ratio of 1.56. These properties were measured by means of isothermal depolarization currents (TSDC)17 and dielectric relaxation techniques,18 respectively.…”

Section: Introductionmentioning

confidence: 99%

“…This procedure proved to be a suitable way to prepare model polymers with well‐defined stereochemical microstructure. By comparing their properties, the above novel property/microstructure relationships could be straightfordwardly proposed 1–14…”

Section: Introductionmentioning

confidence: 99%

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Corrosion of tungsten coils after peripheral vascular embolization therapy: Influence on outcome and tungsten load

Bachthaler

Lenhart

Paetzel

et al. 2004

Cathet Cardio Intervent

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The purpose of this study was to evaluate coil corrosion and the long-term outcome after peripheral vascular embolization therapy performed with tungsten coils. We studied 14 patients who received tungsten coils on an average of 26 months prior to follow-up. The protocol included plain radiography and contrast-enhanced magnetic resonance angiography to investigate corrosion of tungsten coils and recanalization of the embolized vessels. Whole blood, hair, and urine tungsten levels were assayed when available. Corrosion of tungsten coils was detected in 9 of 14 patients by plain radiography. No evidence of recanalization of the embolized vessel and no adverse clinical effects of tungsten resorption were detected. Blood levels of tungsten were elevated in 6 of 14 patients and urine levels of tungsten were elevated in all 12 patients tested. Tungsten coil corrosion and elevated tungsten levels in blood, hair, and urine were found in most patients, although no adverse clinical effects of tungsten resorption were detected. Since the overall effect of high tungsten blood levels remains unclear, its use as an implant should be avoided.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Corrosion of tungsten coils after peripheral vascular embolization therapy: Influence on outcome and tungsten load

Bachthaler

Lenhart

Paetzel

et al. 2004

Cathet Cardio Intervent

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A stereochemical microstructure‐based attempt to explain the dielectric behavior of poly(vinyl chloride) (PVC)

Guarrotxena

Val

Elicegui³

et al. 2004

J Polym Sci B Polym Phys

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A poly(vinylchloride) (PVC) obtained by bulk polymerization at 70 °C was modified through substitution reaction with sodium benzenethiolate (NaBT) in cyclohexanone solution at 25 °C, at various conversions up to 15 mol %. According to earlier work, this allows to change, in a controlled way, the stereochemical microstructure in terms of mainly the content of mmr (meso, meso, racemic) tetrad termini of isotactic sequences of at least one heptad in length, and of its likely chain conformations. The samples were all studied by Dielectric Relaxation Spectroscopy, which allows to measure the real and the imaginary parts of the complex dielectrical constant in a frequency range between 1 and 106 Hz, and a temperature range between 100 and 600 K. Most of the changes in the physical quantities that can be analyzed by this technique were found to parallel the changes in stereochemical microstructure with substitution extent. The temperature of the maximum of the dipolar losses, which relates to the temperature range where α relaxation occurs, appeared to increase somewhat up to 0.7% molar conversion. Then the tendency is towards stabilization. The relaxation time τ(T) as deduced from the Havriliak‐Negami (NH) function, tends to decrease between 0 and 0.7 substitution percent, and to increase afterwards. The evolution of the Ngai's β parameter with substitution degree is also highly illustrative. It clearly decreases up to 0.7% and then it increases rapidly up to 7% and slowly afterwards. These changes are discussed by taking into account that 0.7 and 7% substitution extents agree with the removal of mmr under GTTG−TT conformation and of the same structure under GTGTTT conformation, respectively. From the results, some original correlations between stereochemical microstructure and molecular dynamic behaviors are proposed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2337–2347, 2004

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Stereochemical microstructure dependence of physical properties of poly(vinylchloride) (PVC). Principles and some recent correlations

Guarrotxena

2001

Vinyl Additive Technology

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As described in earlier work and surveyed herein, stereospecifc substitution reactions on PVC produce controlled changes in stereochemical microstructure. The corresponding changes in Tg are analyzed for each of the reactants utilized. A linear correlation is found between Tg and the ratio between the mmr tetrad reacting through its central mm triad and the mmmr pentad reacting through its mr triad plus the rrmr pentad reacting through its mr triad. The proposed explanation lies in the nature of the conformational changes which each of these reactions involves. Interestingly, the absolute value of the microstructure/Tg correlation is independent of the nucleophile, the nature of which can, however, determine the sign of that correlation. In addition, the evolution of both the amount and nature of the space charges that originate when applying an electrical field to the polymer films has been systematically studied by the thermal step method. The correlations obtained just@ the mmr tetrad as being the main trap of either heterocharges or homocharges, depending upon whether mmr takes the GTTG-TT or the GTGTTT conformation, respectively. This result agrees with the results of a tentative attempt with the stretched films. Some novel approaches toward understanding the physical behavior are proposed.

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Irreversibility of stretching-induced local conformational changes as verified through an FTIR dichroism study for PVC

Cited by 3 publications

References 18 publications

Corrosion of tungsten coils after peripheral vascular embolization therapy: Influence on outcome and tungsten load

Corrosion of tungsten coils after peripheral vascular embolization therapy: Influence on outcome and tungsten load

A stereochemical microstructure‐based attempt to explain the dielectric behavior of poly(vinyl chloride) (PVC)

Stereochemical microstructure dependence of physical properties of poly(vinylchloride) (PVC). Principles and some recent correlations

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