Degradation Of Polymer Solutions Research Articles

Mechanical shear degradation of polymers in solution by turbulent flow, 3. The influence of chemical constitution and thermodynamic quality of the solvent on shear degradation

AbstractMechanical shear degradation of polyisobutylene, polystyrene, poly(vinyl chloride), poly(methyl methacrylate), poly(decyl methacrylate), poly(methyl acrylate), and 1,4‐polybutadiene in dilute solutions of tetrahydrofuran (THF) are studied under turbulent flow conditions through a capillary, in order to study the effect of the chemical constitution on shear degradation. In addition the influence of solvent quality on shear degradation is investigated. The changes of the molecular weight distribution curves were followed by gel permeation chromatography (GPC), in order to determine the degradation constants ki for the corresponding molecular weight distribution fractions M̄i. GPC calibration via the concept of universal calibration, Mark‐Houwink relations for polyisobutylene, poly(methyl methacrylate), poly(methyl acrylate), 1,4‐polybutadiene, and poly(dimethylsiloxane) in THF as solvent had to be established for this purpose. Substantial differences in the rate constants ki were observed as a function of M̄i, whereas a master curve resulted for all polymers except 1,4‐polybutadiene when ki was plotted against the number of main chain carbon atoms n̄i for each molecular weight M̄i. From this the shear degradation of CC single bond polymers can be represented by ki = C · n̄, C being independent of the chemical nature of the CC single bond polymer, and a varying from 1,7 to 2,6. This means that in addition to the shape of the deformed macromolecule to be degraded not only its hydrodynamic volume (in rest) but also its chain length plays an important role. As to the influence of solvent quality, the degradation constants were found to increase with decreasing solvating power of the solvent. Mechanical shear degradation of the type discussed here takes place in drag reduction by polymers.

On the kinetics of polymer degradation in solution, 9. Pulse radiolysis of poly(ethylene oxide)

AbstractPoly(ethylene oxide) was irradiated with pulses of 16 MeV electrons (pulse length up to 100 ns) in aqueous and acetonitrile solutions in the absence and presence of oxygen. The change of the light scattering intensity (LSI) after the pulse was monitored. In acetonitrile solution, at a concentration of 2,3 · 10−2 base mol/1, main chain rupture occurred both in the presence and in the absence of O2. In aqueous solutions at [PEO] = 2,3 · 10−2 base mol/1 the LSI increased after the pulse in the absence of O2 (crosslinking) and decreased at [O2] = 1,4. 10−3 mol/1 (main chain scission). The rate of LSI decrease was correlated with a diffusion process in the case of O2 free acetonitrile solution and with a chemical reaction in the cases of O2 saturated aqueous and acetonitrile solutions. In the latter two cases it was found that a bimolecular reaction precedes bond scission in the main chain. It is assumed that peroxyl macroradicals (PO) react with each other forming oxyl macroradicals (PO•) which decompose relatively rapidly by main chain scission.

Irreversibility of degradation of polymer solutions

The degradation of polymer solutions of different concentration was investigated. It was found that a polymer solution that has been degraded by prolonged subjection to shear stress does not recover its drag-reducing properties after freezedrying and re-solution.

The Effect of Ultrasonics On the Injectivity And Viscosity of Xanthan Gum For Enhanced Recovery Applications

Abstract This paper outlines preliminary studies which have indicated that the injectivities of xanthan gum solutions can be improved by ultrasonic treatment without adversely affecting formation viscosities in enhanced recovery methods. Introduction One of the major concerns in applying polymer flooding to reservoirs with relatively tight oil sands (less than 100 md) is to have good injectivity while maintaining high solution viscosities(l). If the solution is mixed well and the molecules are dispersed thoroughly without being mechanically degraded, then this optimum situation is reached. Ultrasonic waves have been used to disperse particles of the micrometre Size(2). The capability of ultrasonic waves to disperse particles or agglomerates stems from the cavitation caused by ultrasonics. Cavitation occurs in the regions of the liquid which are subjected to rapidly alternating pressures of high amplitude(3). Besides dispersion, ultrasonic waves have been utilized to break up polymer molecules. The ultrasonic degradation of polymers in solution is of a mechanical nature. The stresses set up in the polymer molecule are caused by the friction forces generated by the relative movement of the molecules of solvent and the polymer molecule as a result of the collapse of cavitation bubbles(4). The permanent degradation can be measured by determining viscosities and by chemical reactions. A recent review of the work in this area is presented by A. M. Basedow and K. H. Ebert(4). Ultrasonics were also found to be effective in liquefying gels(5). The polymer molecules that are used as- mobility control agents in enhanced oil recovery are between 0.1 µm and 0.5 µm in diameter(6). Xanthan gum molecules (Kelzan -XC) have been reported to be around 0.3-0.4 µm(7). These molecules have bonds between them that are weaker than the covalent bonds between the units of the chains. Morris suggests that these weak non-covalent associations between aligned molecules build up a tenuous gel-like network. He also proposes that this network is progressively broken down with increasing shear rate(8). These bonds lead to an increase of entanglements between the polymer chains. Moorhouse et al. characterize the bonds between the molecules as hydrogen bonds(9). If one can break the hydrogen bonds and decrease the degree of entanglement without destroying the covalent bonds, then he can increase the injectivity of the solution and still maintain the high viscosity level. It has been suggested that the larger polymer aggregates present more resistance to flow and accumulate greater shear stresses; hence they are more vulnerable to rupture than the smaller species or the dispersed molecules(4). The principle of utilizing ultrasonic waves to improve the flow properties of polymer solutions through porous media without decreasing the viscosities is examined in this investigation. Procedure In a previous study, the optimum blending of xanthan gum solutions was obtained by the shearing of the solution through several orifice plates, with 100 psi pressure drop each plate(7). Excessive pressure drops across the orifices leads to mechanical breakdown of the molecules. Some of these solutions prepared by optimum blending were subjected to ultrasonic radiation; their injectivities and viscosities were determined.

Effects of Long‐Chain Branches on the Degradation Kinetics of Polymers

Degradation of polymers in solution is greatly influenced by long side chains. Quantitative information about the number of branches and the length of the side chains etc., can be obtained from the molecular weight distribution by mathematical simulation.

On the Kinetics of Polymer Degradation in Solution. 8. Laser Flash Photolysis of Polystyrene

On the Kinetics of Polymer Degradation in Solution. 8. Laser Flash Photolysis of Polystyrene

A theoretical approach to the kinetics of polymer degradation in solution

AbstractAfter main‐chain scission in a polymer, the frequency of encounter between segments in the different fragments is related to the separating process between the fragments. The relationship obtained shows that the separating time is proportional to M½, where M is the molecular weight, when the excluded volume disappears. When good solvent is used, the half‐time for the separation is obtained as τ½ = const. M0.16–0.22, which is approximated to the experimental data obtained previously (τ½ = const. M0.34 and τ½ = const. M0.22) for the degradations of polyisobutene and poly(phenyl vinyl ketone), respectively. The increase of the half‐time with increasing coil density can be explained by the excluded volume. The inverse proportionality of the diffusion of segments to solvent viscosity explains the proportionality of the half‐time to microviscosity. The above separating process reverses the reaction between polymer radicals. From their dependence on the chain length, τ½/kD = const. M½ (where kD is the specific rate for the reaction), is estimated. Such an approximation holds, regardless of the type of solvent.

On the kinetics of polymer degradation in solution—VII. Laser flash photolysis of poly-α-methylstyrene in solution

Poly-α-methylstyrene (PαMS) was degraded in CHCl 3 and CCl 4 solution by flash photolysis ( λ = 265 nm). The degradation, as detected by light scattering measurements, is caused by the attack on PαMS by solvent radicals, assumed to be formed mainly by energy transfer processes. The direct effect did not lead to detectable main chain cleavage as evidenced by experiments with PαMS dissolved in dioxane or methylene chloride. The time dependence of the decrease of the light scattering intensity (LSI) after the flash was measured. The observed first order lifetime τ(LSI) corresponds to the lifetime of lateral macroradicals P′ that decompose by main chain cleavage ( k = 3.5 × 10 2 sec −1). Molecular oxygen reacts with the lateral macroradicals with k = (5.5 ± 0.5) 10 5 M −1 sec −1. Only a minor portion of the product of this reaction (PO 2′) decays by main chain scission. Thus O 2 inhibits main chain scission significantly. By addition of cyclohexane and ethyl mercaptan, the main chain cleavage is inhibited. τ(LSI) was not affected by these compounds in the concentration range investigated ([C 6H 12]: up to 8.4 M; [C 2H 5SH]: up to 3 × 10 −3 M), indicating that they reacted with solvent radicals which otherwise attack the polymer forming lateral macroradicals.

On the Kinetics of Polymer Degradation in Solution. 5. Pulse Radiolysis of PMMA Using the Light Scattering Detection Method

On the Kinetics of Polymer Degradation in Solution. 5. Pulse Radiolysis of PMMA Using the Light Scattering Detection Method

On the kinetics of polymer degradation in solution—VI Laser flash photolysis and pulse radiolysis studies of polymethylvinylketone in solution using the light scattering detection method

Polymethylvinylketone (PMVK) was irradiated in solution with 2 μs pulses of 15 MeV electrons or with 15 ns flashes of 265 nm light. The change of the intensity of the light scattered by the solution (LSI) after the irradiation was measured. For the radiolysis experiments, a main chain scission process ( τ 1 2 ( decr) ≈ 20 μ s ) and a subsequent crosslinking process [ τ 1 2 ( incr) ≈ 0.4 sec ] could be discriminated. The LSI change pertaining to the main chain degradation was found to be due to disentanglement diffusion, whereas the LSI change pertaining to the crosslinking process could be correlated to a chemical reaction. The rate constant for combination of lateral macroradicals in acetone solution was estimated as 2 k 2 = (4.5 ± 1.5)10 6M −1 sec −1. Stationary irradiations with 60Co-γ-rays showed that PMVK is predominantly crosslinked to form a macrogel when irradiated in the solid state or in solution at concentrations greater than 100 g/l. At lower concentrations, microgel formation occurred. Photolysis of PMVK in solution yielded only main chain degradation. The LSI change was found to be due to disentanglement diffusion as during radiolysis. It was concluded that the same mechanism for main chain rupture is operative as in radiolysis. Stationary irradiations with u.v. light ( λ > 260 nm) resulted in main chain degradation; no indication of crosslinking was obtained.

On the kinetics of polymer degradation in solution—IV: Laser flash photolysis studies on copolymers containing phenylvinylketone using the light scattering detection method

Copolymers of methylmethacrylate (MMA) with phenylvinylketone (PVK) and of styrene (St) with PVK were degraded in solution by irradiation with 25 nsec flashes of 347.1 nm light from a ruby laser. The time dependence of the change of light-scattering intensity (LSI) (due to the decrease of molecular weight) was measured. It was found that the half-life τ 1 2 (LSI) decreases with increasing polymer concentration according to [( τ 1 2 (LSI)] −1 ∝ C Polymer and that τ 1 2 (LSI) is proportional to the microviscosity (viscosity of the solvent). This was taken as evidence that τ 1 2 (LSI) corresponds to a diffusion process. τ 1 2 (LSI) decreased with increasing scattering angle, explained by the fact that at low scattering angles the diffusion of long fragments was predominantly monitored. Upon addition of naphthalene to an acetone solution of a copolymer of MMA and PVK, τ 1 2 (LSI) increased with increasing naphthalene concentration and approached a limiting value. This effect was attributed to preferential solvation of the copolymer by naphthalene. From intrinsic viscosity measurements, it could be confirmed that MMA base units are preferentially solvated by an acetone/naphthalene mixture.

On the kinetics of polymer degradation in solution—III: Pulse radiolysis studies on polyisobutene using the light-scattering detection method

Polyisobutene (PIB) dissolved in saturated hydrocarbons was degraded by irradiation with 2 μs impulses of 15 MeV electrons. The time dependence of the change of light-scattering intensity (LSI) (due to the decrease of molecular weight) was measured. The half life τ 1 2 (LS) of the decrease of LSI was not influenced by the addition of cyclohexene, which on the other hand drastically reduced the extent of degradation, leading to the conclusion that the time of establishing bond scissions in the main chains is much shorter than τ 1 2 (LS) and the latter corresponds to disentanglement diffusion. This is furthermore evidenced by the following experimental findings: τ 1 2 (LS) increases with decreasing PIB concentration, i.e. with decreasing macroviscosity. However, τ 1 2 (LS) increases linearly with increasing microviscosity as shown by measuring τ 1 2 (LS) in different hydrocarbon solutions (C 5-C 16) τ 1 2 (LS) is proportional to M 0.34, i.e. significantly weaker dependence on M̄ than expected for translational diffusion. Thus, it is believed that disentanglement diffusion and translational diffusion may be distinguished. As n-propanol was successively added to n-hexane solutions of PIB. τ 1 2 (LS) increased. indicating that disentanglement diffusion is easier for loosely than for tightly coiled macromolecules.

Ultrasonic degradation of polymers in solution and its computer simulation (author's transl)

Ultrasonic degradation of polymers in solution and its computer simulation (author's transl)

On the Kinetics of Polymer Degradation in Solution. II. Laser Flash Photolysis Studies on Poly(phenyl vinyl ketone) and Butyrophenone

Using the nanosecond flash photolysis technique transient absorption spectra of poly(pheny1 vinyl ketone) (PPVK) and butyrophenone (BPI in benzene solution at room temperature were recorded. Samples were irradiated with 347.1-nm light flashes. With both substances the transient spectra decayed by a first-order process with k 1 = 1.0 f 0.2 X lo7 sec-'. In PPVK and BP solutions containing naphthalene or biphenyl the established triplet absorption of these compounds is sensitized. It is concluded that the observed transient absorptions are due to triplet states of PPVK and BP, respectively. The quencher studies yielded as an estimate a triplet quantum yield d3PPVK*) equal to 0.1 to 0.3. kq (bimolecular rate constant of energy transfer) is about two times smaller for bi- phenyl than for naphthalene. For BP kq is about two and a half times higher than for PPVK (in the case of naph- thalene: ~Q(BP) = 5.0 f 1.5 X lo9 M-' sec-' and kQ(PPVK) = 2 i 1 X lo9 M-' sec-'). This result reflects the in- fluence of the diffusion constant of the polymer on ks as expected for diffusion-controlled reaction and agrees with earlier findings'O concerning rate constants of the reaction of scavengers with macroradicals.

On the kinetics of polymer degradation in solution—I. Laser flash photolysis and pulse radiolysis studies using the light scattering detection method

An apparatus for measuring the time dependence of light scattering intensity (LSI) in the μsec range was developed. Using this equipment, the degradation of polyphenylvinylketone (PPVK) in benzene solution and that of polymethylmethacrylate (PMMA) in acetone solution were investigated at room temperature. PPVK was irradiated with 25 nsec flashes of 3471 Å light and PMMA with 2 μsec pulses of 15 MeV electrons. The following results were obtained: PPVK: the quantum yield for main chain scission φ(S) is 0·4–·6. Quencher experiments yielded Stern-Volmer constants which agree with literature data. Half lives ( τ 1 2 ) of the change of LSI amount to about 20 μsec and are not influenced by quenchers. The dependence on molecular weight M̄ is τ 1 2 ∝ M 0·22 ± 0·02 . It is assumed that τ 1 2 corresponds to disentanglement diffusion. Oxygen has no influence on φ(S) and τ 1 d2 . PMMA: the G-value is about 2 for oxygen-free solutions and 0·7 in the presence of O 2. The time dependence of LSI is significantly influenced by oxygen and presumably determined by the life time of activated centres in the polymer chains. From the decay curves, evidence was obtained for two different intermediates: one decaying rapidly with τ 1 2 < 100 μ sec , the other decaying relatively slowly with τ 1 2 = 4·0±0·2 msec (rate constant: 170/sec. The slowly decaying species is scavenged completely by oxygen and is presumably a macroradical whereas the fast decay might indicate a scission process via excited states.

Development of an ultrasonic device for studying the mechanical degradation of polymer solutions

1. The principal use of the ultrasonic generator UZG-0.1, one of a series of generators being manufactured, for evaluating the mechanical degradation of polymers in solution, especially highly polymerized additives, has been demonstrated. 2. The ultrasonic apparatus developed in this work, equipped with the catenoid concentrator, makes it possible to greatly shorten the experimental time, in addition to requiring only a small volume of the liquid to be studied, in contrast with other methods used for such investigations. 3. The ultrasonic apparatus developed in this work, equipped with the catenoid concentrator, makes it possible to greatly shorten the experimental time, in addition to requiring only a small volume of the liquid to be studied, in contrast with other methods used for such investigations.

Degradation of polymers in solution by freezing

AbstractPolyvinylpyrrolidone in aqueous solutions of various concentration has been degraded by freezing the solvent. The kinetics and mechanism of degradation of linear polymer molecules under these conditions has been elaborated and the similarities with ultrasonic degradation by cavitation, which is mechanical in nature, have been pointed out. Experimental results for the degradation of polystyrene in benzene and of polyvinylpyrrolidone in water follow the proposed kinetics and mechanism.

Degradation of poly(ethylene oxide) by high‐speed stirring

AbstractDegradation of poly(ethylene oxide) (PEO) by violent stirring was studied in various solvents. The chain scission or the limit of the degradation was measured, and the effects of solvents, polymer concentration, stirring speed and degree of polymerization (DP) were investigated. It was found that the number of bonds broken per polymer chain was independent of the concentration but increased with the stirring speed and with decrease in the DP. The rate was much affected by the solvent used, being larger in a poor solvent. It was also found that the rate could be represented either by Jellinek's or Ovenall's rate equations, which have been applied to the ultrasonic degradation of polymers in solution.

The concentration effect in the degradation of a number of polymers in dimethylformamide

One of the fundamental problems in the chemistry and physics of macromolecular compounds is that of the resistance of polymers to the action of various physical and chemical agents. In the literature the thermal and thermal-oxidative degradation of polymers in the condensed phase (in bulk) have been examined in greatest detail [1–4]. The degradation of polymers in solution has not been studied sufficiently [5]. In the present work a study was made of the degradation of a polymer under mild conditions (at 95°) in solution at various concentrations, in order to ascertain the type of reaction between the macroradicals.

Studies in the mechano-chemistry of polymers—XIV. The importance of the concentration of acoustic energy in the ultrasonic degradation of polymers in solution

Studies in the mechano-chemistry of polymers—XIV. The importance of the concentration of acoustic energy in the ultrasonic degradation of polymers in solution