Dilute Solutions Of Polyisobutylene Research Articles

Gamma radiolysis of dilute polyisobutylene solutions: influence of solvent

Solutions of polyisobutylene have been irradiated with gamma rays from a Cobalt source. One percent concentrations (w/v) in the solvents methyl cyclohexane, toluene, and carbon tetrachloride were used, and of the solution in each solvent one portion was subjected to a ca. 10 kGy dose and another to a ca. 25 kGy dose. No detectable cross-linking occurred as a result of the radiolyses, but there were drastic reductions of MW in all cases, the effect being greatest for CCl 4 and smallest for toluene as solvent. The radiation damage was also assessed as the number of chain scissions caused, and in terms of the G values for scission. Attempts were made to correlate the latter parameter with properties of the solvents as indicated by their Hildebrand Solubility Parameters and by their C s values (chain transfer constants), and also with the reactivities of radicals resulting from solvent scission. The results indicate that neither the hydrodynamic volume of the polymer molecules in solution, nor the tendency of the solvent molecule to donate an atom to a polymer radical, have a predominant influence on the mechanism. It is concluded that in dilute solution, the direct interaction of the gamma radiatiuon with the polymer is not the important factor in determining the overall radiation damage, but that the predominant mechanism involves primary radiolysis of solvent molecules to form products which then attack the polymer molecules to cause the scissions. On this basis, recommendations can be made about choice of solvents for polymers to be used in a radiative environment.

Elongation and subsequent relaxation measurements on dilute polyisobutylene solutions

The elongation and subsequent relaxation of dilute polyisobutylene solutions in mixtures of polybutene and kerosine and in mixtures of polybutene and toluene have been investigated using an extensional rheometer based on the principle of droplet stretching. Single exponential stretching functions have been applied and the resulting non-idealities of the experiment will be addressed. The results show that the transient Trouton ratio for different values of the applied axial extension rate between 1 and 6 s −1 scales with the strain for values larger than 3. The magnitude of non-ideal stretching effects on the Trouton ratio for strain values up to 3 is found to be fairly small. For strains larger than 5.5 the onset of steady-state values of the extensional viscosity is found, but true steady-state values are not obtained below the maximum strain of 7.2. The measurements provide an indication for increasing plateau values with increasing concentration and with increasing molecular weight of the polymer. The results also show that the relaxation after stretching up to a specific axial strain value with different extension rates scales with the product of the extension rate at the start of the relaxation process and the time.

Stress relaxation in uniaxial extension

The elongation and subsequent relaxation of dilute polyisobutylene solutions in mixtures of polybutene and kerosene have been investigated using a filament stretching device first introduced by Tirtaatmadja and Sridhar [J. Rheol., 37 (1993) 1081–1102]. A novel experimental technique has been developed which enables the nature of the total stress measured by experiment to be investigated. A sudden decrease in stress is observed on cessation of the extensional flow. This is followed by a much slower relaxation. The results can be interpreted in terms of viscous and elastic stresses. An alternative explanation in terms of the dumbbell model is also explored. The viscous stresses were observed to scale with strain rate at any given value of chain extension, whilst at steady state, the elastic stresses remained constant over a range of strain rates. Computations using a FENE-P model, with parameters evaluated from steady shear data, are shown to predict the growth of the elastic stress component. The same model seems to predict the relaxation of stresses reasonably well. A new stretching technique has also been developed which allows excellent agreement between radially and axially computed strain rates, indicating homogeneous defomation of the fluid sample.

Atomization of dilute polyisobutylene/mineral oil solutions

AbstractAtomization experiments, motivated by the need to suppress misting of machining oils, were conducted on dilute solutions of polyisobutylene (PIB) in mineral oil using a coaxial air blast atomizer and an optical (Fraunhofer diffraction) particle sizer. Polymer concentrations (0.1 to 1.0 kg/m3) and molecular weight (1.0 to 2.2 million) were varied to determine their effects on aerosol drop‐size distributions. The pure oil and PIB ‐ oil solutions were atomized at air/liquid mass ratios near 10 and atomizing air velocities of 150–270 m/s, producing droplet‐size distributions with mass mean diameters (MMD) in the range of 7–15 μm for the pure oil. Under identical atomization conditions, the MMDs of PIB solutions were 20–200% higher than pure oil. These observed increases in MMD correspond to significant reductions in the fraction of droplets falling below 5 μm in diameter that constitute the misting problem in industrial machining applications. Observed effects of PIB on atomization are ascribed to the viscoelastic properties of PIB ‐ oil solutions as characterized by the elongational viscosity ηE. This relationship is examined by correlating the change in MMD caused by PIB addition with the stress‐dependent elongational viscosity of PIB‐oil solutions as predicted by the FENE‐P dumbbell kinetic theory. The increase in MMD due to PIB varies linearly with the predicted ηE at constant atomization tensile stress.

Conformational changes of macromolecules in transient elongational flow

AbstractCalculations are reported which describe the elongation of flexible macromolecules in a pulse‐like elongational How. The polymer molecules are modeled as FENE (finitely extendable nonlinear elastic) dumbbells. The results are in qualitative agreement with experimental results on dilute solutions of polyisobutylene in decalin (10) which form a two parameter family of extension versus position curves. The two parameters‐in the FENE model that are used to fit the data are λH, a time constant and b, which is related to the maximum extension that can be achieved by the molecules. Quantitative comparisons are frustrated by difficulty in estimating the model parameter, b. It is suggested, based on this work, that internal self entanglements in the polymers must be considered in the determination of b.

Time dependence of viscosity of dilute polyisobutylene solutions

Shearing at constant gradient of polyisobutylene (PIB) solutions in viscous polybutene oils results in time dependent changes of their viscosities. Two PIB fractions (M=8·106 and 3.8·106) have been studied in a variety of solvents, covering the viscosity range from 5 to 0.5·10−2 poise. The overall phenomenon is similar to that already observed for polymethylmethacrylate, polystyrene, and polyethylene oxide solutions in Aroclor.

Normal Freezing of Solutions of Isobutylene Polymers and Copolymers

Abstract Normal freezing of dilute solutions of polyisobutylene in cyclohexane was examined. Variation in distribution coefficient with freezing rate and molecular weight of the solute was observed, as well as establishment of a gradient for molecular weight in the frozen charge. Polyisobutylene-polystyrene or poly (methyl methacrylate) copolymers were likewise frozen, in benzene solution.

Dynamic Viscoelastic Properties of Dilute Polyisobutylene Solutions

In order to examine the Rouse and the Zimm theories, measurements have been made on complex rigidity G* of very dilute solutions of polyisobutylene (Mυ = 1.76 × 106) by means of the torsional crystal method at high frequencies. The complex intrinsic rigidity, [G*] = lim c→0 (G* − iωηs) / c, and the limiting relaxation time, (τp)0 = lim c→0 Kp(η − ηs)M / cRT, have been obtained by extrapolation to zero concentration, where Kp is the pth relaxation time factor determined on the basis of the above theories. In benzene at the theta temperature, curves based upon the Zimm theory excellently represent the experimental plots of log[G*]M / RT vs logωηs[η]M / RT, in which (τ1)0 = 2.54 × 10− 5sec (nondraining). In cyclohexane at 15.0° and 30.0°C, the results are intermediate between the Rouse and the Zimm theories (partial draining). The draining effect seems to correlate with the excluded volume effect.

Study on dilute solutions of polyisobutylene in n-heptane

Study on dilute solutions of polyisobutylene in n-heptane

Effect of Degradation by Pumping on Normal Stresses in Polyisobutylene Solutions

Normal stress measurements were made on dilute solutions of polyisobutylene in three low-viscosity solvents at high shear rates with a jet thrust apparatus in which the thrust tube was mounted on the frame of an analytical balance. Thrust measurements could be easily read to 0.01 g and replicate measurements agreed closely with the original ones. Mechanical degradation of polyisobutylene in cyclohexane and toluene caused significant reductions in (P11−P22)w values at high shear rates and in the amount of drag reduction in turbulent flow. Molecular weight distribution curves and estimates of viscosity-average molecular weights of the fresh and degraded solutions in toluene indicate that these effects noted in this solvent are caused by the breakdown of small amounts of high molecular weight polymer, with only a small change in the viscosity-average molecular weight.

Dynamic Mechanical Properties of Dilute Polyisobutylene Solutions and Their Interpretation by an Extension of the Zimm Theory1a

Dynamic Mechanical Properties of Dilute Polyisobutylene Solutions and Their Interpretation by an Extension of the Zimm Theory^1a

Viscosity/temperature relationships for dilute solutions of high polymers

Values of Q and A in the expression η = Ae Q RT have been obtained for dilute solutions of polyisobutylene, polyvinyl acetate, polymethyl methacrylate, cellulose trinitrate and cellulose triacetate in representative solvents. The apparent activation energy of viscous flow Q is given by Q= Q o + K e Mc where Q 0 is the value for the solvent, M and c are the molecular weight and concentration of polymer and K e depends on polymer and solvent. Values of K e for the cellulose triesters are much larger than for the other polymers and it is suggested that this is due to their greater chain stiffness and extension. For the polymers with flexible chains A= A o + K a Mβc over a limited molecular weight range but with the cellulose triesters A= A o exp (- K a ′ Mλc where A 0 is the value for the solvent and K a, K′ a, α and β depend on polymer and solvent. Application of rate theory suggests that the entropy of activation of viscous flow decreases with increasing c and M for solutions of flexible chain polymers but that the reverse is true for solutions of stiff, extended cellulose derivative chains. Equations are derived relating the intrinsic viscosity to K e, K a or K′ a, α or β, M and T.

Unperturbed Chain Dimensions of Polymeric Chains

Methods are given for the calculation of polymer chain dimensions unperturbed by excluded volume effects but dependent on restricted rotation around the chain bonds as a result of interactions between substituents on neighboring chain atoms. The matrix methods used by most previous investigators are valid only for cases where the rotations, or pairs of neighboring rotations, are noninteracting. The methods recently developed by Lifson to account for interactions between any two consecutive rotations in chains of the type (CR2)i are extended to chains of the type (CH2–CR2)i and isotactic chains of the type (CH2–CHR)i. As an illustration the chain dimensions of polyisobutylene are calculated by using parameters from x-ray data in the crystalline state and results from stress-temperature measurements on amorphous networks. Reasonable agreement is obtained with experimental data on dilute solutions of polyisobutylene.

Mechanical Degradation of Dilute Polyisobutylene Solutions

Mechanical Degradation of Dilute Polyisobutylene Solutions

Mechanical properties of discrete polymer molecules

AbstractA frequency‐dependent stiffness μB was found from the action of high frequency shear waves on dilute solutions of polyisobutylene, polypropylene, polyethylene, polystyrene, hevea rubber, and polybutadiene microgel. A dynamic viscosity associated with streaming of solvent through the molecular coil, ηB, dropped far more rapidly with rising temperature than solvent viscosity, denoting that it, too, reflected configurational changes. (The μB for polyisobutylene in solution declined moderately with rising temperature, corresponding to an exponential coefficient of 2.3 kcal.) This behavior suggested three chief mechanisms for deformation of isolated chains: (1) viscoelastic configuration changes (W. Kuhn's “macroconstellation changes”) with contribution to rigidity per average molecule per cubic centimeter of solution of 〈 μ2 〉 or force constant 〈 f2 〉; (2) temporary entanglements of interpenetrating segments in the chain coil (like the interchain entanglements in concentrated solutions of J. D. Ferry), with contribution to rigidity 〈 μ3 〉; and (3) restrictions to rotational flexibility around chain linkages, with rigidity contribution 〈 μ4 〉. Arrangement of these processes in parallel with solvent viscosity yielded frequency‐independent constants in agreement with the limited data so far obtained in the 103 to 108 cycle range.Such a model gave molecular mechanical constants correlating roughly with chemical structures. For polyisobutylene, force constants per average molecule were 〈 f2 〉 = 17.1 × 10−13 dyne cm., 〈 f3 〉 = 6.3 × 10−12 and 〈 f4 〉 = 1.6 × 10−10. Lower molecular weight (1.2 × 106 vs. 3.9 × 106) gave slightly lower values. 〈 f4 〉 represents restrictions to rotation per isobutylene residue in the chain of 2.3 × 10−15, or about 104 less than valence bond infrared vibrational or twisting force constants for hydrocarbons. The combined average chain rigidities expressed by the force constant 〈 fB 〉, at 20 kc. and 25°C. were, for polyisobutylene of M̄V ∼ 106, 1.8 × 10−12; hevea rubber of M̄V = 2.3 × 105, 1.5 × 10−15; polystyrene of M̄V = 2.3 × 105, 4.5 × 10−16. Hence, single polystyrene chains are quite flexible, but polybutadiene microgel has 〈 fB 〉 = 5.2 × 10−11, for M̄W ∼ 18 × 106, showing effect of internal cross‐linking.“Poor” solvents (“solvent power” μ > 0) caused chain rigidity of polyisobutylene and polystyrene to decrease, compared to good solvents (“solvent power” μ ∼ 0), and viscosity decreased also. Apparent decrease in 〈 fB 〉 apparently means external (solvent) “compression” of chain, and agrees with technological efficiency of poorly compatible plasticizers.Complete theory of effects has been outlined by Kirkwood, for a rod model. Great range of rigidities shown even by hydrocarbon chains (intrinsic rigidity of polyethylene soln., [μ] = 906 dynes/cm.2, of polypropylene soln., [μ] = 92 dynes/cm.2) has not yet been treated, however.