Polyisobutylene viscosity

Inspection of Fig. 3.9 suggests that for polyisobutylene at 25°C, Ti is about lO hr. Use Eq. (3.101) to estimate the viscosity of this polymer, remembering that M = 1.56 X 10. As a check on the value obtained, use the Debye viscosity equation, as modified here, to evaluate M., the threshold for entanglements, if it is known that f = 4.47 X 10 kg sec at this temperature. Both the Debye theory and the Rouse theory assume the absence of entanglements. As a semi-empirical correction, multiply f by (M/M. ) to account for entanglements. Since the Debye equation predicts a first-power dependence of r) on M, inclusion of this factor brings the total dependence of 77 on M to the 3.4 power as observed. 

The low molecular weight materials produced by this process are used as lubricants, whereas the high molecular weight materials, the polyisobutylenes, are used as VI improvers and thickeners. Polybutenes that are used as lubricating oils have viscosity indexes of 70—110, fair lubricating properties, and can be manufactured to have excellent dielectric properties. Above their decomposition temperature (ca 288°C) the products decompose completely to gaseous materials. 

Viscosity (Viscosity-Index) Improvers. Oils of high viscosity index (VI) can be attained by adding a few percent of ahnear polymer similar to those used for pour-point depressants. The most common are polyisobutylenes, polymethacrylates, and polyalkylstyrenes they are used in the molecular weight range of about 10,000 to 100,000 (18). A convenient measure for the viscosity-increasing efficiency of various polymers is the intrinsic viscosity Tj, as given by the function... 

Polyisobutylene is produced ia a range of mol wts, and has found a host of uses. The low mol wt Hquid polybutenes have appHcations as adhesives, sealants, coatings, lubricants, and plasticizers, and for the impregnation of electrical cables (7). Moderate mol wt polyisobutylene was one of the first viscosity-iadex modifiers for lubricants (8). High mol wt polyisobutylene is used to make uncured mbbery compounds, and as an impact additive for thermoplastics. 

Other polymers used in the PSA industry include synthetic polyisoprenes and polybutadienes, styrene-butadiene rubbers, butadiene-acrylonitrile rubbers, polychloroprenes, and some polyisobutylenes. With the exception of pure polyisobutylenes, these polymer backbones retain some unsaturation, which makes them susceptible to oxidation and UV degradation. The rubbers require compounding with tackifiers and, if desired, plasticizers or oils to make them tacky. To improve performance and to make them more processible, diene-based polymers are typically compounded with additional stabilizers, chemical crosslinkers, and solvents for coating. Emulsion polymerized styrene butadiene rubbers (SBRs) are a common basis for PSA formulation [121]. The tackified SBR PSAs show improved cohesive strength as the Mooney viscosity and percent bound styrene in the rubber increases. The peel performance typically is best with 24—40% bound styrene in the rubber. To increase adhesion to polar surfaces, carboxylated SBRs have been used for PSA formulation. Blends of SBR and natural rubber are commonly used to improve long-term stability of the adhesives. 

IV. Viscosity Average Molecular Weights of Polyisobutylenes 1. Introduction... 

Fig. 50.—Intrinsic viscosity-molecular weight relationship for polyisobutylene in diisobutylene (DIB) at 20° and in cyclohexane at 30°C. Open circles from Ref. 7 filled circles, Ref. 8.

The results of intrinsic viscosity measurements for four polymer-solvent systems made at the -temperature of each are shown in Fig. 141. The four systems and their -temperatures are polyisobutylene in benzene at 24°C, polystyrene in cyclohexane at 34°C, poly-(di-methylsiloxane) in methyl ethyl ketone at 20°C, and cellulose tricapry-late in 7-phenylpropyl alcohol at 48°C. In each case a series of poly-... 

Fig. 143.—The intrinsic viscosity of a polyisobutylene fraction of high molecular weight plotted against temperature in four solvents cyclohexane, diisobutylene (DIB), toluene and benzene. The lines shown have been calculated according to theory. (Fox and Flory. )...

Fig. 144.—The treatment of expansion factor-temperature data obtained from intrinsic viscosities of polyisobutylene fractions in three pure solvents and in ethyl-benzene-diphenyl ether mixtures. Data for fractions having molecular weights Xl6 of 1.88, 1.46, and 0.180 are represented by O,, and Q, respectively. (Fox and Flory. 2)...

Fig Intrinsic viscosity-Molecular weight relationships for polyisobutylene in disobutylene and cyclohexane. 

Similarly, the polymerization process will pull the isobutylene selectively out of the C4 stream. Polyisobutylene is used mainly as a viscosity index improver in lubricating oils and in caulking and sealing compounds. Some of the low molecular weight polyisobutylenes are particularly suited for use in the construction field because it doesn t solidify. They remain a tacky fluid and when properly formulated with clay fillers, etc., take on the properties of a sticky, putty-like substance. 

Fig. 4.4 Scaling representation of the spin-echo data at Q ax- Different symbols correspond to different temperatures. Solid line is a KWW description (Eq. 4.8) of the master curve. The shift factors are taken from macroscopic viscosity measurements, a Polyisobutylene at Qmax l-0 A [125] measured on INI 1 (viscosity data from [34]). b Atactic polypropylene at Qmax=l-ll (viscosity data from [131]). (b Reprinted with permission from [126]. Copyright 2001 Elsevier)...

Person 1 Calculate the intrinsic viscosity, [rj], for the polyisobutylene sample in decalin. Person 2 Calculate the intrinsic viscosity, [rj], for the polyisobutylene sample in decalin-cyclohexanol. 

Viscosity is relatively higher in good solvents and lower in poor solvents. Polyisobutylene is used as an additive for motor oils. The oil is a poor solvent for the polymer at room temperature but becomes a good solvent at the operating temperatures of the gasoline combustion engine. Thus although the viscosity of an untreated 10-40 motor oil decreases as the temperature increases, the decrease is counteracted when polyisobutylene is present. Only traces (1-2%) of polyisobutylene are required to achieve the desired viscosity. 

Like dissolves like, and this is true with both polymers and smaller molecules. Thus linear amorphous polymers with nonpolar groups are typically soluble in nonpolar solvents with solubility parameter values within 1.8 H of that of the polymer. Thus polyisobutylene (PIB) is soluble in hot lubricating oils, and small amounts of high-molecular-weight PIB are used as viscosity improvers. 

Polyisobutylene. The solution viscosity of an irradiated polyisobutylene block was measured in CC14 at 30 °C. to determine the degree of degradation (5). The variation of viscosity-average molecular weight, Mv, with the dose, r, is shown in Figure 3. Nitrous oxide reduced the... 

Polyisobutylene. The viscosity of irradiated polyisobutylene is plotted against N20 pressure in Figure 5. The curve increases monotonically with increasing pressure. If nitrous oxide is effective in reducing the amount of degradation, the behavior of the curve seems to be reasonable since the gas concentration in the polymer solid should increase with the gas pressure. 

Fig. 5.7. Characteristic molecular weight for the viscosity vs concentration for the polyisobutylene-toluene system. The open circles (O) were obtained from >/0 vs c at constant molecular weight (159) the open squares ( ) were obtained from >/0 vs Mw at constant concentration (159) the solid square ( ) was obtained on undiluted polyisobutylene (9)...

Fig. 3. Effective viscosity versus time at extension under conditions of constant strain velocities in molten polyisobutylene [23]...

The major difference between dependencies of ct/x upon t, in case of polyethylene, and the similar curves in case of polyisobutylene (see Fig. 4) was that even at very low values of tensile strain velocities x in case of polyethylene, the flow failed to remain linear during the entire time interval of the experiment. Dependencies of effective viscosity a(t)/x at low values of x reached a constant value (stationary flow) exceeding 3r during times t, significantly exceeding the similar time under shear. With further increase in strain velocity x, the value t started to decrease in the same way as it was in experiments with polyisobutylene (PIB). 

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