Polyisobutylene parameter

Polyisobutylene is readily soluble in nonpolar Hquids. The polymer—solvent interaction parameter Xis a. good indication of solubiHty. Values of 0.5 or less for a polymer—solvent system indicate good solubiHty values above 0.5 indicate poor solubiHty. Values of X foi several solvents are shown in Table 2 (78). The solution properties of polyisobutylene, butyl mbber, and halogenated butyl mbber are very similar. Cyclohexane is an exceUent solvent, benzene a moderate solvent, and dioxane a nonsolvent for polyisobutylene polymers. 

Table 2. Polymer—Solvent Interaction Parameters for Polyisobutylene and Butyl Rubber...

Another study looked at the miscibihty of E-plastomer-polyisobutylene blends. Blends were prepared from linear E-plastomers and a polyisobutylenes in the entire composition range. Flory-Huggins interaction parameters were determined from DMTA and DSC measurements. The usual technique had to be modified in the case of DSC data, since the Tg of E-plastomers cannot be detected by this technique. The two methods yielded identical results and indicated good interaction of the components, which was supported also by a SEM study and the mechanical properties of the blends. 

FIGURE 20.10 (a,b) Phase images of cryo-ultramicrotomed surfaces of triblock copolymer styrene and ethylene-butylene (SEES) samples of neat material and loaded with oil (40 wt%), respectively. (c,d) Phase images of film of triblock copolymer poly(methyl methacrylate-polyisobutylene-poly(methyl methacrylate) (PMMA-PIB-PMMA) immediately after spin-casting and after 3 h annealing at 100°C, respectively. Inserts in the top left and right comers of the images show power spectra with the value stmctural parameter of microphase separation. 

When this procedure is applied to the data shown for polystyrene in Fig. 116 and to those for polyisobutylene shown previously in Fig. 38 of Chapter VII, the values obtained for t/ i(1 — /T) decrease as the molecular weight increases. The data for the latter system, for example, yield values for this quantity changing from 0.087 at AT-38,000 to 0.064 at ilf = 720,000. This is contrary to the initial definition of the thermodynamic parameters, according to which they should characterize the inherent segment-solvent interaction independent of the molecular structure as a whole. 

Entropy of dilution parameters xj/i are calculable, according to Eq. (7), from the slopes of the lines in Fig. 122. Values obtained in this manner are 0.65 and 1.055 for the polyisobutylene and the polystyrene systems, respectively. These are considerably higher than the values... 

Thermodynamic parameters deduced as described above are shown in Table XLI for polyisobutylene and for polystyrene. It will be recalled that these primary parameters are obtained only with consider-... 

Liu and Zhong introduced a number of QSPR models based on molecular connectivity indices [151, 152], In a first iteration, the researchers developed polymer-dependent correlations descriptors were calculated for a set of solvents and models were developed per polymer type [151], Polymer classes under consideration were polystyrene, polyethylene, poly-1-butene, poly-l-pentene, poly(4-methyl-l-pentene), polydimethylsiloxane, and polyisobutylene. As the authors fail to provide any validation for their models, it is difficult to asses their predictive power. In a subsequent iteration and general expansion of this study, mixed and therefore more general models based on the calculated connectivity indices of both solvent and polymers were developed. While it is unclear from the paper which polymer representation was used for the calculation of the connectivity indices, the best regression model (eight parameter model) yields only acceptable predictive power (R = 0.77, = 0.77, s = 34.47 for the training set, R = 0.75... 

The principal polyolefins are low-density polyethylene (ldpe), high-density polyethylene (hope), linear low-density polyethylene (lldpe), polypropylene (PP), polyisobutylene (PIB), poly-1-butene (PB), copolymers of ethylene and propylene (EP), and proprietary copolymers of ethylene and alpha olefins. Since all these polymers are aliphatic hydrocarbons, the amorphous polymers are soluble in aliphatic hydrocarbon solvents with similar solubility parameters. Like other alkanes, they are resistant to attack by most ionic and most polar chemicals their usual reactions are limited to combustion, chemical oxidation, chlorination, nitration, and free-radical reactions. 

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. 

Three polymer pairs, polyethylene (PE)/polyisobutylene (PIB), PIB/ polystyrene (PS), and natural rubber (NR) /PS, are considered. The characteristic parameters, t>, p, T, for each of these polymers have been evaluated by Flory and co-workers and are used here as given. 

The calculated detonation parameters as well as the equations of state for the detonation products (EOS DP) of the explosive materials TKX-50 and MAD-X1 (and also for several of their derivatives) were obtained using the computer program EXPL05 V.6.01. These values were also calculated for standard explosive materials which are commonly used such as TNT, PETN, RDX, HMX, as well as for the more powerful explosive material CL-20 for comparison. The determination of the detonation parameters and EOS DP was conducted both for explosive materials having the maximum crystalline density, and for porous materials of up to 50 % in volume. The influence of the content of the plastic binder which was used (polyisobutylene up to 20 % in volume) on all of the investigated properties was also examined. 

It is seen that NMR properties, specific to polymeric systems, are not due to the absence of motions but to the non-isotropic character of these motions. It is worth emphasizing that the search for a characterisation of dynamical properties leads actually to the observation of non-isotropic rotations of monomeric units which result from the presence of entanglements. As3Tnmetry properties are observed instead of dynamic ones. Equation (17) is general and applies also to polyisobutylene solutions or to polyisoprene by using different values of the parameters. 

Figure 3.2 Trouton ratio, Tr, of uniaxial extensional viscosity to zero-shear viscosity jq after start-up of steady uniaxial extension at a rate of 1 sec i for a Boger fluid consisting of a 0.185 wt% solution of flexible polyisobutylene (Mu, = 2.11 x 10 ) in a solvent composed mostly of viscous polybutene with some added kerosene (solid line). The dashed line is a fit of a multimode FENE dumbbell model, where each mode is represented by a FENE dumbbell model, with a spring law given by Eq. (3-56), without preaveraging, as described in Section 3.6.2.2.I. The relaxation times were obtained by fitting the linear viscoelastic data, G (co) and G"(cu). The slowest mode, with ri = 5 sec, dominates the behavior at large strains the best fit is obtained by choosing for it an extensibility parameter of = 40,000. The value of S — = 3(0.82) n/C(x, predicted from the...

Figure 1. Calculation of polymer solubility parameters at 25°C for poly(dimethyl siloxane), PDMS, ethylenepropylene rubber, EPR, and polyisobutylene, PIB.

The van Krevelen method should be used in those cases where the deviation with GCVOL is over 6% (polyisobutylene, polyvinyl propionate) and for those polymers for which the GCVOL group parameters are not available. The density of polymers is important in many calculations. Several of the free-volume activity coefficient models discussed in Section 16.4 require the densities of polymers (and solvents) as input. We will see then that certain models are quite sensitive to the values of the densities employed. Moreover, polymer density data are often employed in equations of polymers for obtaining the pure polymer parameters. 

Devices are secured to the skin by use of a skin-compatible pressure-sensitive adhesive, usually based on silicones, acrylates or polyisobutylenes. These adhesives are evaluated by shear-testing and assessment of rheological parameters (Musolf 1987). Standard rheological tests include creep compliance (measurement of the ability of the adhesive to flow into... 

So while not perfect, the value of the Flory parameter chosen, 0.475, gives a reasonably good description of the cyclohexane-polyisobutylene system. 

In the processing of polymers, and also for polyrfier devolatilization (the removal of the solvent from the polymer), it is important to be able to calculate the equilibrium partial pressure of a solvent above solvent-polymer mixtures of different compositions. Calculate the partial pressure of benzene in benzene + polyisobutylene (PIB) mixtures at 298.15 and 312.75 K. In this calculation you can assume that polyisobutylene has a negligible vapor pressure, and that the Floty-Huggins model describes the solution behavior of this polymer + solvent mixture. Do the calculations fdr values of the Flory-Huggins y parameter equal to 0.5 to 1.0. 

Determine the value of the Flory y parameter in the Flor> -Huggins model that gives the best fit of the data above, and compute the equilibrium partial pressure of cyclohexane over cyclohexane-polyisobutylene mixtures. 

Blending within the family of PO has, however, been more common [Plochocki, 1978]. Although they are usually immiscible with each other, there exists some degree of mutual compatibihty between them. The similarity of their hydrocarbon backbones and the closeness of their solubility parameters, although not adequate for miscibility, accounts for a relatively low degree of interfacial tension. Eor example, the solubility parameters of polyethylene, polyisobutylene, ethylene-propylene rubber and polypropylene are estimated to be 16.0, 15.4,... 

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