Polyisobutylene, diffusion

FIG. 2 Mean-square displacement (MSD) of helium atoms dissolved in polyisobutylene. There is a regime of anomalous diffusion (MSD a followed by a crossover at 100 ps to normal (Einstein) diffusion (MSD a r) [24],... 

In polyisobutylene in the melt and in solution (CC14, CS2), McCall, Douglass, and Anderson 17) found that the activation energies for polymer diffusion increased with polymer concentration from the value at infinite dilution (approaching the pure solvent value) to the value in the melt. Solvent diffusion, and solvent effect on polymer diffusion, were also measured. The Stokes-Einstein model applied to this data yielded molecular dimensions too small by a factor of two or three. 

Several graft copolymerizations were described by Ballantine (17, 64), Henglein (104, 105) and coworkers. Different monomer-polymer systems were examined styrene on polymethyl methacrylate, poly-2, 5-dichlorostyrene, polytetrafluoroethylene, polyethylene, polypropylene and polyisobutylene, acrylonitrile on polyethylene, rubber, polymethyl methacrylate and dimethyl polysiloxane, vinylpyrrolidone and acroleine on polymethyl methacrylate. The results agree with the preceding ones moreover they show the influence of the swelling and diffusion of the monomer into the polymer. 

Thin films of many polymeric materials exhibit good adhesive i operties and are easily applied to most substrates. In addition, relatively rapid diffusion and a high capacity for organic solutes make amorphous rubbery polymers attractive as sensor coatings. An example of this rapid and sensitive detection is shown in Figure 5.17, the response of a polyisobutylene-coated SAW device to trichlraoeth-... 

Muller-Plathe, F.. Rogers, S.C., Gunstern, W.F.v. Diffusion coefficients of penetrant gases in polyisobutylene can be calculated correctly by molecular dynamics simulations. Macromolecules 25, 6722-6724 (1992)... 

It is known that an elevated permeability of usual SPC based on liquid glass is intimately connected with the big porosity and filtering defects. Because of this, application of commonly used SPC requires a leak proof and chemically stable lining of expensive materials (lead, polyisobutylene, etc.). Filtration and diffusive permeability of SPC with monomeric additives (TFS, FA) in aggressive environments were studied. 

The commercially available transdernal systen of clonidine consists of an outer layer of pigmented polyester a drug reservoir of clonidine, mineral oil, polyisobutylene, and colloidal silicon dioxide a microporous polypropylene membrane that controls the rate of diffusion of the drug and a final adhesive layer that provides an initial release of drug and contains those ingredients found in the reservoir. The adhesive layer is covered by a protective strip which is removed prior to application (1). 

FIGURE 6.18 Normalized difference in thermal diffusivity versus normalized birefringence for polyisobutylene after imposition of a shear strain = 8. The line is the linear fit to the data (Venenis etal., 1999). 

Calculation of fast polymerisation processes with consideration of the longitudinal diffusion R < R, demonstrates that the dependence of LIV) ff - lkp A Q at different [A values are close to those calculated by Equation 1.46 (Figure 1.5). This opened the door to the easy and effective experimental estimation of constants kp and k in processes of this type. Studying the dependence of the polyisobutylene yield on a reaction zone length and/or flow rate at various catalyst concentrations enabled the estimation of the constants kp and k, if two areas of ratios [Pg.17]

Fox TG, Floiy PJ (1948) Viscosity-molecular weight and viscosity- temperature relationships for polystyrene and polyisobutylene. J Am Chem Soc 70 2384—2395 Frischknecht AL, Milner ST (2000) Diffusion with contour length fluctuations in linear polymer melts. Macromolecules 33 5273-5277... 

In a more recent study, Muller-Plathe, Rogers, and van Gunsteren have pointed out a case of anomalous diffusion in polyisobutylene near room temperature [48], in harmony with the findings by TSA for gas motion in dense polymers [56]. For He in PIB, anomalous behavior could be clearly shown, and the transition to normal diffusion at around 0.1 ns could be captured. The log-log plot that shows this crossover, is reproduced in Fig. 6. For the much slower diffusing O2, the mean-square displacement data were not accurate enough to determine unambiguously if the curve represented diffusive behavior... 

Incorporation of the chain into the network is difficult. It is not enough to put a swollen gel into contact with a solution of chains. Even if thermodynamic eqitilibrium allows for a finite concentration of chains in the gel, the kinetics of chain diffusion ate usually too slow. However, it is possible to prepare a mixture of chains P with other chains C, and to crosslink the C chains in a second stage. This was done by the Wisconsin group using two different pathways 1) with P = polyisobutylene and C = butyl rubber, and 2) with P = saturated ethylene propylene copolymer, C = ethylene propylene terpolymer [+ crosslinking agent (sulfiir)]. ... 

It is possible, however, to speak of relative consistencies of the polymers of Fig. 5-10 or, in another sense, of the relative mobilities of diffusing species in them. If such a distinction is made, the materials could be arranged (in order of increasing consistency or decreasing diffusing species mobility) as polyethylene, polypropylene, polyisobutylene, and polystyrene. This fact checks with Einstein s original relation, which showed diffusivity to be related directly to the mobility of the diffusing species. 

Fig. 5-8 Diffusivity divided by the square of gas collision diameter versus gas collision diameter for polyisobutylene (8, 9).

Polyisobutylene PSA is also used. Procedures for the prediction of drug solubility and diffusion in a polymer matrix are described. 16 refs. 

Molecular dynamics (MD) is an invaluable tool to study structural and dynamical details of polymer processes at the atomic or molecular level and to link these observations to experimentally accessible macroscopic properties of polymeric materials. For example, in their pioneering studies of MD simulations of polymers, Rigby and Roe in 1987 introduced detailed atomistic modeling of polymers and developed a fundamental understanding of the relationship between macroscopic mechanical properties and molecular dynamic events [183-186]. Over the past 15 years, molecular dynamics have been applied to a number of different polymers to study behavior and mechanical properties [187-193], polymer crystallization [194-196], diffusion of a small-molecule penetrant in an amorphous polymer [197-199], viscoelastic properties [200], blend [201,202] and polymer surface analysis[203-210]. In this article, we discuss MD studies on polyethylene (PE) with up to 120,000 atoms, polyethylproplyene (PEP), atactic polypropylene (aPP) and polyisobutylene (PIB) with up to 12,000 backbone atoms. The purpose of our work has been to interpret the structure and properties of a fine polymer particle stage distinguished from the bulk solid phase by the size and surface to volume ratio. 

FIG. 17-5. Logflc plotted against V2 for solutions of polyisobutylene in -hexadecane. 4S Data froni diffusion open circles 24.0°C slotted circles, 40.0°C black circles, 48.4°C. Data from viscoelastic measurements in the transition zone circles with tags, 25.0°C. 

One mechanism for doing this is to use a transdermal patch. This is essentially an adhesive plaster with the drug mixed into the adhesive. Polyisobutylene adhesives are often used for this purpose. The drug then diffuses out of the polymer and through the skin at a preplanned rate. Of course this only works for drugs that can be absorbed through the skin. 

Studied the time evolution of the interfacial tension when polyisobutylene (PIB)-b-PDMS was introduced to PIB/PDMS blend, with the copolymer added to the PIB phase in that study both homopolymers were poly disperse. The time dependence of the interfacial tension was fitted with an expression that allowed the evaluation of the characteristic times of the three components. The characteristic time of the copolymer was the longest, whereas the presence of the additive was found to delay the characteristic times of the blend components from their values in the binary system. The possible complications of slow diffusivities on the attainment of a stationary state of local equilibrium at the interface were thoroughly discussed by Chang et al. [58] within a theoretical model proposed by Morse [279]. Actually, Morse [279] suggested that the optimal system for measuring the equilibrium interfacial tension in the presence of a nearly symmetric diblock copolymer would be one in which the copolymer tracer diffusivity is much higher in the phase to which the copolymer is initially added than in the other phase because of the possibility of a quasi-steady nonequilibrium state in which the interfacial coverage is depleted below its equilibrium value by a continued diffusion into the other phase. 

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