Polyisoprene, diffusion

Bueche et al. (1952) derived that the coefficient for self-diffusion of poly(n-butyl acrylate) is inversely proportional to the bulk viscosity of this polymer. Also in the natural rubber (polyisoprene) diffusion system a clear connection appears to exist between diffusion coefficient and bulk viscosity. In general the following expression may be used as a good approximation ... 

Measurements of diffusion of tracer polymers in ordered block copolymer fluids is another potentially informative activity, since molecular diffusion is one of the most basic dynamic characteristics of a molecule. Balsara, et al. have measured the retardation of diffusion due to ordering in the diffusion of polystyrene tracer homopolymers in polystyrene-polyisoprene matrices of various domain sizes [167]. Measurement of the tracer diffusion of block copolymer molecules will also be important. Several interesting issues are directly addressable via measurements... 

Table 7. Molecular masses, functionalities, calculated and measured radii of gyration, and translational diffusion coefficients of the investigated polyisoprene stars...

When a chain has lost the memory of its initial state, rubbery flow sets in. The associated characteristic relaxation time is displayed in Fig. 1.3 in terms of the normal mode (polyisoprene displays an electric dipole moment in the direction of the chain) and thus dielectric spectroscopy is able to measure the relaxation of the end-to-end vector of a given chain. The rubbery flow passes over to liquid flow, which is characterized by the translational diffusion coefficient of the chain. Depending on the molecular weight, the characteristic length scales from the motion of a single bond to the overall chain diffusion may cover about three orders of magnitude, while the associated time scales easily may be stretched over ten or more orders. 

Fig. 4. Self-diffusion in cis-polyisoprene melts as function of molecular weight, at five temperatures. Curves are single fit of Eq. (8) with Eq. (9) to all data. (Ref.41>, with permission).

An industrial oil-extended synthetic cis-polyisoprene was investigated by von Meerwall and Ferguson30). Following Boss, et al. 29), they substracted the unattenu-atable spin echo arising from the rubber, obtaining the diffusivity of the extender oil from the remainder. They demonstrated that no departures from Fickian diffusion occur, and measured the diffusion of the oil, both in the rubber and in the pure liquid, between —10 °C and 130 °C. Since the plot of log D vs. 1/T was not a straight line it was necessary to invoke the Williams-Landel-Ferry temperature dependence,... 

In their study of the NMR T2 and T2 of crosslinked cis-polyisoprene sheets under extension, von Meerwall and Ferguson 65) found that T2 of the rubber had much smaller anisotropy ( magic angle effect) than that of trace penetrants at the same extension ratio X < 3. However, the penetrant diffusion (referred to the strained dimensions) was within experimental error isotropic these findings are equally valid for C6F6 and n-hexadecane as penetrant. The authors concluded that segment orien-... 

Fig. 11. Diffusion of n-paraffins in a cis-polyisoprene as function of concentration at 51 °C. Lines are two-parameter fits of Eq. (17) to data. Paraffin carbon numbers are indicated. (Ref.70), with permission).

Fleisher G, Appel M (1995) Chain length and temperature dependence of the self-diffusion of polyisoprene and polybutadiene in the melt. Macromolecules 28(21) 7281-7283 Flory PJ (1953) Principles of polymer chemistry. Cornell Univ. Press, New York Flory PJ (1969) Statistics of chain molecules. Interscience, New York... 

Here the PFGE results for two elastomers EPDM and polyisoprene [24] are compared. The EPDM investigated here is, for an elastomer, highly crystalline (30%). While crystalline domains are expected to behave as diffusion barriers for Xe, this was thought to be an interesting case for the determination of the diffusion coefficient as a function of the diffusion time A. As a comparison the completely amorphous polyisoprene was used. 

The results of the time dependent PFGE experiments are shown in Figure 12.24. This figure shows that the Xe diffusion in polyisoprene is faster than in the EPDM sample... 

Figure 12.24 The effective diffusion coefficient as a function of the diffusion time A for polyisoprene (top curve) and EPDM (lower curve)...

The self-diffusion of benzene in PIB [36], cyclohexane in BR [37] and toluene in PIB [38-40] has been investigated by PFG NMR. In addition more recently Schlick and co-workers [41] have measured the self-diffusion of benzene and cyclohexane mixtures in polyisoprene. In the first reported study of this kind, Boss and co-workers [36] measured the self-diffusion coefficients of benzene in polyisoprene at 70.4 °C. The increase in Dself with increasing solvent volume fraction could be described by the Fujita-Doolittle theory which states that the rate of self-diffusion scales with the free volume which in turn increases linearly with temperature. At higher solvent volume fractions the rate of selfdiffusion deviates from the Fujita-Doolittle theory, as the entanglement density decreased below the critical value. 

Th-FFF can be applied to almost all kinds of synthetic polymers, like polystyrene, polyolefins, polybutadiene, poly(methyl methacrylate), polyisoprene, polysulfone, polycarbonate, nitrocelluloses and even block copolymers [114,194,220]. For some polymers like polyolefins, with a small thermal diffusion coefficient, high temperature Th-FFF has to be applied [221]. Similarly, hydrophilic polymers in water are rarely characterized by Th-FFF, due to the lack of a significant thermal diffusion (exceptions so far poly(ethylene oxide), poly(vi-nyl pyrrolidone) and poly(styrene sulfonate)) [222]. Thus Th-FFF has evolved as a technique for separating synthetic polymers in organic solvents [194]. More recently, both aqueous and non-aqueous particle suspensions, along with mixtures of polymers and particles, have been shown to be separable [215]. 

FAD allows to study rather precisely and unambiguously the OACF of polymer chains. Thanks to the unique statistical nature of the single photon method, and to the performances of the synchrotron source, it has proved very useful in the discussion of the nature of motions. For instance, it led to the first observation of the diffusion of orientational motions along the chains in polymer melts. Of course, the labeling nature of this kind of experiments implies two limitations. The first one, technical, is the necessity of labeling chains. Indeed, many different polymers can be labelled and several species have been or are studied in our laboratory (Polystyrene polybutadienes -20.37) polyisoprenes poly-... 

This theory also gives good quantitative agreement with available experimental data for these properties. For example, for the non-LC backbone polymer polyisoprene [see Figure 3(a)] at infinite dilution in hexane [CHj-(Cl -CHj] in the I liquid phase at T - 293 K, the infinite dilution diffusion coefficient D g (in units of... 

Viovy, Monnerie, and Brochon have performed fluorescence anisotropy decay measurements on the nanosecond time scale on dilute solutions of anthracene-labeled polystyrene( ). In contrast to our results on labeled polyisoprene, Viovy, et al. reported that their Generalized Diffusion and Loss model (see Table I) fit their results better than the Hall-Helfand or Bendler-Yaris models. This conclusion is similar to that recently reached by Sasaki, Yamamoto, and Nishijima 3 ) after performing fluorescence measurements on anthracene-labeled polyCmethyl methacrylate). These differences in the observed correlation function shapes could be taken either to reflect the non-universal character of local motions, or to indicate a significant difference between chains of moderate flexibility and high flexibility. Further investigations will shed light on this point. 

The basic form of the model of P D used in this work, which will be described elsewhere in detail, [22] treats the diffusion of small amounts of "simple" spherical penetrants, such as gas molecules, in "smooth-chained" polymers, such as poly (ethylene terephthalate) (PET) and cis-polyisoprene (natural rubber). [12] Whenever necessary, generalized equations are being used, for example for simple nonspherical penetrants [13] and for polymers which possess closely spaced, bulky side groups such as poly(vinyl chloride) (PVC). [14]... 

The theory proposed for equilibrium swelling and diffusion is based on the assun tlon that the hydrophilic impurities are present in particulate form and are dispersed throughout the rubber. The precise nature of this impurity in natural rubber is not known so it was decided to make a model rubber by adding 0.17. of a hydrophilic Impurity (sodium chloride) to a solution polymerised synthetic rubber (cis-polyisoprene) Ich is chemically the same as natural rubber. Using this model rubber it is possible to check the theory more precisely since both the nature and concentration of the hydrophilic lgq>urlty in the model rubber are known. It is proposed that the water diffuses through the rubber and forms droplets of solution inside the rubber where there are particles of the hydrophilic impurity thereby causing a non-uniform distribution of water in the rubber. The... 

Unlike regular block copolymer micelles which are well permeable for reagents, triblock nanospheres with hydroxylated polyisoprene coronas, cross-linked poly(2-cinnamoyloxyethyl methacrylate) shells, and poly(acrylic acid) cores, filled with Pd nanoparticles, showed slower hydrogenation of alkenes than Pd blacks due to the need for the reactant(s) to diffuse into and the products to diffuse out of the encapsulating nanospheres [13]. On the other hand, microspheres formed by diblock poly(t-butyl acrylate)-hlocfe-poly(2-cinnamoyloxyethyl methacrylate) and filled with Pd nanoparticles demonstrated good permeability and higher catalytic activity in the hydrogenation of methyl methacrylate than the commercial Pd black catalyst [14]. 

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