Polybutadiene self-diffusion

Fig. 3.28 Melt self-diffusion data for hydrogenated (or deuterated) polybutadiene samples adjusted to 175 °C as a function of molecular weight [82] [83], S [84],H[85],S [86], [87]. (Reprinted with permission from [82]. Copyright 1999 The American Physical Society)...

Fig. 7. Self-diffusion of linear (open symbols) and three-armed star (filled symbols) polystyrenes (squares) and polybutadienes (circles) in CC14 extrapolated to infinite dilution, as function of polymer molecular weight (Ref. 53>, 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... 

Since the pioneering work of Stejskal, the pulse field gradient method is currently used to characterize the diffusion process of small molecules or of macromolecules in dilute or semi-dilute solutions [18-20]. In this Chapter, the NMR approach is illustrated from the self-diffiision of ( dohexane molecules through polybutadiene. Variations of the Ds self-diffusion coefficient of cyclohexane in polybutadiene have been reported as a temperature function considering several concentrations [21]. 

Grinberg, F. A., Skirda, V. A., Maklakov, V. A., Ragovina, L. Z., and Niki-forova, G. G. (1987). Self-diffusion in solutions of polyblock polysulfone-polybutadiene copolymer. Vysokomol. Soedin. Ser. A 29, 2029-2034 (in Russian). 

Fig. 11 The dynamic structure factor C(, r) of polybutadiene star 12880 (nominally f = 128, Ma = 80kgmol ) in cyclohexane at ci = 0.016gmL and q = 0.035nm , along with the fit (solid line) from the ILT analysis. The corresponding relaxation distribution function L(ln(T)) (shown here for f i and q = 0.023gmL ) embraces the cooperative diffusion (1), the collective apparent diffusion (2), and the self-diffusion (3). The slowing-down of the middle structural mode (2) and the increase of its intensity with q are shown in the upper inset whereas the lower cartoon illustrates the liquid-like ordering [43,189]. The core regions are drawn out of scale (larger) for clarity...

As the glass transition temperature Tg is approached, the friction coefficient C sharply increases [3] and hence becomes too small to be measured. Thus, self-diffusion measurements on undiluted polymers are usually made at temperatures far above Tg. For example, all the reported data on polystyrene melts (Tg 100°C) were taken in the range 150 - 250° C. Working at such high temperatures, however, is not simple for various technical reasons including polymer degradation. It is therefore advantageous to study polymers with Tg far below room temperature if nearly monodisperse samples are available (use of polydisperse samples should be avoided for basic research). Extimples of such polymers are poly(isoprene) and polybutadiene. 

Self-diffusion in the melt of polyethylene (PE) (or hydrogenated polybutadiene) has also been investigated rather extensively. Figure 8-4, taken from Tirrell s review [2], shows typical experimental data. Each set of data points is fitted closely by a straight line of slope -2, consistent with the reptation theory. However, we see again that the NMR data [17, 18, 22, 23] appear above those from tracer diffusion [24, 25] and neutron scattering [26]. The reason for the discrepancy was left unexplained in Tirrell s paper. 

Figure 33.12 Self-diffusion coefficient D of seven different types of polymers (polystyrene, poly(ethyleneoxide), polyisoprene, polybutadiene, poly(dimethylsiloxane), poly(ethylene oxide), poly(methylstyrene)) versus molecular weight shows that D oc N - which differs somewhat from the N...

Bartels, C.R., Crist, B., and Graessley W.W. (1984) Self-diffusion coefficient in melts of linear polymers Chain length and temperature dependence for hydrogenated polybutadiene. Macromolecules, 17 (12), 2702-2708. 

E. D. von Meerwall, D. H. Tomich, J. Grigsby, et al. Self-diffusion of threearmed star and linear polybutadienes and polystyrenes in tetrachloromethane solution. 

M. H. Blees, J. M. Geurts, and J. C. Leyte. Self-diffusion of charged polybutadiene latex particles in water measured by pulsed field gradient NMR. Langmuir, 12 (1996), 1947-1957. 

Blees, M. H., Geurts, J. M., Leyte, J. C., Self-Diffusion of Charged Polybutadiene Latex Particles in Water Measured by Pulsed Field Gradient NMR, Langmuir, 19%, 12, 1947-1957. 

Headspace sampling and GC have been used to quantitatively follow the thermal oxidation of a low molecular weight hydroxyl-terminated polybutadiene [26]. Rate studies using this simple, efficient technique revealed an induction period for the oxidation followed by self-catalysed oxidation. The rate for this latter step was quickly controlled by the diffusion of oxygen into the polymer. 

---