Styrene and isoprene friction factors in styrene-isoprene matrices

Abstract

Monomeric friction factors, Ξ, for polystyrene (PS), polyisoprene (PI), and a polystyrene–polyisoprene (SI) diblock copolymer have been determined as a function of temperature in four poly(styrene‐b‐isoprene‐b‐styrene‐b‐isoprene) tetrablock copolymer matrices. The Rouse model has been used to calculate the friction factors from tracer diffusion coefficients measured by forced Rayleigh scattering. Within the experimental temperature range the tetrablock copolymers are disordered, allowing for measurement of the diffusion coefficient in matrices with average compositions determined by the tetrablock copolymers (23, 42, 60, and 80% styrene by volume). Remarkably, for a given matrix composition the styrene and isoprene friction factors are essentially equivalent. Furthermore, at a constant interval from the system glass transition temperature, Tg, all of the friction factors (obtained from homopolymer, diblock copolymer, and tetrablock copolymer dynamics) agree to within an order of magnitude. This is in marked contrast to results for miscible polymer blends, where the individual components generally have distinct composition dependences and magnitudes at constant T − Tg. The homopolymer friction factors in the tetrablock matrices were systematically slightly higher than those of the diblock, which in turn were slightly higher than those of the homopolymers in their respective melts, when all compared at constant T − Tg. This is attributed to the local spatial distribution of styrene and isoprene segments in the tetrablocks, which presents a nonuniform free energy surface to the tracer molecules. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 3079–3086, 1998

Homopolymer and small‐molecule tracer diffusion in a gyroid matrix

“…For all plots, the intensities are normalized by subtraction of the baseline, B , and division by the maximum intensity, I peak , to compare different decays. For temperatures between 120 and 150 °C, an initial d 2 independent decay is observed at times less than 1 s. This d 2 ‐independent decay has been observed in measurements made with ONS36 and is attributed to the somewhat complicated ring‐closing photochemical reaction of the dye 37. Therefore, the d 2 ‐independent portion is ignored during the fitting, as shown in Figure 9(a), where the fits for data at 120 °C were started at 0.5 s.…”

“…To test this hypothesis, we assumed a sinusoidal PS composition profile. Previously, we determined the friction factor for PI in matrices of arbitrary PI and PS composition over the relevant temperature range 36. We then estimated the average friction factor for the gyroid via a Boltzmann‐weighted average corresponding to the enthalpic penalty for the PI‐8* to reside in regions with higher PS concentrations: where ζ is the friction factor ( D ∼ 1/ζ) calculated for a composition, ϕ, at position x .…”

Dynamics in disordered block copolymers and miscible blends composed of poly(vinyl ethylene) and polyisoprene

“…Furthermore, the effect of the chemical linkage between different polymer chains on the dynamics of disordered diblock copolymers (BCPs) also needs to be clarified. Many studies of dynamics in miscible blends1–24 and disordered block copolymers12, 25–30 have been performed thus far. Blends commonly exhibit broader relaxation spectra than those of the components.…”

Using neutron reflectivity to determine the dynamic properties of a copolymer in a homopolymer matrix

“…However, the local segmental relaxation processes in multicomponent polymer systems are not well understood 1–8. The impact of the dynamics of one component on the dynamics of the other is not simply proportional to the relative amounts of each component, as one might expect from simple mixing rules.…”

“…Recent work has shed some light on ζ(Φ, T )1–16 with techniques that are sensitive to local dynamics, such as rheology, quasi‐elastic neutron scattering (QENS), and NMR. However, these techniques often measure different timescales and ensembles and do not provide a clear picture of the composition and temperature dependence of the relaxation processes that occur in multicomponent polymer systems.…”