The structure factor, viscosity, and diffusivity of four (styrene-b-isoprene-b-styrene-b-isoprene) tetrablock copolymers have been examined as functions of temperature (T). The copolymers have styrene compositions (f) of 23, 42, 60, and 80 vol % and total degrees of polymerization ca. 120; polystyrene and polyisoprene homopolymers with similar degrees of polymerization have been used for comparison. Small angle neutron scattering (SANS) measurements in the disordered state are well-described by the appropriate Leibler/RPA structure factors, and extrapolation of the inverse peak intensities to lower T yields estimates of the order−disorder transition temperatures, which are at or below −50 °C. Consequently, over the T range of interest (25−180 °C) and over length scales greater than the chain dimensions, the tetrablocks provide homogeneous matrices containing varying amounts of styrene and isoprene, in which the f and T dependence of segmental friction may be examined. The diffusivity (determined by pulsed-field-gradient NMR and forced Rayleigh scattering) and viscosity provide estimates of the effective monomeric friction factor ζeff(f,T) via the Rouse model; the two dynamic properties yield equivalent values of ζeff. The T dependence of ζeff is well-described by the WLF function, with the f dependence almost entirely contained in the composition dependence of the glass transition temperature (T g). Thus, when compared at constant T − T g, ζeff(f) is only slightly larger than ζPS° or ζPI°, in marked contrast to the results for miscible blends such as PS/PVME and PS/PPO. Prediction of ζeff(f,T) on the basis of the homopolymer values alone, i.e., ζPS° (T) and ζPI°(T), is only successful when T g(f) is incorporated explicitly. An approach using equation of state estimates of free volume is significantly less successful, implying that the most important determinant of local friction in the mixture is the effective T g sensed by each chain; T g(f) does not represent an iso-free volume state.

m: Forced Rayleigh scattering has been employed to measure tracer and selfdiffusion in block copolymer melts, for both entangled and unentangled systems, and in both the ordered and disordered stam. It is shown that entanglements are particularly effective in retarding the motion of copolymers parallel to the interface between microdomains. The mechanisms of "activated reptation" and "block retraction" are proposed for parallel diffusion. The importance of large amplitude composition fluctuations in the disordered state near the ordering transition is also demonstrated, for both copolymer and homopolymer tracers; the results suggest that copolymer tracers are more affected than homopolymers of comparable molecular weight.

The composition (φ) and temperature dependence (T) of the monomeric friction factor (ζ) has been examined for styrene (S) and methyl methacrylate (MMA) in five SMMA diblock copolymers and the corresponding homopolymers. In all cases the degree of polymerization was approximately 150, sufficiently low to ensure that the chain dynamics follow the Rouse model and that the copolymers are far above the order−disorder transition. The five diblock copolymers had styrene compositions of 91, 70, 39, 19, and 9 wt %. Values of an effective friction factor, ζ eff, were obtained from measurements of the steady flow viscosity via the Rouse model, whereby ζ eff represents an average over the S and MMA contributions. Values of the component friction factors, ζ PS and ζ PMMA, were extracted from forced Rayleigh scattering tracer diffusion measurements of dye-labeled PS, PMMA, and SMMA chains. In accord with previous studies, ζ PMMA in pure PMMA is significantly greater than ζ PS in pure PS, whether compared at equal T or equal T − T g, an effect attributable to specific details of local relaxation in PMMA. This difference between ζ PMMA and ζ PS persists in a common SMMA matrix, an effect which can be quantitatively accounted for by the recently introduced concept of self-concentration. The values of ζ eff increase monotonically with MMA content at fixed T and with decreasing T at fixed φ. The φ dependence of ζ eff is consistent with both “Rouse” and “Arrhenius” mixing rules, utilizing the pure component friction factors as input. The T dependence of ζ eff follows the standard Williams−Landel−Ferry relation, but the data for different φ do not collapse to a single curve when plotted against T − T g. In this respect, the PS/PMMA system is more complicated than the previously studied PS/polyisoprene system.

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

Forced Rayleigh scattering was used to measure the tracer diffusion coefficients of the photochromic dye tetrathioindigo (TTI) and a 1,4‐polyisoprene (PI) homopolymer (8000 g/mol) in a poly(styrene‐b‐isoprene) (SI) diblock copolymer matrix that formed a bicontinuous gyroid microstructure. The diblock copolymer contained 63% polystyrene (PS) by volume and had a total molecular weight of 21,300 g/mol. Rheology and small‐angle X‐ray scattering confirmed that the diblock copolymer microphase‐separated into the bicontinuous gyroid over the temperature range 60–230 °C, where the sample disordered. For both the TTI and PI tracers, two distinct modes of transport were observed. The faster mode displayed a temperature dependence consistent with diffusion within a PI matrix, whereas the slower mode had a temperature dependence more similar to diffusion within PS. The fast diffusivities were both over an order of magnitude lower than in a corresponding PI homopolymer matrix. For TTI, this was attributed to the preferential selectivity of the dye for PS and, therefore, an averaging of the mobility between the PS and PI domains. The slow mode was consistent with a small fraction of the TTI dye molecules becoming trapped within the much slower PS domains. For the PI tracer, the reduction in the diffusion coefficient for the fast mode was attributed to a combination of the tortuosity of the struts, the suppression of constraint release within the diblock matrix, and additional friction due to the presence of some styrene segments within the PI domains. The inevitable presence of grain boundaries or defects within the matrix interrupted the percolation of the PI struts, thereby forcing some of the PI tracers to diffuse through PS. Consequently, the slow mode was attributed to the diffusion through these defects, where the PI diffusion was retarded by both the increased segmental friction and the thermodynamic barrier to entering the PS domains. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 843–859, 2001