Rouse–Bueche theory and the calculation of the monomeric friction coefficient in a filled system

Direct experimental access to the monomeric friction coefficient (ζ₀) relies on the availability of a suitable polymer dynamics model. Thus far, no method has been suggested that is applicable to filled systems, such as filled rubbers or microphase‐segregated A–B–A thermoplastic elastomers (TPEs) at T_g,B < T < T_g,A. Building upon the procedure proposed by Ferry for entangled and unfilled polymer melts, the Rouse–Bueche theory is applied to an undiluted triblock copolymer to extract ζ₀ from the linear behavior in the rubber‐glass transition region, and to estimate the size of Gaussian submolecules. When compared at constant T – T_g, the matrix monomeric friction factor is consistent with the corresponding value for the homopolymer melt. In addition, the characteristic Rouse dimensions are in good agreement with independent estimates based on the Kratky–Porod worm‐like chain model. These results seem to validate the proposed approach for estimating ζ₀ in filled systems. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1437–1442     

Chain dynamics in entangled polymers: Diffusion versus rheology and their comparison

This review article scrutinizes and reanalyzes the extensively available literature data on the tracer and self chain diffusion coefficients D_tr and D_s along with the corresponding zero‐shear viscosity η₀ to show that D_s ∝ M^?ν starts with ν > 2.0 and converges to the asymptotic scaling exhibited by D_tr ∝ M^?2.0 as the molecular weight M increases beyond M/M_e = 10–20, in contrast to the onset of the asymptotic scaling M³ for η₀ taking place typically for M/M_e ? 10–20. A coherent analysis of these observations leads to the suggestion that the observed crossover in D_s is due to the constraint release effect, which diminishes around M/M_e = 10–20 and is negligible in measurements of D_tr when the matrix molecular weight P is much greater than M. The contour length fluctuation (CLF) effect, which is believed to cause the molecular weight scaling of η₀ to deviate significantly from its limiting behavior of M³, has little direct influence on the chain diffusion. The absence of the CLF effect on D_s leads to a much stronger than linear dependence of the product η₀D_s on M, which has been observed previously. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1589–1604, 2003     

Confinement effect of polystyrene on the relaxation behavior of polyisobutylene

The dynamic mechanical loss tangent (tan δ) peak of polyisobutylene (PIB) reveals an asymmetrical broad structure with a maximum on the high‐temperature side and a shoulder on the low‐temperature side. By comparing with the literature results, it is suggested that the shoulder and the maximum originate from local segmental motion and Rouse modes, respectively. Blending polystyrene (PS) with PIB has two effects on the relaxation behavior of PIB. One effect is that the maximum and the shoulder are both suppressed, but the maximum is suppressed to a higher extent. After PS forms the continuous phase, the maximum becomes lower than the shoulder, and even almost disappears when the weight ratio of PIB/PS is under 20/80. The other effect is that, before PS forms the continuous phase, the temperature position of the maximum (T_s) and that of the shoulder (T_α) remains constant, but after PS forms the continuous phase, both of them are reduced with decreasing particle size of the PIB phase, in a way similar to nano‐confinement effect on the depression of glass transition temperature. The depression amplitude of T_s is larger than that of T_α. The aforementioned two effects can be interpreted in terms of the limited expansion of free volume of the PIB phase exerted by the PS phase, which affects the maximum to a higher extent than the shoulder because Rouse modes are more sensitive to the free volume than local segments. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Syntheses and characterization of physically crosslinked hydrogels from dithiocarbamate‐derived polyurethane macroiniferter

A dithiocarbamate (DC)‐based polyurethane macroiniferter (PUMI) was synthesized and used to prepare physically crosslinked polyurethane‐block‐poly (acrylamide) (PU‐b‐PAAm) and polyurethane‐block‐poly(vinyl pyrrolidone) (PU‐b‐PVP) hydrogels. The success of the reactions has been confirmed by FTIR, ¹H‐NMR, and ¹³C‐NMR Spectroscopy analyses. The number average molecular weight of the block copolymers increased linearly with conversion and copolymerization time and thus followed a “living” radical mechanism. The water transport behavior of these polyurethane‐based hydrogels such as water uptake rate, equilibrium water content (EWC), transport number (n), characteristic diffusion rate constant (K), diffusion coefficient (D), and pH effect on EWC has been investigated. The results revealed that PU‐b‐PAAm hydrogels followed Fickian diffusion suggesting diffusion controlled swelling kinetics, whereas the PU‐b‐PVP hydrogels followed non‐Fickian diffusion indicating that both diffusion and structural relaxation controlled the water transport. The PU‐b‐PAAm hydrogels showed higher swelling at both low and high pH than at a neutral pH. This is attributed to protonation of the tertiary amines of N,N′‐diethyl‐N,N′‐bis(2‐hydroxyethyl) thiuram disulfide (DHTD) at low pH and base hydrolysis of amide segments at high pH. In the thermogravimetric analysis; PUMI, PU‐b‐PVP and PU‐b‐PAAm have degraded in three distinct stages related to CS₂ evolution, hard segment degradation, and soft segment degradation. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6272–6284, 2008     

Diffusion of camphorquinone in uniaxially drawn polycarbonate films

Employing the laser-induced holographic grating relaxation technique, we have measured tracer diffusion coefficients of a phtochromous dye, camphorquinone, in uniaxially drawn polycarbonate films as a function of stretch ratio. Anisotropy in the tracer diffusion coefficient has been observed with D_∥ greater than D_⟂ by at least a factor of 4 for the film stretched to the stretch ratio δ = 2.3. The diffusion coefficient along the direction of stretch D_∥ increases significantly with increasing δ, whereas D_⟂ decreases slightly with increasing δ. The stretch ratio dependence of D_∥ and D_⟂ is interpreted according to a modified free volume theory. The strain rate and stretch temperature dependence of the anisotropic tracer diffusion coefficient has also been investigated. © 1992 John Wiley & Sons, Inc.     

Structural studies of poly(N‐isopropylacrylamide) microgels: Effect of SDS surfactant concentration in the microgel synthesis

Thermoresponsive colloidal microgels were prepared by polymerization of N‐isopropylacrylamide (NIPAM) in the presence of a crosslinking monomer, N,N‐methylenebisacrylamide, in water with varying concentrations (<CMC) of an anionic surfactant, sodium dodecylsulphate (SDS). Volume phase transitions of the prepared microgels were studied in D₂O by ¹H NMR spectroscopy including the measurements of spin–lattice (T₁) and spin–spin (T₂) relaxation times for the protons of poly(N‐isopropylacrylamide) (PNIPAM) at temperature range 22–50 °C. In addition, microcalorimetry, turbidometry, dynamic light scattering, and electrophoretic mobility measurements were used to characterize the aqueous microgels. As expected, increasing SDS concentration in the polymerization batch decreased the hydrodynamic size of an aqueous microgel. Structures with high mobilities at temperatures above the LCST of PNIPAM were observed in the microgels prepared with small amount of SDS, as indicated by the relaxation times of different PNIPAM protons. It was concluded that the high mobility at high temperatures is in connection to a mobile surface layer with polyelectrolyte nature and with high local LCST. High SDS concentration in the synthesis was observed to prevent the formation of permanent, solid PNIPAM particles. The results from different characterization methods indicated that PNIPAM microgels prepared in high SDS concentrations appear to be more homogeneously structured than their correspondences prepared in low SDS concentration. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3305–3314, 2006     

High‐resolution solid‐state NMR study of the domain structure and molecular motion in drawn films of a vinylidene fluoride and trifluoroethylene copolymer with 73 mol % vinylidene fluoride

The heterogeneous higher order structure and molecular motion in a single crystalline film of a vinylidene fluoride (VDF) and trifluoroethylene (TrFE) copolymer with 73 mol % VDF was investigated with the ¹H–¹³C cross‐polarization/magic‐angle spinning NMR technique. A transient oscillation was observed in plots of the ¹³C peak intensity versus the contact time for the CH₂, CHF, and CF₂ groups. On the basis of the extended cross‐relaxation theory of spin diffusion, we determined that the oscillation behavior was caused by the TrFE‐rich segments in the chain and that the crystal consisted of VDF‐rich and TrFE‐rich domains. The former had TrFE‐rich segments in VDF and TrFE fractions of 0.24 and 0.27, respectively, and the latter had VDF‐rich segments in a VDF fraction of 0.49. The spin–lattice relaxation time T_1ρH in the rotating frame for each group was minimal in the three temperature regions of β, α_b, and α_c (↑) on heating and in the two temperature regions of α_1D and α_c (↓) on cooling. The α_c (↑) and α_c (↓) processes depended on the first‐order ferroelectric phase‐transition regions on heating and cooling, respectively. The motional modes for the other processes were confirmed by the T_1ρH minimum behavior of the VDF and TrFE groups in the TrFE‐rich domain and the VDF‐rich segments in the VDF‐rich domain. The β and α_b processes were attributed to the flip–flop motion of the TrFE‐rich segments and the competitive motion of the TrFE‐ and VDF‐rich segments in the ferroelectric phase, respectively. The α_1D process was due to the one‐dimensional diffusion motion of the conformational defects along the chain in the paraelectric phase, accompanied by the trans and gauche transformation of the VDF conformers of ttg⁺tg^? and g⁺tg^?tt. The effect of the competitive motion of the TrFE‐rich segment on the thermal stability of the VDF‐rich segment in the chain near the Curie temperature was examined. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1026–1037, 2002     

Carbon-13 spin–lattice relaxation in some polyfluoroaromatic compounds

Carbon-13 chemical shifts, spin-lattice relaxation times and nuclear Overhauser enhancement factors are reported for five polyfluoroaromatic compounds at 28°C. In all cases the relaxation of the fluorine bearing carbon is predominantly dipolar. Effective correlation times are smaller than those of the analogous benzene derivatives by a factor of 3–4, in qualitative agreement with predictions from the Stokes–Einstein diffusion theory. The T₁ values for the para-carbon of monosubstituted fluorobenzenes is clearly shorter than the T₁ values for the ortho- and meta-carbons. This phenomenon was traced to anisotropic tumbling, and D∥ and D⊥ diffusion coefficients were computed using Woessner's equations for molecules assumed to behave like symmetric rotors about their C₂ in-plane principal symmetry axis. Equal tumbling ratios, D∥/D⊥, were found in this way for toluene and perfluorotoluene.     

Correlation of Activation Energies of Gas Diffusivity and Local Matrix Mobility in Polycarbonate/POSS Nanocomposites

According to basic phenomenological models describing the solution‐diffusion based mechanism of penetrant diffusion in dense polymers, a connection between the diffusive transport of gas molecules in a polymeric matrix and the molecular mobility of that matrix on a certain length scale is, in principle, established for a long time. However, experimental data directly showing this correlation are rare. The investigation of a series of nanocomposites based on a polyhedral oligomeric silsesquioxane (POSS) and a polycarbonate matrix allows a systematic change of the molecular mobility on a local length scale (β‐relaxation) and of the corresponding activation energy E_A, both determined by broadband dielectric spectroscopy. Independently, activation energies of penetrant diffusion (E_D) of these nanocomposites were determined for N₂, O₂, CO₂, and CH₄ and a clear linear correlation between the two activation energies was established for the first time. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1593–1597     

A Monte Carlo study of a tethered polymer chain in a uniform field

We study the non‐uniform stretching and relaxation of a long flexible end‐anchored polymer chain of N monomers (32 ≤ N ≤ 1 024) in a uniform field B by means of an off‐lattice bead‐spring Monte Carlo model. Our simulational results for the case of a Rouse‐like polymer in the good solvent regime confirm the existence of “trumpet”‐ and “flower”‐type chain conformations, predicted recently by scaling analysis based on the notion of Pincus tensile blobs. The observed elongation of the chain and the critical fields, separating three different regimes of chain deformation, are found to obey the predicted scaling behavior. The segment density distribution matches that of a DNA molecule pulled from one end at constant velocity in a good solvent. As expected, the relaxation of the stretch to coil transition of the polymer of length N is determined by the typical Rouse time τ ∝ N^2ν+1.     

Styrene and isoprene friction factors in styrene–isoprene matrices

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, T_g, 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 − T_g. 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 − T_g. 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     

Synthesis of amphiphilic tadpole‐shaped copolymers by combination of glaser coupling with living anionic polymerization and ring‐opening polymerization

The tadpole‐shaped copolymers polystyrene (PS)‐b‐[cyclic poly(ethylene oxide) (PEO)] [PS‐b‐(c‐PEO)] contained linear tail chains of PS and cyclic head chains of PEO were synthesized by combination of Glaser coupling with living anionic polymerization (LAP) and ring‐opening polymerization (ROP). First, the functionalized polystyrene‐glycerol (PS‐Gly) with two active hydroxyl groups at ω end was synthesized by LAP of St and the subsequent capping with 1‐ethoxyethyl glycidyl ether and then deprotection of protected hydroxyl group in acid condition. Then, using PS‐Gly as macroinitiator, the ROP of EO was performed using diphenylmethylpotassium as cocatalyst for AB₂ star‐shaped copolymers PS‐b‐(PEO‐OH)₂, and the alkyne group was introduced onto PEO arm end for PS‐b‐(PEO‐Alkyne)₂. Finally, the intramolecular cyclization was performed by Glaser coupling reaction in pyridine/Cu(I)Br/N,N,N′,N″,N″‐pentamethyldiethylenetriamine system under room temperature, and tadpole‐shaped PS‐b‐(c‐PEO) was formed. The target copolymers and their intermediates were well characterized by size‐exclusion chromatography, proton nuclear magnetic resonance spectroscopy, and fourier transform infrared spectroscopy in details. The thermal properties was also determined and compared to investigate the influence of architecture on properties. The results showed that tadpole‐shaped copolymers had lower T_m, T_c, and X_c than that of their precursors of AB₂ star‐shaped copolymers. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Transitions between the B2 phase and more usual smectic phases in binary systems of banana-shaped with calamitic mesogens

Deuterium NMR spectroscopy is used to study a ring-deuteriated chiral liquid crystal 4-(2-methylbutyl)oxycarbonylphenyl 4-(10-undecenyloxy)benzoate. The quadrupolar and proton-deuteron dipolar splittings, and deuteron quadrupolar and Zeeman spin-lattice relaxation times were measured as a function of temperature in the smectic A phase at two different Larmor frequencies. The derived spectral densities of motion at different temperatures were analysed simultaneously using a rotational diffusion model which also includes internal ring rotations. Motional parameters (D _⊥, D _∥, D _R) and order parameter tensors (S_zz , S_xx -S_yy ) were obtained. Although the present data seem insufficient to draw a definitive conclusion, we believe that it is possible for this particular chiral molecule to have D_⊥ >D_∥ , which is different from non-chiral rod-like liquid crystals.     

Critical behavior of brittle‐ductile transition of polymers

We report that the brittle‐ductile transition of polymers induced by temperature exhibits critical behavior. When t close to 0, the critical surface to surface interparticle distance (ID_c) follows the scaling law: ID_c ∝ t^?v, where t = 1 ? T/T (T and T are the test temperature and brittle‐ductile transition temperature of matrix polymer, respectively) and v = 2/D. It is clear that the scaling exponent v only depends on dimension (D). For 2, 3, and 4 dimension, v = 1, 2/3, and 1/2 respectively. The result indicates that the ID_c follows the same scaling law as that of the correlation length (ξ), when t approach to zero. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 766–769, 2008     

Viscoelasticity of nanobubble‐inflated ultrathin polymer films: Justification by the coupling model

The nanobubble inflation method is the only experimental technique that can measure the viscoelastic creep compliance of unsupported ultrathin films of polymers over the glass–rubber transition zone as well as the dependence of the glass transition temperature (T_g) on film thickness. Sizeable reduction of T_g was observed in polystyrene (PS) and bisphenol A polycarbonate by the shift of the creep compliance to shorter times. The dependence of T_g on film thickness is consistent with the published data of free‐standing PS ultrathin films. However, accompanying the shift of the compliance to shorter times, a decrease in the rubbery plateau compliance is observed. The decrease becomes more dramatic in thinner films and at lower temperatures. This anomalous viscoelastic behavior was also observed in poly(vinyl acetate) and poly (n‐butyl methacrylate), but with large variation in the change of either the T_g or the plateau compliance. By now, well established in bulk polymers is the presence of three different viscoelastic mechanisms in the glass–rubber transition zone, namely, the Rouse modes, the sub‐Rouse modes, and the segmental α‐relaxation. Based on the thermorheological complexity of the three mechanisms, the viscoelastic anomaly observed in ultrathin polymer films and its dependence on chemical structure are explained in the framework of the Coupling Model. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Electrochemical Studies for the Interaction of DNA with an Irreversible Redox Compound – Hoechst 33258

An electrochemical equation suitable for examining the interaction of irreversible redox compounds with DNA is established. According to the equation, diffusion coefficients of both free and binding compounds (D_f , D_b), binding constant (K) and binding site size (s) of compounds with DNA could be obtained simultaneously by nonlinear fit analysis of electrochemical data. Bis‐benzimidazole derivative (Hoechst 33258), as an irreversible redox compound, was investigated for its electrochemical behavior and the interaction with natural fish sperm DNA (fsDNA) using cyclic voltammetry, chronocoulometry, bulk electrolysis and scanning electrochemical microscope technique. A nonlinear fit analysis of the experimental data yielded: D_f=8.3×10^?5 cm² s^?1, D_b=6.0×10^?6 cm² s^?1, K=2.1×10⁸ cm³ mol^?1, s=3.9. The overall results suggest that Hoechst 33258 binds tightly to the minor groove of fsDNA and covers four base pairs.     

Can the Theoretical Fitting of the Proton‐Nuclear‐Magnetic‐Relaxation‐Dispersion (Proton NMRD) Curves of Paramagnetic Complexes Be Improved by Independent Measurement of Their Self‐Diffusion Coefficients?

The self‐diffusion (D_c) coefficients of various lanthanum(III) diamagnetic analogues of open‐chain and macrocyclic complexes of gadolinium used as MRI contrast agents were determined in dilute aqueous solutions (3–31 mM ) by pulsed‐field‐gradient (PFG) high‐resolution ¹H‐NMR spectroscopy. The self‐diffusion coefficient of H₂O (D_w) was obtained for the same samples to derive the relative diffusion constant, a parameter involved in the outersphere paramagnetic‐relaxation mechanism. The results agree with an averaged relative diffusion constant of 2.5 (±0.1)×10^?9 and of 3.3 (±0.1)×10^?9 m² s^?1 at 25 and 37°, respectively, for 'small' contrast agents (M_r 500–750 g/mol), and with the value of bulk H₂O (2.2×10^?9 and 2.9×10^?9 m² s^?1 at 25° and at 37°, respectively) for larger complexes. The use of the measured values of D_c for the theoretical fitting of proton NMRD curves of gadolinium complexes shows that the rotational correlation times (τ_R) are very close to those already reported. However, differences in the electronic relaxation time (τ_SO) at very low field and in the correlation time (τ_V) related to electronic relaxation were found.     

Variable temperature 19F solid‐state NMR study of the effect of electrostatic interactions on thermally‐stimulated molecular motions in perfluorosulfonate ionomers

This study uses variable temperature ¹⁹F solid‐state nuclear magnetic resonance (SSNMR) spectroscopy to determine the influence of electrostatic interactions on the T₁, T_1ρ, and T₂ values of Nafion®. Because of a “homogenizing” of the T₁'s as a result of spin diffusion, it was not possible to resolve from the T₁ experiments the relative motions of the side‐ and main‐chain. The initial increase in T_1ρ as a function of increasing temperature has been attributed to backbone rotations that increase with increasing temperature. The maxima observed in the T_1ρ plots suggest a change in the dominant relaxation mechanism at that temperature. The similarity in relaxation behavior of the side‐ and main‐chains suggests that the motions are dynamically coupled, because of the fact that the side‐chain is directly attached to the main‐chain. Two T_1ρ values were observed for the main‐chain at high temperatures, which has been attributed to a thermally activated ion‐hopping process. The results of T₂ studies show that correlated motions of the side‐ and main‐chain exist at low temperatures. However, at elevated temperatures the T₂ values for the side‐chain increase rapidly while remaining relatively constant for the main‐chain, indicating an onset of mobility of the side‐chains. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2177–2186, 2007     

A carbon-13 study of relaxation in the mesophases of 5O·7 and the 5CB homologous series

Abstract

Carbon-13 spin-lattice relaxation times of the protonated ring carbons have been measured at 22·6 MHz in the nematic and all four smectic phases of 5O·7 (4-n-pentyloxybenzylidene-4′-n-heptylaniline). Dong has obtained the deuterium spectral densities J ₁ and J ₂ at 15·4MHz for the deuterated aniline ring of 5O·7-d ₄, and has presented and applied a theory in which the spectral densities are expressed in terms of the diffusion constants D∥ and D?. His results are used to calculate ¹³C relaxation times from the spectral densities J ₀, J ₁ and J ₂. The calculated ¹³C spin-lattice relaxation times are then compared with our experimental values to test the theory. The ¹³C spin-lattice relaxation times of all the resolved resonances in the various phases of the first four members of the 5CB homologous series have been published previously. Dong has also published an analysis of 5CB deuterium data, and we use his results for the diffusion constants D∥ and D? to calculate ¹³C relaxation times of the protonated aromatic carbons of 5CB, 6CB, 7CB and 8CB. The ¹³C relaxation times of the unprotonated aromatic carbons of the 5CB series are calculated in the manner of Wittebort et al., but using the spectral density expressions developed by Dong. The calculated ¹³C spin-lattice relaxation times of the 5CB homologous series are then compared with our experimental values to test the theory for the protonated and unprotonated ring carbons.     

Soret Coefficients for Aqueous Polyethylene Glycol Solutions and Some Tests of the Segmental Model of Polymer Thermal Diffusion

A thermogravitational cell is used to measure Soret coefficients (s) for dilute binary aqueous solutions of ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and polyethylene glycol (PEG) fractions with average molecular weights from 200 to 20,000 g-mol^–1. The cell design allows the top and bottom halves of the solution column to be withdrawn and injected into a high-precision HPLC differential refractometer detector for analysis. Previously reported mutual diffusion coefficients D and the measured Soret coefficients are used to calculate thermal diffusion coefficients D _T. s and D vary with the PEG molecular weight M as M ^+0.53 and M ^–0.52, respectively; hence, D _T = sD is essentially independent of M. The segmental model of polymer thermal diffusion predicts D _T = D_seg U _S/RT ², where D _seg is the segment diffusion coefficient, U _S the solvent activation energy for viscous flow, R the gas constant, and T the temperature. The predicted D _T values, although independent of M, are too large by a factor of five. Additional tests of the segmental model are provided using literature data for polystyrene + toluene, n-alkane + CCl₄, and n-alkane + CHCl₃ solutions. Agreement with experiment is not obtained. In particular, the measured D _T values for the alkane solutions are negative.