Blends of poly[ethylene(vinyl acetate)] and polychloroprene: Studies on capillary and dynamic flows

Rheological properties of the blends of poly[ethylene(vinylacetate)] (EVAc; vinylacetate content 28%) and polychloroprene (CR) have been measured through capillary and dynamic uniaxial elongational flows. Capillary flow indicates their shear thinning behavior. The decrease in the out of phase viscosities with increasing frequency is in accordance with the power law equation, whereas dynamic elongational viscosities follow nonlinear relationship in log-log plot with an initial increase at 11 Hz, followed by a very sharp drop. With an increase in temperature, the viscosity for capillary flow of all blends goes down due to their positive activation energy of flow but for dynamic elongational flow of EVAc blended with CR, viscosity increases, except for 30/70 blend and pure CR, in which case the dynamic elongational viscosity decreases with an increase in temperature. This abnormal behavior in dynamic elongational viscosity is due to the process of melting and recrystallization of EVAc at low heating rate (1°C/min) beyond the melting temperature. Capillary viscosities of all blends show positive deviation from the log additive values of pure polymers. But in the case of dynamic elongational flow, all blends show positive deviation at frequencies of 3.5 and 35 Hz and at higher temperatures (80–120°C). © 1997 John Wiley & Sons, Inc.     

Effects of emulsion parameters on relaxation behaviors for immiscible polymer blends

The relaxation behaviors of the binary immiscible blends reflected on the plots of the storage modulus and the imaginary part of complex viscosity were investigated using the Maxwell and the Palierne models. It was revealed that the peaks in the high‐ and low‐frequency regions on the complex viscosity imaginary part plot are owing to the relaxations of the blend and deformed dispersed droplets, respectively. Based on these two models, six emulsion parameters (interfacial tension, relaxation times and viscosities of two components, and dispersed phase volume fraction) were investigated in terms of their effects on the shape features of the plots of the imaginary part of complex viscosity and the Cole–Cole. The results showed that the viscosities of two components and dispersed phase volume fraction play key roles in the radii of the two circular arcs on the Cole–Cole plot. Furthermore, the two circular arcs are well separated in the case of lower interfacial tensions and dispersed phase viscosities, shorter matrix relaxation times, and higher matrix viscosities and dispersed phase volume fractions. The total relaxation time of the deformed dispersed droplets increases with increasing the viscosities of two components, especially with decreasing the interfacial tension. Three types of polymer blends were prepared and their dynamic frequency sweep testing results demonstrated the effectiveness of the corresponding predicted results. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39690.     

Study of the phase morphology and toughness in poly (vinyl chloride)/acrylonitrile–styrene-acrylic/styrene–butadiene–styrene ternary blends influenced by interfacial/surface tension

The effect of interfacial interaction on the phase morphology and toughness of poly (vinyl chloride) (PVC)/acrylonitrile–styrene-acrylic (ASA) terpolymer/styrene–butadiene–styrene (SBS) block copolymer ternary blends has been investigated. Water and diiodomethane liquids were used for static contact angle measurements to get surface tension and calculate interfacial tension. A dispersed phase morphology of ASA and SBS in the PVC matrix was predicted by the spreading coefficient theory, which was calculated through interfacial tensions between different polymer pairs. Extraction experiment and scanning electron microscopy were combined to verify this morphology. When the volume fraction of SBS was small, SBS was dispersed in the matrix as droplets and the strong PVC/styrene–acrylonitrile interfacial interaction made up for the poor interfacial adhesion between SBS and PVC. Herein, SBS showed an effective toughening effect on PVC/ASA blends. With the addition of 2.5- and 5-phr SBS, the blends had the highest impact strength of 88.75 kJ/m² at 23 °C and 9.98 kJ/m² at 0 °C, respectively. With the further increase of the SBS content, the diameter of the SBS drops increased largely and the poor interfacial adhesion between SBS and PVC played a leading role, resulting in a sharp decrease in toughness and a sharp ductile–brittle transition. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47721.     

Flow properties of biodiesel fuel blends at low temperatures

The dynamic viscosities of biodiesel derived from ethyl esters of fish oil, no. 2 diesel fuel, and their blends were measured from 298 K down to their respective pour points. Blends of B80 (80 vol.% biodiesel–20 vol.% no. 2 diesel), B60, B40 and B20 were investigated. All the viscosity measurements were made with a Bohlin VOR Rheometer. Cloud point and pour point measurements were made according to ASTM standards. Arrhenius equations were used to predict the viscosities of the pure Biodiesel (B100), no. 2 diesel fuel (B0) and the biodiesel blends (B80, B60, B40, and B20) as a function of temperature. The predicted viscosities agreed well with measured values. An empirical equation for calculating the dynamic viscosity of these blends as a function of both temperature and blend has been developed. Furthermore, based on the kinematic viscosity and density measurements of B100 up to 573 K by Tate et al. [Tate RE, Watts KC, Allen CAW, Wilkie KI. The viscosities of three biodiesel fuels at temperatures up to 300 °C. Fuel 2006;85:1010–5; Tate RE, Watts KC, Allen CAW, Wilkie KI. The densties of three biodiesel fuels at temperatures up to 300 °C. Fuel 2006;85:1004–9] an empirical equation for predicting the dynamic viscosity of pure biodiesel for temperatures from 277 K to 573 K is given. Empirical equations for predicting the cloud and pour point for a given blend give values in good agreement with experiments. The dynamic viscosity of biodiesel and its blends increases as temperature decreases and show Newtonian behaviour down to the pour point. Dynamic viscosity, cloud point and pour point decreases with an increase in concentration of no. 2 diesel in the blend.     

Linear dynamic mechanical properties of an SBS block copolymer

Dynamic viscosity and elastic modulus for a low molecular weight styrene-butadiene-styrene (SBS) block copolymer ate measured as a function of temperature (80-170°C) and frequency using the eccentric rotating disc geometry. These linear properties are superimposed to yield master curves each of which exhibits two branches below different (critical) reduced frequencies. At lower temperatures, the non-Newtonian behavior characteristic of SBS block copolymers is observed. In contrast, Newtonian response occurs at higher temperatures. As a consequence, plots of the viscoelastic properties vs temperature exhibit discontinuities below the critical frequencies, reflecting a narrow transition at about 142°C. Above this temperature, it is inferred, consistent with the equality of dynamic and steady state viscosities, that the polystyrene (S) blocks, existent in dispersed domains at low temperatures, exceed a critical degree of compatibility with the continuous polybutadiene phase. The activation energies indicate that the S blocks affect the temperature dependence of the dynamic properties in proportion to their presence in an interphase which is assumed to continuously grow in size as temperature is raised to the transition temperature. Below the critical reduced frequencies, it is inferred that S domain disruption may increasingly occur in conjunction with the observed property enhancement due to these domains, relative to the miscible blocks, as reduced frequency is lowered. However, above these frequencies, the presence of frequency-temperature superposition implies that the S domains and the miscible blocks are equivalent in their effects on properties. At still higher reduced frequencies, the domains present at the low temperatures studied are assumed to remain intact, but plateau behavior similar to the response characteristic of homopolymers is observed.     

Vulcanization characteristics of asphalt/SBS blends in the presence of sulfur

The vulcanization of asphalt/styrene–butadiene–styrene (SBS) triblock copolymer blends in the presence of elemental sulfur was followed with a strain-controlled rheometer. The vulcanization of the blends took place at temperatures greater than 140°C. From 150 to 180°C, the curing rate of the blends increased significantly with increasing temperature, and the apparent activation energy of vulcanization was 45.2 kJ mol⁻¹. A suitable processing temperature for good mechanical and thermally stable properties was between 170 and 180°C. Both the structure of SBS and the sulfur level had important effects on the vulcanization of the blends. A plot of the electric current versus time showed the process of the dynamic vulcanization of the blends. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 989–996, 2001     

Phase segregation behavior in PE/DOP blends and glass‐transition temperatures of polyethylene

Phase segregation behavior in PEs/DOP blends, interactions between PEs and DOP, and glass‐relaxation transitions of PEs were investigated. FTIR, DSC, and TGA data demonstrated that molecular interactions were present between PEs and DOP. DMA data demonstrated that pure PEs each (except HDPE) exhibited two loss maxima at about ?20 and ?120°C but the PEs/DOP blends (including the HDPE/DOP blend) yielded one new loss maximum at about ?60°C. The glass‐relaxation transitions corresponding to the three loss maxima on the DMA curves were designated α (?20°C), β (?60°C), and γ (?120°C) transitions and were attributed to the relaxation of the amorphous phases in the interlamellar, interfibrillar, and interspherulitic regions, respectively, based on DMA, WAXD, SAXS, and POM measurements. The controversial T_g values of PEs and their origin were thus clarified in this study. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3591–3601, 2001     

Blends of SBS triblock copolymer with poly(2,6‐dimethyl‐1,4‐phenylene oxide)/polystyrene mixture

Blends of styrene–butadiene–styrene (SBS) or styrene–ethylene/1‐butene–styrene (SEBS) triblock copolymers with a commercial mixture of polystyrene (PS) and poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) were prepared in the melt at different temperatures according to the chemical kind of the copolymer. Although solution‐cast SBS/PPO and SBS/PS blends were already known in the literature, a general and systematic study of the miscibility of the PS/PPO blend with a styrene‐based triblock copolymer in the melt was still missing. The thermal and mechanical behavior of SBS/(PPO/PS) blends was investigated by means of DSC and dynamic thermomechanical analysis (DMTA). The results were then compared to analogous SEBS/(PPO/PS) blends, for which the presence of a saturated olefinic block allowed processing at higher temperatures (220°C instead of 180°C). All the blends were further characterized by SEM and TGA to tentatively relate the observed properties with the blends' morphology and degradation temperature. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2698–2705, 2003     

Biodegradable polymer blends of poly(3-hydroxybutyrate) and poly(DL-lactide)-co-poly(ethylene glycol)

The melting and crystallization behavior and phase morphology of poly(3-hydroxybutyrate) (PHB) and poly(DL-lactide)-co-poly(ethylene glycol) (PELA) blends were studied by DSC, SEM, and polarizing optical microscopy. The melting temperatures of PHB in the blends showed a slight shift, and the melting enthalpy of the blends decreased linearly with the increase of PELA content. The glass transition temperatures of PHB/PELA (60/40), (40/60), and (20/80) blends were found at about 30°C, close to that of the pure PELA component, during DSC heating runs for the original samples and samples after cooling from the melt at a rate of 20°C/min. After a DSC cooling run at a rate of 100°C/min, the blends showed glass transitions in the range of 10–30°C. Uniform distribution of two phases in the blends was observed by SEM. The crystallization of PHB in the blends from both the melt and the glassy state was affected by the PELA component. When crystallized from the melt during the DSC nonisothermal crystallization run at a rate of 20°C/min, the temperatures of crystallization decreased with the increase of PELA content. Compared with pure PHB, the cold crystallization peaks of PHB in the blends shifted to higher temperatures. Well-defined spherulites of PHB were found in both pure PHB and the blends with PHB content of 80 or 60%. The growth of spherulites of PHB in the blends was affected significantly by 60% PELA content. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 1849–1856, 1997     

Study on rubber blends: Influence of epoxidation on phase morphology and interphase

A discussion about phase morphology and interphase is presented taking into account the influence of the epoxidation on NR/SBR blends. Unfilled blends were examined in a broad composition range to investigate the morphology by TEM (transmission electron microscopy) and to estimate the volume fraction of the interphase by means of DMA (dynamic mechanical analysis). It was observed that the domain sizes and the volume fraction of the interphase depend on the difference in polarity of rubbers caused by the presence of the epoxidized phase and the polarizability caused by the difference on the vinyl content. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2377–2384, 2007     

A novel combination of sandwich and co‐continuous structure based on polypropylene and styrene‐butadiene‐styrene block copolymer formed with wide range of polypropylene content

The styrene–butadiene–styrene block copolymer (SBS)/polypropylene (PP) blends with a unique sandwich layered co‐continuous structure were prepared by melt compounding. Differing from single conventional co‐continuous and sandwich structure, this structure was formed, where pure PP and co‐continuous SBS/PP phase acting as the face sheets and core. Even though the volume content was 20 or 10 vol %, PP always amazingly formed a continuous phase in SBS/PP blends, whereas the morphology of SBS phase relatively changed from dispersed particles to continuous network as its content increased to 50 vol %. For immiscible SBS/PP blends, due to the huge difference of complex viscosity and surface tension between SBS and PP, a pure PP layer existed on the surface of blends which can be ascribed to the PP enrichment. Herein, the structure of blends with more than 50 vol % SBS was presented as sandwich layered co‐continuous structure by combining the pure PP layer and co‐continuous structure. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46580.     

Using modulated‐temperature differential scanning calorimetry to study interphases in blends of styrene–butadiene and polybutadiene rubbers filled with a silanized silica nanofiller

Polybutadiene and styrene–butadiene rubber compounds containing a high loading of a precipitated silica nanofiller were prepared. The silica surfaces were pretreated with bis(3‐triethoxysilylpropyl) tetrasulfide to prevent the silica from interfering with the reaction mechanism of sulfur cure in the rubber. The rubber compounds were mixed together for different times and at different temperatures to produce styrene–butadiene rubber/polybutadiene rubber blends. The mass fraction and composition of the interphase in the blends were subsequently determined with modulated‐temperature differential scanning calorimetry. At 60–65°C, the mass fraction of the interphase in the blend increased after the rubbers were mixed together for 10 min, and then it decreased significantly when the mixing time was increased to 20 min. When the two rubbers were mixed together for 7 min at 60–105°C, the mass fraction of the interphase in the blend increased slightly because of a higher mixing temperature. The composition of the interphase in the blend also changed with the mixing time and mixing temperature. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Fabrication of Damping Material over Broad Temperature Range: Blending Amorphous Styrene‐Butadiene‐Styrene Triblock Copolymer with Semi‐Crystalline Syndiotactic 1,2‐Polybutadiene

Broad‐temperature‐range (?85.4 to 96.2 °C) damping material was fabricated by blending amorphous styrene‐butadiene‐styrene triblock copolymer (SBS) with semicrystalline syndiotactic 1,2‐polybutadiene (s‐PB). According to dynamic mechanical thermal analysis (DMTA) analysis, SBS/s‐PB blends exhibited three consecutive damping peaks at ?85.4, 2.7, and 96.2 °C. The peaks at ?85.4 and 96.2 °C were associated with the glass transition of polybutadiene and polystyrene in SBS, and peak at 2.7 °C belonged to the glass transition of s‐PB. The analysis of rheological behavior and thermal properties showed that the mobility and thermal stability of SBS/s‐PB blends improved with the introduction of semi‐crystalline s‐PB. Moreover, regarding the results of DMTA, Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM) measurements, SBS and s‐PB were compatible in the macroscopic scale while they were immiscible in thermodynamic scale. Wide‐angle X‐ray diffraction (WAXD) results present the crystal structure of blends were unchanged. Besides, with the introduction of s‐PB in blends, 100% tensile modulus increased from 3.2 to 5.8 MPa and tear strength increased from 49.2 to 84.2 kN/m. The Kerner–Uemura–Takayanagi model was employed to compare with experimental data. Thus, broad‐temperature‐range damping material was fabricated by blending SBS with s‐PB and the material combined with good processability, thermal stability, and mechanical properties. J. VINYL ADDIT. TECHNOL., 26:336–347, 2020. © 2019 Society of Plastics Engineers     

Investigation of morphology formation in SBS block copolymer/homopolystyrene blends

Polymer blends comprising a polystyrene‐block‐polybutadiene‐block‐polystyrene (SBS) block copolymer and atactic homopolystyrene (hPS) were investigated using injection molded and solution cast samples. The morphology of the materials was studied by means of transmission electron microscopy (TEM) and scanning force microscopy (SFM). Dynamic mechanical analysis (DMA) was used to characterize the phase behavior and the morphology formation of the block copolymer as well as of the SBS/hPS blends. The glass transition temperatures seem to strongly depend on the homogeneity of the corresponding phases. A distinct difference was found between the morphologies of the blends prepared by different methods. While the SBS block copolymer always shows a lamellar morphology in injection molded or as‐cast samples, the injection molded blends show a disturbance in the morphology consisting of alternating layers. In contrast, in the case of as‐cast samples, added hPS forms polystyrene domains dispersed in a matrix of the pure block copolymer. Regarding the change in the glass transition temperature, in the effective volume and in the interfacial volume obtained from DMA curves, the morphology formation of the injection molded samples (pure SBS block copolymer and the corresponding blends) was investigated. Two different structural models for the blends are proposed. Polym. Eng. Sci. 44:1534–1542, 2004. © 2004 Society of Plastics Engineers.     

Revisiting the thermal relaxations of poly(vinyl alcohol)

The molecular dynamics of poly(vinyl alcohol) (PVA) were studied by dielectric spectroscopy and dynamic mechanical analysis in the 20–300°C range. The well-established plasticizing effect of water on the glass-transition temperature (T_g) of PVA was revisited. Improper water elimination analysis has led to a misinterpretation of thermal relaxations in PVA such that a depressed T_g for wet PVA films (ca. 40°C) has been assigned as a secondary β relaxation in a number of previous studies in the literature. In wet PVA samples, two different Vogel–Fulcher–Tammann behaviors separated by the moisture evaporation region (from 80 to 120°C) are observed in the low- (from 20 to 80°C) and high- (>120°C) temperature ranges. Previously, these two regions were erroneously assigned to two Arrhenius-type relaxations. However, once the moisture was properly eliminated, a single non-Arrhenius α relaxation was clearly observed. X-ray diffraction analysis revealed that the crystalline volume fraction was almost constant up to 80°C. However, the crystallinity increased approximately 11% when temperature increased to 180°C. A secondary β_c relaxation was observed at 140°C and was related to a change in the crystalline volume fraction, as previously reported. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Shape memory and self-healing behavior of styrene–butadiene–styrene/ethylene-methacrylic acid copolymer (SBS/EMAA) elastomers containing ionic interactions

Ionic interactions were introduced to styrene–butadiene–styrene (SBS) through blending with ethylene-methacrylic acid copolymer (EMAA) and zinc oxide (ZnO), and a following in situ neutralization reaction between the carboxyl groups of EMAA and ZnO. The resultant SBS/EMAA (60/40 wt %) blends containing zinc carboxylate crosslinks exhibited high modulus and strong long-time relaxation characteristics. With 74% of the carboxyl groups neutralized (zinc cation fraction of 1.7 wt %), the tensile strength of the blends was increased from 14.6 to 16.6 MPa, and the stress at 100% extension was increased from 4.8 to 8.1 MPa. The melting temperature of EMAA was utilized to trigger the shape memory behavior of SBS/EMAA, and the reversible ionic bonds endowed SBS with better shape memory and self-healing performance. The shape-fixing ratio and recovery ratio of SBS were increased from 90.2 and 56.5% up to 93.3 and 84.2%, respectively. When the cut surfaces of SBS/EMAA/Zn samples were brought back into contact and annealed at 100 °C for 1 h, the strength and the elongation at break were recovered by 36 and 21%, respectively. This introduction of ionic interactions through the EMAA-ZnO neutralization reactions imparts new functions to SBS thermoplastic elastomers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48666.     

Blends of polyamide1010 with unmodified and maleic‐anhydride‐grafted high‐impact polystyrene

The crystallization behaviors, dynamic mechanical properties, tensile, and morphology features of polyamide1010 (PA1010) blends with the high‐impact polystyrene (HIPS) were examined at a wide composition range. Both unmodified and maleic‐anhydride‐(MA)‐grafted HIPS (HIPS‐g‐MA) were used. It was found that the domain size of HIPS‐g‐MA was much smaller than that of HIPS at the same compositions in the blends. The mechanical performances of PA1010–HIPS‐g‐MA blends were enhanced much more than that of PA1010–HIPS blends. The crystallization temperature of PA1010 shifted towards higher temperature as HIPS‐g‐MA increased from 20 to 50% in the blends. For the blends with a dispersed PA phase (≤35 wt %), the T_c of PA1010 shifted towards lower temperature, from 178 to 83°C. An additional transition was detected at a temperature located between the T_g's of PA1010 and PS. It was associated with the interphase relaxation peak. Its intensity increased with increasing content of PA1010, and the maximum occurred at the composition of PA1010–HIPS‐g‐MA 80/20. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 857–865, 1999     

Blends of epoxy–amine resins with poly(phenylene oxide) as processing aids and toughening agents: I. Uncured systems

The effect of two different bisphenol‐A‐based diepoxides—nearly pure DGEBA340 and a DGEBA381 oligomer—and an aromatic diamine curative (MCDEA) on the solubility and processability of poly(phenylene oxide) (PPO) was studied. The solubility parameters of the diepoxies and the curative calculated from Fedors's method suggest miscibility of PPO with the components, and this was observed at the processing temperature; however, some of the blends were not transparent at room temperature, indicating phase immiscibility and/or partial PPO crystallization. The steady shear and dynamic viscosities of the systems agreed well with the Cox–Merz relationship and the logarithmic viscosities decreased approximately linearly with increasing amounts of DGEBA381, DGEBA340 or MCDEA, thus causing a processability enhancement of the PPO. The dynamic rheology of intermediate PPO:DGEBA compositions at 200 °C showed gel‐like behaviour. Dynamic mechanical analysis of blends with varying PPO:DGEBA ratios showed that the main glass transition temperature (T_g) of the blends decreased continuously with increasing epoxy content, with a slightly higher plasticizing efficiency being exhibited by DGEBA340 compared to DGEBA381. However, blends with 50 and 60 wt% PPO had almost identical T_g due to the phase separation of the former blends. The blends of MCDEA and PPO were miscible over the concentration range investigated and T_g of the blends decreased with increasing MCDEA concentration. © 2013 Society of Chemical Industry     

The mechanical properties of styrene-butadiene-styrene (SBS) triblock copolymer blends with polystyrene (PS) and styrene-butadiene copolymer (SBR)

Measurements were made of linear viscoelastic properties and nonlinear stress-strain properties of phase-separated styrene-butadiene-styrene (SBS) copolymers and their blends with several homopolymer polystyrenes (PS) and one random copolymer (SBR). Torsion pendulum testing yielded shear moduli G′, G″, and Rheovibron experiments produced tensile moduli E′, E″, over a 220°K range of temperature, both at low frequencies. For pure copolymers and their PS blends, G′ and E′ correlated quite well with the total PS content, but G″ and E″ were more sensitive to how the additive was distributed. Results suggest that a PS additive whose molecular weight (M) is less than that of the copolymer PS-block (M_s) causes expansion of both the interphase and the homogeneous PS-rich phase, while an additive with M > M_s mixes less well with these phases (probably forming separate domains of pure PS) and is less effective in enhancing the linear moduli. The blending with SBB produced reduction in G′ but a broad midrange peak in G″, suggesting that SBR was localized almost entirely within an expanded interphase. Tensile stress-strain data were obtained with an Material Testing System at room temperature. For PS blends, properties did not correlate well with the total PS content, the blends being always weaker than the SBS of the same overall composition. The amount of set also increased with PS content in the blends. Cyclic tests to increasing strain showed progressive structural alterations (as for the host SBS), with blend behavior resembling host properties more closely with each new cycle. When SBR was the additive, amounts as small as 1 percent reduced the curves by 15 percent. The yield stress was eliminated entirely with an addition of 10 percent SBR, but for all cases the set was the same. Results are discussed in terms of interphase force barriers to chain flow.     

Dielectric Investigation of Molecular Dynamics of Blends: IV. Effect of Blending on the Normal Mode Process of Polyisoprene/Polystyrene Blends

Polyisoprene/polystyrene (PI/PS) blends have been prepared and investigated for compatibility using dielectric and calorimetric measurements. Various blends were prepared from polystyrene (number average molecular weight, — _n=160 000 g mol^-1) and polyisoprene with — _n values of 13 800, 40 500 and 130000gmol^-1. Dielectric measurements have been carried out over a wide frequency range (10^-2–10⁶Hz) and in the temperature range of the glass and normal mode processes (-70 to +70°C). The glass transition, as well as the corresponding relaxation process, of polyisoprenes were shifted to higher temperatures in the different blends, indicating compatibility. The blends showed a lower critical solution temperature (LCST) at temperatures above 105°C. It was surprising to find that blending of polyisoprene with polystyrene led to a great shift to higher values in the relaxation frequency of the normal mode process for the isoprene segments. The measurements showed that the relaxation time of the normal mode process in the blends was longer than that of the glass process by a constant factor (3·2 decades), regardless of the molecular weight of the polyisoprenes used in the blends. This finding implied that the domain length responsible for the compatibility of the two polymers was consistent regardless of the molecular weight used (where — _n> — _c, the critical molecular weight). In view of the results obtained, and by using a molecular model, it was possible to determine the size of the structural domains responsible for the compatibility. The value obtained (16·7nm) is very similar to that suggested to be responsible for the glass transition in pure polymers. © 1997 SCI.