Hydrogenated Polybutadiene Research Articles

Synthesis of polybutadiene-silica nanoparticles via differential microemulsion polymerization and their hydrogenated nanoparticles by diimide reduction

Polybutadiene (PB)–SiO2 nanoparticles were successfully synthesized via differential microemulsion polymerization. The core-shell structured PB-SiO2 nanoparticles were designed to achieve a monodispersion with reduced nanosilica aggregation. A high monomer conversion (81.5%), grafting efficiency (78.5%) and small particle size (27 nm) with narrow size distribution was obtained under optimum reaction conditions when using an extremely low surfactant concentration, 5 wt% based on monomer. The PB-SiO2 latex could be hydrogenated by diimide reduction in the presence of hydrazine and hydrogen peroxide to provide hydrogenated polybutadiene (HPB)–SiO2. A high hydrogenation degree of 98.6% was achieved at a ratio of hydrazine to hydrogen peroxide of 0.75:1, and showed a maximum degradation temperature of 469.6 °C resulting in excellent thermal stability. A new nanocomposite of PB-SiO2 and HPB-SiO2 could be used as a novel nanofiller in natural rubber. Especially, NR/HPB-SiO2 composites had improved mechanical and thermal properties, and exhibited good resistance toward ozone exposure.

SSA study of early polyethylenes degradation stages. Effects of attack rate, of average branch length, and of backbone polymethylene sequences length distributions

Low-density polyethylenes have been attacked by free radicals in the presence of oxygen to promote chains scission, aiming at showing effects of the molecular structure on the thermal behavior as determined by using a Successive Self-Nucleation and Annealing (SSA) technique. Three types of low-density polyethylenes were used: a hydrogenated polybutadiene (HPB), as a model for a statistical linear ethylene–butene copolymer, a linear ethylene–butene copolymer (LLDPE) with short branches not randomly distributed along the main chains, and a low-density polyethylene (LDPE) with randomly placed long and short branching. All the polymers were subjected to thermal oxidation in air. Additionally, the LDPE and HPB were exposed to gamma irradiation in air, while the HPB was also degraded with an organic peroxide. By virtue of the thermally activated oxidation, the three polymers show signs of molecular scission evidenced by the appearance of endotherms in the high temperature range of the final SSA thermogram. These endotherms are associated with the melting of thicker crystals formed by longer polymethylene sequences that were not available for crystallization in the original polymer. Similar indication of chain scission was detected in some of the irradiated HPB. In the case of the irradiated LDPE or the HPB modified with peroxide, the main effect observed was crosslinking that was identified by a reduction of the area of the higher melting endotherms in the final SSA thermogram.

Monte Carlo Simulation of Short Chain Branched Polyolefins: Structure and Properties

The effect of higher α-olefin comonomer on physical properties of short chain branched (SCB) polyethylene (PE) melts at 450 K has been studied using connectivity altering Monte Carlo simulations. The calculated chain dimensions per molecular mass scale with backbone weight fraction, ϕ, as ⟨S2⟩/M ∼ ϕ1.27±0.03 for the radius of gyration S and ⟨R2⟩/M ∼ ϕ1.27±0.03 for the end-to-end distance R, in very good agreement with the experiment-based result ⟨R2⟩/M ∼ ϕ1.30. The observed dependence is consistent with the decrease in the fraction of trans states along the backbone. The entanglement tube diameter, app, computed for SCB melts scales as ⟨app⟩ ∼ ϕ–0.46±0.01, which is close to the result for model concentrated (⟨R2⟩ = const) PE solutions created by deleting randomly chosen chains from equilibrated melt configurations of linear PE (⟨app⟩ ∼ ϕ–0.41±0.01). The latter result agrees very well with the scaling based on rheological experiments on concentrated hydrogenated polybutadiene (HPB)/C24H50 solutions at 413 K (⟨app⟩ ∼ ϕ–0.45). The tube diameter in model athermal PE solutions scales as ⟨app⟩ ∼ ϕ–0.6±0.03, in excellent agreement with the scaling based on the neutron spin-echo experiments on athermal HPB/C19D40 solutions at 509 K (⟨app⟩ ∼ ϕ–0.6). The computed scaling relationships for both SCB melts and model PE solutions are close to the binary contact model (app ∼ ϕ–0.5) and disagree with the packing model (app ∼ ϕ–1.27). The solubility parameters calculated for poly(ethylene-co-1-butene) (PEB) melts are in excellent agreement with relative solubility parameters based on SANS analysis of appropriate SCB blends, which scale as δ ∼ ϕ0.18. The SANS-derived relative solubility parameters for poly(ethylene-co-1-hexene) (PEH) and poly(ethylene-1-octene) (PEO) systems scale more weakly (δ ∼ ϕ0.1) and suggest breakdown of a universal correlation. This pattern is followed by simulated relative solubility parameters.

Quantification of Branching in Model Three-Arm Star Polyethylene

The versatility of a novel scaling approach in quantifying the structure of model well-defined 3-arm star polyethylene molecules is presented. Many commercial polyethylenes have long side branches, and the nature and quantity of these branches varies widely among the various forms. For instance, low-density polyethylene (LDPE) is typically a highly branched structure with broad distributions in branch content, branch lengths and branch generation (in hyperbranched structures). This makes it difficult to accurately quantify the structure and the inherent structure–property relationships. To overcome this drawback, model well-defined hydrogenated polybutadiene (HPB) structures have been synthesized via anionic polymerization and hydrogenation to serve as model analogues to long-chain branched polyethylene. In this article, model 3-arm star polyethylene molecules are quantified using the scaling approach. Along with the long-chain branch content in polyethylene, the approach also provides unique measurements...

Block balance in hydrogenated polybutadiene‐b‐polymethylmethacrylate diblock copolymer for efficient interfacial activity in low‐density polyethylene/polymethylmethacrylate blend: Phase morphology development

AbstractThe objective of the present study was to determine the best molecular balance between the two hydrogenated polybutadiene (HPB) and polymethylmethacrylate (PMMA) blocks that promotes an HPB‐b‐PMMA diblock copolymer with efficient compatibilization activity in a low‐density polyethylene (LDPE)/PMMA immiscible blend. The model blend selected, LDPE/PMMA, is “more immiscible” than the LDPE/polystyrene pair largely reported in open literature. The blends having a composition of 80LDPE/20PMMA exhibit a droplet‐in‐matrix phase morphology whereas in 20LDPE/80PMMA a co‐continuous phase morphology was developed. In the droplet‐in‐matrix phase morphology, the emulsifying efficiency of the copolymer was evaluated based on the maximum reduction of the PMMA droplet size it is able to promote. Whereas, in the co‐continuous phase morphology, the copolymer was evaluated based on its ability to stabilize the maximum phase co‐continuity. The sequences of the best emulsifying copolymer revealed are not symmetrical. An HPB‐b‐PMMA where the ratio of molar mass of the blocks, $\overline{M_{\rm n}}$ HPB/$\overline{M_{\rm n}}$ PMMA, is within 1.8–1.95 exhibits a much better interfacial activity in LDPE/PMMA blends than a copolymer of much lower ratio (longer PMMA block). This is ascribed to the much higher interactions (cohesive energy density) encountered in PMMA (PMMA of the copolymer and PMMA phase of the blend) compared with the LDPE side (HPB of the copolymer and LDPE phase of the blend). © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 837–848, 2005

Stress–strain behavior of low‐density polyethylene/poly(methyl methacrylate) blends with modulated interfaces with a hydrogenated polybutadiene‐block‐poly(methyl methacrylate) diblock copolymer

AbstractThe stress–strain diagrams and ultimate tensile properties of uncompatibilized and compatibilized hydrogenated polybutadiene‐block‐poly(methyl methacrylate) (HPB‐b‐PMMA) blends with 20 wt % poly(methyl methacrylate) (PMMA) droplets dispersed in a low‐density polyethylene (LDPE) matrix were studied. The HPB‐b‐PMMA pure diblock copolymer was prepared via controlled living anionic polymerization. Four copolymers, in terms of the molecular weights of the hydrogenated polybutadiene (HPB) and PMMA sequences (22,000–12,000, 63,300–31,700, 49,500–53,500, and 27,700–67,800), were used. We demonstrated with the stress–strain diagrams, in combination with scanning electron microscopy observations of deformed specimens, that the interfacial adhesion had a predominant role in determining the mechanism and extent of blend deformation. The debonding of PMMA particles from the LDPE matrix was clearly observed in the compatibilized blends in which the copolymer was not efficiently located at the interface. The best HPB‐b‐PMMA copolymer, resulting in the maximum improvement of the tensile properties of the compatibilized blend, had a PMMA sequence that was approximately half that of the HPB block. Because of the much higher interactions encountered in the PMMA phase in comparison with those in HPB (LDPE), a shorter sequence of PMMA (with respect to HPB but longer than the critical molecular weight for entanglement) was sufficient to favor a quantitative location of the copolymer at the LDPE/PMMA interface. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 22–34, 2005

Experimental analysis of the grafting products of diethyl maleate onto linear and branched polyethylenes

This paper is focused on establishing the grafting products of diethylmaleate onto ethylene–α-olefin copolymers of varying comonomer contents. Several commercial ethylene/α-olefin copolymers ranging in comonomer contents from 0.35 to 3.70mol% were used, as well as a hydrogenated polybutadiene (HPB) with a 1,2 unit content of 13.9mol%. The polymers were functionalized with DEM in solution. The experimental techniques employed to verify the grafting and to ascertain the exact positioning of the insertion with respect to the branching points were: Fourier transform infra red spectroscopy (FTIR), carbon 13 nuclear magnetic resonance (13C NMR) and Distortionless enhancement polarization transfer NMR (13C NMR-DEPT). Thermal fractionation was performed by Differential Scanning Calorimetry (DSC) employing the successive self-nucleation and annealing technique (SSA).The results obtained show that the DEM insertion onto polyethylene chains occurs in secondary carbons of the main chain regardless of the copolymer branch type and content. The reasons for this behavior may be related to a statistical factor being involved in the peroxide radical attack since there is an excess of secondary carbons as compared to tertiary ones per PE chain. Also, steric effects produced by the size of the DEM molecules are probably involved in the DEM insertion step. Our 13C NMR-DEPT results suggest that DEM not only avoids the tertiary carbons where the branches are located but also, in polyethylenes with less than 4mol% branch content, it prefers to insert in the secondary carbons that are at least 5 carbon atoms away from the branch point. In those cases where unsaturations are present in PE chain ends, FTIR shows that they can also be depleted by DEM grafting. However, in the HPB case where no unsaturations are present and the branching content is very high, the insertion still occurs only in the secondary carbons of the main chain. The thermal fractionation performed by SSA corroborated the aforementioned results since the fractions with the longest linear chains were always the first to be depleted by the grafting reactions.

Effect of block copolymers of various molecular architecture on the phase morphology and tensile properties of LDPE rich (LDPE/PS) blends

The emulsification efficiency of three different block copolymers consisting of hydrogenated polybutadiene (HPB) and polystyrene (PS), i.e. a pure diblock , a tapered diblock and a triblock copolymer has been compared in low density polyethylene/polystyrene (LDPE/PS) blends rich in polyethylene. The comparison relies upon the ability of these potential interfacial agents to stabilize fine phase dispersion and to promote good interfacial adhesion. Based on the phase morphology, the ultimate tensile properties and the dynamic viscosity of the modified blends, the tapered diblock copolymer is clearly the most efficient emulsifier. For instance a plateau is observed in the property-copolymer content dependence when 2 wt% tapered diblock are used compared to ca. 5 wt% in case of the pure diblock. In contrast, no plateau is observed when the triblock copolymer is used. This is assumed to result from a less quantitative localization of these two copolymers i.e. the pue diblock or the triblock at the LDPE/PS interface.

Crystallization and Melting of Model Ethylene-Butene Random Copolymers: Thermal Studies

Crystallization and melting of a copolymer depend on both intrachain and interchain distributions of noncrystallizable comonomer. Hydrogenated polybutadiene (HPB) is a model ethylene-butene (EB) random copolymer with known intrachain distribution and no interchain distribution of branching. Differential scanning calorimetry (DSC) was used to study HPB having 21 to 106 ethyl branches per 1000 backbone carbon atoms. Crystallization during continuous cooling occurs in two stages: a rapid primary transformation over a temperature interval of about 5°C, followed by more gradual crystallization at lower temperatures. The crystalline fraction α is below the value from Flory's theory, but the two quantities converge for high branching. Isothermal crystallization of these homogeneous copolymers results in crystals having two distinct melting ranges. This unexpected result is accounted for by a model that partitions crystallizable ethylene sequences into two fractions on the basis of lengths established by crystallization temperature and kinetics. The fraction of the longest sequences creates a kinetically controlled distribution of crystal thickness l similar to that in a homopolymer. Segments of intermediate length form stable, but thinner, crystals that melt at a lower temperature. One ethylene-butene copolymer prepared with a metallocene catalyst behaves like the homogeneous model copolymers.

Blends of Linear Low-Density Polyethylene and a Diblock Copolymer of Hydrogenated Polybutadiene and Methyl Methacrylate

Blends of linear low-density polyethylene (LLDPE) and a diblock copolymer of hydrogenated polybutadiene and methyl methacrylate [P(HB-b-MMA)] were studied by transimission electron microscope (TEM), differential scanning calorimetry (DSC), and wide angle X-ray diffraction (WAXD). At 10 wt% block copolymer content, block copolymer chains exist as spherical micelles and cylindrical micelles in LLDPE matrix. At 50 wt% block copolymer content, block copolymer chains mainly form cylindrical micelles. The core and corona of micelles consist of PMMA and PHB blocks, respectively. DSC results show that the total enthalpy of crystallization of the blends varies linearly with LLDPE weight percent, indicating no interactions in the crystalline phase. In the blends, no distortion of the unit cell is observed in WAXD tests.

Crystallization-induced phase separation in mixtures of model linear and short-chain branched polyethylenes

Abstract The possibility of cocrystallization is investigated in a model system of linear and short-chain branched polyethylene. Both components have low molecular weight and narrow molecular weight distribution; the branched component, hydrogenated polybutadiene (HBD), contains one ethyl branch per 60–70 backbone carbon atoms. Cocrystallization was not observed even for the most rapid cooling conditions attainable, despite the essentially identical unit cells of the two materials. A combination of microscopy and scattering techniques was used to demonstrate that the HBD and linear polyethylene (LPE) crystallize into separate lamellar stacks. The rapid growth rate of the LPE creates volume-filling spherulites which trap the HBD in micron-size inclusions, within which it subsequently crystallizes on further cooling.

Ostwald ripening in immiscible polyolefin blends

AbstractThe coarsening in the quiescent melt of the phase‐segregated particles of a polymer blend, composed of a narrow molecular weight fraction of an unbranched high‐density polyethylene (HDPE) and a highly branched (100 ethyl branches/1000 C atoms) hydrogenated polybutadiene (HPB) was studied. The system was effectively binary, due to the narrow molecular weight and composition distributions of each component. The system was composed of 90 wt % of the HDPE and 10 wt % of the HPB and it formed a two‐phase system in the melt at 177°C. The blend was precipitated from xylene solution in order to obtain an initially intimately mixed system. This was the third study in a series of studies of the coarsening of phase‐segregated particles in polymer blends. This study was unique in that the system studied was binary in this case while the previous systems were multicomponent. Since the present system was binary, exact thermodynamic calculations of the phase state of this system could be applied with a high level of confidence. The droplet phase particles, which were mainly composed of the HPB, were observed to coarsen on storage in the melt for times of from 5 s to 1 h. At the shortest storage time of 5 s the particles had an average radius of about 0.05 μm and coarsened to about 0.2 μm after 1 h storage in the melt state. Particle dimensions were measured by scanning electron microscopy of n‐heptane‐etched and gold‐coated sections. It was found that the volume of the particles increased linearly with time and that the rate constant of coarsening was Kexp = 1.23 × 10−18 cm3/s and this agreed fairly well with the rate constant calculated from Ostwald ripening theory of Kce = 0.86 × 10−18 cm3/s. In contrast the rate constant for direct particle diffusion and coalescence was Kc = 3.6 × 10−20 cm3/s. Since this was two orders of magnitude smaller than the rate constant for Ostwald ripening, it was concluded that, although the linear increase of volume with time was also consistent with the particle diffusion and coalescence mechanism, this was not a significant contributor to the coarsening mechanism. The major cause for the insignificance of the particle diffusion and coalescence mechanism was the high melt viscosity of the matrix polymers. The application of the Ostwald ripening theory to this system could be made with a high level of confidence because it was binary. It was found that the phase concentration of the droplet phase apparently underwent a rapid increase during the first 1‐2 min of storage in the melt, indicating that the system did not reach phase equilibrium (i.e., did not completely phase‐segregate) for about 1‐2 min. This further indicated that the long‐time coarsening regime was not entered until after this length of time. The particle size distributions remained approximately self‐similar over the period of coarsening, as predicted by Ostwald ripening theory. © 1995 John Wiley & Sons, Inc.

Studies on the tumor-promoting activity of polyurethanes: depletion of inhibitory action of metabolic cooperation on the surface of a polyalkyleneurethane but not a polyetherurethane.

Methanol extracts prepared from three polyetherurethanes (PEUs), namely PU4, PU6, and PU8, which were synthesized using 4,4'-diphenylmethanediisocyanate, poly(tetramethylene oxide), and 1,4-butanediol, showed an inhibitory action on the gap-junctional intercellular communication in a V79 metabolic cooperation (MC) test system. However, the inhibitory potentials of methanol extracts did not correlate with the tumorigenic potential of the polyurethanes in 1-year rat implantation studies. When the MC test was carried out using glass dishes partly coated with low molecular weight PEU, the inhibitory activity was clearly detected on the surface of the polyurethane coating but not on that of the noncoated glass area. The inhibitory activity of the three PEUs investigated using polyurethane-coated dishes correlated with the values of the polyurethane's tumorigenic potential in the rat implantation study. Various polyurethanes containing polybutadiene (PBD), hydrogenated polybutadiene (HPBD), or a fluoropolyether glycol (FPEG) as the soft segment were also tested using coated dishes in the MC assay. The threshold inhibitory response of FPEG-PU was 10-fold less than that of PU4, and neither PBD-PU nor HPBD-PU showed any inhibition in the MC test system. Both the FPEG and aliphatic soft segment containing polyurethanes decreased, and had minimal influence on the gap junctional intercellular communication. Thus, the tumor-promoting potential of PBD-PU, HPBD-PU, and FPEG-PU was considered to be lower than those of the PEUs based on these in vitro test results.

Ostwald ripening in an immiscible hydrogenated polybutadiene and high‐density polyethylene blend

AbstractThe long‐time regime coarsening in a phase‐segregated blend of hydrogenated polybutadiene (HPB) with high‐density polyethylene (HDPE) was studied. The blend consisted of 10 wt% of HPB in a HDPE matrix. The morphology of the system was studied by etching the HPB particles from the HDPE matrix and observing the etched specimens in a scanning electron microscope. The average volume of the HPB particles was found to increase with storage time in the melt, and to follow a temporal exponent of 1 in agreement with the predictions of the Ostwald ripening theory. This indicated that the particles coarsen by the evaporation‐condensation mechanism on which the Ostwald ripening theory is based. The rate constant from the Ostwald ripening theory was calculated and compared to the rate constant determined from the experimental data. The theoretical rate constant, K, calculated from Ostwald ripening theory, was 3.6 × 10−18 cm3/s compared to an experimentally determined rate constant of 4.8 × 10−18 cm3/s. The agreement between the theoretical and experimental rate constants was quite good. The significance attached to the good agreement between the theoretical and experimental rate constants might be mollified to some extent by the uncertainty involved in the parameters used to calculate the theoretical rate constant; viz. the interfacial tension, mutual‐diffusion coefficient, and equilibrium concentration of the HPB in the matrix phase that are not known to high accuracy. In reality, because other theories were used to determine the interfacial tension, mutual‐diffusion coefficient, and equilibrium phase compositions, this study was a test of several theories simultaneously. However, the agreement of the experimental temporal exponent and rate constant with the predictions of Ostwald ripening theory strongly indicates that the HPB/HDPE system coarsens by the evaporation‐condensation mechanism upon which the Ostwald ripening theory is based. © 1994 John Wiley & Sons, Inc.

Hybrid organic-inorganic materials synthesized by reaction with alkoxysilanes: Effect of the acid-to-alkoxide ratio on morphology

The gelation phenomenon of hybrid organic-inorganic materials is investigated as a function of the temperature and the catalyst-to-alkoxide ratio. These ceramers are prepared in a two-step synthesis: First, an α-hydroxy, ω-methyl poly(ethylene oxide) and an α-hydroxy-terminated hydrogenated polybutadiene (H-PBD) are reacted with isophorone diisocyanate (IPDI); second, these isocyanate-terminated prepolymers are reacted with γ-aminopropyltriethoxysilane (γ-APS) to form alkoxysilane-terminated macromonomers. These macromonomers are cross-linked using the well-known sol-gel process. The gelation time is found to be sensitive to the acid-to-alkoxide ratio. The large difference in the activation energies of the gelation process of the two kinds of macromonomers could be attributed to the amount of the IPDI/γ-APS copolymers. This results in an incomplete reaction of IPDI during the first stages of synthesis: The final morphology of the cured hybrid materials, based on the H-PBD macromonomer, depends on the amount of H+ and indicates that the acid-to-alkoxide ratio modifies not only the rate of hydrolysis of the alkoxide, but also the structure of the ceramer. The model of the microstructure of such hybrid materials, described previously, could explain the two relaxation peaks observed by dynamic mechanical spectroscopy. The relaxation close to the glass transition temperature of the initial H-PBD is attributed to the glass transition region of the organic-rich matrix. The second peak, 50°C above, is associated with the glass transition temperature of the interface between the organic-rich region and the inorganic clusters (H+/Si, >0.05). The second relaxation is easily observed at a low H+/Si ratio (<10−3).

Hydrogenated polybutadiene morphology and its effects on small molecule diffusion

The transport behavior of n-decyl alcohol (C 10 OH) into hydrogenated polybutadienes (HPBD) (MW=100 000; M w /M n <1.1) with varied branch contents was investigated using a FTIR-ATR sampling method. A significant difference in crystallinities determined by DSC and density measurements was evident. A nonlinear dependence of the equilibrium sorption on the density of HPBDs was observed and an exponential dependence of diffusivities on the density of the polymers was evident. The observed transport behaviors deviate from those predicted using a simple two-phase model

Organic-inorganic hybrid materials. 2. Compared structures of polydimethylsiloxane and hydrogenated polybutadiene based ceramers

Different ceramer networks were successfully prepared in bulk or in solution. High transparency was observed for all the samples based on hydrogenated polybutadiene (H-PBD) and polydimethylsiloxane (PDMS) oligomers. These materials are microphase-separated materials. A similar microstructure exists in both types of samples: silicate clusters including the cross-link points are dispersed in the oligomer-rich phase. The morphology of the PDMS ceramers can be described as a three phase system including the soft phase, practically pure in PDMS, the silicate clusters and an interfacial region containing the urethane-urea units

Synthesis and properties of polyurethanes based on polyolefin: 2. Semicrystalline segmented polyurethanes prepared under heterogeneous or homogeneous synthesis conditions

Semicrystalline segmented polyurethanes based on hydrogenated polybutadiene (H-PBD) soft segments and butanediol (BDO) or di-β-hydroxyethyl hydroquinone (HQEE) as chain extenders were synthesized under different homogeneous or heterogeneous conditions, in solution or in bulk. Segmented semicrystalline H-PBD polyurethanes exhibit two glass transitions: a soft-phase transition T g(S) and a hard-phase transition T g(H). Thermal treatments show rearrangements in the two-phase materials. The dielectric relaxations, α S and α H, confirm the thermal behaviour and also the presence of a mixed interfacial region ( α′ H). Increasing the hard-segment content increases this mixed-phase relaxation. This effect is also observed in the polyurethanes prepared in bulk instead of in solution, because of the decrease in the segregation ratio of the soft segments. Bulk samples also contain short isolated or amorphous hard segments as shown by size exclusion chromatography results and the conduction process appearing in the dielectric measurements. Such different routes of preparation induce various characteristics and tensile properties of the corresponding polyurethanes attributed mainly to premature phase separation occurring during the polymerization and the competition between the phase separation rate and the polymerization rate.

Effect of diblock copolymers on dynamic mechanical properties of polyethylene/polystyrene blends

AbstractA systematic investigation of the dynamic mechanical properties of high‐density polyethylene (HDPE)/high‐impact polystyrene (HIPS)/copolymer blends was carried out. Blends of 80/20 weight percent of HDPE/HIPS were prepared in the melt state at 180°C in a batch mixer. Synthesized pure diblock (H77) and tapered diblock (H35) copolymers of hydrogenated polybutadiene (HPB) and polystyrene (PS) were added at different concentrations (1, 3, and 5 wt %), and the dynamic mechanical properties were investigated. The results show that: (1) both the tapered and the pure diblock copolymers enhance the phase dispersion and the interphase interactions; (2) structure and molecular weight are both important parameters in the molecular design of copolymers; (3) important effects occur when only small amounts of copolymer are added (up to the interface saturation concentration SC); (4) a micellar structure formation is possible when the copolymer is in excess in the blend; (5) the effect of the copolymer structure on the SC and the critical micellar concentration (CMC) is more pronounced than the effect of molecular weight. These concentrations are found to be lower for the tapered diblock copolymer. The analysis of the dynamic mechanical thermal analysis (DMTA) results obtained for the 20/80 HDPE/HIPS blend leads to the conclusion that the copolymers also enhance the interactions between heterogeneous phases. Similar conclusions based on electron microscopy were reported in the literature. DMTA shows great potential to relate macroscopic observations to the state of a copolymer in an immiscible blend.

Dielectric studies of segmented polyurethanes based on polyolefine: relations between structure and dielectric behaviour

Pure hand-block, amorphous and semi-crystalline segmented polyurethanes based on hydrogenated polybutadiene (H.PBD) were synthesized under homogenous conditions in solution. The synthesis was also realized in bulk in the case of the semi-crystalline polyurethanes. Dielectric relaxations studies were carried out to obtain better insight in the morphology of such polyurethanes and to monitor the phase separation during their synthesis.