Styrene-butadiene Block Copolymers Research Articles

Electrical conductivity of polystyrene/styrene-butadiene block copolymer blends containing carbon black

The electrical resistivity and mechanical properties of carbon black (CB)-filled polystyrene (PS)/styrene-butadiene block copolymer (SB) blends have been studied. Good electrical performance was achieved with pure SB and PS/SB blends indicating an inhomogeneity of these materials and the heterogeneous micro-dispersion of the CB particles. The percolation threshold of the filler inside SB or PS/SB blends is around 3.6wt%, which is lower than that expected for incompatible PS/PBD blend. The addition of small amount CB decreases the elongation at break of PS/SB blends indicating some disturbance at the interface of these compatible material.

A hot-melt pressure-sensitive adhesive based on styrene-butadiene-styrene rubber. The effect of adhesive composition on the properties

Hot-melt pressure-sensitive adhesives based on styrene-butadiene block copolymers with aliphatic and aromatic tackifying resins and plastifying oils have been analyzed. The importance of the resin structure in the compatibility with the block copolymer and the influence of the different paraffinic-naphthenic character of the oil in PSA performance have been shown. Ternary systems with a fixed polymer content (30%) and with variable resin and oil contents show a good miscibility over the whole range of compositions, and only one glass transition temperature was found in each composition. The relationship between chemical composition and bulk performance are expressed in terms of the visco-elastic behavior of the adhesives, measured by DMTA. It has been shown that at a given resin content there is a minimum on tan δ peak vs. temperature, the melt viscosities present a plateau region and the tack strength shows a maximum. An important conclusion is that phase separation is not a requirement for maximum tack; some restricted miscibility is enough, present in a few microdomains of the blend. © 1996 John Wiley & Sons, Inc.

The role of matrix molecular weight in rubber toughened nylon 6 blends: 1. Morphology

The effects of polyamide molecular weight on morphology generation in nylon 6 blends with maleated elastomers are described. The elastomers used include styrene—butadiene—styrene block copolymers with a hydrogenated mid-block, SEBS, and versions with X % grafted maleic anhydride, SEBS-g-MA- X%, and an ethylene/propylene copolymer, EPR, and a maleated version EPR-g-MA. The molecular weight of the nylon 6 phase governs the melt viscosity of the blend matrix and the number of amine end groups available for reaction with the maleic anhydride groups in the rubber phase; both of which influence the size, shape, and size distribution of the rubber phase formed during blending. In general, rubber particle size, distribution, and the amount of occluded material in the rubber phase decreases as the nylon 6 molecular weight increases. Measurement of the extent of reaction between the amine end groups and the grafted maleic anhydride revealed that a higher fraction of nylon 6 chains are grafted to the rubber matrix as the nylon 6 molecular weight increases. The weight average rubber particle size and size distribution for blends based on SEBS-g-MA- X% are smaller than corresponding blends based on SEBS/SEBS-g-MA-2% mixtures containing the same amount of maleic anhydride. EPR/EPR-g-MA mixtures produce non-spherical morphologies that are typically larger and more polydisperse than SEBS type elastomers. One reason for this difference is the fact that SEBS elastomers react more readily with nylon 6 than do EPR/EPR-g-MA mixtures as determined by extent of amine reaction and torque rheometry. The weight average rubber particle size for blends of the various rubbers and nylon 6 materials were correlated using a modified Taylor theory analysis. A master curve was generated by determining shift factors needed to superimpose the maleated rubber/nylon 6 curves onto a reference curve for the non-maleated rubber, SEBS. The overall shift factors correlate linearly with the maleic anhydride content of the rubber phase.

Effects of tetrahydrofuran as a structure modifier in preparation of SBS thermoplastic block copolymers in cyclohexane

Linear styrene-butadiene block copolymers of polyA-block-polyB-block-polyA type (SBS) were synthesized in the presence of varying amounts of THF functioning as the polar structure modifier. The efficiency of this modifier was studied by analyzing the microstructure of synthesized polymers using 13C-NMR, and the effect of THF on polymerization kinetics was determined by progressive buildup of the molecular weight measured by GPC. Polymerization at 4000 ppm THF concentration resulted in the highest styrene polymerization rate while a 1 wt % concentration gave the highest butadiene polymerization rate. The vinyl content increased from 20 to 64% with an increase in the amount of THF from 200 ppm to 1 wt % while the content of trans-1,4 and cis-1,4 units decreased. For SBS polymer synthesized via a sequential process, the use of THF as the structure modifier enhanced the crossover efficiency that would otherwise result in a skewed molecular weight distribution with a higher polydispersity. For SBS polymer made via a coupling process, the coupling efficiency decreased when the amount of THF exceeded a certain limit. The temperature dependence of the coupling efficiency was also investigated. © 1996 John Wiley & Sons, Inc.

Epoxidation of partially hydrogenated styrene-butadiene block copolymers using peracetic acid in a cyclohexane/water heterogeneous system

The preparation of partially saturated lightly functionalized styrene-butadiene block copolymers of polyA-block-polyB-block-polyA type (SBS) is described. The work involves epoxidizing partially hydrogenated SBS block copolymers using peracetic acid in a cyclohexane/water heterogeneous system. Five partially hydrogenated model polymers containing low levels of unsaturated aliphatic double bonds were used to study the epoxidation reaction and kinetics. The existence of the epoxide functional group on the product polymer was evidenced by IR and 1H-NMR spectra and the epoxide concentration was determined by direct titration. The partially hydrogenated SBS copolymers were more difficult to epoxidize than the unhydrogenated ones. The temperature dependence of the epoxidation rate was studied and the activation energy was determined as 8.8 kcal/mole of double bonds. © 1996 John Wiley & Sons, Inc.

Synthesis of high-vinyl polymers and copolymers of butadiene on the basis of a new soluble organosodium catalyst

A new process for the synthesis of high-vinyl (50–70 % 1.2-units) butadiene polymers and copolymers on the basis of hydrocarbon-soluble organosodium catalyst is proposed. The catalyst can be readily synthesized in aliphatic solvents from commercially available starting materials; the equipment common for the synthesis of organolithiums is suitable. Main parametres of butadiene polymerization and styrene-butadiene copolymerization including kinetics, molecular weights and monomer reactivity ratios for copolymerization were investigated. The synthesis of polystyrene, 3.4-polyisoprene, styrene-butadiene block-copolymers, non-functional butadiene and styrene-butadiene liquid rubbers, and other high-vinyl polymers is also possible.

The oxidation of hindered amine light stabilisers to nitroxy radicals in solution and in polymers. Part II

Different types of hindered amine light stabilisers (HALS) have been oxidised by peroxy radicals generated by gamma irradiation of air saturated cyclohexane solutions. In all cases the concentration of nitroxy radicals, measured by EPR spectroscopy, increases linearly with absorbed dose. The sequence of reactivity observed is: amino ether > sec. amine > tert. amine The same HALS have been oxidised in a hydroperoxidised styrenebutadiene-styrene block copolymer by peroxy radicals resulting from the decomposition of clustered hydroperoxides. At room temperature the nitroxy radical concentration slowly increases with time and tends to a limit corresponding to the fraction of HALS molecules that are in a suitable environment to be oxidised. The sequence of reactivity observed is the reverse of that mentioned above. In this case, it reflects the ability of the different HALS to catalyse the decomposition of clustered hydroperoxides.

Compatibilization of high-impact polystyrene/polypropylene blends

Effects of three different linear styrene—butadiene block copolymers on morphology and selected mechanical properties of high-impact polystyrene/polypropylene blends were investigated. Scanning and transmission electron microscopy and small-angle X-ray scattering were used for the determination of the blend morphology. Impact strength, elongation at break and flexural modulus were measured for further evaluation of the compatibilizer efficiency. A similar effect on the particle dispersion was found for all three copolymers but both the styrene-terminated multiblocks influence formation of interfacial layer and consequently the related mechanical properties in a much more pronounced way than the diblock. Small-angle X-ray scattering was found to be the appropriate technique for the determination of triblock concentration necessary for covering a given interfacial area (critical concentration).

Modification of Interfacial Properties of Polymer Blends with Diblock Copolymer

ABSTRACTThe effect of diblock copolymer on the phase-separation process of polymer blends has been investigated by using light scattering and optical microscopic observations. To quench the system into the two phase region, a shear-jump technique is employed instead of the conventional temperature-jump technique. The samples studied are blends of low-molecular-weight polystyrene and polybutadiene with and without added styrene-butadiene block copolymer as a compatibilizer. It was observed that the addition of diblock copolymers could accelerate the phase separation kinetics depending on the shear history. As the concentration of diblock copolymer increases, the distribution of domain sizes becomes narrower and the growth rate slows down. The extent of slowing-down depends on the molecular weight and concentration of the copolymer. The time dependence of domain growth is clearly observed with optical microscopy.

Studies on the Stability of a Styrene-Butadiene Copolymer for use in Biomedical Applications

Two samples of commercially-available styrene-butadiene block copolymers (SBC) were tested for suitability for use in biomedical applications. A 30% sample and a 40% sample of styrene-containing polymers with very similar molecular weights (approximately 300,000) were characterized before and after being placed in a physiological serum for a period of six months. SEM, FTIR, and atomic absorption spectroscopy were used to characterize the polymers. Scanning and transmission electron micrographs showed that the SBC's morphology was clearly affected by the serum. A difference was observed with the higher styrene-containing polymer which showed no degradation of the elastomeric portion of the copolymer, whereas the 30% sample showed that considerable degradation occurred in this area. Atomic absorption results showed a clear difference in the capability of both materials to absorb K+, Na+ and Caions with a clear advantage for the 40% styrene-containing material. FTIR results indicate that both polymer samples degraded in the serum, showing loss of both the polystyrene and polybutadiene portions, as well as oxidation of the double bonds in the latter.

Polymerization of Styrene-Butadiene Block Copolymers Using a Dicarbanion Initiator Made by the Reaction of Lithium with .alpha.-Methylstyrene

Linear styrene-butadiene block copolymers of the polyA-block-polyB-block-polyA type (SBS) have been synthesized using a dicarbanion initiator formed by the reaction of metal lithium and α-methylstyrene. While being unable to initiate polymerization in cyclohexane and/or n-hexane, the diinitiator performed well in benzene. Various promoters such as tetrahydrofuran (THF), tetramethylethylenediamine, and hexamethylphosphoric triamide have been added during the making of diinitiators, resulting in initiators of different functionalities and activities. The presence of THF facilitated the formation of the diinitiator, and the resulting polymers made with this diinitiator have been analyzed and mechanically tested. The effect of process variables on the polymerization kinetics and molecular characteristics was also investigated.

Synthesis of SBS thermoplastic block copolymers in cyclohexane in the presence of diethylether used as a structure modifier

Diethylether (DEE) was used as a structure modifier during the synthesis of linear styrene-butadiene block copolymers of poly A-block-polyB-block-polyA type (SBS). The microstructures of synthesized polymers were analyzed, and the effect of DEE on polymerization kinetics was studied. Addition of DEE at 2 wt% concentration results in the highest styrene polymerization rate, while addition at 6 wt% concentration gives the highest butadiene polymerization rate. The vinyl content of the polybutadiene portion increases from 14 to 47% with an increase in the DEE concentration from 500 ppm to 10 wt% while thetrans- l,4 andcis-1,4 isomers decrease. For SBS polymer synthesized via a sequential method, the addition of DEE as a structure modifier minimizes the crossover deficiency which would otherwise result in a skewed molecular weight distribution with a higher polydispersity. For SBS polymers made via a coupling method, the coupling efficiency appears to be constant in a range of DEE concentration from 500 ppm to 1 wt% before declining with a further increase in DEE.

Miscibility, Microstructure, and Dynamics of Blends Containing Block Copolymer. 2. Microstructure of Blends of Homopolystyrene with Styrene-Butadiene Block Copolymers

Miscibility, Microstructure, and Dynamics of Blends Containing Block Copolymer. 2. Microstructure of Blends of Homopolystyrene with Styrene-Butadiene Block Copolymers

Miscibility, Microstructure, and Dynamics of Blends Containing Block Copolymer. 1. Miscibility of Blends of Homopolystyrene with Styrene-Butadiene Block Copolymers

The microstructures of styrene-butadiene triblock (SBS) and styrene-butadiene four-arm star block (SB-4A) copolymers and their blends with homopolystyrene (PS) of different molecular weights, MPS, have been investigated by means of small-angle X-ray scatt

Miscibility, Microstructure, and Dynamics of Blends Containing Block Copolymer. 3. Molecular Motion in Homopolystyrene and Polystyrene/Four-Arm Styrene-Butadiene Star Block Copolymer Blends

The proton spin-spin relaxation times (T-2(H)) at different temperatures (from 160 to 390 K) have been determined for polystyrene (PS) and four-arm star styrene-butadiene block copolymer (SB-4A) and its blends with PS of different molecular weights (M(PS)

Crystal transformation of styrene-butadiene block copolymer

The crystal transformation of styrene-butadiene block copolymer, which has the attribute of shape-memory, has been studied. It is demonstrated from differential scanning calorimetry and wide-angle X-ray diffraction measurements that reversible crystal transformation takes place with temperature; two distinct crystal forms exist above and below the crystal transformation temperature of ∼45°C.

Comparison of some butadiene‐based impact modifiers for polycarbonate

AbstractThe relationship of blend morphology to deformation mechanisms and notched Izod impact strength was studied with three butadiene‐based impact modifiers for polycarbonate (PC). The impact modifiers were a linear polybutadiene (PB), a styrene–butadiene–styrene block copolymer (SBS), and a structured latex particle having a PB core and methyl methacrylate/styrene shell (MBS). The particle‐size distribution in the blends was determined from transmission electron micrographs (TEM). Fractographic analysis combined with TEM examination of thin sections from impacted specimens provided insight into the failure mechanisms. Good impact was achieved with PC/MBS blends when cavitation of the core–shell particles relieved triaxiality and enabled the matrix to fracture by the plane stress ductile tearing mode that is characteristic of thin PC. The best impact properties were obtained with PC/SBS blends when the modifier was dispersed as aggregates of small particles. Cavitation at the weak internal boundaries relieved triaxiality, but subsequent coalescence of cavitated particles during ductile drawing of the matrix created critical size voids and the resulting secondary cracks reduced the toughness of the blend. In general, PB did not significantly enhance the impact strength of PC. © 1994 John Wiley & Sons, Inc.

Preparation and structure of cross‐linked asymmetric membranes based on polystyrene and divinylbenzene

AbstractAsymmetric polystryene‐based membranes were prepared by photocross‐linking with divinylbenzene (DVB) combined with phase‐inversion steps. The primary variables examined were original polystrene concentration in the membrance casting solution and degree of cross‐linking. The effects of these upon membrane morphology and reverse osmosis performance were determined. At higher DVB concentration, skin was formed at the top due to phase separation and at the bottom due to preferential polymer absorption at the support interface. An attempt was made to increase membrane ductility by incorporating low levels of liquid polybutadiene or styrene‐butadiene block copolymer, but no significant change was measured. © 1994 John Wiley & Sons, Inc.

Waxs and saxs investigation of polypropylene crystalline phase in blends with high-impact polystyrene and compatibilizers

On the basis of combination of wide-angle and small-angle X-ray scattering, the character of the polypropylene crystalline phase and its content were studied in polypropylene-high impact polystyrene blends, compatibilized by styrene-butadiene block copolymers. Addition of a copolymer slightly reduces the crystallinity of polypropylene. In the absence of the compatibilizer no miscibility of the components was observed. In all samples polypropylene maintains its α-crystalline phase.

Compatibilisation of polystyrene-polyolefin blends

The impact properties of 1:1 polyolefin-polystyrene blends compatibilised with a series of hydrogenated styrene-butadiene block copolymers of various structures have been studied with a view to establishing a structure-property realationship. The most effective compatibiliser in this context appears to be a low molecular weight triblock (Kraton G1652). Addition of only 5% Kraton G1652 affords a ca. three-fold improvement in the impact strength for a 1:1 PP/PS blend over the uncompatibilised blend and leads to near HIPS impact strength for a 1:1 LDPE/PS blend. This compatibiliser is as effective as a high molecular weight tapered diblock and appears to be substantially more effective than either low molecular weight diblocks or a higher molecular weight triblock.