Compatibilization effects of styrenic/rubber block copolymers in polypropylene/polystyrene blends

Compatibilizing effects of styrene/rubber block copolymers poly(styrene‐b‐butadiene‐b‐styrene) (SBS), poly(styrene‐b‐ethylene‐co‐propylene) (SEP), and two types of poly(styrene‐b‐ethylene‐co‐butylene‐b‐styrene) (SEBS), which differ in their molecular weights on morphology and selected mechanical properties of immiscible polypropylene/polystyrene (PP/PS) 70/30 blend were investigated. Three different concentrations of styrene/rubber block copolymers were used (2.5, 5, and 10 wt %). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to examine the phase morphology of blends. The SEM analysis revealed that the size of the dispersed particles decreases as the content of the compatibilizer increases. Reduction of the dispersed particles sizes of blends compatibilized with SEP, SBS, and low‐molecular weight SEBS agrees well with the theoretical predictions based on interaction energy densities determined by the binary interaction model of Paul and Barlow. The SEM analysis confirmed improved interfacial adhesion between matrix and dispersed phase. The TEM micrographs showed that SBS, SEP, and low‐molecular weight SEBS enveloped and joined pure PS particles into complex dispersed aggregates. Bimodal particle size distribution was observed in the case of SEP and low‐molecular weight SEBS addition. Notched impact strength (a_k), elongation at yield (ε_y), and Young's modulus (E) were measured as a function of weight percent of different types of styrene/rubber block copolymers. The a_k and ε_y were improved whereas E gradually decreased with increasing amount of the compatibilizer. The a_k was improved significantly by the addition of SEP. It was found that the compatibilizing efficiency of block copolymer used is strongly dependent on the chemical structure of rubber block, molecular weight of block copolymer molecule, and its concentration. The SEP diblock copolymer proved to be a superior compatibilizer over SBS and SEBS triblock copolymers. Low‐molecular weight SEBS appeared to be a more efficient compatibilizer in PP/PS blend than high‐molecular weight SEBS. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 291–307, 1999     

Blends of syndiotactic polystyrene with SEBS triblock copolymers

Blending of styrene-b-(ethylene-co-1-butene)-b-styrene (SEBS) triblock copolymers with syndiotactic polystyrene (PSsyn) has been performed in a Brabender mixer above the higher glass transition temperature of the triblock copolymer but below the PSsyn melting point. The large excess of the triblock copolymer over the homopolymer as well as the significant amount of plasticized amorphous PSsyn phase allowed the easy processing under the used temperature conditions with good interface compatibility. The consequent interfacial adhesion between the amorphous PS phase and the unmelted PSsyn crystallites affects both the final morphology of the blend as well as its dynamic behavior. Indeed, such solid particles act as reinforcing point of the overall blend structure, as evidenced by scanning electron microscopy. Moreover, they contribute to a T_g increase in the order of 20 °C with respect to pure SEBS and to an appreciable conservation of mechanical properties at temperatures higher than the T_g of the PS blocks of SEBS. The mechanical and thermal behavior of the synthesized blends has been studied and tentatively correlated to the molecular weight ratio between PSsyn and the PS blocks of SEBS.     

Thermoresponsive core-shell-corona micelles of poly(ethyleneglycol)-b-poly(N-isopropylacrylamide)-b-polystyrene

Core-shell-corona micelles with a thermoresponsive shell self-assembled by triblock copolymer of poly(ethyleneglycol)-b-poly(N-isopropylacrylamide)-b-polystyrene (PEG₄₅-b-PNIPAM₁₆₈-b-PS₄₆) are studied by ¹H NMR, light scattering and atomic force microscopy. The thermoresponsive triblock copolymer, which has a relatively short hydrophobic PS block, can disperse in water at room temperature to form core-shell-corona micelles with the hydrophobic PS block as core, the thermoresponsive PNIPAM block as shell and the hydrophilic PEG block as corona. At temperature above lower critical solution temperature (LCST) of the PNIPAM block, the PNIPAM chains gradually collapse on the PS core to shrink the size and change the structure of the resultant core-shell-corona micelles with temperature increasing. It is found that there possibly exists an interface between the PNIPAM shell and PEG corona of the core-shell-corona micelles at temperature above LCST of the PNIPAM block.     

Characterization of morphology and mechanical properties of block copolymers using atomic force microscopy: Effects of processing conditions

The effect of preparation methods and processing conditions on morphology and mechanical properties of poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS) triblock copolymer were investigated with atomic force microscopy (AFM) tapping mode and nanomechanical mapping, tensile testing, and gel permeation chromatograph (GPC). It was found that the samples prepared by solution casting and melt processing show large difference in morphology and mechanical properties. High shear rate does not induce alignment of lamellar block copolymer melts but leads to serious degradation of SEBS. As increase of rotational speed from 0 to 400 rpm, the molecular weight including M_n and M_w decreases from 67,100 to 26,000 and 70,000 to 43,000, respectively. Such large molecular weight decrease causes greatly decreased tensil strength but there is almost no evident effect on the well-phase separated morphology and Young's modulus of the SEBS. The Young's modulus distribution revealed by nanomechanical mapping becomes narrow as the increase of rotational speed. The amount of SEBS molecular having higher Young's modulus, which play a very important role in tensile strength of SEBS, also decreases.     

Morphology and flame‐retardancy properties of ternary high‐impact polystyrene/elastomer/polystyrene‐encapsulated magnesium hydroxide composites

The effects of elastomer type on the morphology, flammability, and mechanical properties of high‐impact polystyrene (HIPS)/polystyrene (PS)‐encapsulated magnesium hydroxide (MH) were investigated. The ternary composites were characterized by cone calorimetry, mechanical testing, and scanning electron microscopy. Morphology was controlled with poly[styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene] (SEBS) triblock copolymer or the corresponding maleinated poly[styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene] (SEBS‐g‐MA). The HIPS/SEBS/PS‐encapsulated MH composites exhibited separation of the filler and elastomer, whereas the HIPS/SEBS‐g‐MA/PS‐encapsulated MH composites exhibited encapsulation of the filler by SEBS‐g‐MA. The flame‐retardant and mechanical properties of the ternary composites were strongly dependent on microstructure. The composites with an encapsulation structure showed higher flame‐retardant properties than those with a separation structure at the optimum use level of SEBS‐g‐MA. Furthermore, the composites with a separation structure showed a higher modulus and impact strength than those with an encapsulation structure. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Synthesis of ABA triblock copolymer of poly(potassium acrylate-styrene-potassium acrylate) by atom transfer radical polymerization and the self-assembly in selective solvents

A series of well-defined ABA triblock copolymers of poly(methyl acrylate)-polystyrene-poly(methyl acrylate) (PMA-b-PS-b-PMA) with different molecular weights were synthesized using Cl-PS-Cl as macroinitiator, CuCl/N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) as catalyst system via atom transfer radical polymerization (ATRP). Amphiphilic triblock copolymer poly(potassium acrylate)-polystyrene-poly(potassium acrylate) (PKAA-b-PS-b-PKAA) was obtained by hydrolyzing PMA-b-PS-b-PMA. The self-assembly behavior of the triblock copolymers in organic solutions, which is a good solvent for the PS block and in aqueous solutions, which is a good solvent for the PKAA blocks was studied by high performance particle sizer (HPPS). The results showed that the Z-average size of the micelles obviously increases with increase in molecular weight of triblock copolymers, and the micelles in organic solutions are relatively more stable than in aqueous solutions. The effect of the length of PS block on the Z-average size of the micelles is more obvious in organic solution than in aqueous solution. The morphology of triblock copolymers PKAA-b-PS-b-PKAA in aqueous solution, which is a nearly ‘pearl-necklace’-like shape, was examined by transmission electron microscopy (TEM) at room temperature.     

Near-surface morphology effect on tack behavior of poly(styrene-b-butadiene-b-styrene) triblock copolymer/rosin films

The correlation between near-surface morphology and tack behavior of poly(styrene-b-butadiene-b-styrene) triblock copolymer (SBS)/rosin ester films was investigated using probe tack tests, transmission electron microscopy and small-angle X-ray scattering. The SBS/rosin films with rosin composition between 10 and 20 wt% rosin, prepared by slow evaporation of toluene during solvent casting, exhibited uniform near-surface morphology of lamellae oriented parallel to the surface. However, due to the limited solubility of rosin in the PS domains, the rosin started to phase-separate from the PS domains at 15 wt%, and formed fully separated micron-sized domains above 20 wt% rosin. The probe tack force of the SBS/rosin films increased steadily when the near-surface domain orientation changed from perpendicular cylinder to parallel lamellae on addition of rosin. Specifically, for a given lamellar morphology and surface orientation, macrophase separation of rosin plays a critical role in determining the tack properties of SBS/rosin films.     

Synthesis and morphological studies of polyisoprene-block-polystyrene-block-poly(vinyl methyl ether) triblock terpolymer

The triblock terpolymer (PI-b-PS-b-PVME) consisting of polyisoprene (PI), polystyrene (PS) and poly(vinyl methyl ether) (PVME) was synthesized by coupling reaction between living PI-b-PS anion and end-chlorinated PVME prepared via living cationic polymerization. This polymer is an amphiphilic block polymer and unique in a sense that it exhibits complex phase behavior because PS and PVME have a lower critical solution temperature (LCST)-type phase diagram while PI and PS (or PVME) have an UCST-type phase diagram. This unique architecture would result in a step-wise microphase separation to form a three-phase microdomain structure. It was observed by transmission electron microscopy with ultrathin sections that the toluene-cast film of PI-b-PS-b-PVME has a two-phase lamellar structure consisting of PI microdomains and mixed PS/PVME microdomains. Applying a drop of water onto the ultrathin sections induced further microphase separation between PS and PVME within the lamellar microdomains resulting in the three-phase structure. Water is a selective solvent for PVME and might have lowered the order-disorder temperature between PS and PVME. This step-wise microphase separation may be a new technique to control microphase-separated structures in triblock terpolymers.     

Nanophase morphology and crystallization in poly(vinylidene fluoride)/polydimethylsiloxane‐block‐poly(methyl methacrylate)‐block‐polystyrene blends

An approach to achieve confined crystallization of ferroelectric semicrystalline poly(vinylidene fluoride) (PVDF) was investigated. A novel polydimethylsiloxane‐block‐poly(methyl methacrylate)‐block‐polystyrene (PDMS‐b‐PMMA‐b‐PS) triblock copolymer was synthesized by the atom‐transfer radical polymerization method and blended with PVDF. Miscibility, crystallization and morphology of the PVDF/PDMS‐b‐PMMA‐b‐PS blends were studied within the whole range of concentration. In this A‐b‐B‐b‐C/D type of triblock copolymer/homopolymer system, crystallizable PVDF (D) and PMMA (B) middle block are miscible because of specific intermolecular interactions while A block (PDMS) and C block (PS) are immiscible with PVDF. Nanostructured morphology is formed via self‐assembly, displaying a variety of phase structures and semicrystalline morphologies. Crystallization at 145 °C reveals that both α and β crystalline phases of PVDF are present in PVDF/PDMS‐b‐PMMA‐b‐PS blends. Incorporation of the triblock copolymer decreases the degree of crystallization and enhances the proportion of β to α phase of semicrystalline PVDF. Introduction of PDMS‐b‐PMMA‐b‐PS triblock copolymer to PVDF makes the crystalline structures compact and confines the crystal size. Moreover, small‐angle X‐ray scattering results indicate that the immiscible PDMS as a soft block and PS as a hard block are localized in PVDF crystalline structures. © 2019 Society of Chemical Industry     

Physical properties of poly(cyclohexyl methacrylate)-b-poly(iso-butyl acrylate)-b-poly(cyclohexyl methacrylate) triblock copolymers synthesized by controlled radical polymerization

The microphase segregation of different poly(cyclohexyl methacrylate)-b-poly(iso-butyl acrylate)-b-poly(cyclohexyl methacrylate), PCH-b-PiBA-b-PCH, triblock copolymers obtained by atom transfer radical polymerization has been evaluated by dynamic mechanical thermal analysis through location of the two relaxations ascribed to cooperative motions of each block. Additionally, other secondary relaxations have been found, whose characteristics are also dependent on molecular weight of outer and rigid segments. The length of these hard blocks influences significantly the stiffness and microhardness found in these triblock copolymers. These two mechanical parameters increase as molecular weight of poly(cyclohexyl methacrylate) does. The morphological aspects have been examined by small angle X-ray scattering and atomic force microscopy.     

Amphiphilic block copolymer poly(lactic acid)‐block‐(glycidylazide polymer)‐block‐polystyrene: synthesis and self‐assembly

The triblock energetic copolymer poly(lactic acid)‐block‐(glycidylazide polymer)‐block‐polystyrene (PLA‐b‐GAP‐b‐PS) was synthesized successfully through atom‐transfer radical polymerization (ATRP) of styrene and ring‐opening polymerization of d,l ‐lactide. The energetic macroinitiator GAP‐Br, which was made from reacting equimolar GAP with α‐bromoisobutyryl bromide, firstly triggered the ATRP of styrene with its bromide group, and then the hydroxyl group on the GAP end of the resulting diblock copolymer participated in the polymerization of lactide in the presence of stannous octoate. The triblock copolymer PLA‐b‐GAP‐b‐PS had a narrow distribution of molecular weight. In the copolymer, the PS block was solvophilic in toluene and improved the stability of the structure, the PLA block was solvophobic in toluene and served as the sacrificial component for the preparation of porous materials, and GAP was the basic and energetic material. The three blocks of the copolymer were fundamentally thermodynamically immiscible, which led to the self‐assembly of the block copolymer in solution. Further studies showed that the concentration and solubility of the copolymer and the polarity of the solvent affected the morphology and size of the micelles generated from the self‐assembly of PLA‐b‐GAP‐b‐PS. The micelles generated in organic solvents at 10 mg mL^?1 copolymer concentration were spherical but became irregular when water was used as a co‐solvent. The spherical micelles self‐assembled in toluene had three distinct layers, with the diameter of the micelles increasing from 60 to 250 nm as the concentration of the copolymer increased from 5 to 15 mg L^?1. © 2017 Society of Chemical Industry     

Nanostructured polymer blends based on polystyrene‐b‐polybutadiene‐b‐poly(methyl methacrylate) triblock copolymers modified with polystyrene and/or poly(methyl methacrylate) homopolymers

Morphologies of polymer blends based on polystyrene‐b‐ polybutadiene‐b ‐poly(methyl methacrylate) (SBM) triblock copolymer were predicted, adopting the phase diagram proposed by Stadler and co‐workers for neat SBM block copolymer, and were experimentally proved using atomic force microscopy. All investigated polymer blends based on SBM triblock copolymer modified with polystyrene (PS) and/or poly(methyl methacrylate) (PMMA) homopolymers showed the expected nanostructures. For polymer blends of symmetric SBM‐1 triblock copolymer with PS homopolymer, the cylinders in cylinders core?shell morphology and the perforated lamellae morphology were obtained. Moreover, modifying the same SBM‐1 triblock copolymer with both PS and PMMA homopolymers the cylinders at cylinders morphology was reached. The predictions for morphologies of blends based on asymmetric SBM‐2 triblock copolymer were also confirmed experimentally, visualizing a spheres over spheres structure. This work presents an easy way of using PS and/or PMMA homopolymers for preparing nanostructured polymer blends based on SBM triblock copolymers with desired morphologies, similar to those of neat SBM block copolymers. © 2017 Society of Chemical Industry     

Morphology and thermomechanical properties of nanostructured thermosetting blends of epoxy resin and poly(?-caprolactone)-block-polydimethylsiloxane-block-poly(?-caprolactone) triblock copolymer

Poly(?-caprolactone)-block-polydimethylsiloxane-block-poly(?-caprolactone) triblock copolymer (PCL-b-PDMS-b-PCL) was synthesized via the ring-opening polymerization of ?-caprolactone with dihydroxypropyl-terminated PDMS (HTPDMS) as the initiator. The triblock block copolymer was characterized by means of Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR) and gel permeation chromatography (GPC). The triblock copolymer was incorporated to prepare nanostructured thermosetting blends. The morphology of the epoxy thermosets containing PCL-b-PDMS-b-PCL were investigated by means of atomic force microscopy (AFM), transmission electronic microscopy (TEM) and small-angle X-ray scattering (SAXS). The thermomechanical properties of the nanostructured blends were investigated by means of differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The formation of the nanostructures in the thermosetting composites was judged to follow the self-assembly mechanism in terms of the difference in miscibility of PDMS and PCL subchains with epoxy resin after and before curing reaction.     

Nanostructured silica-type hybrids from poly(styrene-b-ethylene oxide-b-caprolactone) copolymers

By employing a triblock copolymer, poly(styrene-b-ethylene oxide-b-caprolactone) copolymer, as a structure-directing agent, a series of silica-type hybrid materials were prepared via a sol-gel method of (3-glycidyloxypropyl) trimethoxy silane and aluminum sec-butoxide. Small angle X-ray scattering and transmission electron microscopy analyses demonstrated that ordered nanostructures, from lamellar to 2-dimensional hexagonal columnar with a disordered intermediate morphology, were exhibited as a function of the amount of loaded silica nanoparticles. Among the observed morphologies, the silica particles in the lamellar sample were localized at the PS/PEO interface, which could be elucidated by the dominant translational entropy of small silica particles.     

Exfoliation of organoclay nanocomposites based on polystyrene-block-polyisoprene-block-poly(2-vinylpyridine) copolymer: Solution blending versus melt blending

Exfoliated nanocomposites based on polystyrene-block-polyisoprene-block-poly(2-vinylpyridine) (SI2VP triblock) copolymer were prepared by solution blending and melt blending. Their dispersion characteristics were investigated using transmission electron microscopy, X-ray diffraction, and small-angle X-ray scattering (SAXS). For the study, SI2VP triblock copolymers with varying amounts of poly(2-vinylpyridine) (P2VP) block (3, 5, and 13 wt%) and different molecular weights were synthesized by sequential anionic polymerization. In the preparation of nanocomposites, four different commercial organoclays, treated with a surfactant having quaternary ammonium salt, were employed. It was found from SAXS that the microdomain structure of an SI2VP triblock copolymer having 13 wt% P2VP block (SI2VP-13) transformed from core-shell cylinders into lamellae when it was mixed with an organoclay. It was found further that the solution-blended nanocomposites based on a homogeneous SI2VP triblock copolymer having 5 wt% P2VP block (SI2VP-5) gave rise to an exfoliated morphology, irrespective of the differences in chemical structure of the surfactant residing at the surface of the organoclays, which is attributable to the presence of ion-dipole interactions between the positively charged N⁺ ion in the surfactant residing at the surface of the organoclay and the pyridine rings in the P2VP block of SI2VP-5 and SI2VP-13, respectively. Both solution- and melt-blended nanocomposites based on microphase-separated SI2VP-13 having an order-disorder transition temperature (T_ODT) of approximately 210 °C also gave rise to exfoliated morphology. However, melt-blended nanocomposite based on a high-molecular-weight SI2VP triblock copolymer having a very high T_ODT (estimated to be about 360 °C), which was much higher than the melt blending temperature employed (200 °C), gave rise to very poor dispersion of the aggregates of organoclay. It is concluded that the T_ODT of a block copolymer plays a significant role in determining the dispersion characteristics of organoclay nanocomposites prepared by melt blending.     

Compatibilizing effect of poly(styrene)‐block‐poly(isoprene) copolymers in heterogeneous poly(styrene)/natural rubber blends

Compatibility of poly(styrene) (PS)/natural rubber (NR) blend is improved by the addition of diblock copolymer of poly(styrene) and cis‐poly(isoprene) (PS‐b‐PI). The compatibilizing effect has been investigated as a function of block copolymer molecular weight, composition and concentration. The effect of homopolymer molecular weight, processing conditions and mode of addition on the morphology of the dispersed phase have also been investigated by means of optical microscopy and scanning electron microscopy. A sharp decrease in phase dimensions is observed with the addition of a few percent of block copolymers. The effect levels off at higher concentrations. The leveling off could be an indication of interfacial saturation. For concentrations below the critical value, the particle size reduction is linear with copolymer volume fraction and agrees well with the prediction of Noolandi and Hong. The addition of the block copolymer improves the mechanical properties of the blend. An attempt is made to correlate the mechanical properties with the morphology of the blends. © 2001 Society of Chemical Industry     

Optimum toughening via a bicontinuous blending: toughening of PPO with SEBS and SEBS-g-maleic anhydride

The poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) was toughened by melt extrusion through its blending with a styrene-b-ethylene/butadiene-b-styrene triblock copolymer (SEBS), or with maleic anhydride (MA) grafted SEBS (SEBS-g-MA). Their morphology, mechanical properties, and rheology have been investigated. Transmission electron microscopy revealed that both kinds of blends had an island-sea structure at low concentrations of SEBS or SEBS-g-MA and a bicontinuous one at sufficiently high concentrations. However, the percolation threshold was higher for SEBS than for the SEBS-g-MA. The Izod impact strength of PPO could be significantly improved through its blending with SEBS-g-MA, particularly in a blend with 20 wt% of SEBS-g-MA at which it had a maximum value. The rheological experiments indicated that the incorporation of SEBS increased and that of SEBS-g-MA decreased the melt viscosity of the system.     

Effects of micelle structures formed in selective solvents on crystallization behaviors of poly(ethylene glycol)-b-poly(styrene) copolymers

Well-defined amphiphilic block copolymers, poly(ethylene glycol) methyl ether-b-poly(styrene) (mPEG-b-PS), in which the PS blocks had different molecular weights, were synthesized by atom transfer radical polymerization (ATRP). Through introduction of selective solvents for the blocks, crystalline and amorphous blocks were self-assembled into different micelle structures in solutions. Atomic force microscopy (AFM) was used to characterize the micelle structures. It was observed that spherical micelles were always formed, whereas lamellar aggregates appeared only in the PS-selective solvent when the molecular weight of the PS block in mPEG-b-PS was low. The crystallizable mPEG blocks were self-assembled into either the core or corona of the micelles formed. The effects of the self-assembled structures on the crystallization behavior of mPEG blocks were then investigated with differential scanning calorimeter (DSC). When the PS molecular weight was much larger than that of mPEG, the result showed that the crystallinity of the mPEG block was lower when mPEG blocks crystallized in the corona than that in the core of the micelles. In this case, when mPEG blocks crystallized in micelle coronae, the micelle core formed by insoluble PS blocks was very big, so mPEG chains had to distribute sparsely in the micelle coronae. It was hard for mPEG chains in one micelle or among different micelles to gather together to crystallize. However, when the PS molecular weight was lower than that of mPEG, the crystallinity of mPEG was higher when the mPEG chains crystallized in the micelle corona, as the core formed by insoluble PS was small and the mPEG chains in the corona were easy to aggregate and crystallize.     

Synthesis and properties of polystyrene‐b‐poly(ethylene oxide)‐b‐polystyrene triblock copolymers

A series of well‐defined and property‐controlled polystyrene (PS)‐b‐poly(ethylene oxide) (PEO)‐b‐polystyrene (PS) triblock copolymers were synthesized by atom‐transfer radical polymerization, using 2‐bromo‐propionate‐end‐group PEO 2000 as macroinitiatators. The structure of triblock copolymers was confirmed by ¹H‐NMR and GPC. The relationship between some properties and molecular weight of copolymers was studied. It was found that glass‐transition temperature (T_g) of copolymers gradually rose and crystallinity of copolymers regularly dropped when molecular weight of copolymers increased. The copolymers showed to be amphiphilic. Stable emulsions could form in water layer of copolymer–toluene–water system and the emulsifying abilities of copolymers slightly decreased when molecular weight of copolymers increased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 727–730, 2006