Polystyrene Homopolymer Research Articles

Modification of styrene–ethylene/butylene–styrene copolymer microstructure by polystyrene homopolymer and evolution of a cocontinuous blend morphology

AbstractStyrene–ethylene/butylene–styrene (SEBS) copolymer was blended with the homopolymer polystyrene (hPS) in a counter‐rotating twin‐screw extruder to prepare hPS/SEBS blends. The morphology of the hPS/SEBS blends was studied by environmental scanning electron microscopy (ESEM) and by transmission electron microscopy (TEM). TEM imaging of pure SEBS revealed a microphase‐separated morphology, showing ordered regions or grains where the discrete styrene blocks formed hexagonally packed cylindrical structures within the ethylene/butylene matrix. Blending of small quantities of the homopolymer hPS showed an interesting result. The TEM images of the SEBS‐rich blends revealed that the added hPS was absorbed within the bulk of the SEBS phase resulting in a new SEBS‐rich phase, and the absorbed hPS was found to join the styrene cylinders of pure SEBS thereby modifying its original microstructure. As the hPS concentration in the blends was increased further, the ESEM and TEM images showed that the excess homopolymer hPS phase separated, forming a cocontinuous morphology with the hPS‐modified SEBS‐rich phases. Linear viscoelastic tests on the SEBS‐rich blends also revealed the existence of a synergistic effect, showing increased elastic behavior compared with that of pure SEBS. Small‐angle X‐ray scattering results showed an additional periodicity in the SEBS‐rich phase because of the modification of the SEBS microstructure by hPS. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

Surface Organization of a Perfluorocarbon-Functionalized Polystyrene Homopolymer

We use the perfluorocarbon-functionalized polymer, poly(4-((1H,1H,2H,2H-perfluorodecyl)oxycarbonyl)styrene) [PPFOCS], as a model system with both surface molecular segregation and molecular orientation to test the capabilities of a near-edge X-ray absorption fine structure (NEXAFS) spectroscopy analysis scheme for polymer surfaces. Both NEXAFS spectroscopy and angle-resolved X-ray photoelectron spectroscopy (XPS) show segregation of the −(CF2)7CF3 chain to the air/polymer interface with the styrenic portion underneath. Postedge analysis of the NEXAFS spectra indicates a low carbon atom density surface layer, of thickness 1.0–1.4 nm, due to the overlayer of perfluorocarbon chains. An analysis of the NEXAFS C 1s → π*C═C and C 1s → σ*C–F transitions accounting for the different depth distributions of the phenyl rings and fluorocarbon helices reveals strong orientational ordering with the orientational order parameter SC═C for the phenyl ring equal to −0.27 and for the C–F bonds in the fluorocarbon helix SC–F...

Structural Parameters for Nanocylinder Microdomains of Polystyrene-polybutadiene- Polystyrene Triblock Copolymer and its Blends with Polystyrene Homopolymer

We illustrate that the redistribution of a compatible homopolymer blended in a certain block copolymer results in a shift of phase boundaries and in the stabilization of well-ordered structures by using polystyrene (PS) homopolymer blended in polystyrenepolybutadiene- polystyrene triblock copolymer (SBS1102) as a model system. The addition of the homopolymer into the asymmetric triblock copolymer increases the periodic orientation normal to the substrate, enabling directed self-assembly of the block copolymers into arrays of highly oriented, high-aspect-ratio cylindrical nanostructures over large areas. Thus, we show that blending a homopolymer with well controlled molecular weight provides an effective ordering process for self-assembly of block copolymers. Keywords: Block copolymer self-assembly, orientation transition of block copolymer nano-cylinders, polystyrene homopolymer blended in polystyrenepolybutadiene-polystyrene triblock copolymer, periodic orientation normal to the substrate, blend microdomain structural parameters

Lateral spacing of adhesion peptides influences human mesenchymal stem cell behaviour

Mesenchymal stem cells (MSCs) have attracted great interest in recent years for tissue engineering and regenerative medicine applications due to their ease of isolation and multipotent differentiation capacity. In the past, MSC research has focussed on the effects of soluble cues, such as growth factors and cytokines; however, there is now increasing interest in understanding how parameters such as substrate modulus, specific extracellular matrix (ECM) components and the ways in which these are presented to the cell can influence MSC properties. Here we use surfaces of self-assembled maleimide-functionalized polystyrene-block-poly(ethylene oxide) copolymers (PS-PEO-Ma) to investigate how the spatial arrangement of cell adhesion ligands affects MSC behaviour. By changing the ratio of PS-PEO-Ma in mixtures of block copolymer and polystyrene homopolymer, we can create surfaces with lateral spacing of the PEO-Ma domains ranging from 34 to 62 nm. Through subsequent binding of cysteine-GRGDS peptides to the maleimide-terminated end of the PEO chains in each of these domains, we are able to present tailored surfaces of controlled lateral spacing of RGD (arginine-glycine-aspartic acid) peptides to MSCs. We demonstrate that adhesion of MSCs to the RGD-functionalized block-copolymer surfaces is through specific attachment to the presented RGD motif and that this is mediated by α5, αV, β1 and β3 integrins. We show that as the lateral spacing of the peptides is increased, the ability of the MSCs to spread is diminished and that the morphology changes from well-spread cells with normal fibroblastic morphology and defined stress-fibres, to less-spread cells with numerous cell protrusions and few stress fibres. In addition, the ability of MSCs to form mature focal adhesions is reduced on substrates with increased lateral spacing. Finally, we investigate differentiation and use qRT-PCR determination of gene expression levels and a quantitative alkaline phosphatase assay to show that MSC osteogenesis is reduced on surfaces with increased lateral spacing while adipogenic differentiation is increased. We show here, for the first time, that the lateral spacing of adhesion peptides affects human MSC (hMSC) properties and might therefore be a useful parameter with which to modify hMSC behaviour in future tissue engineering strategies.

Helical phase from blending of chiral block copolymer and homopolymer

The phase behavior of the binary blends of polystyrene-b-poly(L-lactide) chiral block copolymer (BCP*) and polystyrene homopolymer (HS) is found to be strongly dependent on the molecular weight (M(n)) of the HS. A helical phase is formed in the blends with low-M(n) HS due to an enhancement of helical steric hindrance.

Alkyne–azide coupling of tailored poly(vinylidene fluoride) and polystyrene for the synthesis of block copolymers

The synthesis of block copolymers consisting of poly(vinylidene fluoride) (PVDF) and polystyrene (PS) is reported. Firstly, a propargyl-functionalized alkoxyamine initiator (PgOTIPNO) was prepared and subsequently used for the preparation of a propargyl-terminated PS homopolymer of different chain lengths with low dispersities via nitroxide-mediated radical polymerization. A tailored PVDF homopolymer with iodine end groups originating from iodine transfer polymerization was transformed to PVDF with azide end group. Then, alkyne-terminated PS with different molecular weights and azide-terminated PVDF were joined together via copper-catalyzed alkyne–azide coupling. The block copolymers were characterized using 1H-NMR, 19F-NMR, IR, SEC, and DSC.

Relationship between morphology and conductivity of block-copolymer based battery separators

Nanoporous battery separators were made by blending a polystyrene-block-polyethylene-block-polystyrene copolymer (SES) and polystyrene (PS) homopolymers, casting films of the blend, and selectively dissolving the homopolymer. The efficacy of the separators thus obtained was determined by measurement of the ionic conductivity of separators soaked in 1M lithium hexafluorophosphate in ethylene carbonate/diethyl carbonate (1:1, v/v, Novolyte Technologies, Inc.), a standard lithium battery electrolyte. We focus on the effect of chain length of the sacrificial homopolymer on separator morphology and ion transport. In highly porous separators with a nominal pore volume fraction of 0.43, conductivity peaked at α=0.22, where values as high as 0.39mScm−1 were achieved (α is the molecular weight of the PS homopolymer normalized by that of the PS block in the SES copolymer). Nitrogen adsorption experiments and scanning electron microscopy were used to determine the underpinnings of this observation. At α=0.12, extremely small pores with low surface area are formed. Increasing α to 0.22 results in a film with well-connected nanoscale pores. A further increase in α to 2.02 results in films with micron-sized pores that are not effective for ion transport.

Nanoparticles as delivery vehicles for sunscreen agents

Sunscreen filters, which block hazardous UV radiation, are commonly applied in cosmetic products to protect the skin, the hair, or the product itself. Most sunscreen formulations are emulsions or creams. However, formulations based on nanoparticles as the delivery vehicle for the sunscreen compounds potentially have advantages in terms of retention on the skin, lack of penetration across the epidermal layer and UV attenuation by both absorption and scattering. In this study, sunscreen nanoparticle suspensions are prepared via the novel Flash NanoPrecipitation process (FNP), which involves rapid micromixing followed by block copolymer directed assembly of nanoparticles. The block copolymer stabilizer is polystyrene-block-polyethylene glycol (PS-b-PEG) with a homopolymer polystyrene (PS) as the co-solute in the nanoparticle core. By changing the filter and/or PS concentration, stable nanoparticles with sizes from 80 to 200nm are prepared. Most importantly, FNP enables incorporation of both organic and inorganic hydrophobic filters into nanoparticles, and thus offers broad-spectrum sun protection. The nanocolloids offer enhanced UV protection because they attenuate light by both adsorption and scattering. Three organic filters, ethylhexyl triazone (Uvinul T 150), benzophenone-3 (Uvinul M 40), and diethylamino hydroxybenzoyl hexyl benzoate (Uvinul A Plus) and two nano-sized inorganic filters, zinc oxide and titanium dioxide are examined. In addition it is found the polystyrene core material offers significant UV blocking in the UVC range of 200–280nm. Dynamic light scattering (DLS) reveals that the nanoparticles’ size distribution is narrow and remains stable (over 80 days). The combination of organic and inorganic filters enables tunable UV protection over the wavelength range 280–400nm. In conclusion, flash nanoprecipitation provides a new formulation method of encapsulating hydrophobic organic and inorganic sunscreen filters.

Synthesis, purification, and characterization of “perfect” star polymers via “Click” coupling

The copper (I)-catalyzed azide-alkyne cycloaddition “click” reaction was successfully applied to prepare well-defined 3, 6, and 12-arms polystyrene and polyethylene glycol stars. This study focused particularly on making “perfect” star polymers with an exact number of arms, as well as developing techniques for their purification. Various methods of characterization confirmed the star polymers high purity, and the structural uniformity of the generated star polymers. In particular, matrix-assisted laser desorption ionization-time-of-flight mass spectrometry revealed the quantitative transformation of the end groups on the linear polymer precursors and confirmed their quantitative coupling to the dendritic cores to yield star polymers with an exact number of arms. In addition to preparing well-defined polystyrene and poly(ethylene glycol)homopolymer stars, this technique was also successfully applied to amphiphilic, PCL-b-PEG star polymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Preparation of monodispersed and lipophilic attapulgite and polystyrene nanorods via surface‐initiated atom transfer radical polymerization

AbstractA new kind of initiator, 3‐(2‐bromo‐2‐methylacryloxy)propyltriethysiliane (MPTS‐Br), was prepared with a simply hydrobrominated commercial silane coupling agent (3‐methacryloxy‐proplytriethysilane, MPTS). It has been one‐step self‐assemble onto the surface of attapulgite (ATP) nanorods in the dispersion system, and by using this initiator‐modified nanorod (MPTS‐Br‐modified ATP nanoparticles, ATP‐MPTS‐Br) as macroinitiator for atom transfer radical polymerization (ATRP). Structurally well‐defined homopolymer polystyrene (PS) and block polymer poly(styrene‐b‐methyl methacrylate) (PS‐b‐PMMA) chains were then grown from the needle‐shaped nanorods surface to yield monodispersed nanorods composed of ATP core and thick‐coated polymer shell (ATP and PS). The graft polymerization parameters exhibited the characteristics of a controlled/”living” polymerization. The PS‐grafted ATP nanorods could be dispersed well in organic solvent with nanoscale. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Characterization of Polydimethylsiloxane‐block‐polystyrene (PDMS‐b‐PS) Copolymers by Liquid Chromatography at Critical Conditions

AbstractIn this study, liquid chromatography at critical conditions (LCCC) is used to determine the block lengths and molar masses of polydimethylsiloxane‐block‐polystyrene copolymers synthesized via atom transfer radical polymerization (ATRP) techniques. In addition, the analysis allows for the determination of the presence of homopolymers in the samples. LCCC at the critical point of polydimethylsiloxane (PDMS) on a reversed phase column allows for the determination of PDMS homopolymer and the length of the polystyrene (PS) block in the block copolymer which elutes in the size exclusion chromatography (SEC) regime under these conditions. The PDMS block length and PS homopolymer can be obtained under normal phase conditions. The results of LCCC are compared with data from conventional SEC. magnified image

Micelles of poly(styrene- b-2-vinylpyridine- b-ethylene oxide) with blended polystyrene core and their application to the synthesis of hollow silica nanospheres

Core–shell–corona (CSC) micelles of asymmetric triblock copolymer, poly(styrene- b-2-vinylpyridine- b-ethylene oxide) (PS–PVP–PEO), containing polystyrene homopolymer (homo-PS) in the core were successfully prepared in aqueous media. The influence of homo-PS contents over the formation of the micelles was investigated thoroughly by various techniques such as dynamic light scattering (DLS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and fluorescence spectroscopy. It was found that the size of the PS core of the micelle was increased by the addition of homo-PS as observed by DLS and TEM techniques. The SEM and TEM measurements confirm the spherical morphology of the micelles and enlargement of PS core over the addition of homo-PS. The increase in the PS core volume of the PS–PVP–PEO micelles is attributed to the insertion of homo-PS in the PS core. The micelles have also been demonstrated as facile soft templates for synthesis of hollow silica nanospheres. The average diameter of the spherical hollow particles could be tuned between 30.6 and 38.8 nm with cavity sizes ranging from 20.7 to 28.5 nm using tetramethoxysilane as silica precursors under mild acidic conditions. The facile synthesis of hollow silica using the CSC micelles with different homo-PS contents indicates that the hollow void size can be controlled within a range of several nanometers.

Organic-metalloblock copolymers via photocontrolled living anionic ring-opening polymerization

A new method for the preparation of organic-organometallic diblock copolymers including a polyferrocenylsilane (PFS) metalloblock through photocontrolled ring-opening polymerization (ROP) is reported. Polystyrene (PS) homopolymers end-capped with a cyclopentadienyl group (1) were used as macroinitiators for the photocontrolled ROP of sila[1]ferrocenophanes [Fe(η-C5H4)2Si{C≡CtBu}2] 3a and [Fe(η-C5H4)2Si(Me)(C≡CSiMe3)] 3b to afford diblock copolymers with controlled molecular weights and block ratios, as well as low polydispersities (PDI < 1.2). Block copolymer PSm-b-[Fe(η-C5H4)2Si{C≡C(t-Bu)}2]n4 was clusterized with [Co2(CO)8], forming the highly metallized PSm-b-[Fe(η-C5H4)2Si{Co2(CO)6C2(t-Bu)}2]n (PS-bb-(Co-PFS), 7). The diblock PSm-b-[Fe(η-C5H4)2Si(Me)(C≡CH)]n6 was prepared by selective desilylation of PSm-b-[Fe(η-C5H4)2Si(Me)(C≡CSiMe3)]n5 was then reacted with ClAuP(n-Bu)3 in the presence of an amine as HCl acceptor to afford PSm-b-[Fe(η-C5H4)2Si(Me){C≡CAuP(n-Bu)3}]n (PS-bbb-(Au-PFS), 8). Preliminary studies on the self-assembly of these materials in thin films showed phase separation with metal-rich nanodomains within an organic matrix.

Methacrylate-based monolithic layers for planar chromatography of polymers

A series of macroporous monolithic methacrylate-based materials was synthesized by in situ free radical UV-initiated copolymerization of functional monomers, such as glycidyl methacrylate (GMA), butyl methacrylate (BuMA), 2-aminoethyl methacrylate (AEMA), 2-hydroxyethyl methacrylate (HEMA) and 2-cyanoethyl methacrylate (CEMA), with crosslinking agent, namely, ethylene glycol dimethacrylate (EDMA). The materials obtained were applied as the stationary phases in simple and robust technique – planar chromatography (PLC). The method of separation layer fabrication representing macroporous polymer monolith bound to the specially prepared glass surface was developed and optimized. The GMA–EDMA and BuMA–EDMA matrixes were successfully applied for the separation of low molecular weight compounds (the mixture of several dies), as well as poly(vinylpyrrolidone) and polystyrene homopolymers of different molecular weights using reversed-phase mechanism. The materials based on copolymers AEMA–HEMA–EDMA and CEMA–HEMA–EDMA were used for normal-phase PLC separation of 2,4-dinitrophenyl amino acids and polystyrene standards.

General approach for fabricating nanoparticle arrays via patterned block copolymer nanoreactors

A general approach to fabricate nanoparticle arrays of different kinds of materials is demonstrated in this paper. It was found that the center-to-center distance of the nanoparticles or the nanoclusters can be controlled using patterned block copolymer nanoreactors by adding polystyrene (PS) homopolymer to poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) diblock copolymer thin film. The number of the nanoparticles formed in the P4VP nanodomains can also be adjusted by addition of polystyrene (PS) homopolymer to poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) diblock copolymer. In fabrication of Au nanoparticle arrays, HAuCl4 precursor was directly loaded into P4VP nanodomains of the diblock copolymer thin film by using a methanol solvent, which is a good solvent for P4VP but non-solvent for PS. The Au nanoparticle arrays were then obtained by reducing HAuCl4 with sodium citrate dihydrate, and then in situ transferred to silicon substrate by a two-step calcination method. ZnO and FexOy nanoparticle arrays were also synthesized by this approach with thermal decomposition and double decomposition reactions, respectively. Additionally, the advantage of using two-step calcination method over the air plasma method was discussed.

Nonsolvent Annealing Polymer Films with Ionic Liquids

Neutron reflectometry has been used to determine the interface structure and swelling of thin polymer films, when annealed in contact with a series of 1-alkyl-3-methylimidazolium ionic liquids (ILs). By choosing immiscible polymer/IL combinations, we have established that thin polymer films can be annealed for several hours in contact with ILs at temperatures well above the glass transition temperature and that this nonsolvent annealing environment can be exploited to direct self-assembly in polymer films. The ingress of IL into polymer films was quantified in terms of the swelling up to 10%. The polymer/IL interfacial width generally also increased from 0.9 nm up to ∼3 nm, but there was remarkably little correlation between interfacial width and swelling. For one combination of polymer and IL (deuterated PMMA and Bmim-BF(4)) the interfacial width decreased slightly with increasing temperature, consistent with LCST behavior for this system. All of the ILs tested had a profound influence the distribution of carboxy-end-functionalized deuterated polystyrene, "dPS-COOH", in blended films with polystyrene homopolymers. The ILs promoted dPS-COOH adsorption at the film/IL interface and the simultaneous rapid desorption at the film silicon-oxide interface. The rate of desorption was found to correlate with the swelling behavior of the polymer with respect to the IL anion species: PF(6)(-) < Br(-) < Cl(-) < BF(4)(-), suggesting that the polymer films are plasticized by the IL as it penetrates the film.

Microcapsules with Tailored Nanostructures by Microphase Separation of Block Copolymers

Colloidal microcapsules of thin nanoshell membranes were prepared by the evaporation-induced self-assembly of poly(styrene)-block-poly(butadiene)-block-poly(styrene) (SBS) triblock copolymers inside the oil phase of a water-in-oil-in-water (W/O/W) double emulsion, which was prepared via a two-step sequential emulsification process. To see the nanoconfinement effect, the shell thickness was kept very thin and comparable to the feature scale of self-organized nanostructure. By exploiting the density mismatch between the microcapsules and the continuous medium, single-cored microcapsules with thin shells were selectively separated from mixtures of multicored microcapsules or thick-shelled microcapsules. The internal morphology of the membrane could be modulated by controlling the volume fractions of styrene and butadiene blocks, which was achieved simply by adding polystyrene homopolymer of relatively low molecular weight. By varying the amount of homopolymer, various morphologies were produced in the microcapsule membranes, including lamellae, perforated lamellae, and cylindrical and spherical phases. Moreover, the addition of polystyrene homopolymer could be used to control the mechanical characteristics of the microcapsules.

Morphological Characterisation and Dynamic Rheology of Nano-Structured Blends of Polystyrene and SEBS

Polystyrene homopolymer (hPS) was melt-blended with styreneethylene/ butylene-styrene (SEBS) in a counter-rotating twin-screw extruder to produce hPS/SEBS blends. The morphology of the hPS/SEBS blends was investigated using environmental scanning electron microscopy (ESEM) and transmission electron microscopy (TEM). The dynamic rheological behaviour of the blends was studied using a parallel plate rheometer. TEM and ESEM images of the hPS/SEBS blends showed three different morphologies at three different SEBS concentration ranges. When SEBS concentration was less than 30 wt%, the hPS-rich blends hPS/SEBS 90/10 and 80/20 showed a droplet/matrix morphology. When SEBS concentration was between 30 and 70 wt%, the blend morphology revealed a co-continuous nano-structure. At SEBS concentrations 80 wt% and above, TEM images of the SEBS-rich blends showed that the homopolymer hPS was absorbed within the bulk of SEBS, resulting in a modification of its original microstructure. Dynamic rheological tests showed that the blend morphology had significant effect on their rheological behaviour at low frequencies.

Importance of Molecular Coupling for Mechanical Performance of Block Copolymer Compounds

AbstractMixtures of polystyrene‐block‐polyisoprene‐block‐polystyrene (SIS) triblock copolymer and various styrenic block copolymers (having diblock and triblock architectures) as well as polystyrene homopolymer (PS) were prepared via solution blending to determine the influence of molecular coupling on the large strain mechanical performance of the block copolymers. The techniques used were transmission electron microscopy (TEM) as well as scanning electron microscopy (SEM) for the morphological characterization and uniaxial tensile testing for the determination of mechanical properties. In the block copolymer blends, it was possible to tailor the mechanical properties as long as the molecular coupling was present among the outer polystyrene blocks. The mechanical performance of the triblock copolymer was found to deteriorate by the presence of dangling chains in the microphase‐separated domains. In the blends comprising an SIS triblock copolymer and polystyrene homopolymers, the macrophase‐separated compounds containing PS having molar mass exceeding the entanglement molar mass showed the optimum mechanical properties. The observed mechanical behaviour has been correlated with the fracture surface morphology of the corresponding blends.

Nitroxide‐Mediated Bulk and Miniemulsion Polymerization in a Continuous Tubular Reactor: Synthesis of Homo‐, Di‐ and Triblock Copolymers

AbstractIn previous work, a modified nitroxide‐mediated miniemulsion polymerization was demonstrated in a continuous tubular reactor to prepare a latex of polystyrene homopolymer dispersed in water. There, the initial reaction step (low conversion bulk polymerization to prepare the macroinitiator) was done in a batch reactor while the miniemulsion polymerization step was done in a continuous tubular reactor. The present paper describes an extension of that work in which all the reaction steps have been achieved in the continuous tubular reactor. Chain extension of the polystyrene latex to give polystyrene‐block‐poly(butyl acrylate) diblock and polystyrene‐block‐poly(butyl acrylate)‐block‐polystyrene triblock copolymers is also described.magnified image