Polystyrene Homopolymer Research Articles

Sequence analysis of styrenic copolymers by tandem mass spectrometry.

Styrene and smaller molar amounts of either m-dimethylsilylstyrene (m-DMSS) or p-dimethylsilylstyrene (p-DMSS) were copolymerized under living anionic polymerization conditions, and the compositions, architectures, and sequences of the resulting copolymers were characterized by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and tandem mass spectrometry (MS(2)). MS analysis revealed that linear copolymer chains containing phenyl-Si(CH3)2H pendants were the major product for both DMSS comonomers. In addition, two-armed architectures with phenyl-Si(CH3)2-benzyl branches were detected as minor products. The comonomer sequence in the linear chains was established by MS(2) experiments on lithiated oligomers, based on the DMSS content of fragments generated by backbone C-C bond scissions and with the help of reference MS(2) spectra obtained from a polystyrene homopolymer and polystyrene end-capped with a p-DMSS block. The MS(2) data provided conclusive evidence that copolymerization of styrene/DMSS mixtures leads to chains with a rather random distribution of the silylated comonomer when m-DMSS is used, but to chains with tapered block structures, with the silylated units near the initiator, when p-DMSS is used. Hence, MS(2) fragmentation patterns permit not only differentiation of the sequences generated in the synthesis, but also the determination of specific comonomer locations along the polymer chain.

Dynamics of Cadmium Sulfide Nanoparticles within Polystyrene Melts

We present a detailed study of the dynamics of cadmium sulfide nanoparticles suspended in polystyrene homopolymer matrices using X-ray photon correlation spectroscopy for temperatures between 120 and 180 °C. For low molecular weight polystyrene homopolymers, the observed dynamics show a crossover from diffusive to hyper-diffusive behavior with decreasing temperatures. For higher molecular weight polystyrene, the nanoparticle dynamics appear hyper-diffusive at all temperatures studied. The relaxation time and characteristic velocity determined from the measured hyper-diffusive dynamics reveal that the activation energy and underlying forces determined are on the order of 2.14 × 10–19 J and 87 pN, respectively.

Order‐order transitions of a triblock copolymer with a homopolymer (ABC/A) blend film induced by saturated solvent vapor annealing

ABSTRACTThe morphology transition of binary mixtures of polystyrene‐block‐poly(butadiene)‐block‐poly(2‐vinylpyridine)(SBV) triblock and polystyrene (PS) homopolymer thin films was investigated as a function of the volume fraction of added homopolymer and the annealing time in benzene vapor. It was found that the weight ratio of PS in the blends influenced the transition process. When PS content was >5%, the order‐order transition (OOT) of core‐shell cylinders (C) →sphere in “diblock Gyroid” (sdG) → sphere in lamella (sL) → sphere (S) was observed, which was similar to ABC triblock copolymer except for the increased surface area of the PS phase. When PS content reached to 10–30%, the OOT in the sequence of C → sL → S was observed. The disappearance of the Gyroid phase is due to the change of the effective volume fraction. Further increasing the PS content, C phase also disappeared and sL → S was expected to take place. © 2014 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2014, 52, 1030–1036

Distinct Adsorption Configurations and Self-Assembly Characteristics of Fibrinogen on Chemically Uniform and Alternating Surfaces including Block Copolymer Nanodomains

Understanding protein–surface interactions is crucial to solid-state biomedical applications whose functionality is directly correlated with the precise control of the adsorption configuration, surface packing, loading density, and bioactivity of protein molecules. Because of the small dimensions and highly amphiphilic nature of proteins, investigation of protein adsorption performed on nanoscale topology can shed light on subprotein-level interaction preferences. In this study, we examine the adsorption and assembly behavior of a highly elongated protein, fibrinogen, on both chemically uniform (as-is and buffered HF-treated SiO2/Si, and homopolymers of polystyrene and poly(methyl methacrylate)) and varying (polystyrene-block-poly(methyl methacrylate)) surfaces. By focusing on high-resolution imaging of individual protein molecules whose configurations are influenced by protein–surface rather than protein–protein interactions, fibrinogen conformations characteristic to each surface are identified and statistically analyzed for structural similarities/differences in key protein domains. By exploiting block copolymer nanodomains whose repeat distance is commensurate with the length of the individual protein, we determine that fibrinogen exhibits a more neutral tendency for interaction with both polystyrene and poly(methyl methacrylate) blocks relative to the case of common globular proteins. Factors affecting fibrinogen–polymer interactions are discussed in terms of hydrophobic and electrostatic interactions. In addition, assembly and packing attributes of fibrinogen are determined at different loading conditions. Primary orientations of fibrinogen and its rearrangements with respect to the underlying diblock nanodomains associated with different surface coverage are explained by pertinent protein interaction mechanisms. On the basis of two-dimensional stacking behavior, a protein assembly model is proposed for the formation of an extended fibrinogen network on the diblock copolymer.

A Novel Method of Extraction of Blend Component Structure from SANS Measurements of Homopolymer Bimodal Blends.

A new method is presented for the extraction of single-chain form factors and interchain interference functions from a range of small-angle neutron scattering (SANS) experiments on bimodal homopolymer blends. The method requires a minimum of three blends, made up of hydrogenated and deuterated components with matched degree of polymerization at two different chain lengths, but with carefully varying deuteration levels. The method is validated through an experimental study on polystyrene homopolymer bimodal blends with . By fitting Debye functions to the structure factors, it is shown that there is good agreement between the molar mass of the components obtained from SANS and from chromatography. The extraction method also enables, for the first time, interchain scattering functions to be produced for scattering between chains of different lengths.

Preparation and physico-chemical characterization of large-mesopore silica thin films templated by block copolymers for membrane technology

Highly selective membranes with controlled porosity can be obtained by growing thin films of mesoporous oxides on an appropriate support. This can be achieved employing organic/inorganic mixed micellar solutions based on metal oxide precursors and commercial templates. In particular amphiphilic block copolymers are very attractive materials as soft-templating agents because they self-assemble into micelles whose morphology and size depend on block composition and solution parameters.Large-mesopore silica films with narrow pore size distribution and high porosity have been obtained by sol–gel reaction of a silicon oxide precursor (TEOS) and using polystyrene-block-poly(ethylene-oxide) (PS-b-PEO) copolymers as templates.In order to modulate size, shape and alignment of the pores, many variables were changed: block copolymer chain length, TEOS/block copolymer ratio, solvent ratio, additives (i.e. polystyrene homopolymer addition). The effect of the different parameters on the porous system was studied by microscopy techniques and gas-volumetric analyses.Final aim of this work is the preparation of silica membranes to be used as selective gates for controlled dosing and transport of chemical species in solution.

Synthesis of arborescent polystyrene‐g‐[poly(2‐vinylpyridine)‐b‐polystyrene] core–shell–corona copolymers

ABSTRACTArborescent copolymers with a core‐shell‐corona (CSC) architecture, incorporating a polystyrene (PS) core, an inner shell of poly(2‐vinylpyridine), P2VP, and a corona of PS chains, were obtained by anionic polymerization and grafting. Living PS‐b‐P2VP‐Li block copolymers serving as side chains were obtained by capping polystyryllithium with 1,1‐diphenylethylene before adding 2‐vinylpyridine. A linear or arborescent (generation G0 – G3) PS substrate, randomly functionalized with acetyl or chloromethyl coupling sites, was then added to the PS‐b‐P2VP‐Li solution for the grafting reaction. The grafting yield and the coupling efficiency observed in the synthesis of the arborescent PS‐g‐(P2VP‐b‐PS) copolymers were much lower than for analogous coupling reactions previously used to synthesize arborescent PS homopolymers and PS‐g‐P2VP copolymers from the same types of coupling sites. It was determined from static and dynamic light scattering analysis that PS‐b‐P2VP formed aggregates in THF, the solvent used for the synthesis. This presumably hindered coupling of the macroanions with the substrate, and explains the low grafting yield and coupling efficiency observed in these reactions. Purification of the crude products was also problematic due to the amphipolar character of the CSC copolymers and the block copolymer contaminant. A new fractionation method by cloud‐point centrifugation was developed to purify copolymers of generations G1 and above. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1075–1085

Effect of desiccant characteristics on the properties of PS/zeolite functional packaging materials

Desiccant composites were prepared from a polystyrene homopolymer (PS) and a high impact copolymer (HIPS). Five zeolites were used as adsorbents, which included the A and X types frequently used in industrial practice. Composites containing zeolites up to 50 vol% were homogenized in an internal mixer and then compression molded to 1 mm thick plates. The results proved that the water adsorption capacity of zeolites depends on the total volume of the pores, whereas the rate of adsorption on thermodynamics, on the equilibrium constant of adsorption. On the other hand, zeolite characteristics influence the moisture adsorption of the composites only marginally; adsorption capacity is determined by zeolite content, whereas the rate of adsorption is determined by the properties of the polymer. Composites prepared with X type zeolites have somewhat smaller water adsorption capacity than those containing their A type counterparts. The dispersion of the zeolite is good both in PS and in HIPS composites. Mechanical properties are excellent mainly because of the good interfacial adhesion between the components. Because of their larger surface energy, composites containing X type zeolites have larger viscosity and they reinforce the polymer more than A type desiccants. Matrix characteristics influence mainly application related properties; reinforcement and ductility is better in HIPS than in PS composites. POLYM. COMPOS., 35:2112–2120, 2014. © 2014 Society of Plastics Engineers

Morphological Control of Helical Structures of an ABC-Type Triblock Terpolymer by Distribution Control of a Blending Homopolymer in a Block Copolymer Microdomain

The control of microphase-separated structures in a poly(styrene-block-butadiene-block-methyl methacrylate) (SBM) was investigated in three dimensions by transmission electron microtomography. Neat SBM self-assembled into a double-helical structure of polybutadiene (PB) domains around hexagonally packed core polystyrene (PS) cylinders in a poly(methyl methacrylate) matrix. When PS homopolymer with a lower molecular weight than that of the PS block in SBM was added to the SBM, the PB domains transformed from double-helical structures to spherical domains, while maintaining the helical trajectories. In contrast, adding a higher molecular weight PS to the SBM changed the helical structures from double- to triple-stranded structures and even to four-stranded structures. The helical structures of the PB domains were strongly affected by the distribution of the blended polystyrenes in the core cylindrical PS domains.

Rapid integrated rheo-optical and polarized Fourier-transform infrared spectrometry measurement system for polymer films undergoing chemo-mechanical changes

The design and performance of a multisensory instrument to track physical and chemical changes of thin polymer films (typically 5 μm < thickness < 100 μm) subjected to thermal and mechanical treatments are described in this paper. For the first time, real-time measurements of spectral birefringence, true stress, true strain, and temperature are integrated together with ultra-rapid-scan polarized FT-IR spectrometer (URS-FT-IR) to investigate the relationships between true mechanical measures and structural features at different length scales. The rheo-optical properties (birefringence-true stress-true strain) are collected at a rate of 10 data points∕s and URS-FT-IR data are collected at a rate of 300 complete spectra∕s. The IR dichroism measurement is performed by exposing the sample to non-polarized IR beam in transmission mode with two mutually perpendicular polarizations, parallel and perpendicular to the stretching direction, received by detector unit. This design allows to analyze both polarizations simultaneously wavenumbers in the range of 500 cm(-1)-4000 cm(-1). Controlled processing parameters include air speed, air temperature, stretching rate, stretching ratio, stretch cycling, and holding times; while simultaneously measuring optical retardation, sample width, temperature, load cell, and both parallel and perpendicular IR spectra. Calibration and performance of this instrument is demonstrated with several film samples. These are: A polystyrene standard, an atactic polystyrene (homo-polymer), a polyurethane (consists of hard and soft segments) for physical changes during uniaxial deformation, and a polyamic acid during imidization reaction. This measurement system is particularly useful in unraveling molecular level details of complex physical and chemical events that take place during very fast deformation schemes (uniaxial stretching, retraction, relaxation, annealing, etc.) relevant to industrial processes. These include specific orientation behavior of each phase, block or filler, crystallization, relaxation and orientation state. It is also suited to track reaction rates and products in polymers undergoing thermal or photo curing.

Glass Transition Temperature of Polymer–Nanoparticle Composites: Effect of Polymer–Particle Interfacial Energy

Numerous studies have shown that the glass transition temperature, Tg, of polymers may change visibly upon addition of even small amounts of nanoparticles. In this study, we examine the effect of polymer–nanoparticle interfacial energy on this phenomenon in nanocomposite films containing polystyrene-grafted nanoparticles mixed with polystyrene homopolymer at low particle loadings. A previous experiment showed that the interfacial energy of this system modulates with the grafting density of the grafted polymer and the molecular weight ratio of the matrix and grafted polymers. We find that the changes in Tg vary with both parameters in manners that quantitatively agree with the interfacial energy.

Thermal annealing as an easy tool for the controlled arrangement of gold nanoparticles in block-copolymer thin films

Thermal annealing was used for the bottom-up fabrication of morphologically controlled gold–block-copolymer (Au–BC) nanocomposites. Three different blends formed by polystyrene (PS) homopolymer and PS-coated gold nanoparticles (PSSH@Au) were used as modifiers of asymmetric polystyrene-b-polymethylmethacrylate (PS-b-PMMA): PS26/PS26SH@Au, PS75/PS75SH@Au and PS167/PS167SH@Au (where the subscripts refer to the number of styrene monomeric units). The results indicated that all three blends used as modifiers (PSn/PSnSH@Au) were successfully located in the PS phase during thermally induced BC self-assembly for a composition range from 5 to 43 wt% without macro-phase separation. The PSnSH@Au moiety experienced molecular desorption, nanocrystal core coalescence and partial molecular re-encapsulation processes during thermal annealing, leading to sphere-like gold NPs with a larger average size (without exceeding an interdomain distance). Ligand chain length regulated the degree of coalescence and re-encapsulation, defining ultimate core size. Furthermore, proper combination of chain length and composition enabled tuning of NP partitioning and arrangement on different length scales through thermally activated cooperative assembly processes. These results have not only significant impact for establishing thermal processing as a useful tool for the precise control of NP size and distribution, but also much broader implications for many nanoparticle-based technologies.

Effect of Nonsolvent Exposure on Morphology of Mesoporous Semicrystalline Block Copolymer Films

Polystyrene-block-polyethylene-block-polystyrene (SES) copolymers were blended with homopolymer polystyrene (PS), and films of the blend were solvent cast using a doctor blade. The nonporous SES and PS films were exposed to both tetrahydrofuran (THF) and methanol (MeOH) in an alternating fashion for 1 min intervals three times, without letting the films dry between solvent immersions. At this point, either the films were removed from MeOH and dried or the films were immersed in THF and then dried. THF is a nonsolvent for crystalline polyethylene (PE) but a good solvent for both amorphous PE and PS. Methanol is a nonsolvent for semicrystalline PE, amorphous PE, and PS. Films that were dried with MeOH as the final nonsolvent were highly porous and exhibited high conductivity when swollen in a liquid electrolyte. In contrast, films that were dried with THF as the final nonsolvent were nonporous and exhibited poor conductivity when swollen in a liquid electrolyte. We study the fundamental effect of nonsolvent...

Nanoparticle encapsulation in thin film micellar structures: a physical method for functional materials design

We investigate the confinement of gold nanoparticles, onto which poly(2-vinylpyridine) (P2VP) are end-tethered, within diblock copolymer polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) micelles in a polystyrene (PS) host. The micellar nanocomposites were prepared by spin casting mixtures of the nanoparticles, the copolymer and the homopolymer chains onto a substrate, to form films approximately 110 nm thick. The samples were then annealed above the glass transitions of the polymers, resulting in the formation of spherical micelles, composed of inner cores of the P2VP segments and outer coronas comprising the PS blocks, throughout the PS homopolymer thin film host. All nanoparticles were encapsulated within micelle cores; on average each micelle contains one, or no, nanoparticle. The micelles exhibited a strong tendency to self-organize at interfaces when the PS homopolymer chain length is large compared to the PS corona chain length; they otherwise remain distributed throughout the film. In comparison to pure PS-b-P2VP/PS blends, the nanoparticle/PS-b-P2VP/PS blends contain a higher density of, on average, smaller micelles. This sample fabrication procedure is straightforward and compliments the current “toolbox” used to create functional materials from block copolymer–nanoparticle systems.

Electrochemical Preparation of Controllably Large-sized Mesoporous Platinum Films by Using Diblock Copolymers and an Organic Expander

Abstract Mesoporous Pt films with controllably large-sized mesopores were prepared by using a diblock copolymer (polystyrene-b-poly(ethylene oxide), PS-b-PEO) and an organic expander (polystyrene homopolymer, h-PS). With the increase in the molecular weight of PS-b-PEO, the mesopore size gradually increased. All films possess spherical cage-type mesopores irrespectively of both the molecular weight of PS-b-PEO and the use of the expander.

Bioinspired Photo‐Core‐Crosslinked and Noncovalently Connected Micelles From Functionalized Polystyrene and Poly(ethylene oxide) Homopolymers

AbstractIn this paper, we report a simple and effective method for the preparation of stable core‐crosslinked micelles after the self‐assembly of thymine‐functionalized polystyrene (PVBT) and adenine‐terminated poly(ethylene oxide) (PEO‐A) homopolymers, and subsequent bioinspired photo‐crosslinking of the thymine units in PVBT. We obtained “graft‐like” copolymers from the interactions of PEO‐A with the PVBT chains through complementary multiple hydrogen bonding in a common solvent (dimethylformamide) after the addition of selective solvents (H2O and MeCN for PVBT and PEO‐A, respectively). Stable micelles featuring PVBT as the core and PEO‐A as the shell were formed via selective solvent pairs; they were clearly visualized using transmission electronic microscopy and staining techniques. The shapes and sizes of the core/shell micelle structures did not change after exposure to UV light, revealing the enhanced dimensional stability of these photo‐core‐crosslinked micelles.

Tailored Morphologies of Poly(styrene‐block‐butadiene‐block‐methyl methacrylate) Triblock Copolymers and Their Blends with Polystyrene Homopolymers

AbstractSummary: Self‐assembly is an interesting strategy for the creation of periodic structures at the nanoscale. The microphase separation in a linear ternary block copolymer consisting on three immiscible components (ABC), give rise to the formation of different final morphologies that can be controlled by various parameters. In this work, the morphologies of three poly(styrene‐b‐butadien‐b‐methyl methacrylate) triblock copolymers with similar molecular weight and their blends with PS homopolymers were studied by atomic force microscopy (AFM). Redistribution of the homopolymer in blends generates new structures could be tailored according to the desired applications.

Synthesis and characterization of high molecular weight and low dispersity polystyrene homopolymers by RAFT polymerization

AbstractHigh molecular weight polystyrene homopolymers with low dispersity were synthesized by a reversible addition-fragmentation chain transfer (RAFT) polymerization method using 0.03 and 0.3 wt% of cumyl dithiobenzoate (CDB) vs. styrene (St) and the azobis(isobutyronitrile) initiator, at the polymerization temperature of 60 or 70 °C. The optimal high molecular weight polystyrene via this synthetic scheme shows Mw = 46.5×104, Mn = 33.3×104, and a dispersity of 1.40. The polystyrene chain contains a dithiobenzoate C=S moiety and thus can be used as a macro-chain-transfer agent for the polymerization of other monomers and for the synthesis of diversified block copolymers under mild conditions. The changes of the polystyrene molecular weight and dispersity were studied by the influences of the initial concentration ratio of CDB to styrene ([CDB]0/[St]0), the polymerization temperature, and the polymerization time. The PS molecular weight is inversely proportional to the [CDB]0/[St]0 ratio. Decreasing CDB from 0.3 to 0.03 wt%, a high MW PS was obtained, while the dispersity was observed to increase from 1.10 to 1.40. The PS molecular weight increases with the increase of the reaction time, while the dispersity of PS varies little from 1.12 to 1.23. The molecular weight and dispersity increase with the increase of the polymerization temperature. As the temperature arises from 60°C to 70°C, the conversion increases considerably from 25.8% to 39.9%, and the dispersity increases slightly from 1.15 to 1.17. As the temperature reaches 80°C, the conversion increases considerably to 64.7%, and the dispersity increases to 1.53. The polymer molecular weight of the polystyrene prepared by the RAFT method is suitable for the applications of engineering materials.

Mesoporous Block Copolymer Morphology Studied by Contrast-Matched Resonant Soft X-ray Scattering

We demonstrate the use of contrast-matched resonant soft X-ray scattering (RSoXS) for studying the morphology of mesoporous polystyrene-block-polyethylene-block-polystyrene (SES) copolymer membranes. The mesoporous membranes were obtained by blending the SES copolymer and polystyrene (PS) homopolymer to obtain a nonporous membrane, followed by selective dissolution of the PS. If the PS homopolymer chains are initially located within the PS microphase of the SES copolymer, then one obtains a porous film wherein the pores are lined with PS. We refer to this as the templated morphology. The membranes are thus composed of three phases: voids, PS, and PE. Conventional techniques such as small-angle X-ray scattering (SAXS) and scanning electron microscopy (SEM) only distinguish between the polymer and the voids. The main advance in this paper is to show that microphase separation between PS and PE can be studied by contrast-matched RSoXS in spite of the presence of voids. Under certain circumstances, we obtain ...

Determining the Polydispersity in Chemical Composition and Monomer Sequence Distribution in Random Copolymers Prepared by Postpolymerization Modification of Homopolymers.

We report on establishing the polydispersity in chemical composition (PCC) and polydispersity in monomer sequence distribution (PMSD) in random copolymers of poly(styrene-co-4-bromostyrene) (PBrxS), where x = (0.385 ± 0.035) is the mole fraction of the 4-bromostyrene units (4-BrS), prepared by electrophilic substitution of bromine in the para-position of the phenyl ring of the parent polystyrene. Upon fixing the total number of repeating units, we tune the distribution of styrene and 4-BrS segments in PBrxS by carrying out the bromination reaction on polystyrene homopolymers in different solvents. While PBrxS with relatively random comonomer distribution is prepared in 1-chlorodecane, random-blocky sequences of 4-BrS in PBrxS are achieved by carrying out the bromination reaction in 1-chlorododecane. The PCC in both copolymers is established by fractionating both polymers using interaction chromatography (IC) and determining the chemical composition of the individual fractions by neutron activation analysis (NAA). The NAA data along with IC experiments reveal that the random-blocky sample possesses a narrowed PCC relative to a specimen with a more random comonomer sequence distribution. The full width at half-maximum (fwhm) in the chemical composition profile from IC is used to quantify PCC; the random mother sample possessed a 25% fwhm, while the random blocky mother sample has a fwhm equal to 8.7%. The change in the adsorption enthalpy per brominated segment due to adsorption is determined to be ≈1.5 times greater for the random-blocky than the relatively random sample, proving that more pronounced cooperative adsorption occurs in the case of the random-blocky sample relative to the random copolymer sample. Computer simulation employing the discontinuous molecular dynamic scheme further reveals that the distribution of comonomer sequences, that is, PMSD, in the random-blocky copolymer is narrower than that in the copolymer with a random distribution of both monomers.