PS Chains Research Articles

Synthesis and characterization of PS‐b‐PDMS‐b‐PS triblock copolymer

AbstractA series of polystyrene‐b‐poly(dimethylsiloxane)‐b‐polystyrene (PS/PDMS/PS) triblock copolymers had been synthesized by atom transfer radical polymerization (ATRP). The products had been characterized by Fourier transform infrared, gel permeation chromatography, differential scanning calorimetry, thermogravimetric analysis, contact angle, and scanning electron microscope. The results indicate that the PS chains have been successfully blocked onto the PDMS back bone, and the PS‐b‐PDMS‐b‐PS triblock copolymers have low‐surface tension, good thermal stability, and microphase separation configuration. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Clicked (AB)2 C-type miktoarm terpolymers: Synthesis, thermal and self-assembly properties, and preparation of nanoporous materials

A well-defined (PEO-PS)2-PLA miktoarm terpolymer (1) was synthesized by stepwise click reactions of individually prepared poly(ethylene oxide) (PEO), polystyrene (PS, polymerized by atom transfer radical polymerization), and polylactide (PLA, polymerized by ring-opening polymerization) blocks. As characterized by differential scanning calorimetry and small-angle X-ray scattering techniques, the terpolymer self-assembled into a hexagonal columnar structure consisting of PLA/PEO cylindrical cores surrounded by PS chains. In contrast, the ion-doped sample (1-Li+) with lithium concentration per ethylene oxide = 0.2 exhibited a three-phase lamellar structure, which was attributed to the microphase separation between PEO and PLA blocks and to the conformational stabilization of the longest PLA chain. The two-phase columnar morphology before the ion doping was used to prepare a nanoporous material. PLA chains in the cylindrical core region were hydrolyzed by sodium hydroxide, producing nanopores with a pore diameter of about 14 nm. The resulted nanoporous material sank to the bottom in water, because of water-compatible PEO chains on the walls. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Preparation and Morphology of Hybrids Composed of a Block Copolymer and Semiconductor Nanoparticles via Hydrogen Bonding

We report a systematic study on preparation and morphological observation of hybrids composed of a block copolymer and hydroxy-capped semiconductor nanoparticles via hydrogen bonding. Three polystyrene-b-poly(4-vinylpyridine) (PS–P4VP) block copolymers with exactly the same PS chain length but with different P4VP chain length were synthesized via reversible addition–fragmentation chain transfer polymerization. To prepare hybrids, each PS–P4VP was mixed with hydroxy-capped nanoparticles made of cadmium selenide (h-CdSe), by varying a weight ratio of PS–P4VP:h-CdSe. Morphology of three series of hybrids was observed by both transmission electron microscopy and small-angle X-ray scattering. Hybrids composed of h-CdSe and PS–P4VP bearing a long P4VP block represents uniform morphology of a single nanophase-separated structure, where domain spacing expansion and morphology transition induced by addition of h-CdSe were observed. On the other hand, nonuniform morphology, i.e., macrophase separation accompanied by overflow of h-CdSe from nanophase-separated domains, was observed in hybrids containing PS–P4VP bearing a short P4VP block. These results are attributed to hydrogen-bonding formation and the stoichiometric balance of functional groups.

Block and Hetero Ethyl Cellulose Graft Copolymers Synthesized via Sequent and One‐pot ATRP and "Click" Reactions

AbstractEthyl cellulose graft copolymers with block and hetero side chains, ethyl cellulose graft [polystyrene‐b‐poly(ethylene glycol)] [EC‐g‐(PS‐b‐PEG)] and ethyl cellulose graft polystyrene and polyethylene glycol [EC‐g‐(PS‐PEG )] were synthesized by atomic transfer radical polymerization (ATRP) and alkyne‐azide "click" reactions and "one‐pot" ATRP and "click" reactions, respectively. For the synthesis of EC‐g‐(PS‐b‐PEG), the macroinitiator for ATRP was first synthesized via the esterification of hydroxyl groups of EC with 2‐bromoisobutyryl bromide to result ethyl cellulose 2‐bromoisobutyryl ester (EC‐Br). The degree of substitution of bromide groups, which determined the graft density, can be tailored by varying the feeding ratios of the hydroxyl groups to 2‐bromoisobutyryl bromide. Then ATRP was carried out for preparing EC‐g‐PS‐Br with well‐defined length of PS chains. The EC‐g‐PS‐Br copolymers were then converted to EC‐g‐PS‐N3 and then reacted with end alkyne‐functionalized PEG via click to result in EC‐g‐(PS‐b‐PEG). The EC‐g‐(PS‐PEG) copolymers were synthesized by converting bromide groups of EC‐Br to azide groups (EC‐Br‐N3) and then by one‐pot ATRP and "click" reactions. The resultant graft copolymers were characterized by FTIR and 1H NMR. The results indicate the success of the synthetic procedure of the cellulose graft copolymers with block and hetero side chains.

Microdomain expansion and transition behavior of PS-b-PMMA/PS homopolymers by SAXS analysis

We present the microdomain expansion and transition behavior of binary blends of polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA)/PS homopolymers using small-angle X-ray scattering (SAXS) analysis, where the PS molecular weight (or chain length) was varied with chain length ratios (α) of 0.3, 1, and 2 with respect to the PS block length of the PS-b-PMMA. The d-spacing and order-to-disorder transition (ODT) by addition of PS homopolymers were significantly influenced by the PS molecular weight. In contrast to the typical decrease in d-spacing with increasing temperature in PS-b-PMMA, the d-spacing for PS-b-PMMA/PS homopolymers showed unusual behavior; specifically, it increased for shorter PS chains of α ≤ 1, but was independent of temperature for PS chains of α = 2. This variation can be attributed to a competing interaction between the thermal expansion effects of the microdomains with homopolymers and the decrease in the chain stretching between the two block components.

Synthesis of Polyisobutylene-Based Miktoarm Star Polymers from a Dicationic Monoradical Dual Initiator

A dicationic monoradical dual initiator 3-[3,5-bis(1-chloro-1-methylethyl)phenyl]-3-methylbutyl 2-bromo-2-methylpropionate (DCCBMP) was designed for the preparation of A2B type miktoarm star copolymers, where A is a polyisobutylene (PIB)-based homo or block copolymer that is produced by living carbocationic polymerization (LCP), and B is a polyacrylate or other polymer block produced by atom transfer radical polymerization (ATRP). DCCBMP was obtained by chlorination of 3-[3,5-bis(1-hydroxy-1-methylethyl)phenyl]-3-methylbutyl 2-bromo-2-methylpropionate (DCOHBMP), which was synthesized in a pure form via aerobic oxidation of 3-(3,5-diisopropylphenyl)-3-methylbutyl 2-bromo-2-methylpropionate using N-hydroxyphthalimide (NHPI)/Co(OAc)2·4H2O catalyst system. Initiation efficiency of DCCBMP was 0.89–0.98 for LCP of isobutylene (IB) at −70 °C targeting molecular weights of 5K, 10K, and 20K g/mol, which was comparable to the standard dicationic initiator 5-tert-butyl-1,3-(1-chloro-1-methylethyl)benzene (t-Bu-m-DCC). Sequential monomer addition under LCP conditions produced narrow-polydispersity poly(styrene-b-isobutylene-b-styrene) (PS–PIB–PS) triblock copolymers. These polymers possessed a 2-bromo-2-methylpropionate (bromoester) ATRP initiating site in the approximate middle of PIB segment and two sec-benzylic chloride groups at the PS chain ends, which were also effective in initiating ATRP. With these PS–PIB–PS macroinitiators, poly(tert-butyl acrylate-b-styrene-b-isobutylene)2-s-poly(tert-butyl acrylate) [(PtBA–PS–PIB)2-s-PtBA] miktoarm star polymers were readily synthesized via ATRP of tert-butyl acrylate (tBA). The sec-benzylic chloride functionality was alternatively eliminated at high temperature (180–200 °C) under vacuum, yielding PS–PIB–PS macroinitiators containing only the bromoester site (thermolyzed PS–PIB–PS). Size exclusion chromatography (SEC) and nuclear magnetic resonance (NMR) spectroscopy showed that thermolysis removed all sec-benzylic chlorides without destruction of bromoester moieties. Thermolyzed PS–PIB–PS allowed synthesis of poly(styrene-b-isobutylene)2-s-poly(tert-butyl acrylate) [(PS–PIB)2-s-PtBA] star polymers with the potential hydrophilic segment attached only to the core of PS–PIB–PS. For both star terpolymer configurations, the PtBA blocks were converted to PAA via thermolysis at 150 °C to produce amphiphilic PIB-based miktoarm star polymers with narrow polydispersity indices (<1.1).

Morphology stabilization of the polypropylene/polystyrene nanoblends prepared by diffusion and polymerization of styrene in isotactic polypropylene pellets during melt mixing by the incorporation of divinylbenzene

AbstractDivinylbenzene (DVB) was used as a comonomer of styrene (St) during the preparation of polypropylene/polystyrene (PP/PS) nanoblends by diffusion and polymerization of St in isotactic PP pellets to make the PS domains crosslinked and further to reduce the coalescence of the PS domains during melt mixing. Different morphologies were obtained after melt mixing with different amounts of the initiator benzoyl peroxide (BPO) and DVB, which was explained by different morphology evolutions during melt mixing with different crosslinked structures of the PS chains. With relatively high amounts of BPO and DVB, the nanosized PS domains almost kept their shape and size, and only simple aggregates of a few PS particles with an average size of 130 nm were observed after melt mixing of the PP/PS blends. It can be concluded that DVB is useful for morphology stabilization of the PP/PS nanoblends during subsequent melt processing. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Recyclability of Polystyrene/Clay Nanocomposites

PS/organo-modified clay (5% w/w) nanocomposite has been subjected to a series of eight processing cycles in a twin screw extruder. The influence of multiple recycling on the properties of the nanocomposite was studied by following the changes in the morphology, the molecular structure, the melt flow index (MFI) and the thermal properties. The WAXS results indicate a strong intercalation of PS chains between silicate layers of the organoclay and the extent of intercalation appears to increase with increasing the number of cycles. The main effects of recycling are a reduction in molecular weight due to chain scission, although the occurrence of a crosslinking fraction is probable after 8 cycles. The thermal properties remain almost stable during reprocessing.

Dielectric Behavior of Guestcis-Polyisoprene Confined in Spherical Microdomain of Triblock Copolymer.

Dielectric behavior was examined for ternary blends of guestcis-polyisoprene (PI) chains, coguest PS chains, and host PS–PI–PS triblock copolymers. The guest PI chains had the molecular weight Mg-PI well below Mb-PI of the PI blocks and were mixed in the spherical PI domains formed in the copolymers. PI has the type-A dipoles parallel along the chain backbone and its end-to-end vector fluctuation activates dielectric relaxation. The dielectric test was conducted at temperatures well below the glass transition temperature of the PS blocks, so that the PI blocks had their ends fixed on the glassy PS matrix and exhibited no end-to-end vector fluctuation. Thus, the slow dielectric response of the systems exclusively detected the global motion of the guest PI chains confined in the spherical PI domain. The dielectric mode distribution of the guest PI chains thus observed was broader than that of the same chains in bulk systems, reflecting the osmotic and spatial constraints on the chain dynamics in the spherical domains. The guest PI chains of different Mg-PI exhibited nearly the same extent of mode broadening, despite their average coil size approached the domain size with increasing Mg-PI. This result suggested that the osmotic constraint was the primary factor affecting (broadening and retarding) the guest chain dynamics. The osmotic constraint appeared to be stronger in the spherical domain than in the lamellar domain, the latter being examined in literature.

Chemical Patterns from Surface Grafted Resists for Directed Assembly of Block Copolymers

We demonstrate a direct e-beam patternable one-component block copolymer (BCP) resist to fabricate a chemical pattern for the directed assembly of a symmetric block copolymer. The resist consists of a low molecular weight poly(styrene-block-methyl methacrylate) with a hydroxyl group at the PMMA chain end (PS-b-PMMA-OH), which anchors the chains to the surface. This short-tethered PMMA block provided sufficient sensitivity to allow scission by e-beam. The length of the untethered PS block was fine-tuned to impart the required contrast between the patterned and the unpatterned region for 1:1 assembly of an overlying BCP blend. Two BCP resists with a PS fraction of 0.25 (16SM) and 0.34 (18SM), with a total molecular weight less than 20K, were synthesized, and the assembly of a ternary BCP blend was studied. 16SM- and 18SM-anchored substrates showed nonpreferential and PS preferential surfaces, respectively. Both 18SM and 16SM could be patterned by e-beam to fabricate a 1:1 chemical pattern with a line pitch of 70 nm for the assembly of a BCP ternary blend. 18SM gave fewer defects than 16SM due to an increased contrast in interfacial energies between adjacent stripes in the chemical surface pattern. Two additional PS-b-PMMA-OH polymers with a molecular weight of 39K (F(PS) = 0.76) and 69K (F(PS) = 0.83) were synthesized to study the effect of PS cross-linking upon exposure to e-beam. As the PS fraction increases, the line pattern becomes blurred and ultimately ineffective in guiding the BCP assembly. The blurring is attributed to cross-linking of adjacent PS chains.

SAXS and SANS characterization of gelable polystyrene-b-poly(acryloxy propyl triethoxysilane) (PS-b-PAPTES) diblock copolymer micelles before and after hydrolysis–condensation

Diblock copolymers of styrene and gelable acryloxy propyl triethoxysilane (APTES) were successfully prepared through Nitroxide-Mediated Polymerization (NMP). Their micellar behaviour in dioxane–methanol solutions was investigated by Small Angle X-ray Scattering (SAXS) and Neutron Scattering (SANS) measurements. The micelles were found to be spherical whatever the copolymer composition with a PS core size varying from 13.5 nm to 37.8 nm depending on the PS chain length and the swelling ratio. The thickness of the PAPTES corona increased from 6.0 nm to 10.8 nm when increasing the PAPTES polymerization degree from 91 to 336. Two micellar structural regimes were identified, depending on the chain length of the PAPTES soluble block. For PAPTES polymerization degrees higher than 100, the PS core radius in dried state RDC can be consistently described by a scaling relationship RDC α (NPS0.34NPAPTES−0.069) and the aggregation number Nagg obeys the relationship Nagg α (NPS0.021NPAPTES−0.21), consistent with previous studies. For polymerization degrees of the soluble block lower than 100, it was shown that RDC and Nagg do not follow the expected scaling relationships with higher values of Nagg, possibly due to complete chain incorporation in the micelle core. After the cross-linking process, a decrease of the hydrodynamic diameter of 1.6 to 4.7 nm was observed. This is mainly due to the corona shrinkage, the aggregation number and the core radius being directly dependent of the parent non-crosslinked micelles.

Controlled Positioning of Activated Ester Moieties on Well‐Defined Linear Polymer Chains

The successful sequence-controlled installation of an activated ester using a newly designed monomer pentafluorophenyl 4-maleimidobenzoate is demonstrated. Pentafluorophenyl 4-maleimidobenzoate is kinetically installed at different stages of a nitroxide-mediated polymerization, namely, near the α-chain end and in the middle of a PS chain. In addition, successful installation of apolar and polar functional groups is achieved via post-polymerization functionalization, which demonstrated the versatility of the synthesis of a universal precursor for locally functionalized polymers.

Micellar Transitions in Solvent-Annealed Thin Films of an Amphiphilic Block Copolymer Controlled with Tunable Surface Fields

We investigated the response of symmetric poly(styrene-block-4vinylpyridine) P(S-b-4VP) diblock copolymer micelles to surface fields of variable strength at free surfaces and substrate interfaces when the micelles as spun were subjected to solvent annealing. Free surface interactions were controlled with solvent annealing in solvents of varied selectivity. On exposure to vapors of a solvent strongly selective for PS, the micelles retained their spherical shape but grew into cylindrical micelles or lamellar nanostructures via fusion on exposure to slightly selective or neutral solvent vapors. Giant 2D disks that completely wetted PS-grafted substrates resulted when spherical micelles were exposed to vapors of a highly selective solvent for P4VP. The interfacial interactions were controlled through subjecting them to UV/ozone (UVO) substrates initially coated with an end-grafted layer of short PS chains, with which the grafted PS chains became oxidized, degraded, or totally removed through UVO treatment for a controlled duration. When thin films were annealed in vapors of THF, the structural transition from spherical to cylindrical micelles depended on the interfacial field. On applying selective UVO exposure of optimal duration, we fabricated a substrate with two interfacial chemistries that promoted varied micellar species (spherical and cylindrical micelles) with a sharp boundary developed within thin films through solvent annealing for a controlled duration.

Mechanical behavior of a single polymer chain in a non-solvent

Mechanical properties of a single polystyrene chain in mixtures of dioxane and methanol were measured with AFM. The effect of the solubility of the surrounding liquid on mechanical behavior of a polymer chain was examined. In good and Θ solvents, the force-extension curves exhibit a freely jointed chain (FJC)-like trend with good reproducibility. In a non-solvent, the profile of force-extension curve was dependent on the extension speed: an FJC-like nature emerged at the lower speed of 200 nm/s while saw-toothed curves were obtained at the higher speed of 2000 nm/s. The shape of saw-toothed curves varied from measurement to measurement. A force relaxation was also observed in the non-solvent under a fixed extension distance after 2000 nm/s extension. The mechanical behavior in non-solvents suggests that inhomogeneous deformation of a PS chain occurs due to reduction of the chain mobility.

High-concentration organic solutions of poly(styrene- co-butadiene- co-styrene)-modified graphene sheets exfoliated from graphite

A simple method is developed to produce high-concentration organic solutions of graphene sheets noncovalently modified with poly(styrene- co-butadiene- co-styrene) (SBS). Once exfoliated from natural graphite under sonication, the graphene sheets can be stabilized by SBS through the π–π stacking with the PS chains. The PS–graphene interaction is confirmed by DSC, since the glass transition temperature of the PS blocks increases by ∼8 °C, while that of the PB block remains unchanged. The content of SBS adsorbed on the graphene sheets is determined by TGA as ∼63 wt.%. Direct morphological observation is achieved by HRTEM, which reveals an amorphous polymer layer on the graphene sheets with individual polymer chains climbing on the edges. A freestanding, highly flexible film of SBS-modified graphene is prepared. The improved solubility of graphene in the organic solvents opens up a new opportunity for the solution-phase incorporation of graphene in the polymer matrices. The graphene/SBS composite has an excellent electrical conductivity with a percolation threshold of ∼0.25 vol.%. Besides, it is proven that SBS can also be adsorbed on chemically modified graphene and carbon nanotubes, demonstrating the versatility of the π–π stacking between the PS chains and the graphitic planes.

Microphase Separation of Phenylene Oligomers with Polymeric Side Chains: A Dissipative Particle Dynamics Study

The microphase-separated morphologies of p-phenylene oligomers with POx, PCL, PS, and PEO side chains are studied using DPD simulations. It is shown that the microphase-separated morphologies depend significantly on the degree of chemical incompatibility between the components as indicated by the Flory-Huggins interaction parameters. The good agreement of the microphase separated morphologies as simulated by DPD with the experimentally determined thin film morphologies suggests that DPD can produce convincing morphological information at the nanoscale. The results show that grafting of polymeric side chains can be an important tool to control the morphology of polymers with a rigid backbone.

Catalytic Degradation of Polystyrene: Modeling of Molecular Weight Distribution

AbstractTwo of the most abundant polymers in household waste streams, PS and PE, may be recycled by compatibilization through a Friedel‐Crafts alkylation. This reaction produces a graft copolymer PE‐g‐PS that improves the properties of the blend, but simultaneously degrades PS chains. Since the copolymer efficiency as a compatibilizer depends both on the molecular weight and MWD of its two blocks, the operating conditions for the copolymer synthesis must be carefully tuned. To aid in this task, we present a preliminary mathematical model that focuses on the effect of the catalyst and cocatalyst of the Friedel‐Crafts alkylation on the MWD of the PS chains. The model's predictions are shown to agree with experimental data. magnified image

A Nanotechnology Pathway to Arresting Phase Separation in Soft Nanocomposites

Direct observation of the miscibility improving effect of ultra-small polymeric nanoparticles (radius ≈4 nm) in model systems of soft nanocomposites is reported. We have found thermodynamically arrested phase separation in classical poly(styrene) (PS)/poly(vinyl methyl ether) blends when PS linear chains were totally replaced by ultra-small, single chain PS nanoparticles, as determined by thermo-optical microscopy measurements. Partial arrested phase splitting on heating was observed when only some of the PS chains were replaced by unimolecular PS nanoparticles, leading to a significant increase of the lower critical solution temperature (LCST) of the system (up to 40 °C at 15 vol.-% nanoparticle content). Atomic force microscopy and rheological experiments supported these findings. Thermodynamic arrest of the phase separation process induced by replacement of linear polymer chains by unimolecular polymer nanoparticles could have significant implications for industrial applications requiring soft nanocomposite materials with excellent nanoparticle dispersion in a broad temperature range.

A novel strategy for enhancing propagation rate of polystyrene grown from silica nanoparticles or carbon nanotubes

Addition of PS into St monomer can accelerate the SI-ATRP and the PS chains were grown to high molecular weight in a short time from silica nanoparticles and carbon nanotubes.

Kinetically controlled self-assembly of monolayered micelle films of P(S-b-4VP) on bare and PS-grafted substrates

We investigated the temporal evolution of micellar nanostructures in solvent-annealed poly(styrene-block-4-vinylpyridine) P(S-b-4VP) monolayer films on bare and PS-grafted substrates under tetrahydrofuran (THF) vapor. The size of end-grafted PS homopolymers on Si substrates has a large effect on the kinetics of transitions between spherical and cylindrical micelles at the early and intermediate stages of solvent annealing. At these stages, cylindrical micelles developing via micellar merger were dominant over spherical micelles growing via micellar splitting on substrates grafted with a layer of short PS brushes (PS4k–SiOx/Si). On substrates having an attractive surface (SiOx/Si) or a grafted layer of long PS chains (PS19k–SiOx/Si), the dominant surface morphology was inverted through the dominance of micellar splitting. Upon solvent annealing for a given interval in THF, micellar structures existed as a single morphology of cylindrical micelles on PS4k–SiOx/Si, but appeared as spherical micelles on SiOx/Si and PS19k–SiOx/Si. On immersion of these micelles in ethanol to give rise to opening of the micelles, dimple-like nanopores in hexagonal arrays were induced on SiOx/Si but stripe-like nanogrooves were induced on PS4k–SiOx/Si. We demonstrate a novel method of kinetically controlled hierarchical self-assembly of P(S-b-4VP) micellar species. On combining the chemical micropatterning of the grafted layer of PS brushes with UV/ozone etching, we prepared P(S-b-4VP) films that have dimple-like nanopores and stripe-like nanogrooves coexisting with a micro-scale order within the same monolayer.