Sequential Anionic Polymerization Of Styrene Research Articles

Enhancement of mechanical and optical performance of commercial polystyrenes by blending with siloxane‐based copolymers

ABSTRACTWell‐defined poly(styrene‐block‐dimethylsiloxane) copolymers (PS‐b‐PDMS) with low polydispersity index (Mw/Mn) and different compositions were synthesized by sequential anionic polymerization of styrene (S) and hexamethyl(ciclotrisiloxane) (D3) monomers. Synthesized PS‐b‐PDMS copolymers were characterized by 1H‐nuclear magnetic resonance, size exclusion chromatography, Fourier transform infrared spectroscopy, and transmission electron microscopy. The physicochemical characterization determined that block copolymers have molar mass values close to ∼135,000 g mol−1, narrow Mw/Mn < 1.3, and chemical composition ranging from low to intermediate PDMS content. Blends of these copolymers with a commercial polystyrene (PS) were obtained by melt mixing and subsequently injection. Films obtained were flexible, and showed lower transparency than the original PS matrix. On the other hand, a 10 wt % incorporation of PS‐b‐PDMS copolymers leads to better mechanical performance by enhancing elongation at break (∼8.8 times higher) and opacity values (∼18 times higher). In addition, UV–Vis barrier capacity of the resulting blends is also increased (up to 400% higher). © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45122.

Preparation, characterization, and properties of poly(styrene-b-sulfonated isoprene)s membranes for proton exchange membrane fuel cells (PEMFCs)

A series of poly(styrene-b-isoprene) block copolymers (PSI) were synthesized by sequential anionic polymerization of styrene and isoprene. Poly(styrene-b-sulfonated isoprene) block copolymers (PSsI) were prepared via reacting the double bonds of the isoprene block with 1,4-dioxane/sulfur trioxide. The spherical-shaped ionic clusters within the PSsI membranes produce a comparable proton conductivity (10−1S/cm above 60°C) but benefits from approximately 50% lower methanol permeability than that of Nafion-117. Properties, such as proton conductivity and water content values, of PSsI membranes correlate highly to the content of the sulfonated isoprene block in PSsI samples even in the cases of similar IEC. As the hydrophilic block length is increased, the water content and proton conductivity also increased.

Preparation and self-assembly of two-length-scale A-b-(B-b-A)n-b-B multiblock copolymers

A-b-(B-b-A)n-b-B multiblock copolymers composed of short middle diblock units (B-b-A)n and two long A- and B-outer blocks were successfully prepared. The multiblock copolymers consist of polystyrene (S) and poly(p-hydroxystyrene) (pHS) and were prepared through sequential anionic polymerization of styrene and 4-tert-butoxystyrene, followed by hydrolysis of the tert-butoxy group. A hexablock and an octablock copolymer with a low overall polydispersity were synthesized. The self-assembled structures were investigated using Small Angle X-ray Scattering (SAXS) and Transmission Electron Microscopy (TEM). Due to the smaller number of inner blocks and their relatively small molar mass, a single periodic lamellar morphology was observed for the hexablock copolymer while a lamellar-in-lamellar morphology with two thin layers within successive thick layers was observed for the octablock copolymer with larger middle diblock units. These observations are in excellent agreement with existing theories.

Structure and Mechanical Behavior of Elastomeric Multiblock Terpolymers Containing Glassy, Rubbery, and Semicrystalline Blocks

Multiblock copolymers containing glassy poly-(cyclohexylethylene) (C), rubbery poly(ethylene-alt-propylene) (P), and semicrystalline poly(ethylene) (E) were synthesized by sequential anionic polymerization of styrene, isoprene, and buta-diene followed by catalytic hydrogenation. The resulting CECP-CEC (denoted XPX) and CECP (XP) multiblock copolymers each contain 50 vol % of P and equal amounts of C and E. These materials have been studied by dynamic mechanical spectroscopy (DMS), transmission electron microscopy (TEM), small- an wide-angle X-ray scattering (SAXS and WAXS), di!erential scanning calorimetry (DSC), and tensile deformation to characterize the morphology, phase behavior, and mechanical properties. Microphase separation in these compounds is induced by crystallization of Eand/or chemical incompatibility between the three blocks, leading to a new type of morphology which contains continuous region of P and continuous region ofmicrophase-separated X, resulting inmechanically resilientmaterials.Highmolecular weight block copolymers microphase separate with two di!erent length scales associated with segregation between C and E and X and P. These structural features produce a nonclassical scaling relationship for the C!E domain spacing, d ! N0.31, where N is the degree of polymerization of CEC portion. The role of semicrystalline E domains during uniaxial deformation has been exposed withWAXS experiments, which support a two-stepmechanisminvolving recoverable and nonrecoverable deformation to di!erent extents.more » Strain hardening is observed in double-anchored XPX, but not in single-anchored XP, at large tensile strains.« less

Cyclic and Multiblock Polystyrene-block-polyisoprene Copolymers by Combining Anionic Polymerization and Azide/Alkyne “Click” Chemistry

An α,ω-heterotelechelic block copolymer of polystyrene (PS) and polyisoprene (PI), α-acetylene-ω-azido-PS-b-PI, with Μn = 18 900 and PDΙ = 1.05, was synthesized by (a) sequential anionic polymerization of styrene and isoprene with 5-triethylsilyl-4-pentynyllithium (TESPLi) as initiator to afford α-(TES-acetylene)-ω-lithium-PS-b-PI, (b) reaction of the living heterofunctionalized copolymer with 1,4-dibromobutane and sodium azide to give α-(TES-acetylene)-ω-azido-PS-b-PI, and (c) deprotection of the acetylene group to afford the final product α-acetylene-ω-azido-PS-b-PI. This α,ω-heterotelechelic block copolymer with “clickable” groups, in the presence of CuBr and N,N,N′,N′′,N′′-pentamethyldiethylenetriamine, led to cyclic block copolymer in dilute solution (lower than the equilibrium concentration <6 × 10−5 g/mL), whereas in concentrated solutions (5.3 × 10−2 g/mL) gave multiblock copolymers.

Synthesis of Well-Defined Polystyrene-Block-Polyglycidol (PS-b-PG) Block Co-polymers by Anionic Polymerization

Well-defined polystyrene-block-polyglycidol (PS-b-PG) block co-polymers of various composition were prepared in two steps: (i) sequential anionic polymerization of styrene in benzene initiated with sec. butyl lithium followed by the polymerization of ethoxy ethyl glycidyl ether in the presence of the phosphazene base P4-t-Bu and (ii) deprotection of the corresponding polystyrene-block-poly(ethoxy ethyl glycidyl ether) block co-polymers with concentrated HCl or an acidic ion-exchange resin, respectively. The polymers were characterized by size-exclusion chromatography, nuclear magnetic resonance spectroscopy and differential scanning calorimetry, proving that narrow distributed block co-polymers of predetermined composition were obtained, which, based on their amphiphilic character, self-organize into hydrophilic and hydrophobic domains.

Structure of Poly(styrene-b-ethylene-alt-propylene) Diblock Copolymer Micelles in Squalane

The temperature dependence of the micellar structures formed by poly(styrene-b-ethylene-alt-propylene) (SEP) diblock copolymers in squalane, a highly selective solvent for the PEP blocks, has been studied using dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS). Four SEP diblock copolymers were prepared by sequential anionic polymerization of styrene and isoprene, followed by hydrogenation of the isoprene blocks, to yield SEP(17-73), SEP(26-66), SEP(36-69), and SEP(42-60), where the numbers indicate block molecular weights in kDa. All four polymers formed well-defined spherical micelles. In dilute solution, DLS provided the temperature-dependent mean hydrodynamic radius, R(h), and its distribution, while detailed fitting of the SAXS profiles gave the core radius, R(c), the equivalent hard sphere radius, R(hs), and an estimate of the aggregation number, N(agg). In general, the micelles became smaller as the critical micelle temperature (CMT) was approached, which was well above the glass transition of the core block. As concentration increased the micelles packed onto body centered cubic lattices for all four copolymers, which underwent order-disorder transitions upon heating near the dilute solution CMTs. The results are discussed in terms of current understanding of block copolymer solution self-assembly, and particular attention is paid to the issue of equilibration, given the high glass transition temperature of the core block.

Synthesis and crystallization behaviors of poly(styrene- b-isoprene- b- ε-caprolactone) triblock copolymers

The triblock copolymers, poly(styrene- b-isoprene- b- ε-caprolactone)s (PS- b-PI- b-PCL) have been synthesized successfully by combination of anionic polymerization and ring-opening polymerization. Diblock copolymer capped with hydroxyl group, PS- b-PI-OH was synthesized by sequential anionic polymerization of styrene and isoprene and following end-capping reaction of EO, and then it was used as macro initiator in the ring-opening polymerization of CL. The results of DSC and WAXD show big effect of amorphous PS- b-PI on the thermal behaviors of PCL block in the triblock copolymers and the lower degree of crystalline in the triblock copolymer with higher molecular weight of PS- b-PI was observed. The real-time observation on the polarized optical microscopy shows the spherulite growth rates of PCL 27, PCL 328 and PS- b-PI- b-PCL 344 are 0.71, 0.46 and 0.07 μm s −1, respectively. The atomic force microscopy (AFM) images of the PS 90- b-PI 66- b-PCL 28 show the columns morphology formed by it’s self-assembling.

Control of Mechanical Behavior in Polyolefin Composites: Integration of Glassy, Rubbery, and Semicrystalline Components

The mechanical properties of a homologous series of polyolefin block copolymers comprised of glassy poly(cyclohexylethylene) (C), elastomeric poly(ethylene-alt-propylene) (P), and semicrystalline poly(ethylene) (E) are documented. Monodisperse CPEPC, CPE, and CEPEC with mass fractions wC ∼ 0.39−0.44 and 0 ≤ ξ ≤ 1, where ξ = wE /(wE + wP), were synthesized by sequential anionic polymerization of styrene, isoprene, and butadiene followed by catalytic hydrogenation. These materials hierarchically microphase separate into lamellae, within which templated crystallization-induced segregation occurs. As ξ increases, the unoriented, polydomain CPEPC materials exhibit monotonically increasing elastic moduli and yield stresses, comparable ultimate tensile strengths, and decreasing failure strains. Cold drawing the CPEPC polymers yields high-strength materials, the structures of which are examined by small- and wide-angle X-ray scattering. Drawn CPEPC-70 (ξ = 0.70) exhibits improved toughness with an ultimate tensile strength σfail = 75 ± 10 MPa and elongation at break of εfail = 1.22 ± 0.22, as compared to σfail = 92 ± 21 MPa and εfail = 0.86 ± 0.18 for drawn CEC (ξ = 1.00). Elasticity measurements on the drawn samples demonstrate that materials with ξ > 0 exhibit low degrees of stress softening, while smaller permanent sets and higher failure strains are observed as ξ decreases.

Poly(styrene-b-4-vinylphenoxyphthalonitrile)−Cobalt Complexes and Their Conversion to Oxidatively Stable Cobalt Nanoparticles

Oxidatively stable, magnetic cobalt nanoparticles have been prepared by heating cobalt nanoparticles encapsulated in poly(styrene-b-4-vinylphenoxyphthalonitrile) block copolymers at elevated temperatures. The block copolymers were synthesized through the sequential anionic polymerization of styrene and tert-butyldimethylsilyloxystyrene. The silyl ether protecting groups on the second block were hydrolyzed under acidic conditions to afford poly(styrene-b-4-vinylphenol), and then the pendent phenols of the diblock copolymer were chemically modified with 4-nitrophthalonitrile to afford poly(styrene-b-4-vinylphenoxyphthalonitrile). Stable suspensions of ∼8−10 nm diameter cobalt metal nanoparticles were formed by thermolysis of dicobalt octacarbonyl in solutions of toluene containing poly(styrene-b-4-vinylphenoxyphthalonitrile). The cobalt−polymer nanoparticle complexes were pyrolyzed under argon to afford highly magnetic cobalt nanoparticles encased in graphitic-like coatings. Magnetic susceptibility measurem...

Synthesis and characterization of poly[styrene‐b‐methyl(3,3,3‐trifluoropropyl)siloxane] diblock copolymers via anionic polymerization

AbstractA series of narrow molecular weight distribution (MWD) polystyrene‐b‐poly[methyl(3,3,3‐trifluoropropyl)siloxane] (PS‐b‐PMTFPS) diblock copolymers were synthesized by the sequential anionic polymerization of styrene and trans‐1,3,5‐trimethyl‐1,3,5‐tris(3′,3′,3′‐trifluoropropyl)cyclotrisiloxane in tetrahydrofuran (THF) with n‐butyllithium as the initiator. The diblock copolymers had narrow MWDs ranging from 1.06 to 1.20 and number‐average molecular weights ranging from 8.2 × 103 to 37.1 × 103. To investigate the properties of the copolymers, diblock copolymers with different weight fractions of poly[methyl(3,3,3‐trifluoropropyl)siloxane] (15.4–78.8 wt %) were prepared. The compositions of the diblock copolymers were calculated from the characteristic proton integrals of 1H NMR spectra. For the anionic ring‐opening polymerization (ROP) of 1,3,5‐trimethyl‐1,3,5‐tris(3′,3′,3′‐trifluoropropyl)cyclotrisiloxane (F3) initiated by polystyryllithium, high monomer concentrations could give high polymer yields and good control of MWDs when THF was used as the polymerization solvent. It was speculated that good control of the block copolymerization under the condition of high monomer concentrations was due to the slowdown of the anionic ROP rate of F3 and the steric hindrance of the polystyrene precursors. There was enough time to terminate the ROP of F3 when the polymer yield was high, and good control of block copolymerization could be achieved thereafter. The thermal properties (differential scanning calorimetry and thermogravimetric analysis) were also investigated for the PS‐b‐PMTFPS diblock copolymers. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4431–4438, 2005

Origins of Anomalous Micellization in Diblock Copolymer Solutions

The phenomenon of “anomalous” micellization is investigated in dilute solutions of two nearly symmetric poly(styrene-b-isoprene) diblock copolymers, via dynamic light scattering. In two polystyrene-selective solvents, diethyl phthalate and dimethyl phthalate, the critical micelle temperatures (cmt) are clearly determined by rather abrupt increases in the hydrodynamic radius and scattered intensity upon cooling; this corresponds to “normal” micellization. In contrast, for the same polymers dissolved in two polyisoprene-selective solvents, tetradecane and squalane, anomalous micellization was consistently observed: the hydrodynamic radius exceeded 1000 A and the intensity was unusually large, over a modest temperature interval just above the cmt. We propose that anomalous micellization is due to the incipient phase separation of small amounts of polystyrene homopolymer, resulting from incomplete crossover during the sequential anionic polymerization of styrene and isoprene. In one sample, the presence of h...

Synthesis of model linear tetrablock quaterpolymers and pentablock quintopolymers of ethylene oxide

AbstractMultiblock copolymers of ethylene oxide, with four and five different blocks, were synthesized by the sequential anionic polymerization of styrene, isoprene, 2‐vinyl pyridine, t‐butyl methacrylate, and ethylene oxide with benzyl potassium as an initiator. The monomer sequence was based on the relative nucleophilicity of the active centers. Characterization of the multiblock copolymers by size exclusion chromatography (with refractive‐index and UV detectors), membrane osmometry, and NMR spectroscopy confirmed that benzyl potassium is an efficient initiator for the synthesis of well‐defined multiblock multicomponent copolymers of ethylene oxide. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2166–2170, 2002

Selectively Thermally Cleavable Fluorinated Side Chain Block Copolymers: Surface Chemistry and Surface Properties

A series of monodisperse poly(styrene-b-isoprene[-g-perfluoroacyl]) block copolymers was synthesized by sequential anionic polymerization of styrene and isoprene. The perfluorinated ester side chains were attached to the remaining double bonds of the isoprene block via oxidative hydroboration and esterification of the resulting alcohol by the corresponding perfluorinated acid chloride. Surfaces of the pure polymers or blends in polystyrene exhibit a notable fractional surface excess of the perfluorinated side chains within the uppermost 100 Å depending on the surface preparation and the block copolymer composition. Thus, these surfaces are highly hydrophobic having advancing water contact angles of up to 122°. When samples are heated to 340 °C, the perfluorinated side chains can be selectively cleaved off by a thermal ester cleavage, leaving the backbone of the polymer completely intact. As a result, the hydrophobicity of the resulting poly(styrene-b-isoprene) polymer surface is reversed to an advancing water contact angle < 90°. The selective thermal ester cleavage in combination with a subsequent chemical surface derivatization may have the potential to selectively change the surface functionality. If the thermal cleavage is done locally, patterning of the surface functionality seems possible.

Diblock copolymers, triblock copolymers andmodel networks synthesized by sequential anionic polymerization of styrene and 2,3-epoxypropyl methacrylate

Diblock and triblock copolymers were synthesized, under standard conditions, by sequential anionicpolymerization of styrene and 2,3-epoxypropyl methacrylate or glycidyl methacrylate (GMA). In both cases, suitable initiators were selected. The ‘living’ carbanions originating from the polymerization of styrene are able to attack GMA. The reverse reaction (attack of styrene monomer by poly (glycidyl methacrylate) anions) cannot occur. Consequently, styrene was polymerized first, yielding well defined poly (styrene) ‘precursors’. The high reactivity of poly (styryl) carbanions was reduced by the addition of 1,1-diphenylethylene. The polymer thus, fitted at chain end(s) with diphenylmethyl anions, served as macroinitiator for the subsequent polymerization of GMA. The synthesis of poly (styrene)-b-poly (GMA) diblock copolymers were carried out using sec-butyllithium as the monofunctional initiator, in the presence of lithium chloride. Potassium-naphthylide was chosen as the bifunctional initiator whenever a poly (GMA)-b-poly (styrene)-b-poly (GMA) triblock copolymer is desired. The poly (styrene) ‘precursors’ and the block copolymers were characterized by size exclusion chromatography, proton nuclear magnetic resonance and analytical titration of the oxirane functions. These methods allowed us to determine the weight- and number-average molar mass of each block, the molar mass distribution and the copolymer composition. The above ‘living’ bifunctional species were used as polymeric ‘precursors’, leading to the formation of model networks by an endlinking process, upon addition of a bisunsaturated monomer, such as ethylene dimethacrylate.

Synthesis and dilute solution properties of divinylbenzene-linked polystyrene stars with mixed arm lengths: Evidence for coupled stars

Sequential anionic polymerization of styrene and divinylbenzene (DVB) is known to lead to the formation of star-shaped polymers. This ‘arms-first’ method has been widely used and studied. It is known that this polymerization forms stars with anionically active cores. This article is concerned with the attempt to make asymmetric-star polymers utilizing these living carbanionic sites present in the core to form a second set of shorter arms growing out from the star core. The presence of remaining unreacted DVB within the core was found to cause the stars to couple to form linked double stars and other larger structures. Results from detailed dilute solution studies of the resulting polymers are reported. It was found that the results obtained from size exclusion chromatography for the double stars were flow rate dependent; only at low flow rates was a true size separation obtained. © 1997 John Wiley & Sons, Inc.

The effect of a partly hydrolyzed styrene‐tert‐butyl acrylate diblock copolymer on the properties of poly(2,6‐dimethyl‐1,4‐phenylene ether) (PPE) and polyamide‐6 (PA) blends

AbstractThe compatibilizing effect of a polystyrene‐hydrolyzed poly(t‐butyl acrylate) diblock copolymer (SBAH) on the phase structure, rheological properties, and mechanical properties of immiscible poly(2,6‐dimethyl‐1,4‐phenylene ether) (PPE) and polyamide‐6 (PA) blends was investigated. The SBAH was prepared by sequential anionic polymerization of styrene and t‐butyl acrylate, followed by acid‐catalyzed hydrolysis of t‐butyl acrylate block. Scanning electron micrographs show that the blends exhibit a more regular and finer dispersion when the SBAH of 47% hydrolyzed t‐butyl acrylate block is added. By addition of small amount of the block copolymer, the blends show non‐Newtonian power‐law behavior, and the contribution of storage modulus (G′) to the total response increases. Solubility tests support the formation of graft copolymer by chemical reaction between amine groups of the PA and carboxyl groups of the SBAH. Both modulus and strength are improved about 20% with addition of the 3 wt% SBAH, while the elongation at break decreases notably; thus, the blends fail in a brittle manner.