Block Copolymers Of Polystyrene Research Articles

Adsorption of polystyrene–poly(ethylene oxide) block copolymers on quartz using a parallel-plate surface-force apparatus and simultaneous neutron reflection

Block copolymers of polystyrene and poly(ethylene oxide) adsorbed on quartz plates under compression have been studied using neutron reflectometry. Adsorption from a good solvent (toluene) leads to the preferential adsorption of the ethylene oxide chains, but because of the very high asymmetry of the polymers and the favourable adsorption energy, the polystyrene is also adsorbed. The extent of the polystyrene adsorbed layer is less than the radius of gyration for both samples studied. On the approach of a second coated plate, the polystyrene volume fraction increases near the interface, indicative of a strong interlayer repulsion. On changing the solvent to octane the profiles indicate collapse of the polymer layer and there is a dramatic decrease in the pressure required to hold the quartz plates at the same separation.

マクロアゾ開始剤によるポリビニルピロリドン‐ポリスチレンブロック共重合体の合成

4, 4'-アゾビス-4-シアノペンタン酸クロリドと1, 6-ヘキサンジオールとの重縮合から合成された高分子ラジカル重合開始剤 (MAI) 用いて, 二段階のラジカル重合法でブロック共重合体を合成した. 二段階の第1段にビニルピロリドンの重合を行い, 続いてスチレンの合を行うことによって, ポリビニルピロリドン-ポリスチレンブロック共重合体を合成できた. NMR法で求めたブロック共重合体のポリニルピロリドン含有率 (X) は, 仕込み組成に依存して8.2～16.0%となり, 第2段のモノマー消費量 [-N=N-] 0.50 [St] 1.20の関係およ (100/X-1) と [St] 1.20/ [-N=N-] 0.50の関係は直線的あった. ポリビニルピロリドン基準のブロック効率, [St] 0の3mol/l以下を除いて比較的高い約80%となった. ブロック共重体の平均分子量は, Mn=100100～162000, Mw=189300～395000となった. これらの値, [St] 0.80/ [-N=N-] 0.50と直線関係が成立し, その切は中間体のアゾ基含有ポリビニピロリドンの分子量と一致した. これらのことは得られたブロック共重合体の構造が- (AB) -n型あるいはABA型であることを示唆してる.

Hydrothermal Processing of BaTiO3/Polymer Films

ABSTRACTHydrothermally derived films of BaTiCO3 were fabricated by reacting thin layers of titanium organometallic liquid precursors in aqueous solutions containing Ba(OH)2 and having a high pH. Cubic submicron polycrystalline films of BaTiCO3 (thickness = 1 μm) were formed at 70°C. Low concentrations of block copolymers of polybutadiene and polystyrene were incorporated into the liquid precursor to prevent precursor film cracking. Higher polymer concentrations allowed fabrication of polymer/ceramic composite films by virtue of the low temperature used in hydrothermal processing.

Adsorbed block copolymer of poly(2-vinylpyridine) and polystyrene studied by neutron reflectivity and surface force techniques

The adsorption of a small block copolymer of poly(2-vinylypyridine) and polystyrene has been studied as a function of solvency. Both neutron reflectometry and surface force measurements have been used to study the structure of the adsorbed layer. The results show that the adsorbed polymer is highly extended in good solvency conditions for the polystyrene but collapses when the solvent worsens. The results are compared with the self-consistent mean-field theory of Evers-Scheutjens-Fleer for the adsorption of block copolymers. Both the extended length of the polymer and the amount of polymer adsorbed on mica have been measured independently

Synthesis and characterization of polymethylphenylsilane–polystyrene block copolymers

AbstractBlock copolymers of polymethylphenylsilane (PMPS) and polystyrene (PS) have been successfully prepared by the condensation of α,ω‐dichloro‐polymethylphenylsilane with polystyryl‐lithium. These new materials have been characterized by UV spectroscopy, 29Si‐NMR, and size exclusion chromatography. These block copolymers show a good emulsifying activity to compatibilize blends of the two homopolymers (PMPS and PS). © 1993 John Wiley & Sons, Inc.

Polyarylate–polystyrene block copolymer from macro‐azoinitiator: Synthesis and its thermal properties

AbstractA macro‐azoinitiator containing polyarylate segment and azo group was prepared by the solution polycondensation of azobiscyanopentanoyl chloride and hydroxy‐terminated polyarylates having viscosity‐average molecular weights of 6200, 8100, and 12 400. These macro‐azoinitiators were used in the radical polymerization of styrene to synthesize polyarylate‐polystyrene block copolymers. Thermal properties measured by the differential scanning calorimetry indicated the phase separated morphology of the block copolymers except at low molecular weight of the block constituents. © 1993 John Wiley & Sons, Inc.

Phase morphology of polymer blends: 2. SEM observation by secondary and backscattered electrons from microtomed and stained surface

A recently developed scanning electron microscopy (SEM) technique, which consists of the preparation of a microtomed flat surface, staining with OsO 4 or RuO 4, and compositional contrast observation using backscattered electrons, was applied for high impact polystyrene and propylene-ethylene block copolymer. A clear contrast was obtained for both polymers. By minor revision, i.e. by employing the secondary electron image under a low accelerating voltage, a much better contrast was observed.

Rheological behavior of homogeneous poly(α-methylstyrene)-block-polystyrene copolymers

Oscillatory shear flow properties of α-methylstyrene)/styrene block copolymers having molecular weights ranging from 120000 to 250000 and different block length ratios prepared by anionic polymerization were measured using a Rheometrics mechanical spectrometer at temperatures ranging from 116 to 251°C. It is concluded that these polymers are homogeneous as determined by DSC and by logarithmic plots of dynamic storage modulus versus dynamic loss modulus. The Stockmayer-Kennedy molecular viscoelasticity theory which was developed on the basis of the Rouse theory was modified using the concept of the tube model

Phase equilibria in mixtures of block copolymer and homopolymer

Phase diagrams were constructed experimentally for mixtures of a polystyrene- block-polyisoprene- block-polystyrene (SIS) copolymer and a homopolymer polystyrene. For the study, two SIS triblock copolymers having spherical and cylindrical microdomain structures, respectively, and a series of homopolymer polystyrenes were synthesized via anionic polymerization. In constructing phase diagrams, we combined the results of dynamic viscoelastic measurement (i.e. logarithmic plots of dynamic storage modulus versus dynamic loss modulus), which allowed us to determine the boundary between the mesophase and homogeneous phase, and turbidity measurement, which allowed us to determine cloud point curves for liquid-liquid (macrophase) separation. Experimental results are compared with predictions made by the theory of Hong and Noolandi. We have found that predicted results are at variance with experimental results.

Rheological behaviour of block copolymers in the disordered state: effects of molecular weight and block length ratio

The effects of molecular weight and block length ratio on the rheological behaviour of polystyrene- block-polyisoprene- block-polystyrene (SIS) copolymers in the disordered state were investigated. For the study, SIS triblock copolymers were synthesized via anionic polymerization, and linear dynamic viscoelastic properties (i.e. dynamic storage and loss moduli, G′ and G″) of the SIS block copolymers were measured at various temperatures as functions of angular frequency (ω), using a cone-and-plate rheometer. The disordered state of the samples was determined by the threshold temperature at which the plot of log G′ versus log G″ becomes virtually independent of temperature as the temperature was increased. It has been found that when the block length ratio is kept the same, the melt elasticity of SIS block copolymers in the disordered state becomes independent of molecular weight, while the viscosity increases with molecular weight, and the block length ratio greatly influences both melt viscosity and elasticity.

Quantitative infrared spectroscopy of polystyrene block copolymer adsorbed on mica

Quantitative infrared spectroscopy of polystyrene block copolymer adsorbed on mica

Light-scattering study of starlike polymeric micelles

It is shown that poly(ethylene oxide)/polystyrene block copolymer micelles in cyclopentane undergo remarkable increases in aggregation number, from 17 to 77 upon saturation with water, resulting in an increase in the hydrodynamic radius and in the radius of gyration. The second viral coefficient and the concentration dependence of the diffusion coefficient in these micelles reflect soft-sphere interactions. At low polymer concentrations, nonvirial changes in micellar size reflect further increases in aggregation number to the order of 100 chains/micelle. The results are interpreted in the context of a starlike micelle model

Phase-separation kinetics in concentrated solutions of linear diblock copolymers of polystyrene and polyisoprene from time-resolved small-angle neutron scattering

Concentrated solutions of block copolymers of polystyrene and polyisoprene have been quenched from a high temperature to a lower temperature. The changes in scattering intensity following such a quench were studied using time-resolved small-angle neutron scattering. From these data the rate constant for the relaxation process, R( Q), was obtained as a function of scattering vector Q. For high concentrations, a maximum in R( Q) as a function of Q 2 was observed as predicted by a time-dependent Ginzburg-Landau model. Values of the Onsager coefficient L o, extracted from these data were several orders of magnitude smaller than those for homopolymer blends.

Thermal elimination of poly(phenylvinylsulfoxide) and its polystyrene block copolymers

L'etude par TGA du homopolymere montre l'existence de 2 stades de degradation thermique: entre 120 et 200°C, il y a elimination d'acide phenylsulfenique, puis a temperature plus elevee, la degradation du polyacetylene forme. L'evolution de l'acide phenylsulfenique forme est etudiee par pyrolyse couplee a la spectrometrie de masse. La conductivite electrique faible du polyacetylene montre qu'il est faiblement conjugue

A study of block copolymer adsorption kinetics via internal reflection interferometry

We present a new experimental approach to investigate polymer adsorption onto dielectric surfaces. This technique, internal reflection interferometry, employs multiple total internal reflections through a prism to measure the average refractive index and thickness of adsorbed layers. The adsorption kinetics of poly(ethylene oxide)–polystyrene block copolymer from dilute solutions in cyclopentane at 23 °C onto sapphire is presented. The sapphire surface is saturated within 30 min, in contrast with homopolymer adsorption, and the copolymer is irreversibly adsorbed with respect to pure solvent. Micellization of block copolymers dramatically affects adsorption kinetics and the final amount adsorbed. We suggest some mechanisms explaining the adsorption behaviour.

Formation and reactions of paramagnetic particles in irradiated polystyrene and butadiene-styrene block copolymers and model systems

To identify the features of energy transfer and migration of active particles in microheterogenous polymeric systems the authors have investigated the formation and photochemical reactions of paramagnetic particles in irradiated butadiene-styrene block copolymers and model systems. It is shown that the effectiveness of far-energy migration in such colloidal systems is low. It is concluded that the processes of energy transfer occur between the polystyrene and polybutadiene units present in direct contact. It is shown that on photobleaching the electrons stablized in polystyrene and the polystyrene phase of the block copolymers react with neutral radicals and in the case of block copolymers the electrons may pass into the polybutadiene phase and interact there with allyl radicals.

Polyester‐polystyrene block copolymers and their influence on phase morphology and mechanical properties in polymer blends

AbstractNew block copolymers of polystyrene with polyesters have been synthesized and investigated as compatibilizing agents. The addition of block copolymers in immiscible blends of polybutylene terephthalate and (i) polystyrene, (ii) polystyrene/poly(2,6‐dimethyl 1,4‐phenylene oxide) as well as (iii) high impact polystyrene drastically reduced the dimensions of the dispersed phase and stabilized the phase growth with annealing time. Stress‐strain curves for the binary blends indicate brittle behavior. The addition of more than 10 wt% of block copolymers transforms their brittle characteristics to ductile behavior.

Ultrasonic absorption and shear viscosity measurements for solutions of polybutadiene and polybutadiene- block-polystyrene copolymers

Ultrasonic measurements are reported on polybutadiene and polybutadiene- block-polystyrene copolymers in toluene. The ultrasonic absorption spectrum of polybutadiene can be described by the equation δα f 2 ∼f −n with the exponent n = 1 3 . The comparison of the measured dynamic shear viscosity with effective viscosity η eff shows that the ultrasonic absorption cannot simply be explained by contributions of the normal-mode relaxation. For the copolymers we can conclude from dynamic shear viscosity measurements that viscoelastic contributions have only a minor effect. The ultrasonic absorption of the diblock copolymers is higher than a pure superposition of the contributions from polystyrene and polybutadiene blocks. Therefore we assume an additional contribution from the relaxation of the volume viscosity (polymer-polymer interaction and/or polymer-solvent interaction) for polybutadiene and the copolymers.

A surface light scattering study of a poly(ethylene oxide)-polystyrene block copolymer at the air-water and heptane-water interfaces

A surface light scattering study of a poly(ethylene oxide)-polystyrene block copolymer at the air-water and heptane-water interfaces

Interaction of polystyrene/ poly(γ-benzyl l-glutamate) and poly(methyl methacrylate)/ poly(γ-benzyl l-glutamate) block copolymers with plasma proteins and platelets

A-B-type block copolymers, consisting of polystyrene (PST) or poly(methyl methacrylate) (PMMA) forming segment (A) and poly(γ-benzyl l-glutamate) {P[Glu(OBzl)]} segment (B), were synthesized and the thrombus formation on these block copolymer films was investigated in relation to the adsorption of8 plasma proteins and the activation of platelets. The relative amount of thrombus formation was higher on homopolymers than on block copolymers. The amount of thrombus formation became less, with decreasing content of P[Glu(OBzl)] in the PST block copolymers and with increasing content of P[Glu(OBzl)] in the PMMA block copolymers. Adsorption of bovine serum albumin(BSA), bovine γ-globulin (BγG) and bovine plasma fibrinogen(BPF) onto polymer films was also investigated. More proteins were adsorbed and denatured when adsorped onto PST and PMMA than onto block copolymers. With increasing content of P[Glu(OBzl)] in the PST block copolymers, the degree of denaturation of adsorbed proteins increased, while the amount of protein adsorption was unaffected. Conversely, with increasing content of P[Glu(OBzl)] in the PMMA block copolymers, the degree of denaturation of adsorbed proteins decreased, while similarly the amount of protein adsorption was unaffected. Adhesion of platelets from platelet suspension (WP) to polymer films coated with one of the plasma proteins showed that the activation of adhered platelets was suppressed when there was a lower degree of denaturation of coated proteins. In the same experiments using platelet-rich plasma(PRP), neither the number of platelets adhered nor the degree of activation of the adhered platelets was correlated with the composition of the polymer films. These experimental results indicated that vinyl polymer/polypeptide block copolymers with certain compositions suppress the denaturation of adsorbed proteins and the activation of adhered platelets, thus leading to a slower rate of thrombus formation. However, the experiments using PRP suggest the intervention of minor plasma proteins other than the three major plasma proteins, and blood clotting factors other than platelets in thrombus formation.