Viscoelastic Properties of Comb-Shaped Polystyrenes

ABSTRACT:Light-scattering studies were made in order to examine conformational anomalies exhibited by solutions in p-xylene (pXY) of nearly equimolar AB-diblock and BAB-triblock copolymers, wherein A denotes polystyrene (PST) and B poly(methyl methacrylate) (PMMA). Particle-scattering function P(0) was calculated on two simplified models: one is a micelle consisting off molecules of AB-diblock type, of which B-subchains constitute the core (star-shape model); and the other represents a BAB-triblock molecule, in which two side B-subchains undergo intramolecular association, forming a droplet, and the conformation of A-subchain is restricted by this droplet (arc-shape model). The calculated P(0) functions were compared with the experimental data obtained in pXY solution at 30°C from AB-diblock and BAB-triblock samples. It was found that the star-shape model fits closely the behavior of the AB-diblock system; whilst the arc-shape model appears to give a reasonable description of the behavior of the BAB-triblock system (although the results are not completely conclusive).KEY WORDS Light-scattering / Particle-Scattering Function / ABDiblock Copolymer / BAB-Triblock Copolymer / Conformational Anomaly / Intramolecular Phase Separation / Micelle Formation / Intramolecular Association / Star-Shape Model / Arc-Shape Model / In the previous papers 1 -5 of this series the dilute solution behavior of nearly equimolar styrene (ST) and methyl methacrylate (MMA) block copolymers was explored in some detail. The materials studied were those of AB-diblock and BAB-triblock type, wherein A denotes polystyrene (PST) and B denotes poly(methyl methacrylate) (PMMA).In the comparison of their behavior the following two points were particularly noticed. 4 ' 5 The one was that in certain selective solvents (e.g., p-xylene at 30°C) having unfavorable solvency toward PMMA, the intrinsic viscosities [17] of some BAB-triblock samples were found to become smaller than those of their precursor PST. The other was that, in such solvents, the AB-diblock samples often underwent stable micelle formation by intermolecular association, whilst under the same condition the BAB-triblock samples did not form micelles but remained in the state of molecular dispersion.To interpret such behavior, a concept of the so-called intramolecular phase separation was introduced. In poor or nonsolvents toward homopolymer B, the B-subchain(s) of an individual block copolymer molecule might collapse; this phenomenon and the poor compatibility of the parent homopolymer pair in the solvent would induce the intramolecular phase separation. 4 Then AB-diblock molecules, each having one soluble A-subchain and one collapsing B-subchain, would undergo intermolecular association forming stable micelles. In such a micelle the collapsing B-subchains would accumulate in the core and the soluble A subchains would protect the micelle from further aggregation. On the

Section: Angular Dependence Of Rayleigh Scatteringmentioning

confidence: 84%

Section: Arc-shape Model For a Bab-triblock Copolymer Moleculementioning

confidence: 99%

Section: Angular Dependence Of Rayleigh Scatteringmentioning

confidence: 99%

See 1 more Smart Citation

Thermodynamic and Conformational Properties of Styrene–Methyl Methacrylate Block Copolymers in Dilute Solution. V. Light-Scattering Analysis of Conformational Anomalies in p-Xylene Solution

Tanaka

Kotaka

Inagaki

1972

“…Although the mean numbers of branches of three comb-shaped samples are not exactly identical, they may be regarded as a series of samples differing only in length of branch, since the viscosity of highly branched polymers are insensitive to the number of branches per molecule. 6 Two kinds of good solvent, a-chloronaphthalene (a-CN) and toluene, were used for PS, while only toluene was used for PaMS. The purification methods and physical properties of these solvents were reported previously.…”

Section: Samples and Solventsmentioning

confidence: 99%

Zero-Shear Viscosity of Branched Polymer Solutions

Takahashi

Suzuki

Murakami

et al. 1986

Self Cite

ABSTRACT:The zero-shear viscosity t/ 0 of star-shaped polymers with different numbers of branches in good solvents were analyzed using the scaling theory of de Gennes. It was concluded that the semidilute region exists in the viscosity behavior of branched polymers if the molecular weight of branches are high enough. The scaling theory agrees with experimental data of the branched polymers if we recognize that the molecular weight dependence of zero-shear viscosity is higher for branched polymers than for linear polymers.KEY WORDS where k=3k'C/Jj4nNA, k' and C/J are the Huggins' constant and the Flory coefficient concerning intrinsic viscosity, respectively. If the polymer concentration is higher than a critical concentration C**, i.e., in concentrated solutions, cannot be expressed as a function of CjC* and increase with concentration with a power higher than in eq 2.Equations 1 and 2 were well supported by experiments 1 • 2 for linear polymers if the molecular weights of polymers are high enough. As the polymer concentration is increased, 1J 0 of linear polymer solutions crossovers from the dilute solution behavior to the concentrated solution behavior via the semidilute solution. If the molecular weight is low, however, the semidilute region is not observed and 1J 0 of the polymer solution crossovers from the dilute solution behavior directly to the concentrated solution behavior.Although the radius of gyration of a branched polymer is much smaller than that of the corresponding linear polymer with 89

“…One of these studies is the measurement of stress relaxation for comb-shaped polystyrenes by Fujimoto, et al, 11 and the other is our study of dynamic viscoelasticity for starshaped polystyrene. 12 These studies for branched polymers having different types of branching show that zero-shear viscosity for the branched by the copolymerization of styrene monomer with a small amount of divinylbenzene (DVB).…”

mentioning

confidence: 99%

Viscoelastic Properties of Concentrated Solutions of Randomly Branched Polystyrenes

Masuda

Nakagawa

Ohta

et al. 1972

ABSTRACT:The viscoelastic properties of concentrated solutions of linear and randomly branched polystyrenes were measured and compared with each other. From the frequency dependence of the storage shear modulus G' and the loss modulus G", the characteristic parameters in the terminal zone, such as zero-shear viscosity r;o and steady-state compliance J.0, were evaluated. The dependence of these parameters on the molecular weight and concentration were discussed. The zero-shear viscosity and its dependence on molecular weight for the solution of randomly branched polystyrene are lower than those of linear polystyrene. The steady-state compliance is proportional to MwO.s4 for the branched samples, while it does not depend on molecular weight for the linear polymer. These results lead to the suggestion that the maximum relaxation time is proportional to Mw2 · 3 and Mw3·5 for branched and linear polystyrene solutions, respectively. The concentration dependence of the steady-state compliance for the branched polymers is also much less than that of the linear ones. Comparing the frequency dependence curves of G' for the randomly branched and linear polystyrenes, there seems to be a significant difference in the shape of the relaxation spectra in the region associated with entanglement coupling. This behavior is considered to be due to the difference in the two chain structures.KEY WORDS Viscoelasticity / Polystyrene / Branched Polymer / Viscosity / Steady-State Compliance / Molecular Weight / Concentration Dependence / The effect of branching on the viscoelastic properties of concentrated systems of high polymers, 1 -10 such as concentrated solutions and melts, is one of the most important subjects of polymer science, both in the academic and industrial sense.polymer is lower than that for the linear polymer so long as molecular weight is not too high and that the steady-state compliance for the former is about ten times higher than that for the latter. Though the relaxation modulus or storage modulus for the star branch polymer is about the same as that of the corresponding linear polymer in the rubbery plateau region, the comb-shaped polymer has a relaxation modulus lower than the corresponding linear polymer in that region.Recently, it has become possible to prepare branched polymers having a well-controlled structure and narrow distribution of molecular weights, and a few measurements of the rheological properties of such samples have been carried out. One of these studies is the measurement of stress relaxation for comb-shaped polystyrenes by Fujimoto, et al.,11 and the other is our study of dynamic viscoelasticity for starshaped polystyrene. 12 These studies for branched polymers having different types of branching show that zero-shear viscosity for the branched * Present address: Sumitomo Chemical Co., 40,