N. Nakajima

Degree of swelling and extent of crowding of flexible polymer coils in low concentration region

Abstract At infinite dilution, a flexible polymer chain is an isolated coil swollen with solvent. The situation may be treated in a manner analogous to the swelling equilibrium of a lightly crosslinked network. From the thermodynamic relation, the degree of swelling of the polymer coil may be estimated (1, 2). This value, the degree of chain extension, was found to be somewhat larger than that estimated from intrinsic viscosity. This finding was interpreted to mean that the chain segments in the periphery of the coil are more extended than the average coil extension (1). In the present work the dilute but finite concentration range was examined. In this case a polymer coil is in equilibrium with solvent containing polymer chains of the same kind. As the concentration is increased, the excess extension of the chain segments in the periphery of the coil diminishes. With further concentration increase, the polymer coil continues to decrease in size to the size defined by the theta condition, when the free so...

Nonuniform extension of chain segments of a polymer coil in dilute solution

Abstract An isolated, flexible polymer chain in dilute solution assumes a random configuration. In reality such a polymer coil is not completely random, because an excluded volume effect requires a modification from randomness. In addition, the coil placed in a better solvent is more expanded than that in a poor solvent. In other words, the polymer chain segments in a better solvent are more extended, compared to those in a neutral solvent. In the present study we have discovered an indication that the chain segments lying on the periphery of the coil are more extended than those in the interior. This discovery has been made in the course of relating intrinsic viscosity to thermodynamic interaction between polymer and solvent. The resulting relationship provides a means of evaluating the thermodynamic interaction parameter from the measured value of intrinsic viscosity, if the molecular weight of the polymer, its intrinsic viscosity in a neutral solvent, and the degree of excess extension of chain segment...

Contraction of swollen coil of flexible polymer chain below theta temperature

Abstract In our previous study on thermodynamic equilibrium at infinite dilution, chain segments at the periphery of a polymer coil were shown to be more extended than the average expansion of the coil. This is because such segments are in contact with pure solvent, whereas inside the coil there is a concentration of the segments. In a subsequent work examining the low concentration range, this excess extension of the segments was shown to diminish as the concentration was increased. Having more and more neighboring coils, the chain segments at the periphery of the coil have less and less excess extension, because the concentration difference between the inside and the outside of the coil decreases. In the present work the range below the theta temperature is examined; for polymers of finite molecular weights there are soluble ranges including partial and critical miscibility. When the limits of miscibility are approached either by lowering the temperature at a constant concentration or by increasing conc...

Relationship between dynamic mechanical property and thermodynamic interaction parameter of concentrated polymer solutions

Abstract The use of concentrated polymer solutions is one of the basic techniques in the application of polymers. They may be coating materials, plasticized polymers, and oil-extended rubber. In these applications the solubility relation is one of the key requirements. The polymer-solvent interaction is expected to influence the mechanical property of the mixture. It is the intent of this study to explore how the dynamic mechanical property is affected by the change of thermodynamic interaction parameter in concentrated polymer solutions. The theoretical development is based on several assumptions: (1) a polymer chain in the amorphous state and in its own environment assumes unperturbed configuration; (2) a polymer chain in a good solvent (poor) is expanded (contracted) relative to the unperturbed dimension; (3) the expanded (contracted) chain configuration results in the higher (lower) entanglement density; (4) both expanded and contracted chains store an elastic energy, the magnitude of which may be est...

Second Plateau Observed in Solutions of Gum Rubbers Containing Gels

Viscoelastic behavior of solutions of rubbers containing macro‐gel and micro‐gel were examined. Macro‐gel is a giant molecule of the rubber having many long branches. Micro‐gel is also a giant molecule but a cross‐linked particle. The sample of macro‐gel was butadiene‐acrylonitrile copolymer (NBR) and the solvent was a plasticizer, dibutylphthalate (DBP). The latter was polyethylacrylate (ACM) in diethylphthalate (DEP). Both rubbers contained about 70% gel, which swelled in the solvent. The rubber concentration was 20%, 10%, and 5%. The frequency range was from 10−2 to 102 rad/s. Measurements were made at room temperature. At 20% and 10% concentration, the storage modulus, G′, and the loss modulus, G″, had the following relation; with NBR‐DBP, G′ was slightly lower than G″ and with ACM‐DEP they were about equal. The gels in the former solution had a degree of swelling lower than did those in the latter. The behavior persisted over the entire range of the frequency. The swollen gel particles are touching each other or almost so. At 5% concentration G′ and G″ curves showed shapes similar to those of the rubber plateau. However, the concentration is much too low to expect to see the rubber plateau. The plateau appears to be the manifestation of the deformation of the gel particle. While the bulk rubber behavior is distinctly different between macro‐gel–containing and micro‐gel–containing rubber, the gel type is not distinguished in the behavior of the semi dilute solution.

Polar Association in Polyethylacrylate Observed at Small Shear and Large Elongation: Effect of Concentration of Polar Solvent*

Polyethylacrylate is a polar rubber that exhibits strain-induced association in elongation, a behavior quite similar to strain-induced crystallization of crystallizable rubbers. Two questions are considered: whether or not strain-induced association is suppressed when the polymer is diluted with polar solvents and whether or not some extent of polar association is present even in the quiescent state and can be detected under small shear deformation. Dynamic mechanical measurements were performed in shear in the linear region of viscoelastic properties for a “gel-free” rubber plasticized with dibutyl-phthalate (DBP). The elongational data were linearized according to a previously developed linearization scheme. The linearized elongation modulus–time curve was in good agreement with the shear modulus–time curve, with a factor of 3, for 15% and 20% DBP. This is similar to the case for nonpolar elastomers. Therefore, at these concentrations, there is no polar association. For 0% and 10% DBP, the elongational curve was significantly higher than three times the shear curve, indicating that strain-induced polar association did occur. The rubbery plateau modulus observed in the shear measurements hardly changed from 0% to 10% DBP. On further dilution, it decreased as expected. At 10% DBP, the polar association appears to be enhanced. When the polymer is diluted beyond 10% DBP, there is no indication of the association under both strained and unstrained condition.

Time-and strain-history-dependent dynamic moduli of semidilute solutions of nitrile rubber containing multiple-branched molecules

Abstract A new type of time-dependent and strain-history-dependent viscoelasticity was discovered in semidilute polymer solutions. Dynamic moduli G′ and G″ of 20% and 10% nitrile butadiene rubber (NBR) solutions were recorded as a function of time while oscillatory shear deformations were maintained. The moduli decrease with time was observed only at lower frequencies. The time dependence of G′ was more pronounced than that of G″. At a higher temperature, the time dependence was extended toward higher frequencies also, and the time dependence became stronger. Lowering the concentration of solution gave a similar effect as increasing temperature. After the cessation of oscillations, a slow recovery was observed. The recovery was somewhat faster at the higher temperature. The time-dependent moduli and their recovery were explained by the change and recovery of structures associated with long branches and gels in the NBR. The structure change occurred at higher frequencies also, but it was not observed durin...

Large shear deformation and estimation of deformational memory for polyethylacrylate rubbers

Rotational shear was imposed on two samples of polyethylacrylate rubber with differing types and amounts of gel in order to observe the stress-growth and subsequent quasi-steady state. The deformation rate was low, 0.02 s -1 , to avoid slippage at the sample-instrument interface. The stress-growth behavior was represented by a strain-time correspondence of the form given by η + = (σ/e)αt, where the symbols are the stressing viscosity, n + , shear stress, σ, shear strain, e, the corresponding extension ratio, α, and time, t. Eventually the growth of strain deviates from that predicted from the linear behavior at a point before the quasi-steady state is reached. The magnitude of shear strain at this point is estimated to be 0.36 to 2.6, depending upon the sample and temperature. Upon continued shearing, this strain memory gradually changes to a level of 0.66 to 1.35. These values were estimated from stress relaxation measurements after cessation of the quasi-steady state. The sample containing about 10% macrogel displayed a higher stress level and a larger magnitude of strain memory; this may be explained on the basis of an extensive entangling of long branches. The other sample, containing 70% microgel, gave a lower stress level and a smaller strain memory. The microgel is a crosslinked particle and less effective in entangling with its neighbors.

Homogenization in mechanical mixing involving polyvinyl chloride. II. Effect of different types of polymers on breakdown of PVC particulate structure and mixing mechanism

Abstract The process of mixing PVC with other polymers, including an examination of how these polymers contribute to the breakdown of the particulate structure of PVC, is described. The polymers were an immiscible nitrile rubber containing 22% acrylonitrile (NBR-22) and two miscible polymers, poly-e-caprolactone (PCL) and copolyester thermoplastic elastomer (trademark Hytrel). The mixing of PVC and NBR-30, as investigated in the previous paper (Part I), was also considered as a reference. The overall progress of mixing for the three systems (i.e., PVC/NBR-22, PVC/PCL, and PVC/Hytrel) was similar to that for PVC/NBR-30; the removal of skins was followed by breakdown of PVC particles. However, the rate of breakdown differed widely from system to system, depending on the inherent thermodynamic and viscoelastic nature of the individual polymers which served as the medium for stress transfer to the PVC particles. Molecular mixing, which provides a strong interfacial adhesion between PVC and the component polym...

Homogenization in mechanical mixing involving polyvinyl chloride. I. Skin removal and breakdown of PVC particulate structure during mixing with miscible polymer

Abstract Suspension-polymerized polyvinyl chloride (PVC) is a powder consisting of particles 100 ∼ 150 μm in diameter, called grains. The grains have a unique hierarchical structure consisting of a skin and internal tight agglomerates of about 10 μm diameter. The agglomerate consists of primary particles of about 1 μm diameter, which in turn consist of domains of about 0.1 μm. The domain is composed of microdomains of about 10 nm. In this work, mechanical mixing of PVC with a miscible polymer, nitrile rubber containing 30% acrylonitrile (NBR-30), was conducted in an internal mixer and the significant events in the mixing period of 150 sec were examined with scanning and transmission electron microcopes. The process of mixing was very different from that of two amorphous polymers in that the skins of the PVC grains were first peeled off and then the agglomerates were broken down to the subsequent smaller particles, eventually becoming microdomains dispersed in the rubber. The NBR was found to be an effecti...