Block copolymers solution properties

AZU Azuma, T., Tyagi, O.S., and Nose, T., Static and dynamic properties of block-copolymer solution in poor solvent I, Polym. J., 32, 151, 2000. 

Dubrovina, L. V Pavlova, S. -S. A. Ponomareva, M. A. Properties of poly (ary lateary lenesulfonoxide) block-copolymers solutions. High-Molecular Compounds. A, 1983, 25(7), 1536-1543. 

Kotaka, T., and Watanabe, H., Rheological and morphological properties of heterophase block copolymer solutions, in Current Topics in Polymer Science, Vol. II, Ottenbrite, R. M. Utracki, L. A., and Inoue, S.,Eds., Hanser-Verlag, Munich, 1987. 

Since rapid collection of erstwhile single cells can be brought about by the use of dielectrophoresis, and the shape of the mass of cells so formed is controlled by the shape of the electrodes, by the frequency of the field, and by the shape of the cells, it appeared worthwhile to see if the shapes so formed could be made more permanent, so as to prepare desired structures of the cellular aggregates. To this end, the gel-forming properties of a relatively nontoxic block copolymer solution in water were used. A concentrated aqueous solution of the block copolymer of polyethylene oxide and polypropylene oxide (PEO-PPO) is quite fluid at 0°C to about 5°C, but sets reversibly to a rather stiff gel at about 30-40°C. The PEO-PPO polymer solutions are reported to be relatively nontoxic to most organisms (Pluronic resin F-127), Wyandotte Chemicals Corp.). 

After presenting the fundamental equations in the preceding chapter we now consider their applications. Continuous thermodynamics is always important if thermodynamic properties or processes are influenced by distribution functions. From the practical point of view the liquid-liquid equilibrium is the most important aspect [29]. The following considerations are first restricted to systems containing random copolymers, especially one copolymer ensemble (which is characterized by a divariate distribution function), and one solvent A. Blends and block copolymer solutions are considered in Sects. 4 and 5. Generalizations to systems with more than one copolymer ensemble and/or more than one solvent are given in Sect. 3.2 (for solutions of random copolymers) and in Sect. 4.2 (for blends of random copolymers). 

Other applications of alcohol alkoxylates also include textile lubricants, agricultural chemicals, rinse aid formulations, and personal care products. Polyoxyethylene block copolymers exhibit properties similar to surfactants, such as the presence of micelles in aqueous solutions, micelle structure, and association number, and are therefore termed polymeric surfactants. These diverse subsets of nonionic surfactants are unique and offer several advantages in manufacturing, and they could be designed for specific uses and applications. A complete Surfactant Science Series volume dedicated to the chemistry, physicochemical properties, applications, and toxicity was published in 1996. Because of these beneficial attributes, alcohol ethoxylates and alcohol alkoxylates are the most important nonionic surfactants in terms of volume usage in consumer products. 

Upon dn ing from solution or treatment witli a nonsolvent such as ethanol most SELF polymer materials are converted to water stable products. Presumably, once induced to crystallize, the cohesion of the silklike blocks dominates the solubility properties of the block copolymer. Tbis property of ProLastin polymers allows them to be processed or formulated rith other compounds in aqueous, physiological solution and then converted to a water stable material by simply diying, lyophilizing, or treating the formulation wdth alcohol. 

Surface activity in 1,4-polyisoprene-polyacetylene, AB, block copolymer solutions was to be expected from the amphiphilic properties of such a diblock system with one moiety so insoluble because of the strong polyacetylene-polyacetylene attractive interactions. The present experiments allow access, for the first time, to some of the thermodynamic parameters of these interactions and give a structural model for the surface excess above and below the critical micelle concentration. This has been identified as about 10" moles/L for the lelated polymer 1,4-polyisoprene-polyacetylene (MW 8000 520) in toluene at 20 C using the drop weight method to determine surface tension. From ca. 10" molar to molar the surface tension drops by about 3.5% to a constant value of ca. 28.4 dyne cm at concentrations above 10 3 molar (ca. 1% w/w). Referring to Figure 3 we see that it is above ca 1% that a broad peak develops in the solution/solvent reflectivity ratio for 0.15 < k / < 0.25. The area per... 

Among the techniques employed to estimate the average molecular weight distribution of polymers are end-group analysis, dilute solution viscosity, reduction in vapor pressure, ebuUiometry, cryoscopy, vapor pressure osmometry, fractionation, hplc, phase distribution chromatography, field flow fractionation, and gel-permeation chromatography (gpc). For routine analysis of SBR polymers, gpc is widely accepted. Table 1 lists a number of physical properties of SBR (random) compared to natural mbber, solution polybutadiene, and SB block copolymer. 

Butadiene copolymers are mainly prepared to yield mbbers (see Styrene-butadiene rubber). Many commercially significant latex paints are based on styrene—butadiene copolymers (see Coatings Paint). In latex paint the weight ratio S B is usually 60 40 with high conversion. Most of the block copolymers prepared by anionic catalysts, eg, butyUithium, are also elastomers. However, some of these block copolymers are thermoplastic mbbers, which behave like cross-linked mbbers at room temperature but show regular thermoplastic flow at elevated temperatures (45,46). Diblock (styrene—butadiene (SB)) and triblock (styrene—butadiene—styrene (SBS)) copolymers are commercially available. Typically, they are blended with PS to achieve a desirable property, eg, improved clarity/flexibiHty (see Polymerblends) (46). These block copolymers represent a class of new and interesting polymeric materials (47,48). Of particular interest are their morphologies (49—52), solution properties (53,54), and mechanical behavior (55,56). 

Currently, more SBR is produced by copolymerizing the two monomers with anionic or coordination catalysts. The formed copolymer has better mechanical properties and a narrower molecular weight distribution. A random copolymer with ordered sequence can also be made in solution using butyllithium, provided that the two monomers are charged slowly. Block copolymers of butadiene and styrene may be produced in solution using coordination or anionic catalysts. Butadiene polymerizes first until it is consumed, then styrene starts to polymerize. SBR produced by coordinaton catalysts has better tensile strength than that produced by free radical initiators. 

AB diblock copolymers in the presence of a selective surface can form an adsorbed layer, which is a planar form of aggregation or self-assembly. This is very useful in the manipulation of the surface properties of solid surfaces, especially those that are employed in liquid media. Several situations have been studied both theoretically and experimentally, among them the case of a selective surface but a nonselective solvent [75] which results in swelling of both the anchor and the buoy layers. However, we concentrate on the situation most closely related to the micelle conditions just discussed, namely, adsorption from a selective solvent. Our theoretical discussion is adapted and abbreviated from that of Marques et al. [76], who considered many features not discussed here. They began their analysis from the grand canonical free energy of a block copolymer layer in equilibrium with a reservoir containing soluble block copolymer at chemical potential peK. They also considered the possible effects of micellization in solution on the adsorption process [61]. We assume in this presentation that the anchor layer is in a solvent-free, melt state above Tg. The anchor layer is assumed to be thin and smooth, with a sharp interface between it and the solvent swollen buoy layer. 

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