Styrenic block copolymers in solution

1 Poly(styrene)-poly(lsoprene) and polystyrene-poly(butadiene) block copolymers 

At higher shear rates, Watanabe and Kotaka (1983) observed thixotropy, i.e. stress decay increasing as a function of shear rate, in PS-PB diblocks in dibutyl phthalate (DBP), which is a selective solvent for PS.The fact that the flow crossed over from plastic to viscous non-Newtonian on increasing the shear rate indicated the breakdown of the micellar lattice structure, rather than of the individual micelles. This was confirmed by parallel measurements on a cross-linked PB-PS system, where stress decay and recovery were also observed. Thus the 

Gast and co-workers (Gast 1996 McConnell et al. 1993,1995) have used SAXS to probe ordered micellar structures in PS-PI block copolymers dissolved in decane, which is a preferential solvent for PI. They determined the form factor of a range of diblocks by performing SAXS in dilute solution (McConnell et al. 1993). The same diblocks in more concentrated solutions were found to form cubic micellar structures, and the gelation (micellar disorder-order) transition on increasing concentration was determined. Remarkably, both BCC and FCC struc- 

In subsequent work, ordering in solutions of the same matched diblock and triblock spanning a broader range of volume fractions, 0.1 j 0.4, was explored (Hamley et al. 1997). For j) 0.2, the rheological response was found to be liquid-like and SAXS showed that there was no inter-micellar order in the liquid. Above a crossover concentration f 0.2, ordering of micelles was shown by the presence of a structure factor peak. The ordered micellar structure, identified as hexagonal-packed cylinders for more concentrated solutions, persisted up to an order-disorder transition located from a discontinuity in the 

For a selective solvent, a scaling relation for the domain spacing in the ordered lamellar phase d (l/T)1 3 was obtained from SAXS experiments on a PS-PB 

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Because the essentials of micellization have been discussed in depth for poly(oxyethylene)-containing block copolymers, we do not describe experimental studies on styrenic block copolymers in solution in great detail. Instead, the features are summarized in tabular form (see Tables 3.1-3.4). Experiments on ionic block copolymers containing polystyrene are discussed in Section 3.6.2. 

PVA in, 25 617 setting speed of, 25 579-580 smectites application, 6 697t solution, 1 532-534 structural, 1 534-545 styrenic block copolymers in, 24 714 use of latex in, 14 711-712 vinyl acetate polymers in, 25 578-583 viscosity of, 25 581 water-borne, 25 475 Adhesive systems, microencapsules in, 16 460... 

This chapter is concerned with these phases, where a substantial amount of the experimental work has been on poly(oxyethylene)-containing block copolymers in aqueous solution. From another viewpoint, the phase behaviour in concentrated block copolymer solutions has been interpreted using the dilution approximation, which considers concentrated solution phases to be simply uniformly swollen melt phases. Work on styrenic block copolymers in concentrated solution has been interpreted in this framework. There is as yet no unifying theory that treats ordered micellar phases and diluted melt phases coherently. 

This chapter is concerned with experiments and theory for semidilute and concentrated block copolymer solutions.The focus is on the thermodynamics, i.e. the phase behaviour of both micellar solutions and non-micellar (e.g. swollen lamellar) phases. The chapter is organized very simply Section 4.2 contains a general account of gelation in block copolymer solutions. Section 4.3 is concerned with the solution phase behaviour of poly(oxyethylene)-containing diblocks and tri-blocks. The phase behaviour of styrenic block copolymers in selective solvents is discussed in Section 4.4. Section 4.5 is then concerned with theories for ordered block copolymer solutions, including both non-micellar phases in semidilute solutions and micellar gels. There has been little work on the dynamics of semidilute and concentrated block copolymer solutions, and this is reflected by the limited discussion of this subject in this chapter. 

The results of light-scattering studies [D. Rahlwes and R. G. Kirste, Makromol. Chem., 178,1793 (1977)] for A = 4360 >1 on a styrene/a-methyl styrene block copolymer in toluene solution were as follows ... 

Block copolymers in solution form micelles when one block is solvated and the other is not. Spin coating of a solution of poly(styrene-fi-4-vinylpyridine) and... 

ESK Eskin, V.E., Grigorev, A.I., Baranovskaya, LA., and Rudkovskaya, G.D., Conformational properties of styrene-vinylpyrrolidone block copolymers in solution, Vysokomol. Soedin., Ser. A, 20, 55, 1978. 

Two types of catalyst systems are used, the so-called Ziegler-Natta types and those based on alkyl lithium. Plants using the latter are often multipurpose producing polybutadiene, solution SBR and styrenic block copolymers in quantities depending on market demands. This makes it difficult to estimate the capacities for each type with any accuracy. For this reason, the plant capacities are expressed in terms of solution rubber in general. 

Depending on the concentration, the solvent, and the shear rate of measurement, concentrated polymer solutions may give wide ranges of viscosity and appear to be Newtonian or non-Newtonian. This is illustrated in Eigure 10, where solutions of a styrene—butadiene—styrene block copolymer are Newtonian and viscous at low shear rates, but become shear thinning at high shear rates, dropping to relatively low viscosities beyond 10 (42). The... 

Of the amorphous block copolymers, styrenic block copolymers are the vast majority. These are synthesized anionically in solution, with butyl lithium commonly employed as the initiator [4]. There are three processes for this polymerization ... 

Weiss et al. [75] have synthesized Na and Zn salt of sulfonated styrene(ethylene-co-butylene)-styrene triblock ionomer. The starting material is a hydrogenated triblock copolymer of styrene and butadiene with a rubber mid-block and PS end-blocks. After hydrogenation, the mid-block is converted to a random copolymer of ethylene and butylene. Ethyl sulfonate is used to sulfonate the block copolymer in 1,2-dichloroethane solution at 50°C using the procedure developed by Makowski et al. [76]. The sulfonic acid form of the functionalized polymer is recovered by steam stripping. The neutralization reaction is carried out in toluene-methanol solution using the appropriate metal hydroxide or acetate. 

Much recent work on micellization in block copolymers has been focussed on this industrially important type of polymer. We therefore describe experiments on micellization in aqueous solutions of poly(oxyalkylene) diblocks and triblocks in some detail. This serves to illustrate many of the important features of micellization of block copolymers, also observed in other systems such as the styrenic block copolymers covered in the following section. 

Poly (ethy lene oxide)/poly (styrene) block copolymers A comprehensive study of crystallization from solution in PS-PEO diblocks was performed in the late 1960s and early 1970s (Gervais and Gallol 1973a,b Lotz and Kovacs 1966 Lotz et al. 1966). 

In a three-necked flask equipped with stirrer, reflux condenser, and N2 inlet, 200 grams of a 1% solution of carboxylated styrene-butadiene block copolymer in o-dichlorobenzene and 2 grams TiOo were stirred at various temperatures for 3 hours. (Typical temperatures in this treatment were 110°, 150°, and 178°C.) After the heat treatment the Ti02 was isolated from the block copolymer solution by centrifuging for 1-2 hours at 2,000-2,200 rpm. After decanting the supernatant solution, the solid particles were washed with solvent and dried in vacuo for about 16 hours at 50°C. 

The formation of block copolymers from styrene-maleic anhydride and acrylic monomers was also indicated by pyrolytic gas chromatography and infrared spectroscopy. A comparison of the pyrograms of the block copolymers in Figure 7 shows peaks comparable with those obtained when mixtures of the acrylate polymers and poly(styrene-co-maleic anhydride) were pyrolyzed. A characteristic infrared spectrum was observed for the product obtained when macroradicals were added to a solution of methyl methacrylate in benzene. The characteristic bands for methyl methacrylate (MM) are noted on this spectogram in Figure 8. 

Monofunctional Initiators. AB, ABA, and multiblock copolymers can be synthesized by initiation of one monomer with a monofunctional initiator like n-butyl lithium. When the first monomer has been reacted, a second monomer can be added and polymerized. This monomer addition sequence can be reversed and repealed if the anion of each monomer sequence can initiate polymerization of the other monomer. The length of each block is determined by the amount of the corresponding monomer which was provided. Styrene-isoprene-styrene block copolymers can be made by this method by polymerizing in benzene solution and adding the styrene first. Addition of a small amount of ether accelerates the slow attack of dienyl lithium on styrene. 

Symmetric SBS block copolymers covering a wide range of compositions and molecular weights have been synthetized and studied by the same techniques as symmetric BSB copolymers In solution in methylethyl ketone, methyl methacrylate, vinyl acetate, or styrene they exhibit a behaviour similar to that of SB and BSB copolymers with respect to the effect of temperature, concentration, and postpolymerization of the solvent. The effect of the molecular weight of the soluble and insoluble blocks on the geometrical parameters of the hex onal and lamellar structures is however different for BSB and SBS copolymers. For SBS copolynKrs, there is a reciprocal interaction between soluble and insoluble blocks. 

For completeness it should be pointed out that many interesting morphologies of the type described above can be obtained by polymerizing a solution of AB or ABA block copolymers in styrene monomer, analogous to the process of HIPS production in which polybutadiene homopolymer is the dissolved species. This approach has been described in detail by Echte... 

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