Polybutadiene diblock copolymer

Fig. 7a, b. PMIM-image of (a) a poly-p-bromostyrene surface [118], (b) a PS/polybutadiene diblock copolymer, PS-b-PB, at approximately 100 fold magnification. The lateral resolution is of the order of 1 pm while the height resolution is of the order of 0.6 nm. The root-mean-square roughness averaged over the area shown is 0.8 nm in (a) close to the resolution limit of the technique. It is much larger (10 nm) in (b) due to the formation of steps after annealing. The scale in z-direction in (a) and (b) is different by a factor of 7... 

Figure 14. Gel permeation chromatograms of polystyrene and polystyrene-polybutadiene diblock copolymer prepared with Ba-Mg-Al. Conditions solvent, cyclohexane 50° C.

In analogy to lipids, amphiphilic block copolymers, i.e., macromolecules composed of at least one hydrophilic and one hydrophobic, covalently linked, polymer chains can form in aqueous solutions vesicles the so-called polymersomes. Generally, in self-assembling copolymer solutions, a rich diversity of morphologies is possible. An overview of the various factors important for vesicle formation, including copolymer architecture, presence of additives, solvent composition, and temperature, is given in [19]. To illustrate polymersome structures we reproduce from [21] on the top row of Fig. 2 cryo-TEM images of vesicles formed by 1.0 wt % aqueous solution of PEO- -PBD (PEO, polyethylene oxide PBD, polybutadiene) diblock copolymer for three different sizes of the PEO and PBD blocks. 

Cycloolefin macromonomers have been recently used in ring-opening metathesis polymerization reactions to manufacture block and graft copolymers of novel macromolecular architectures [84]. For this purpose, a- and co-norbornenyl-polybutadiene macromonomers, a-NBPB (R = CH2) and co-NBPB (R = COO), were reacted in the presence of molybdenum alkylidene complex, Mo(NAr)(CHtBu)(OtBu)2, to form polynor-bornene-polybutadiene diblock copolymers (117), with comb-like structure [85] [Eq. (49)]. 

Sehwier CE, Argon AS, Cohen RE. Crazing in polystyrene-polybutadiene diblock copolymers containing cylindrical polybutadiene domains. Polymer 1985 26(13) 1985—1993. 

Recently, urea was found to form inclusion complexes with poly(e-caprolactone)-polybutadiene diblock copolymer [20]. 

A diblock copolymer, 71% polyisoprene (1) by weight and 29% polybutadiene (B), was blended in different proportions into a 71%-29% mixture of the individual homopolymers. The loss tangent was measured as a function of temperature for various proportions of copolymer. Two peaks are observed ... 

Table 1 lists some of the homopolymers and diblock copolymers which have been employed in our experimental investigations (1-8). Particular emphasis has been placed on blends containing 1,4 polybutadiene (1,4B). In one case, 1,4B was blended with various amounts of 1,2 polybutadiene (1,2B) and the corresponding 1,2B/1,4B diblock copolymer. A second major set of samples was constructed from various combinations of 1,4B and cis 1,4 polyisoprene (1,41) and 1, 41/1,4B diblock copolymers. A large number of ternary blends were studied, the preponderence of which contained either 25%, 50% or 75% (by weight) of a selected diblock copolymer, the remainder of the blend being comprised of one or both of the corresponding homopolymers. Homopolymer blends (0% diblock) and the pure copolymers (100% diblock) were also studied in detail. 

As an example of blends with attractive interactions, Fig. 65 shows a superstructure in which interactions between methacrylic acid groups and pyridine side groups of a polystyrene-fc-polybutadiene-fo-poly(f-butyl methacry-late-staf-methacrylic acid) (PS-b-PB-b-P(MAA-sfaf-fBMA)) triblock quater-polymer and a PS- -P2VP diblock copolymer lead to a wavy lamellar structure with cylinders from mixed P2VP and P(MAA-sfaf-fBMA) blocks [194],... 

Table 19.3 Typical reaction conditions for the hydrogenation of polybutadiene (PB), styrene-butadiene diblock copolymer (SB), styrene-butadiene-styrene triblock copolymer (SBS) and nitrile butadiene rubber (NBR).

The most simple diblock copolymers are linear chains, in which one part of the chain consists of one type of monomer, say polystyrene (PS), and the other one of another type, say polybutadiene (PB), as illustrated in Figure 14. PS and PB usually phase separate at low temperatures however, because of their chemical connectivity, block copolymers cannot unmix on a macroscopic scale. They can only phase separate on a microscopic scale, the size of which is determined by the length of the polymers. 

It is interesting to note that soft segments in the diblock copolymer shown above is the hydrogenated 1,2 polybutadiene. The reason for the rubber characteristic of polybutadiene 1,2 is the presence of the chiral carbon carrying the vinyl units-. This assymmetric carbon is not altered by hydrogenation since the vinyl group is on the side chain of polymers. Therefore, the final product is... 

The experimental studies on phase behavior and pattern formation reviewed here have been done on substrate-supported films of cylinder-forming polystyrene- foc -polybutadiene diblock (SB) [36, 43, 51, 111-114] and triblock (SBS) [49, 62, 115-117] copolymers (Table 1), lamella-forming polystyrene- /ocfc-poly(2-vinyl pyridine) diblock copolymers (SV) [118, 119] and ABC block terpolymers of various compositions [53, 63, 120-131], In simulation studies, a spring and bid model of ABA Gaussian chains has been used (see Sect. 2) [36,42, 58, 59],... 

The morphologies of polystyrene-F-polybutadiene (PS-F-PBD) diblock copolymers confined in a nanopore were observed by Shin and Xiang (Shin et al., 2004), in which a lot of attentions were paid to the layer number of the concentric cylinder barrel structure as a function of the nanopore radius. In this work, the symmetrical and asymmetrical... 

The comparison of BS and symmetric BSB copolymers derived from the BS polymer by addition of a B block identical to the first one has demonstrated that the addition of a third block to a diblock copolymer achieves a stretching of both the polybutadiene and the polystyrene chains92. ... 

Viscoelastic Properties of Homopolymers and Diblock Copolymers of Polybutadiene and Polyisoprene... 

Three diblock copolymers of cis-1,4 polyisoprene (IR) and 1,4-polybutadiene (BR) have been studied in dynamic mechanical experiments, transmission electron microscopy, and thermomechanical analysis. The block copolymers had molar ratios of 1/2, 1/1, and 2/1 for the isoprene and butadiene blocks. Homopolymers of polybutadiene and polyisoprene with various diene microstructures also were examined using similar experimental methods. Results indicate that in all three copolymers, the polybutadiene and polyisoprene blocks are essentially compatible whereas blends of homopolymers of similar molecular weights and microstructures were incompatible. 

Figure 2. Transmission electron micrographs of (a) a blend of polybutadiene (25 vot %) and polyisoprene (75 wt %) (b) polyisoprene homopolymer (c) diblock copolymer 2143. Magnifications as indicated.

The ruthenium catalyst RuCl2(= CHPh)(PCy3)2 is able to promote both alkene metathesis polymerization (ROMP) and atom transfer polymerization (ATRP) [80,81]. The bifunctional catalyst A was designed to promote both ROMP of cyclooctadiene (COD) and ATRP of methyl methacrylate (MMA). Thus, catalyst A was employed to perform both polymerizations in one pot leading to diblock polybutadiene/polymethylmethacrylate copolymer (58-82% yield, PDI = 1.5). After polymerization the reaction vessel was exposed to hydrogen (150 psi, 65 °C, 8h), under conditions for Ru(H2)(H)Cl(PCy3)2 to be produced, and the hydrogenation of diblock copolymer could attain 95% [82] (Scheme 36). 

A detailed study of SB diblock copolymers and diblock/homopolymer blends was conducted in the range of composition in which the polybutadiene cylindrical morphology prevails Stress-strain experiments on a series of samples revealed dramatically varying behavior from essentially brittle response to substantial and attractive levels of toughness. Figures 2a to 2d provide representative stress-strain curves for the initial morphologies shown in Figs. 3a-3d. Table 1 provides the relevant molecular level information for these blends. 

Figure 4.27 Traiumission electron micrographs of a mixture of a star diblock copolymer (polybutadiene-polystyrene) with a homopolymer (polystyrene). The upper EM images show mesh layers viewed end-on. The lower image shows the mesh sheets viewed from above, revealing the dense network of pores in the layers, so that the sheets are in fact a filigree of interconnected tunnels. The large-scale dark (one marked A) and bright (B) fringes are due to variations in the thickness of the specimen only. Pictures reproduced witti permission from [48].

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