Polybutadiene blocks

Thermoplastic Elastomers. These represent a whole class of synthetic elastomers, developed siace the 1960s, that ate permanently and reversibly thermoplastic, but behave as cross-linked networks at ambient temperature. One of the first was the triblock copolymer of the polystyrene—polybutadiene—polystyrene type (SheU s Kraton) prepared by anionic polymerization with organoHthium initiator. The stmcture and morphology is shown schematically in Figure 3. The incompatibiHty of the polystyrene and polybutadiene blocks leads to a dispersion of the spherical polystyrene domains (ca 20—30 nm) in the mbbery matrix of polybutadiene. Since each polybutadiene chain is anchored at both ends to a polystyrene domain, a network results. However, at elevated temperatures where the polystyrene softens, the elastomer can be molded like any thermoplastic, yet behaves much like a vulcanized mbber on cooling (see Elastomers, synthetic-thermoplastic elastomers). 

Whilst, chemically, SBS triblocks are similar to SBR, for example they do not show measurable breakdown on mastication, they are seriously deficient in one respect, they show a high level of creep. This would indicate that the concept of all the styrene blocks being embedded in the domains with all of the polybutadiene blocks being in the amorphous matrix is rather too simplistic. It has also resulted in these materials not being used extensively in traditional rubber applications. One exception from this is in footwear, where blends of SBS and polystyrene have been used with noted success for crepe soles. 

Hydrogenated SBS triblock polymers have become increasingly important (Kraton G by Shell). With the original polybutadiene block comprised of 65% 1,4-and 35% 1,2-structures the elastomeric central block is equivalent to that of a high-ethylene ethylene-butene rubber. 

B = B 4, 1,4-polybutadiene block Bj 2, 1,2-polybutadiene block B y, medium vinyl (35-60%) polybutadiene block) I, 1,4-polyisoprene block. Selective hydrogenation this block not hydrogenated. 

Poly(styrene-fc-butadiene) copolymer-clay nanocomposites were prepared from dioctadecyldimethyl ammonium-exchanged MMT via direct melt intercalation [91]. While the identical mixing of copolymer with pristine montmorillonite showed no intercalation, the organoclay expanded from 41 to 46 A, indicating a monolayer intercalation. The nanocomposites showed an increase in storage modulus with increasing loading. In addition, the Tg for the polystyrene block domain increased with clay content, whereas the polybutadiene block Tg remained nearly constant. 

Figure 21.8 Incorporation of polybutadiene blocks Into growing polystyrene chain ...

We use polystyrene-Z>-polybutadiene block copolymers as the starting material with preformed polymer architecture. These polymers are comparatively cheap and easily accessible.1 For the present problems a series of narrowly distributed polystyrene-6-polybutadiene block copolymers with rather different molecular weights were synthesized via anionic polymerization (Figure 10.4, Table 10.1). As a test for the modification of technological products, a commercial triblock copolymer was also used. 

We chose the tt-bonds of the polybutadiene block as the functional groups to connect different side groups to the polymer block. A direct connection of side groups to the rr-bonds is difficult and leads to unstable products therefore, a two-step synthesis was employed. The first step is a conversion of the Jt-bonds into a more easily accessible species. This can be done by either hydroxylation (hydro-... 

Figure 10.4. Drawing of the polystyrene-b-polybutadiene block copolymers used for amphiphilic modification.

Table 10.1. Polystyrene- -Polybutadiene Block Copolymers Used as Starting Materials 1...

Therefore, at room temperature Fluoro-PSB-II a thermoplastic elastomer with a soft polymer phase (fluorinated block) and a hard phase (PS-block), similar to the parental polystyrene-6-polybutadiene block copolymer. Depending on the relative volume fraction of both components and the continuity of the phases, the resulting bulk material is rubbery or a high-impact solid. 

Styrolux is an example of a nanostructured polymer which is used in food packaging. It is a polystyrene-polybutadiene block copolymer where polymer chains are build up of alternating polystyrene and polybutadiene blocks. These blocks appear as dark lamellae in the TEM image due to the staining of the polybutadiene with OSO4. This structured nanoscale architecture of the pol5mier, which can be controlled during manufacture, allows the optimum combination of impact resistance and transparency. 

In a system of significant interest to the present works, Graillard, et al. [62] studied the ternary phase diagrams of the systems polybutadiene-styrene-polystyrene and polybutadiene-block-polystrene-styrene-polystyrene. They showed that the presence of block copolymer increased the miscibility of the two poljrmers, as the styrene component polymerized. Similar effects are probable in the IPN s, as compared with the corresponding blends. 

The block copolymer made from connecting blocks of PS with blocks of polybutadiene illustrates another use of soft and rigid or hard domains in TPEs. The PS blocks give rigidity to the polymer, while the polybutadiene blocks act as the soft or flexible portion. The PS... 

This ABA block copolymer consists of stiff polystyrene (PS) and resilient polybutadiene blocks. The domains of these TPEs have characteristic Tt values of 100 and —80 C, respectively. The polybutadiene blocks retain their flexibility at low temperatures, and the polystyrene blocks lose their stiffness when the polymer is heated above 110 C. A related thermoplastic is a transparent AB block copolymer of styrene and butadiene (K-resin). 

Because of the coalescence of the bands belonging to the polyacrolein and polybutadiene blocks, the (1,4) and (3,4) units of acrolein cannot be estimated separately. The results of the acrolein microstructure in the PABj4 and PAB15 block polymers are summed up in Table 3. 

Styrene-1,3-butadiene-styrene (SBS) or styrene-isoprene-styrene (SIS) triblock copolymers are manufactured by a three-stage sequential polymerization. One possible way of the synthesis is to start with the polymerization of styrene. Since all polystyrene chains have an active anionic chain end, adding butadiene to this reaction mixture resumes polymerization, leading to the formation of a polybutadiene block. The third block is formed after the addition of styrene again. The polymer thus produced contains glassy (or crystalline) polystyrene domains dispersed in a matrix of rubbery polybutadiene.120,481,486... 

Douy has synthetized polystyrene-polybutadiene (SB) block copolymers of various molecular weights and compositions66 by anionic polymerization, under high vacuum, in tetrahydrofuran dilute solution (less than 5%), at low temperature (—70 °C), and with cumyl potassium as initiator. Resulting from the polymerization conditions, the microstructure of the polybutadiene block is 90% 1,2 and 10% 1,4. 

In the case of the lamellar structure, the increase of the polybutadiene content XB of the copolymer and of the molecular weight MB of the polybutadiene block entails an increase of the total thickness d of a sheet and of the thickness dB of the polybutadiene layer Fig. 10 illustrates this behaviour for copolymer SB 33 and SB 34 which contain, respectively, 39.8% and 50.2% polybutadiene. The values of the thickness dA of the polystyrene layer and of the specific surface X are not independent of the polybutadiene content of the copolymer as it is illustrated by Fig. 11. 

In the case of the hexagonal structure the increase of the molecular weight MB of the polybutadiene block is accompanied by an increase of both the distance D between the axis of two neighbouring cylinders and the diameter 2 R of the polybutadiene cylinders. Figure 12 illustrates these results in the case of copolymers SB 31 and SB 32 whose respective molecular weights of the polybutadiene blocks are 12400 and 21500. 

Block copolymers of butadiene and vinyl-2-naphtalene (BVN) have been synthetized and studied by the same techniques as polybutadiene-poly(a-methyl styrene) and polystyrene-polybutadiene block copolymers86,87. They exhibit the same structures, namely lamellar and cylindrical as SB and BMS block copolymers86,87. ... 

The dynamic viscoelasticity and the thermal behaviour of films of Thermoelastic 125 cast from solutions in four solvents - toluene (T), carbon tetrachloride (C), ethyl acetate (E), and methyl ethyl ketone (M) — have been studied by Miyamato133 The mechanical loss tangent (tan 8) and the storage modulus E dependences exhibit two transitions at —70 °C and 100 °C which have been attributed to onset of motion of polybutadiene and polystyrene segments, respectively. The heights of the polybutadiene peaks on tan 6 curves decrease in the order C > T > E > M, while for polystyrene the order is reversed C < T < E < M. These phenomena have been related to the magnitude of phase separation of the polystyrene and polybutadiene blocks. 

SIS and SI copolymers behave similarly and the addition of a second S block to an SI copolymer has the same effect on the chain conformation like the addition of a polybutadiene block to a BS copolymer (cf 92 ). 

Krappe U, Stadler R et al (1995) Chiral assembly in amorphous ABC triblock copolymers. Formation of a helical morphology in polystyrene-block-polybutadiene-block-poly(methyl methacrylate) block copolymers. Macromolecules 28 4558 1561... 

Further exploration [57] into the variation in properties available in the fully saturated poly(styrene-bl-butadiene-bl-styrene) materials focused on modifying the vinyl content in the polybutadiene block. Exploring practical elastomeric properties such as rebound and modulus, this work showed plainly that the level of vinyl in the polybutadiene block dominated the room temperature elastomeric properties of the block copolymer with a preferred level of about 40mol% percent 1,2-microstructure. 

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