Polystyrene-isoprene

Triblock copolymers, as shown in Fig. 5.8 d), comprise a central homopolymer block of one type, the ends of which are attached to homopolymer chains of another type. As with other block copolymers, the components of triblocks may be compatible or incompatible, which will strongly influence their properties. Of particular interest are triblocks with incompatible sequences, the middle block of which is rubbery, and the end blocks of which are glassy and form the minor phase. When such polymers phase-segregate, it is possible for the end blocks of a single molecule to be incorporated into separate domains. Thus, a number of rubbery mid-block chains connect the glassy phases to one another. These materials display rubber-like properties, with the glassy domains acting as physical crosslinks. Examples of such materials are polystyrene/isoprene/polystyrene and polystyrene/polybutadiene/polystyrene triblock copolymers. 

Literature quotes several types of di- or triblock precursor copolymers for further generation of meso- and nanoporosities [49] poly(4-vinylphenyl-dimethyl-2-propoxysilane)-b-polyisoprene-b-poly(4-vinylphenyl-dimethyl-2-propoxysilane) (PPSPI-PPS), polystyrene (PS)-polybutadiene (PBD) or polystyrene-isoprene (PS-PI),... 

Polystyrene-isoprene Order transition Dynamic mechanical spectroscopy 116... 

Widmaier and Meyer [256] studied the structure of an ABA polystyrene-isoprene block copolymer as a function of temperature by osmium tetroxide staining thin cast films. Hsiue and Yang [257] studied the morphology and properties of a-methylst3n ene-butadiene diblock copolymer films cast from several solvents. Films at a 0.1% concentration were cast on water and stained with 2% osmium tetroxide solution for 1 h. The microstructure was shown to differ for films cast from different solvents as there is a pol)nner-... 

Fig. 1.11 Small angle X-ray scattering of a series of polystyrene-isoprene diblocks (Hashimoto et al. 1980)...

Previous work by Ha and Thomas [37] provided the inspiration for the above work. The block copolymer for this work was polystyrene-isoprene-polystyrene (Vector 4411-D from Dexco Polymers) with a molecular weight of 18000 for the styrene blocks and 44000 for the... 

There are several types including polyester (Hytrel by Du Pont Co.), polystyrene-butadiene—polystyrene block copolymers (Kra-ton —KRATON Polymers U.S LLC., www.kraton. com), polystyrene—isoprene—polystyrene block copolymers (Solprene —Dynasol Elastomers, http // dynasolelastomers.com/), polyolefin (TPR thermoplastics rubber by Uniroyal, Inc.), and polyurethane. 

Styrene-Butadiene-Styrene Block Copolymers. Styrene blocks associate into domains that form hard regions. The midblock, which is normally butadiene, ethylene-butene, or isoprene blocks, forms the soft domains. Polystyrene domains serve as cross-links. 

As we did in the case of relaxation, we now compare the behavior predicted by the Voigt model—and, for that matter, the Maxwell model—with the behavior of actual polymer samples in a creep experiment. Figure 3.12 shows plots of such experiments for two polymers. The graph is on log-log coordinates and should therefore be compared with Fig. 3.11b. The polymers are polystyrene of molecular weight 6.0 X 10 at a reduced temperature of 100°C and cis-poly-isoprene of molecular weight 6.2 X 10 at a reduced temperature of -30°C. 

Polymer-polymer fractal interfaces may result from the interdiffusion of monomers or of polymers themselves. Koizumi et al. [31] annealed the interface between polystyrene and a styrene-isoprene diblock polymer at 150 C and showed extensive roughening of the interface by mutual interdiffusion on a micron scale (Fig. 8). 

Fig. 8. Electron micrograph.s showing the interface between polystyrene (top) and a styrene-isoprene diblock polymer (bottom), annealed at I50°C for the times shown. Isoprene units are stained and appear black) (reproduced from [31], copyright American Chemical Society).

Block copolymer chemistry and architecture is well described in polymer textbooks and monographs [40]. The block copolymers of PSA interest consist of anionically polymerized styrene-isoprene or styrene-butadiene diblocks usually terminating with a second styrene block to form an SIS or SBS triblock, or terminating at a central nucleus to form a radial or star polymer (SI) . Representative structures are shown in Fig. 5. For most PSA formulations the softer SIS is preferred over SBS. In many respects, SIS may be treated as a thermoplastic, thermoprocessible natural rubber with a somewhat higher modulus due to filler effect of the polystyrene fraction. Two longer reviews [41,42] of styrenic block copolymer PSAs have been published. 

The reactivities of substituted monomers are different from those of the unsubstituted ones. For example, in crosspropagation an electron donating methyl group introduced to the C = C bond of a vinyl monomer makes it less reactive in anionic copolymerization, while it increases its reactivity in a cationic process. Thus, in THF at 25 °C the reactivity of isoprene towards polystyrene anion is lower by about a factor of 2 than that of butadiene (only one end of this bivalent monomer is affected),... 

The isoprene units in the copolymer impart the ability to crosslink the product. Polystyrene is far too rigid to be used as an elastomer but styrene copolymers with 1,3-butadiene (SBR rubber) are quite flexible and rubbery. Polyethylene is a crystalline plastic while ethylene-propylene copolymers and terpolymers of ethylene, propylene and diene (e.g., dicyclopentadiene, hexa-1,4-diene, 2-ethylidenenorborn-5-ene) are elastomers (EPR and EPDM rubbers). Nitrile or NBR rubber is a copolymer of acrylonitrile and 1,3-butadiene. Vinylidene fluoride-chlorotrifluoroethylene and olefin-acrylic ester copolymers and 1,3-butadiene-styrene-vinyl pyridine terpolymer are examples of specialty elastomers. 

Conversely, vesicants have also been thickened with various substances to enhance deployment, increase their persistency, and increase the risk of percutaneous exposure. Thickeners include polyalkyl methacrylates (methyl, ethyl, butyl, isobutyl), poly(vinyl acetate), polystyrene, plexiglas, alloprene, polychlorinated isoprene, nitrocellulose, as well as bleached montan and lignite waxes. Military thickener K125 is a mixture of methyl, ethyl, and butyl polymethacrylates. When thickened, agents become sticky with a consistency similar to honey. Typically, not enough thickener is added to affect either the color or odor of the agent. 

Similarly Stable and Posnjak (87) proposed cyclic formulas of four, five, or possibly more structural units for polystyrene. Lebedev (88) first assigned the cyclooctadiene structure to polybutadiene shown below before expanding the concept of the ring to include several isoprene units. 

One of the most sophisticated architectures prepared by this method has the general formula (AB)2(BA)2, where A and B are polystyrene and polyisoprene chains, respectively two arms are linked by the styrene block, the other two arms are linked via the isoprene block to the central core. Moreover, the ratio of inner and outer blocks has been kept constant [65],... 

Table 9.4 Characteristics of arborescent polystyrene substrates used in the preparation of isoprene graft copolymers (adapted from ref. 16)...

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