Styrene incompatible polystyrene

Block copolymers of polystyrene with rubbery polymers are made by polymerizing styrene in the presence of an unsaturated rubber such as 1,4 polybutadiene or polystyrene co-butadiene. Some of the growing polystyrene chains incorporate vinyl groups from the rubbers to create block copolymers of the type shown in Fig. 21.4. The combination of incompatible hard polystyrene blocks and soft rubber blocks creates a material in which the different molecular blocks segregate into discrete phases. The chemical composition and lengths of the block controls the phase morphology. When polystyrene dominates, the rubber particles form... 

ABA triblock copolymers of the styrene-diene type are well known, and owe their unique properties to their heterophase morphology. This arises from the incompatibility between the polystyrene A blocks and the polydiene B blocks, leading to the formation of a dispersion of very small polystyrene domains within the polydiene matrix. This type of elastic network, held together by the polystyrene "junctions", results in thermoplastic elastomer properties. 

It is possible to produce a block copolymer by the anionic polymerisation of styrene and butadiene as depicted below. The polystyrene and polybutadiene are mutually incompatible and hence phase separate to give the morphology also depicted below ... 

In general, block copolymers are heterogeneous (multiphase) polymer systems, because the different blocks from which they are built are incompatible with each other, as for example, in diene/styrene-block copolymers. This incompatibility, however, does not lead to a complete phase separation because the polystyrene segments can aggregate with each other to form hard domains that hold the polydiene segments together. As a result, block copolymers often combine the properties of the relevant homopolymers. This holds in particular for block copolymers of two monomers A and B. 

The constancy of tensile strength of the SIS polymers, above a certain minimum end-block size, can be explained best on the basis of efficiency of phase separation. Since the latter depends on the three parameters—Le.y incompatibility of the two blocks, composition ratios, and block size—the SIS polymers must undergo a much better phase separation at equivalent composition and block size than the SBS polymers, and the latter require a higher styrene content and a longer polystyrene end block to accomplish good phase separation. This is in accord with the generally accepted fact that polyisoprene is more incompatible with polystyrene than is the case for polybutadiene. 

With copolymers an analogous situation is met as with blends Here also the components may be molecularly compatible or not. When the copolymer is random , i.e. the building blocks are arranged in a random sequence, then the copolymer is, as a matter of fact, homogeneous on a molecular scale, even if the components are incompatible. An example is SBR, a copolymer of styrene and butadiene. It shows a single glass transition at about -65 °C, which is roughly in accordance with the styrene content (23%) and the Tg s of polybutadiene (-95 °C) and of polystyrene (90 °C). 

The situation is quite different with block copolymers. As an example we again take a copolymer of styrene and butadiene, but now as a three-block copolymer, SBS. The incompatibility of polystyrene and polybutadiene now results in a phase separation, which is enabled by the circumstance that the blocks can live their own life . The polystyrene chain ends clog together into PS domains, which lie embedded in a polybutadiene matrix. These glassy domains act as physical cross-links, so that the polymer has the nature of a thermoplastic rubber. The glass-rubber transitions of PS and BR both remain present in between these two temperatures the polymer is in a, somewhat stiffened, rubbery condition (see Figure 3.8). This behaviour is dealt... 

The desorganization by dilution of the periodic structures of block copolymers has been studied by electron microscopy after polymerization of the solvent66,70,71. Two types of solvents have been used styrene, which is the monomer for the soluble polystyrene block and which prevents any incompatibility between polymeric chains during polymerization of the monomer, and methyl methacrylate which allows the study of the effect of incompatibility between polymeric chains during polymerization of the solvent. 

Few examples of the homogeneous diblock-incompatible homo-polymer behavior have been reported. One that has received considerable attention is the system polystyrene-poly-a-methylstyrene (2). Block copolymers of styrene and a-methylstyrene exhibit a single loss peak in dynamic experiments (2,3) and have been shown to be thermorheologi-cally simple (4) hence they are considered to be homogeneous. Mechanical properties data on these copolymers also has been used to validate interesting extensions of the molecular theories of polymer viscoelasticity (2,3,4). 

To reach the equilibrium in the system the styrene would migrate into the solution of high-molecular polystyrene from the rubber one, the latter would concentrate. Due to this the lowmolecular polystyrene becomes incompatible with the rubber and the rubber phase becomes turbid,drops of a new phase, representing the lowmolecular polystyrene solution in styrene are formed inside it. 

The grafting is accomplished in the commercial mass polymerization process by polymerizing styrene in the presence of a dissolved rubber. Dissolving the elastomer in the styrene monomer before polymerization produces HIPS grades. Since the two polymer solutions are incompatible, the styrene-rubber system phase separates very early in conversion. Polystyrene forms the continuous phase, with the rubber phase existing as discrete particles having occlusions of polystyrene. Different production techniques and formulations allow the rubber phase to be tailored to a wide range of properties. Typically ... 

POLYMERIC BEADS, EXPANDABLE (POLYSTYRENE or POLYSTYRENE BEADS, EXPANDABLE) (9003-53-6) (CgHg), (flash point 644 to 662°F/340 to 350°C autoignition temp 801°F/427°Cf "l). Incompatible with strong oxidizers, hydrocarbon solvents. Decomposes above 572°F/300°C, producing toxic styrene, benzene, carbon monoxide, and other hydrocarbon fumes. On small fires, use alcohol-resistant foam, dry chemical powder, water spray, or CO extinguishers. Note This material may be shipped in a flammable solvent. Check MSDS and refer to solvent carrier. 

In contrast to the grafting reactions (22), the crosslinking reaction during preparation of high impact polystyrene becomes effective only at very high styrene conversions (> 95%) at which the rubber double bond concentration in the total reaction mixture approaches the monomer concentration. In rubber lamellae, this shift in concentration in favor of the rubber double bonds is even more pronounced because of the incompatibility of polybutadiene and polystyrene. 

Scalco, Huseby, and Blyler (8), Zosel (9), and Bergen and Morris (10). Prest and Porter (23) applied the same principle to homopolymer blends [poly (2,6-dimethylphenylene oxide)-polystyrene]. Recently some papers were published on triblock copolymers of styrene-butadiene-styrene and on their blends with polybutadiene (24, 25). Triblock copolymers can be considered heterophase material as the different constituent blocks are thermodynamically incompatible with each other, and, consequently, polystyrene domains are enclosed in polybutadiene (continuous matrix). The findings indicate that these systems are in general thermorheologically complex, so that the shift factor ar depends not only on temperature but also on time. These conclusions have been extrapolated to other two-phase systems. 

We may find confirmation for our statement about the thermodynamic incompatibility of linear polystyrene with the styrene-DVB copolymer in experiments by Wong et al. [269]. These authors reported similarities in the phase separation power of linear polystyrene and that of linear styrene-methylmethacrylate copolymer, the latter being a priori incompatible with the styrene-DVB network. Complete incompatibility of polystyrene with linear polydimethylsiloxane facihtates phase separation and results in the formation of a porous styrene-DVB network on adding as little as 0.5-1% of the above porogen to the initial comonomer mixture (Fig. 3.2, curves 4). It is also not surprising that the porosity of copolymers induced by linear polystyrene and linear polydimethylsiloxane is almost the same when the DVB content exceeds 10%. At a DVB content that hi, the network formed differs fundamentally from linear polystyrene, as from any alien polymer. 

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