Incompatibility with polystyrene

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. 

Domains in position 2 on Figure 7.17 are filled after free volume voids were already filled. This increases free volume and for this reason the mechanical strength of material decreases. The effect is more dramatic because mineral oil is incompatible with polystyrene (solubility parameters of mineral oil and polystyrene are 7.6 and 9.1 (cal cm ), respectively) therefore mineral oil-mineral oil attractive forces are stronger than mineral oil-polystyrene forces. Thus, the excess of mineral oil (above the amormt required to fill free volume voids in position 1) accumulates in the mineral oil domains (position 2), which increase in size with amormt of mineral oil increasing. It was determined that the domain sizes are kept low ( 0.2 nm) below 6 vol% mineral oil in a low molecular polystyrene but they are about 9 nm at 8 vol%. At 9 nm, domains are above the critical size which causes phase separation and thus more catastrophic decrease in mechanical strength. 

Class and Chu demonstrated that if a tackifier is chosen that is largely incompatible with the elastomer, a modulus increase due to the filler effect is observed and little change in Ta results, and once again a PSA would not be obtained. This was observed for mixtures of low molecular weight polystyrene resin and natural rubber. The same polystyrene resin did tackify SBR, a more polar elastomer that is compatible with the resin. Hydrogenating the polystyrene to the cycloaliphatic polyvinylcyclohexane changed the resin to one now compatible with the less polar natural rubber and no longer compatible with SBR. These authors also provide... 

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... 

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 rather unexpected properties described above seem to be peculiar to PVN, for none of the blends with polystyrene, poIy-4-vinylbiphenyl, and polyacenaphthylene contained significant amounts of amorphous PEO. The modulus curves for these systems are characteristic of blends of incompatible polymers. The photomicrograph in Figure 12 illustrates the different morphologies of PVB and PEO blends. The reason for the apparently different behavior for these polymers as compared with PVN is not yet understood. But there is strong evidence from dilute solution-studies that the conformational properties for these polymers differ markedly. 

C-Alkylations have been performed with both support-bound carbon nucleophiles and support-bound carbon electrophiles. Benzyl, allyl, and aryl halides or triflates have generally been used as the carbon electrophiles. Suitable carbon nucleophiles are boranes, organozinc and organomagnesium compounds. C-Alkylations have also been accomplished by the addition of radicals to alkenes. Polystyrene can also be alkylated under harsh conditions, e.g. by Friedel-Crafts alkylation [11-16] in the presence of strong acids. This type of reaction is incompatible with most linkers and is generally only suitable for the preparation of functionalized supports. Few examples have been reported of the preparation of alkanes by C-C bond formation on solid phase, and general methodologies for such preparations are still scarce. 

Most of these procedures are incompatible with common linkers, and are therefore unsuitable for the transformation of support-bound substrates into carboxylic acids. A more versatile approach for this purpose is the saponification of carboxylic esters. Saponifications with KOH or NaOH usually proceed smoothly on hydrophilic supports, such as Tentagel [19] or polyacrylamides, but not on cross-linked polystyrene. Esters linked to hydrophobic supports are more conveniently saponified with LiOH [45] or KOSiMe3 in THF or dioxane (Table 13.11). Alternatively, palladium(O)-mediated saponification of allyl esters [94] can be used to prepare acids on cross-linked polystyrene (Entries 9 and 10, Table 13.11). Fmoc-protected amines are not deprotected under these conditions [160],... 

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... 

A wide variety of polymeric supports have been investigated giving due considerations to the above criteria. Polystyrene has been the most widely used polymer for this purpose, because of its commercial availability, ease of functionalization and good mechanical characteristics. However, limitations like the nonequivalence of functional groups and physicochemical incompatibility with the substrate observed in the case of this support have led to many strategical improvements in the solid phase methodology. In the. following sections we discuss very briefly the basic features and the intrinsic problems of the polystyrene-based peptide synthesis. 

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. 

It was also Staudinger in 1932 who first proposed that the inability of polystyrene to crystallize was due to its lack of stereoregularity which rendered it amorphous. It is its amorphous nature that is responsible for its solubility -though others claimed that polymer solubility was incompatible with very high molecular weight [3]. 

Figure 13.8 Microstructure of an ABC triblock copolymer, polystyrene-poly(ethylene-butylene)-poly(methyl methacrylate) in which the center B block (representing the white domains) is more incompatible with the end blocks (the black and the gray) than the end blocks are with each other. In this case, the center block forms rings that decorate the dark cylinders. In other cases, the center block forms a thin cord that winds helically around the dark cylinder. (Reprinted with permission from Stadler et al., Macromolecules 28 3080. Copyright 1995, American Chemical Society.)...

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. 

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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