Polystyrene-divinylbenzene crosslinked copolymers

Crosslinked Polystyrene. Polystyrene lightly crosslinked during polymerization by 0.01-0.25% divinylbenzene provides foams, expanded by carbon dioxide or other gases, with greater expandability and resistance to collapse at elevated temperatures (102, 103). Other divinylbenzene copolymers are reported, employing as blowing agent saturated aliphatic or fluoroaliphatic volatile liquids, tetramethylsilane, and azobis-isobutyronitrile (99,106, 108). 

Hradil et al. [395, 396] prepared a set of composite membranes containing fine particles of conventional macroporous resins or hypercrosslinked polystyrene adsorbing materials in films of poly(2,6-dimethyl-l,4-phenylene oxide) as a binder. Hypercrosslinked resins were either a commercial product, Lewatit EP63 (Bayer AG), or were obtained by crosslinking (i) a macroporous styrene—divinylbenzene (DVB) copolymer with carbon tetrachloride (Hyp-St—DVB) or (ii) a finear polystyrene with monochlorodi-methyl ether. In the latter case the reaction of bridging was conducted in a pretty diluted ethylene dichloride solution at stirring, which resulted in obtaining a particulate (1—5 pm) product. 

G. Konig studying the cryolitic behaviour of the polystyrene and of crosslinked copolymer styrene - divinylbenzene swollen in naphthalene proposed a series of comparative models. Figure 3.397 shows a gel that is a swollen unit in saturation, for which is ac-... 

Polystyrene SP5009 (1% divinylbenzene crosslinking) and polystyrene SP5018 (2% divinylbenzene ciosslinking) were purchased from Advanced ChemTech. More highly crosslinked polystyrene macroreticular beads (copolymer XFS 4022 with 20% divinylbenzene) wctc obtained from Dow Chemical Company. The remaining reagents were purchased from standard suppliers. 

At present all commercial polystyrene (with average molecular weights between 100,000 and 400,000) is manufactured by radical polymerization, which yields atactic polymers.476 Peroxides and azo compounds are commonly used initiators. The suspension process (usually as a batch process in water at 80-140°C) produces a product with relatively high residual monomer content.223 More important is the continuous solution process (usually in ethylbenzene solvent at 90-180°C), which yields high-purity product. Styrene can be copolymerized with numerous other monomers.477 One of these copolymers, the styrene-divinylbenzene copolymer produced by free-radical polymerization, has a crosslinked stucture and is used in... 

Polymeric supports can also be used with advantage to form monofunctional moieties from difunctional (Hies. Leznoff has used this principal in the synthesis of sex attractants on polymer supports (67). Starting from a sheap symmetrical diol he blocked one hydroxyl group by the polymer. Functionalization of cross-linked polymers is mostly performed by chloromethylation (65). A very promising method to introduce functional groups into crosslinked styrene-divinylbenzene copolymers is the direct lithiation with butyllithium in presence of N,N,N, N -tetramethyl-ethylenediamine (TMEDA) (69, 70). Metalation of linear polystyrene with butyl-lithium/TMEDA showed no exchange of benzylic hydrogen and a ratio of attack at m/p-position of 2 1 (71). In the model reaction of cumene with amylsodium, a kinetic control of the reaction path is established. After 3h of treatment with amyl-sodiuni, cumene is metalated 42% in a-, 39% m-, and 19% p-position. After 20h the mixture equilibrates to affort 100% of the thermodynamically more stable a-prod-uct (72). 

Crosslinking affects mainly the a relaxation of polystyrene. Crosslink formation inhibits the molecular motion and, therefore, always causes a net increase in Ta. For example, Ishii et al. [34], working on a copolymer of styrene and 4-ethylstyrene (8mol%), found a shift of 34 K (1Hz) in Ta towards high temperature. The crosslinked polystyrenes of major commercial interest are copolymers of styrene and divinylbenzene. Results of a systematic study of this system have shown that Tg could be represented by the equation [35]... 

Polystyrene alone, or polystyrene having different degrees of crosslinking with divinylbenzene is commonly used in numerous copolymers with special purposes. Polymers used as stationary phases in chromatography may include groups such as C18 chains, pyridine, N-vinylpyrrolidone, or iminodiacetic acid groups. The structures of such copolymers are indicated below ... 

The "uncrosslinked limit" of many crosslinked polymers can be defined quite easily. For example, polystyrene is the uncrosslinked limit of styrene-divinylbenzene copolymers. On the other hand, the uncrosslinked limit of many other crosslinked polymers cannot be defined unambiguously, and is an idealization. In such cases, there is no unique uncrosslinked limit for a densely crosslinked polymer synthesized from a monomer or monomers with functionalities able to react by several mechanisms. DVS-BCB2 is an example of such a complicated network polymer. However, even for such cases, reasonable choices of uncrosslinked limit can be made. Furthermore, the general form for the dependence of Tg on the crosslink density can be combined with a very small amount of data (such as one or two data points) to give the proper scale for the Tg values and to provide a good estimate for Tg at other crosslink densities. 

Figure 11.18. Effects of crosslinking on the brittle fracture stress of styrene-divinylbenzene copolymers. Note the catastrophic embrittlement at very high crosslink densities (i.e., at an average number of repeat units between crosslinks less than the Kuhn segment length of 8 repeat units). The data point (not shown) for the uncrosslinked limit (polystyrene) is at (°°,41).

Most environmental samples require some pretreatment, usually in the form of filtration and centrifugation, before these are injected via a sample loop. lEC separation of organic acids is achieved on cation exchange columns which are characterized by their particle diameter, substrate crosslinking, ion exchange capacity, type of functional group, and hydrophobicity. The most commonly used columns are comprised of fully sulfonated, crosslinked divinylbenzene/polystyrene copolymers (e.g., HPICE-AS6 or -ASl, Dionex). However, a comparison smdy found other columns to be equally as effective for organic acid separation. Unmodified silica gel columns... 

It was also reported that HCP networks can be used as stabilizers to produce metal nanoparticles. A hyper-crosslinked polystyrene network (HPS), obtained from a styrene-divinylbenzene copolymer, acts as a matrix to synthesize Co nanoparticles owing to its nano-sized rigid cavities of comparable size. These cavities ean eonsume several Co eomplexes and can control the growth, particle size and size distribution of Co nanopartieles. ... 

More recently bundles of carbon fibers have been immobilized in copolymers of vinylferrocene or vinylpyridine with crosslinked polystyrene. Alternatively, the fibers were coated by electro-co-polymerization of vinylferrocene and divinylbenzene before immobilization in crosslinked polystyrene. These electrodes are also polishable and present an array of polymer-modified ultramicro disk electrodes to the solution (Creasy and Shaw, submitted). 

These polymers constitute the largest group to be discussed in this report and this is mainly because polystyrene and poly(chloromethylstyrene), often crosslinked with divinylbenzene, continue to be widely used in the preparation of functional polymers and resin-supported reagents. In fact most of the examples given here refer to the preparation of functional polymers rather than to new materials. This is a rapidly growing area of polymer chemistry and it is not possible to refer, in a compressed review of this nature, to all reports of functionalized styrene-based resins that have appeared in the past two years. This section falls naturally into three parts the first deals with styrene polymers and copolymers, the second with reactions on chloromethylated polystyrenes, and the third deals with styrene-related polymers. 

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