Polystyrene percent cross-linking

Figure 3. Protein decoupled 13C NMR spectrum at 75 MHz of 17,500 MW polystyrene at 20% w/v in CDCU/CHCU (lower trace). One percent cross-linked polystyrene (Biobeads SX-1) in the same solvent (upper trace).

Spoly(vinylbenzylchloride). -Cross-linked using divinylbenzene. Chloromethylated, cross-linked polystyrene resins were obtained coiranercielly from Bio-Rad Laboratories. Percent chloromethylation js based on the available phenyl groups in the polymer that is minus the percent cross-linking. =D=dioxane E ethanol. Percent of available chloromethyl croups reacted with donor. —Percent reaction x percent chloromethylation. Polymer prepared by free-radical polymerization of 60.00 para-neta chloromethylated sytrene (Dow Chemical). Reaction heated at 50-55°C. 

One percent cross-linked polystyrene and Argopore resin performed equally well. The compatibility with polar solvents makes Argopore the most versatile resin when investigating new reaction conditions. 

The copolymerization of styrene with divinylbenzene (DVB) is necessary to obtain the required mechanical stability of the resin. Upon adding divinylbenzene to styrene, the two functional groups of DVB cross-link two polystyrene chains with each other. Part of the resulting skeleton is depicted schematically in Fig. 3-3. The percentage of DVB in the resin is indicated as percent cross-linking . The degree of cross-liiiking determines the porosity of the resin, which is another characteristic used in the classification of PS/DVB resins. 

Most investigations of polymer-supported onium ion phase transfer catalysts have used cross-linked polystyrenes. Not all of them have the same structure, even when they have the same formal degree of cross-linking with divinylbenzene. (The effect of percent cross-linking is considered in a later section). Two principal methods have been used to functionalize polystyrene for phase transfer catalysts, chloromethylation of pre-formed beads and copolymerization of chloromethylstyrene monomer with styrene and divinylbenzene. The chloromethylation route employs chloromethyl methyl ether (a cancer suspect agent), and a Lewis acid, usually stannic chloride.Substitution proceeds >90% para and is accompanied by some intrapolymer alkylation, which puts additional cross-links into the polymer... 

When, styrene, C6HSCH = CH2 is copolymerized in the presence of a few percent p-divinylbenzene, a hard, insoluble, cross-linked polymer is obtained. Show how this cross-linking of polystyrene chains occurs. 

Oxetanes have also been synthesized by the immobilization of 2,2 -disubstituted 1,3-diols with polymer-bound sulfonyl chloride, followed by intramolecular cyclization/cleavage from the solid support (Scheme 17) <2005TL643>. One percent divinylbenzene (DVB) cross-linked polystyrene and polyethylene glycol (PEG) (average Mn 3400) were used as polymer support in this reaction, and in both cases the properties of the polymer support allowed rapid purification of the intermediate. Intermediates on the insoluble cross-linked polystyrene support could be washed with a range of organic solvents to remove insoluble impurities, whereas the soluble PEG supported products could be purified by recrystallization from isopropanol. This is thought to represent the first reported polymer-supported synthesis of oxetanes. 

Macromolecular materials react quite differently to mechanical stresses. Beakers of conventional polystyrene are very brittle, and a short, quick blow will break them. In contrast, beakers of nylon 6 are very tough. Weakly cross-linked natural rubber expands on stretching by several hundred percent after being released, it returns to what is practically its original form. When plasticine is deformed, on the other hand, it completely retains its new shape. 

Benoit and others (94-98) prepared two types of tagged polystyrene networks (a) type A networks containing labeled (deuterated) cross-link sites. This permitted a characterization of the spatial distribution of the cross-link points, (b) Type B networks containing a few percent of perdeuterated polystyrene chains (see Figure 9.23) (94). Cross-hnking utilized divinyl benzene (DVB). 

FIG. 17-12. Loss tangents of lightly cross-linked polystyrene swollen to various extents in dibuiyl phthalate, plotted against temperature at a frequency of I Hz. Numbers denote polymer concentration in weight percent. (Illers and Jenekel. )... 

Styrene block copolymers are the most widely used TPEs, accounting for close to 45 percent of total TPE consumption worldwide at the close of the twentieth century. They are characterized by their molecular architecture, which has a hard thermoplastic segment (block) and a soft elastomeric segment (block) (see Fig. 3.2). Styrenic TPEs are usually styrene butadiene styrene (SBS), styrene ethylene/butylene styrene (SEES), and styrene isoprene styrene (SIS). Styrenic TPEs usually have about 30 to 40 percent (wt) bound styrene certain grades have a higher bound styrene content. The polystyrene endblocks create a network of reversible physical cross links that allow thermoplasticity for melt processing or solvation. With cooling or solvent evaporation, the polystyrene domains reform and harden, and the rubber network is fixed in position. ... 

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