Para- polystyrene

Several studies have concerned the microstnicture of lamellae in materials such as the block copolymers polystyrene-h/oc/r-poly-l-vinylpyridine [139] and polystyrene-h/oc/r-polybutadiene [140], as well as single crystals of poly-para-xylylene [139], and reveal features (such as intersecting lamellae (figure Bl.19.29)) that had not been previously observed. 

Vinyltoluene, comprising a mixture of ca 33% para- and 67% y /i7-methylstyrene, has been marketed for ca 45 yr by Dow Chemical Company and also by Cosden. However, the performance properties of the polymers prepared from the para isomer are not only superior to those of the polymer prepared from the typical mixed isomers, but are generally superior to those of polystyrene (60). This advantage, coupled with a raw material cost advantage over styrene, suggests that i ra-methylstyrene may displace significant amounts of styrene, currendy a 3.2 x 10 t/yr domestic market. 

Soto, A.M., Justicia, H., and Wray, J.W. et al. (1991). Para-nonyl-phenol an estrogenic xen-obiotic released from modified polystyrene. Environmental Health Perspectives 92, 167-173. 

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. 

Example 2 Chromatography of nitroaniline isomers. The elution order of the nitroaniline isomers was ortho, meta, and para in normal-phase liquid chromatography using H-butanol-w-hexane mixtures as the eluent, when the stationary phase material was either silica gel, alumina, an ion-exchanger, polystyrene gel, or octadecyl-bonded silica gel. The results indicate that the separation of these compounds can be performed on a range of different types of stationary phase materials if the correct eluent is selected. The best separation will be achieved by the right combination of stationary phase material and eluent.68... 

In a study aimed at the identification of products of free radical reactions with polystyrene- and aromatic-based PEMs using model compounds, Hiibner and Roduner observed the addition of free radicals to the aromatic rings, preferentially in the ortho position to alkyl- and RO-substituents (in polystyrene- and aromatic-based PEMs, the para position is blocked by the presence of the sulfonic acid group). This study demonstrated the combined ortho-activation by these substituents and the meta-directing effect... 

Figure 34. The Polystyrenes. Polystyrene is a low sensitivity negative resist, poly (a-methylstyrene) is a low sensitivity positive resist and the para-substituted analogs listed are all sensitive negative resists.

Polystyrene is presently the overwhelming choice as the polymer support [Frechet and Farrall, 1977 Frechet et al., 1988 Messing, 1974]. The polystyrene used is a crosslinked polymer prepared by copolymerization of styrene with divinylbenzene (DVB). (The divinyl-benzene is usually the commercially available mixture containing the meta and para isomers... 

To expedite peptide syntheses of up to 124 amino acid units, beads of solid polystyrene— with chloromethyl groups, —CH CI, para to about every hundredth phenyl group—are used in an automated process. The sequence of steps is (1) attach C-terminal Boc-protected amino acid by... 

Comparison of the UV spectrum of polystyrene in the 2600 A region with that of toluene shows a close relationship in terms of both extinction coefficients and vibronic fine structure. The effect of para substituents is most conveniently characterized by the shift in the band corresponding to the a0-o transition. The comparison of substituent effects on the electronic excited states of thepara substituted polystyrenes parallels those for the corresponding para substituted toluenes. Such a correlation would only be expected if the tr - n transitions were effectively localized within a given pendant group of the polymer system. This conclusion is reinforced by the observation that polystyrene and toluene show similar shake up structure in their ESC A spectra with respect to both band profiles and intensities (when due... 

Fig. 46. Experimentally derived shake up probabilities for components contributing to the low energy stake up satellites in para substituted polystyrenes...

Farrall and Frechet recognized the possibility of forming polymer-bound boronic acids in 1976.66 Supported pnra-benzeneboronic acid groups were generated by direct lithiation of polystyrene, giving a para-lithio intermediate that could be used to generate a host of other resins also (Scheme 27). Conversion to the boronic acid was one of the more successful transformations. The purpose of this transformation was to allow the attachment of sugars to the solid phase via the boronate. 

A flexible means of access to functionalized supports for solid-phase synthesis is based on metallated, cross-linked polystyrene, which reacts smoothly with a wide range of electrophiles. Cross-linked polystyrene can be lithiated directly by treatment with n-butyllithium and TMEDA in cyclohexane at 60-70 °C [1-3] to yield a product containing mainly meta- and para-Iithiated phenyl groups [4], Metallation of noncross-linked polystyrene with potassium ferf-amylate/3-(lithiomethyl)heptane has also been reported [5], The latter type of base can, unlike butyllithium/TMEDA [6], also lead to benzylic metallation [7]. The C-Iithiation of more acidic arenes or heteroar-enes, such as imidazoles [8], thiophenes [9], and furans [9], has also been performed on insoluble supports (Figure 4.1). These reactions proceed, like those in solution, with high regioselectivity. 

Fig. 26a-d. H NMR spectra of polystyrene in CC14 (20 °C, 60 MHz) a, b crosslinked through ortho (o). mela (m) and para (p) positions, equilibrium swollen, c, d linear a, c standard high resolution b, d MAS (reprinted from Ref. 3) with permission)... 

Potential Uses. Because much toluene is demethylated for use as benzene, considerable effort has been expended on developing processes in which toluene can be used in place of benzene to make directly from toluene the same products that arc derived from benzene. Such processes both save the cost of demethylation and utilize the methyl group already on toluene. Most of this effort has been directed toward manufacture of styrene. A11 alternative approach is the manufacture of para-methylstyrene by selective ethylation of toluene, followed by dehydrogenation. Resins from this monomer are expected to displace polystyrene because of price and performance advantages. 

The incorporation of diethyldithiocarbamate groups (Et)2N-C-S-R in a polymer produces active sites which on photolysis can be used for graft or block copolymerization depending on the location of the groups (185). By heating polystyrene with tetraethyl thiuram disulfide, Para substitution occurs... 

Zhao and co-workers848 synthesized macroreticular para-( -sulfonic-perfluor-oalkylated) polystyrene (FPS) and used it in the cyclization of pseudoionone into a-ionone 241a an important fragrance material. The ring closure induced by the catalyst led to complete conversion and the product was formed in low yield but selectively (/3-ionone was not observed) [Eq. (5.309)]. Amberlyst proved to be less active and less selective. A new catalyst loaded with perfluoroalkanesulfonic as well as phenylsul-fonic acid groups (FPSS) exhibited improved performance849 [Eq. (5.309)]. 

When we determine values of 7 for benzene rings attached to polymers, we find that they are much shorter than for benzene itself they are in fact at the lower limit of usefulness of the direct method. We have found (3) that for the phenyl resonance of a low molecular weight polystyrene in carbon disulfide 7 is only about 0.4 0.1 sec. at 25°. For the backbone protons, 7 is even shorter and cannot be measured by the direct method. For the phenyl groups of poly-y-benzylglutamate in trifluoroacetic acid, 7 is 0.7 0.1 sec. Recently, more reliable values have been obtained for polystyrene by the spin echo method (72). For a polymer of molecular weight 63000 in tetrachloroethylene, three 7 X values could be resolved. At 25°, these were 0.033 sec. for the aliphatic protons, 0.076 sec. for the ortho protons and 0.20 sec. for the meta-para protons. The temperature coefficients for all three Tt values correspond to a heat of activation of about 3 kcal/mole. The differences in the absolute Tx values at the aromatic positions can be explained in terms of of differences in the sums of r e in equation (56). The shorter aliphatic Tj value probably reflects also a longer correlation time for backbone... 

For example, the vinyl group on styrene monomers is activating and ortho-para-directing. This leads to macromonomers of polystyrene with styrene end groups functionalized at the p-position [Eq. (92)]. 

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