Pure Solid Polystyrene

At room temperature, atactic polystyrene is well below its glass transition temperature of approximately 100 C. In this state, it is an amorphous glassy material that is brittle, stiff, and transparent. Due to its relatively low glass transition temperature, low heat capacity, and lack of crystallites we can readily raise its temperature until it softens. In its molten state, it is quite thermally stable so we can mold it into useful items by most of the standard conversion processes. It is particularly well suited to thermoforming due to its high melt viscosity. As it has no significant polarity, it is a good electrical insulator. 

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We most often encounter polystyrene in one of three forms, each of which displays characteristic properties. In its pure solid state, polystyrene is a hard, brittle material. When toughened with rubber particles, it can absorb significant mechanical energy prior to failure. Lastly, in its foamed state, it is versatile, light weight thermal insulator. 

These additives usually enhance specific properties of polymers. Thus solid, pure stereoregular polystyrene (PS) is brittle yet, as a result of the addition of the proper impact modifiers and other additives, the modified PS exhibits the properties of a good plastic and rubber. 

Numerous resin supports are commercially available for solid-phase synthesis and some allow the acquisition of quite reasonable quality spectra of compounds bonded to them - and some don t. The resins to avoid (if you intend trying to monitor your reactions by MAS-NMR) are any that are based purely on cross-linked polystyrene. These are too rigid and afford little or no mobility to any bound compound. These resins are relatively cheap and have high specific loadings but will give very poor spectra even in a MAS probe. We see little point in running spectra of compounds on these resins as the quality of the spectra make them virtually useless - and perhaps worse - potentially misleading. 

The synthesis of some multiblock copolymers was attempted by successive polymerization using this iniferter technique. However, pure tri- or tetrablock copolymers free from homopolymers were not isolated by solvent extraction because no suitable solvent was found for the separation. In 1963, Merrifield reported a brilliant solid-phase peptide synthesis using a reagent attached to the polymer support. If a similar idea can be applied to the iniferter technique, pure block copolymer could be synthesized by radical polymerization. The DC group attached to a polystyrene gel (PSG) through a hydrolyzable ester spacer was prepared and used as a PSG photoiniferter (Eq. 53) [186] ... 

Amination (11) and solution carbonation (8) reactions were carried out as described previously. For solid-state carbonations, a benzene solution of poly(styryl)lithium was freeze-dried on the vacuum line followed by introduction of high-purity, gaseous carbon dioxide (Air Products, 99.99% pure). Analysis and characterization of polymeric amines (11) and carboxylic acids (8) were performed as described previously. Benzoyl derivatives of the aminated polystyrenes were prepared in toluene/pyridine (2/1. v/v) mixtures with benzoyl chloride (Aldrich, 99%). 

Catalyzed aldol additions do not generally proceed with high diastereoselectivity at ambient temperature. Improved stereoselectivity can be achieved by using preformed, diastereomerically pure enolates at low temperatures (Entry 5, Table 7.2). This strategy enables the solid-phase preparation of stereochemically defined polyketides. On cross-linked polystyrene, the observed diastereoselectivity in the addition of boron enolates to aldehydes is the same as that in the homogeneous phase reaction [14,18]. 

There are three common types of organic scintillator. The first type is a pure crystalline material, such as anthracene. The second type, the liquid scintillator, is the solution of an organic scintillator in an organic liquid, such as a solution of p-terphenyl in toluene ( 3 g solute/L solution). The third type is the solution of an organic scintillator, such as p-terphenyl, in a solid plastic, such as polystyrene. 

Figure I 1.5. Viscosity of polystyrene with dissolved R-152a at 150 °C measured as a function of shear rate. The Schummer correction and a pressure correction have been applied, as described in the text, to obtain isobaric viscosity curves corresponding to the back-pressures applied during the measurements. The R-152a composition and back-pressure values are O 5.6 wt% R-152a, 12.06 MPa 7.0 wt%, 12.48 MPa A 8.3 wt %, 17.18 MPa V 10.4 wt%, 16.41 MPa. The solid curve is the viscosity curve for pure polystyrene at 150 °C and 1 atm pressure. Data from Kwag (1998).

Figure I 1.6. Master viscosity curve produced by superposing all data for all systems. Viscosity data taken at 175 °C have been shifted to 150°C by employing the temperature scaling factor aT for pure polystyrene. The master viscosity curve is identical to the viscosity curve for pure polystyrene at 1 atm and 150 °C, which is displayed as the solid line. Data from Kwag (1998).

Excimer fluorescence in solid pure polystyrene is observed exclusively ... 

The methodology outlined in Scheme 10.50 has also been adopted to a corresponding stereoselective solid-phase approach to a-amino acids using the galactosylamine 160 immobilized on a polystyrene-based resin, enabling the combinatorial synthesis of stereoisomerically pure compounds (Figure 10.15) [123]. 

The concept of immobilized ionic liquids entrapped, for instance, on the surface and pores of various porous solid materials (supported ionic liquid phase, SILP) is rapidly become an attractive alternative. In addition, the SILPs can also answer other important issues, such as the difficult procedures for product purification or IL recycling, some toxicity concerns and the problems for application in fixed-bed reactors, which should be addressed for future industrial scale-up. This new class of advanced materials shares the properties of true ILs and the advantages of a solid support, in some cases with an enhanced performance for the solid material. Nevertheless, a central question for the further development of this class of materials is to understand how much the microenvironment provided by the functional surfaces is similar or not to that imparted by ILs. Recent studies carried out using the fluorescence of pyrene to evaluate the polarities of a series of SILPs based on polymeric polystyrene networks reveal an increase in polarity of polymers, whereas the polymer functional surfaces essentially maintain the same polarity as the bulk ILs. However, this is surely not a simple task, in particular if we consider that the basic knowledge of pure ILs is still in its infancy, and we are just starting to understand the fundamentals of pure ILs when used as solvents. 

Figure 18.3. H spectra (region of amide protons) of a polystyrene/1 % divinylbenzene resin (0.5 mmol/g in d7-DMF) allow fast and reliable controls of synthesis and cleavage conditions. Top H spectra of the pure HMPA-PS resin center H spectra after the synthesis of an letra-peptidc Gly-Asn-Leu-Ile bottom H spectra after the cleavage of the tetrapeptide with hydrazine. The latter spectrum shows some small amounts of product still attached to the solid support.

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