Networks polystyrene

Figure 6.2. (a). Colloidal silica network on the surface of spores from Isoetes pantii (quill wort). Scale = 20 pm. (b). Polystyrene networks and foams produced as a biproduct of colloidal latex formation. Both types of colloidal system are typical of the diversity of patterns that can be derived from the interactions of minute particles. Scale (in (a)) = 50pm. 

Figure 7. SANS measurements of R versus A. of swollen polystyrene networks. Mc is the molecular weight between cross-links. Key A, DVB/LE — 3 , DVB/ LE = 6 O, DVB/LE = 10. Data from Ref. 19.

This was polymerized to form a polystyrene network, PSN. SIN s containing 10 and 40% elastomer, as well as two corresponding homopolymer networks were studied, see Figure 1. 

SIPN of a polystyrene network and a linear poly(vinyl chloride), see Fig. lb)... 

Prins and co-workers 280) reported moduli on polystyrene networks which had been formed by adding small amounts of divinyl benzene to preformed polystyryl dianions. The gels were dried, reswelled to equilibrium in benzene and tested in simple compression. The equation for G in this case becomes ... 

Allen and co-workers 280a) have recently prepared and studied a series of model polystyrene networks. These networks were formed from narrow distribution polystyrenes (M = 70000-240000) containing small but known amounts of secondary amine side groups. The amines were coupled in solution by reaction with diisocyanates, resulting in networks with known values of vc (Af =7000-17000). Moduli were determined for the networks at the same diluent... 

The fact that macroporous, highly cross-linked polystyrene does not swell makes this support particularly interesting for continuous-flow synthesis in columns. This support has also been successfully used as an alternative to CPG for the solid-phase synthesis of oligonucleotides [90,91]. Furthermore, because reagents do not need to penetrate into the polystyrene network, enzyme-mediated reactions should also proceed smoothly on macroporous polystyrene [85]. 

Fig. 23. Plot of the dipolar broadening parameter AG (left scale) and its relation to the square root of rigid lattice second moment, AM2 = 15 kHz (right scale), for polystyrene networks crosslinked with DVB (solid symbols) and EDM (open symbols) swollen to equilibrium, vs l/n, the reciprocal nominal number of C—C bonds between crosslinks points. Solvents CC14 ( ), CDC13 (A),...

A linear variation of d versus/If1/3 should also be expected for polystyrene networks in cyclohexane at 20 °C, since under these conditions Q is almost independent ofM31 Experimentally, X-ray diffraction measurements confirm that d is propor-... 

Since the reduced modulus G refers to the unswollen, unstrained, isotropic network, the question arises, first, whether it should be the same for a given network, regardless of the swelling solvent. It was found that for PDMS networks as well as for polystyrene networks the value of G is not the same for a given gel whatever the swelling solvent may be14,22. This result, which implies that the swelling solvent influ-... 

This means that the connectivity factor x2 — which was not taken into account — should be close to unity the vast majority of the elastic chains connect first neighbor crosslinks, as long as the average functionality does not exceed S or 6. For PDMS networks the fit is only good up to / = 4. For polystyrene networks the limiting functionality is attained for a proportion of DVB per living end of the order of 5. (Table 3). 

Neutron scattering experiments were also carried out on some model networks with labelled crosslinks, in the unswollen state13 26 To achieve such measurements the dry polystyrene networks are heated above their glass transition temperature, submitted to uniaxial deformation, quenched under stress and studied in the neutron scattering apparatus. 

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. 

The extent of conversion of the polystyrene network was examined as a function of time, see Figure 2. [In this experiment, linear polystyrene was employed rather than decrosslinked polystyrene... 

Gel-Type (Homogeneous) Polystyrene Networks 9 Table 1.2 Monomer reactivity ratios for styrene (rd and p-divinylbenzene (r2) ri 2 r r2 7 References ... 

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