Polystyrene nonaqueous

C. N. Onyenemezu, D. Gold, M. Roman, and W. G. Miller. Diffusion of polystyrene latex spheres in linear polystyrene nonaqueous solutions. Macromolecules, 26... 

Much work on the preparation of nonaqueous polymer dispersions has involved the radical polymerization of acrylic monomers in the presence of copolymers having the A block the same as the acrylic polymer in the particle core 2). The preparation of polymer dispersions other than polystyrene in the presence of a PS-PDMS diblock copolymer is of interest because effective anchoring of the copolymer may be influenced by the degree of compatibility between the PS anchor block and the polymer molecules in the particle core. The present paper describes the interpretation of experimental studies performed with the aim of determining the mode of anchoring of PS blocks to polystyrene, poly(methyl methacrylate), and poly(vinyl acetate) (PVA) particles. 

Stabilization in Nonaqueous Radical Dispersion Polymerization with AB Block Copolymers of Polystyrene and Poly(dimethyl siloxane)... 

Prior to this discovery, in 1954 Silberberg and Kuhn (62) were first to study the polymer-in-polymer emulsion containing ethylcellulose and polystyrene in a nonaqueous solvent, benzene. The mechanisms of polymer emulsification, demixing, and phase reversal were studied. Wetzel and Hocks discovery would then equate the pressure-sensitive adhesive to a polymer-polymer emulsion instead of a polymer-polymer suspension. Since the interface is liquid-liquid, the adhesion then becomes one type of R-R adhesion (35, 36). According to our previous discussion, diffusion is not operative unless both resin and rubber have an identical solubility parameter. The major interfacial interaction is physical adsorption, which, in turn, determines adhesion. Our previous work on the wettability of elastomers (37, 38) can help predict adhesion results. Detailed studies on the function of tackifiers have been made by Wetzel and Alexander (69), and by Hock (20, 21), and therefore the subject requires no further elaboration. 

The reaction engineering aspects of these polymerizations are similar. Good heat transfer to a comparatively inviscid phase makes them suitable for vinyl addition polymerizations. Free-radical catalysis is mostly used, but cationic catalysis is used for nonaqueous dispersion polymerization (e.g., of isobutene). High conversions are generally possible, and the resulting polymer, either as a latex or as beads is directly suitable for some applications (e.g., paints, gel permeation chromatography beads, expanded polystyrene). Suspension polymerizations are run in the batch model. Continuous emulsion polymerization is common. 

Styragel is a polystyrene gel that is useful for purely nonaqueous separations in methylene chloride, toluene, trichlorobenzene, tetrahydrofuran, cresol, dimethyl-sulfoxide, and so on. It cannot be used with water, acetone, or alcohols. Gels of this can be prepared with exclusion limits for molecular weights of from 1600 to 40 million. 

A polymer shell on a metal nanorod imparts better stability and better solubility in nonaqueous solvents. A few examples of metal-core polymer-shell nanorods can be found in the literature. They include Aucore-PolystyrenCsheii (124, 125), and Agcore-Polystyrenesheii (126). One of the examples (124), in which Au nanorods are encapsulated with polystyrene is discussed below. 

Illustrative values of the interaction parameter, measured as a function of the volume fraction of polymer for several nonaqueous systems, are shown in Fig. 3.6. These results clearly indicate that the interaction parameter can be a strong function of the volume fraction of polymer. Usually Xi increases with the volume fraction of polymer (e.g. for polyisobutylene in benzene) but this behaviour is by no means universal (e.g. Xi for polystyrene in toluene decreases with increasing polymer concentration). 

Note that, as reported in Table 6.2, latices stabilized either by poly(a-methyl styrene) in -butyl chloride or by polystyrene in cyclopentane flocculated both on heating and on cooling. Moreover, the UCFT in nonaqueous systems tends to occur as the critical temperature of-the dispersion medium is approached. In aqueous systems, the UCFT can occur well below the critical temperature. 

The critical concentration of free polymer that must be added to cause flocculation decreased with increasing molecular weight (see Fig. 16.9). The value of Cj depended upon the molecular weight with an exponent of -0-7. This value is quite different from the exponent (- 0-25) originally reported by de Hek and Vrij (1979) for nonaqueous silica dispersions stabilized by stearyl alcohol and flocculated by polystyrene. The value measured by Sperry et al. is... 

Little work has been published on depletion stabilization in nonaqueous dispersion media. Clarke and Vincent (1981a) have noted that it is possible to prevent silica particles stabilized by polystyrene in ethylbenzene from undergoing depletion flocculation by adding a high concentration of polystyrene (v2 =0 015 for a free polystyrene molecular weight ofca 2 x 10 ). This was the first reported observation of depletion stabilization in nonaqueous dispersion media. 

Figure 6. The effective susceptibility exponent as a function of AT for xenon (Xe), for isobutyric acid and water (IBAW), for 3-methylpentane and nitroethane (3MPNE) [20], for two 3MP+H20-j-NaBr samples with 8 mass % and 16 mass % NaBr [28], for a nonaqueous ionic solution of tetra-u-butyl ammonium picrate in 1,4-butane-dion/l-dodecanol (0.75/0.25) (TPDB) [20], and for two samples of polystyrene in deute-rocyclohexane with molecular weight 28 (PSl) and 200 (PS4) [24]. From Ref. [53].

The synthetic pathways developed to access the target pyridazinone arrays are based on the assembly of the exocyclic a,P-unsaturated framework through either Knoevenagel (chemotype A) or Claisen-Schmidt (chemotypes B and C) condensations (Scheme 1.11) with silica-supported aluminum chloride anployed as a catalyst. In comparison with conventional aluminum chloride, the silica-supported equivalent offers several advantages over the free catalyst (milder acidity, superior shelf Ufe, and the ability to condnct nonaqueous workups) and the polystyrene-supported version (no swelling and ability to carry out reaction in polar solvents). 

Many polystyrene fractions are available as probe polymer in nonaqueous systems. For aqueous systems, we can use the dextran-oligosaccharide series and poly(ethy1ene oxide) - polyethylene glycol series (polymers that are substantially neutral and with which there will be little possibility of adsorption or conformational change due to the presence of electrolytes). For the latter polymers, the relations between the Stokes radius and molecular weight have been collected as in Fig. 6. 

Block Ionomers. The block ionomers to be discussed are of AB or ABA type, in which one of the blocks is ionic (eg, sodium methacrylate) and the other consists of nonionic units (eg, polystyrene). While ionic block copolymers in a micelle form in both aqueous and nonaqueous solutions have been studied extensively (99-101,130,131), the viscoelastic properties of block ionomers in bulk have not received much attention (132-137). If the short ionic blocks formed micelle-like aggregates, which were surrounded by nonionic blocks, the viscoelastic properties of the diblock ionomers would be very similar to those of stars or polymers of low molecular weight (136). Thus, above the Tg of the nonionic blocks, as the temperature increased the modulus dropped rapidly with a very short rubbery plateau. For example, in a dynamic mechanical study, it was found that a homopolymer containing 490 styrene units showed a Tg at ca 115°C, and started to flow at ca 150°C. However, in the case of a diblock ionomer containing 490 styrene units and 40 sodium methacrylate ionic units showed a Tg at ca 116°C, and flow behavior was observed above ca 165°C, which was only 15°C higher than that of nonionic polystyrene (135). 

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