Polyreactions in dispersion

Suspension and emulsion techniques provide additional means for modifying the properties of the resulting polymers, for example  

This influences the rheology of the latex as well as the properties of the solid film (see Example 3-46). 

This has an influence on the pigment load capacity and on the stability of high solid-containing latices (see Example 3-39). 

Crosslinked rubbery polymers that are used as impact modifiers often do not have sufficient compatibility with the hard matrix of the surrounding ther-moplast. One elegant method is to cover the rubbery modifier particle with a thin layer of a polymer that is compatible with both, the rubbery core and the thermoplastic matrix. 

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The basic characteristics as well as some advantages and disadvantages are illustrated in Sects. 2.2.2 (polyreactions in bulk), 2.2.3 (polyreactions in solution), and 2.2.4 (polyreactions in dispersion). Prior to this some special features... 

Polyreactions in bulk are carried out without solvents or diluents. In this way, high molecular weights can be obtained frequently with high rates of reaction. The resulting products are very pure, because only monomers and, if necessary, initiators and catalysts are added. Polyreactions in bulk are also advantageous for economical and ecological reasons because recycling and purification of solvents or dispersants as well as the disposal of liquid waste (as in the case of aqueous suspension or emulsion polymerizations) are not necessary. On the other hand. 

Polymerization in Bilayers. Upon irradiation with UV light the monomer vesicles are transferred to polymer vesicles (Figure 12.). In the case of the diyne monomers (2,5-9,12,13,14) the polyreaction can again be followed by the color change via blue to red except phospholipids (5,6), which turn red without going through the blue intermediate as observed in monolayers. The VIS spectra of these polymer vesicle dispersions are qualitatively identical to those of the polymer monolayers (Figure 13.). 

Often, size exclusion chromatograms (SEC) (compare section 11.7, Size Exclusion Chromatography) of polymers under study are expressed as differential representations of molar mass dispersity. The chromatographic retention volumes are directly transformed into the molar masses. This approach renders useful immediate information about tendencies of molar mass evolution in the course of building or decomposition polyreactions but the absolute values of molar mass can be only rarely extracted from it. As a rale, polystyrene calibrations are applied for molar mass calculation so that one deals with the polystyrene equivalent molar masses, not with the absolute values. The resulting dispersity (distribution) functions may be heavily skewed because the linear part of the calibration dependence for the polymer under study may exhibit well different slope compared with the polystyrene calibration, which was employed for the transformation of retention volumes into molar masses. 

SEC is presently the most important method for separation and moleeular characterization of synthetic polymers. The method enjoys enormous popularity and most institutions involved in research, production, testing and apphea-tion of synthetie polymers are equipped at least with a simple SEC instrument. Size exclusion chromatograms are often directly transformed into the molar mass dispersity functions (compare section 11.3.3, Molar Mass Dispersity). Often, the molar mass data presented are not absolute, beeause polystyrene or other polymer standards distinct from polymer under study have been employed for the column calibration (see sections 11.6.3 and 11.7.3.1). Still, the data equivalent to the polymer applied to the column cahbration, more or less precisely represent the tendencies of molar mass evolution in the course of building-up or decomposition polyreactions. 

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