Solubility PVAC dispersion

Suspension Polymerization. At very low levels of stabilizer, eg, 0.1 wt %, the polymer does not form a creamy dispersion that stays indefinitely suspended in the aqueous phase but forms small beads that setde and may be easily separated by filtration (qv) (69). This suspension or pearl polymerization process has been used to prepare polymers for adhesive and coating appHcations and for conversion to poly(vinyl alcohol). Products in bead form are available from several commercial suppHers of PVAc resins. Suspension polymerizations are carried out with monomer-soluble initiators predominantly, with low levels of stabilizers. Suspension copolymerization processes for the production of vinyl acetate—ethylene bead products have been described and the properties of the copolymers determined (70). Continuous tubular polymerization of vinyl acetate in suspension (71,72) yields stable dispersions of beads with narrow particle size distributions at high yields. 

We have studied the dispersibility of several pure PVAc-styrene graft copolymers with one PS branch in various selective solvents mainly at room temperature5. The experiment was done with two kinds of dried samples one was recovered from a tetrahydrofuran solution by pouring it into water and the other from a benzene solution which was poured into n-hexane. Let us refer to the former sample as A and the latter sample as B. Due to the difference in solubility of each polymer sequence in those solvents, sample A is supposed to have approximately such a microstructure that PVAc chains are extended and PS chains collapsed, while sample B has the inverse structure. A similar tendency was also pointed out by Merrett12. The results are summarized in Table 2. 

This short discussion of problems associated with stabilizing dispersions of PVAc and its copolymers leads to the conclusion that the hydrophilic nature of VAc make placement of stabilizing species (surfactant, charge, hydrated layer, etc.) difficult without incurring additional problems (decrease in rate of polymerization, increase in the concentration of water-soluble oligomers, increase in viscosity, etc.). As a result, a combination of approaches is often used in commercial latex production. The need for better surfactants, especially reactive surfactants, for the emulsion polymerization of vinyl monomers is still evident... 

Another method involves excimer fluorescence as a molecular probe see Section 2.9. The question may be raised as to whether polymer blends will become more miscible if the differences in their solubility parameters are reduced. Excimer fluorescence provides some evidence see Rgure 4.14 (52). Here, 0.2 wt.% of poly(2-vinyl naphthalene), P2VN, is dispersed in a series of poly (alkyl methacrylates). These include the following, which are identified in Figure 4.14 by acronym methyl, PMMA ethyl, PEMA n-propyl, PnPMA isopropyl, PiPMA n-butyl, PnBMA isobutyl, PiBMA . yec-butyl, PsBMA ferf-butyl, PtBMA phenyl, PPhMA, isobomyl, PiBoMA benzyl, PBzMA and cyclohexyl, PCMA. Two other host polymers were polystyrene, PS, and poly(vinyl acetate), PVAc. 

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