Copolymer PVAC dispersion

PVAC dispersions continue to be used for paper as consolidants (Wachter, 1987) and adhesives, especially the VAE copolymers (Maynor and van der Reyden, 1989 Scheper, 2005). 

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. 

Table 2. Dispersibility of PVAc-styrene graft copolymers in various solvents from dried samples at room temperature graft copolymer/solvent = 1/100 (w/v)...

Dispersions of poly(vinyl acetate) in -alkanes have been prepared using a diblock copolymer of poly(styrene-b-[ethylene-co-propylene]) as the stabilizer for the colloidal PVAc. The dispersing agent contained 38.5% styrene and was used at a concentration of 1-5 wt%. The monomer concentration ranged from 10 to 30 wt% in the various experiments. A typical initiator was 2,2 -azobisisobu-tyronitrile. The particle diameters were in the range of 0.10 to 0.31 fan [179],... 

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... 

Several copolymers were synthesized in an organic solvent in order to analyze the final product in the absence of any additive required for a water dispersion. AIBN was used as the radical initiator and the reactions were performed in nitrogen atmosphere. The spectroscopic characteristics of the copolymers were compared with those of an analogous PVAc homopolymer obtained with the same procedure. 

Poly (vinyl acetate) (PVAC), A oXymec of vinyl acetate at different degrees of polymerization (Fig. 1.6). Solutions or dispersions of its homopolymers and copolymers are used as binders in paints, lacquers, and adhesives. 

Poly (vinyl alcohol-co-vinyl acetate) polymers are surface active species which can be used to stabilise latex and oil in water dispersions. In order to understand the properties of these materials, it is necessary that their sequence distributions are well characterised. A number of NMR studies on the microstructure of PVA/PVAc copolymers have been made [51-53] (see also chapter 3). Moritani and Fujiwara [51], for example, have used proton and carbon-13 NMR spectroscopy to extract dyad distributions for a range of copolymers with different degrees of deacetylation. Samples were prepared using one of three routes direct saponification of PVAc alcoholyis of PVAc using sodium methoxide and reacetylation of PVA. From the polymer composition and the dyad distribution, the parameter rj was calculated for each polymer as follows ... 

Vinyl-containing - (either as a principal or secondary phase). These are mainly water-based dispersions. Included are examples of polyvinylacetate (PVA and PVAC -copolymer) adhesives. Commonly known as white glue , these are widely used in the woodworking industry. Those given here are considered the higher performance, industrial types rather than products for household use. 

Poly(vinyl acetate) (PVAc) and ethylene/vinyl acetate copolymers were prepared by dispersion polymerization in supercritical CO2 using both fluori-... 

As can be seen from the bulk of the work reviewed, CO2 could play an important role in dispersion polymerizations. Various polymers, including PMMA, PS, PVAc, ethylene/vinyl acetate copolymers, and PDVB, have been synthesized by dispersion polymerizations, with the surfactant stabilizers ranging from homopolymers to copolymers, each one specifically designed for the polymerization. As our knowledge of dispersion polymerization increases, stabilizers can continue to be refined so as to be precisely designed to accommodate each polymer. In addition, today s stabilizers are expensive therefore, future work should focus on the design of less costly alternatives. 

PS PVAc PS-g-PVAc The graft copolymer produced by free radical polymerization of a PVAc macromonomer with styrene yields improved dispersion, adhesion and ductility of PS/PVAc blends 63... 

Aqueous miniemulsion polymerization of styrene was performed in the presence of CeFis-I as CTA, yielding particles with a good control of the molecular weights, in contrast to emulsion polymerization where the transfer agent efficiency was low due to a slow diffusion of the hydrophobic perfluor-ohexyl iodide from the monomer droplets to the active particles during polymerization.The chains were capped with iodine as evidenced by the successful chain extension upon addition of butyl acrylate. The miniemulsion process was also successfully applied to the preparation of triblock copolymers PS-b-PDMS-b-PS starting from a telechelic diiodo-poly(dimethylsiloxane) macrotransfer agent. A somewhat similar procedure was used to prepare PVAc-b-PDMS- -PVAc triblock copolymers, but the polymerization was performed under UV irradiation (instead of thermal initiation) and in the absence of radical initiator. In this case, the aqueous dispersion medium was a key parameter to achieve a controlled polymerization (Scheme 19). ... 

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