Application of polyvinylpyrrolidone PVPK30 in dispersion polymerization

The application of PVP in dispersion polymerization

PVP can be used as thickener, stabilizer and particle size regulator in polymer emulsion polymerization and suspension polymerization. Generally speaking, PVP with larger molecular weight (K>60) acts as a protective agent to prevent suspension precipitation, prevent the aggregation of larger particle size particles in the emulsion and dispersion solution, and make it stable. Low molecular PVP is more suitable for dispersing agents, especially for dispersing low density substances. Of course, the molecular weight and its distribution must be compatible with the particle size and distribution of the dispersion.

PVP and NVP copolymers can be used in styrene homopolymerization and copolymerization, suspension polymerization of vinyl chloride, methacrylate and polyurethane, emulsion polymerization of acrylic ester and vinyl carboxylate, which can play an excellent role in dispersion stability, particle size control,viscosity adjustment and resin performance improvement.

In the suspension polymerization of granular polyurethane urea, some of the previous technologies use organic solvents, and some can only get water dispersion or get large chunks after solidification, which brings inconvenience to the use and transportation, increases the processing cost, and affects the product quality. Therefore, it is urgent to develop a one-step synthesis technology of polyurethane urea with small particle size. In this one-step polymerization technique, the obtained solid phase polymer is not easily emulsified and can be separated by conventional separation methods. The particle size of polymer can be controlled by controlling the stirring speed and selecting dispersant. PVP is particularly suitable as a suspension stabilizer for this one-step polymerization. Its addition amount is about 2.5 ~ 5.0% of the water phase, and its molecular weight takes K value of 60. When the reaction is finished, the toluene – water azeotrope is steamed, and the powder urethane can be obtained by cooling, filtering, washing and drying. When the amount of PVP K60 was 2.5%, the polymer particle size was 800 μ-1000 μ. The isocyanate content of the polymer is less than 0.5%, basically non-porous, and can be used in coatings, binkers, flocculants,laminate composites, to make films, with a thickness of 100 μ. As a coating, with a thickness of 10 μ.

It is well known that the type and concentration of suspension stabilizer has a decisive influence on the shape, size and morphology of the polymer. In some suspension polymerization, only the stability of PVP K90 and PVA can produce uniform particle size beads with porous shells. This proves that PVP has a good stabilizing effect.

When methyl methacrylate, vinyl acetate, polyethylene, chloroprene and other monomers are polymerized, the resulting products often have high elasticity only at 120 ~ 150 temperatures, and contain impurities such as unreacted initiators. However, when PVP K30 or PVP K15 was introduced as emulsifier, the high elastic temperature range of methyl methacrylate polymer was 120-280. When emulsion polymerization is performed at 50, the polymerization monomer can be completely transformed in 20 to 100 minutes, and the resulting polymer flow temperature is 270 to 280.

In the suspension polymerization of vinyl chloride, if PVP is used as the dispersion stabilizer, the thermal stability of the polymer is good. When NVP copolymer is used as the stabilizer, the dispersion of PVC can be improved. By using a mixed suspension agent composed of NVP and vinyl acetate copolymer as one of the components, the thermal stability, oil absorption rate, particle size, fish eye and residual bill of the obtained polymer have been greatly improved. The results are shown in Table 43:

Table 43 Comparison of properties of PVC polymers with different suspension agents

(1) Mixed suspension, the remaining components are acetylated PVA or methylhydroxypropyl cellulose.

(2) The ratio of NVP to vinyl acetate was 3/7.

(3) NVP copolymer with isooctyl acrylate, NVP/IOA is 9/1.

In styrene butadiene emulsion polymerization, PVP and surfactant can play a co-stabilizing role, and finally get a low viscosity, high solid content of latex, and small particle size, good water resistance, drying speed, no foaming, solid content up to 60 ~ 65%. The product can be used in coating, carpet glue and many other places where polymer emulsions are used, and the amount of PVP is 0.5 ~ 1.0%. The molecular weight of PVP K15 was the best, and the carpet lamination coating was prepared with the latex obtained with different coordination of surfactants, and the results were shown in Table 44.

Table 44 Comparison of adhesive properties of styrene butadiene latex with different surfactants