Technique, seed latex

The combination of high molecular weight with high polymerization rate is one reason for the popularity of the emulsion technique. Seeded polymerizations can be useful for making large-particle-size latexes by the emulsion technique. Thus a completed seed latex may be diluted to give the desirable value of Np particles per liter of emulsion. No additional surfactant is added, so no new polymer particles are formed. When monomer is fed and initiator is added, polymerization occurs in the previously formed particles, so that each one grows as monomer diffuses into it and is converted. 

Emulsion polymerization leads to a very narrow particle size distribution, which is suitable for use in plastisol applications. Resins having both a monodisperse and bimodal particle size distribution are produced. Blending of latexes is sometimes practiced with the extensive use of seed-latex techniques. A simplified schematic flow sheet for a continuous emulsion polymerization process is given in Figure 7. 

A new process, from Norway, has filled the size gap between emulsion and suspension polymerization techniques [7,8]. This novel polymerization method, the so-called swollen emulsion polymerization has been developed by Ugelstad for producing uniform polymeric particles in the size range of 2-100 /nm. This process comprises successive swelling steps and repolymerizations for increasing the particle size of seed polymer particles by keeping the monodispersity of the seed latex. 

A similar seeding technique can be used to prepare monodispersed polymer latex dispersions by emulsion polymerisation (see page 17). 

The surface area per gram occupied by Siponate DS-10 and Triton X-100 were measured to allow the calculation of surfactant surface coverage on the seed latexes. The experimental procedure and analysis were based on Maron s technique (17,18). The procedure utilized is explained in detail below. 

Few works have appeared on the seeded emulsion polymerization of vinyl chloride (VC). Giskehaug (5) recently used this technique in a kinetic study of the emulsion polymerization of VC, but he has not determined the number and distribution of particles in the final latexes. Kotlyar et al. (6) do not give sufficient experimental data for an exhaustive analysis of the results moreover, most of the growth experiments seem to have been carried out in the presence of free emulsifier. The data reported in some industrial patents (1,9) point out only the impor-... 

Polystyrene can be easily prepared by emulsion or suspension techniques. Harkins (1 ), Smith and Ewart(2) and Garden ( ) have described the mechanisms of emulsTon polymerization in batch reactors, and the results have been extended to a series of continuous stirred tank reactors (CSTR)( o Much information on continuous emulsion reactors Ts documented in the patent literature, with such innovations as use of a seed latex (5), use of pulsatile flow to reduce plugging of the tube ( ), and turbulent flow to reduce plugging (7 ). Feldon (8) discusses the tubular polymerization of SBR rubber wTth laminar flow (at Reynolds numbers of 660). There have been recent studies on continuous stirred tank reactors utilizing Smith-Ewart kinetics in a single CSTR ( ) as well as predictions of particle size distribution (10). Continuous tubular reactors have been examined for non-polymeric reactions (1 1 ) and polymeric reactions (12.1 31 The objective of this study was to develop a model for the continuous emulsion polymerization of styrene in a tubular reactor, and to verify the model with experimental data. 

The technique involves first producing a seed latex by emulsifier-free emulsion polymerisation. A polystyrene latex of about 1 pva diameter is usually used. The seed particles are initially swollen using a microemulsion of a free radical initiator and a low molecular weight activating solvent , such as dibutyl phthalate, emulsified in water by sonication using sodium dodecyl sulphate as stabiliser. The seed... 

Wu and Zhao studied LIPN systems by a two stage emulsion polymerization technique [Wu and Zhao, 1995]. A latex seed (polymer 1) was synthesized first by a semi-continuous emulsion polymerization process, swollen by the second... 

One patent reports the use of a seed -polymerization technique to produce an allyl acetate-ethyl acrylate copolymer [. In a typical example, to 305 gm of a 3.28% solution of poly(vinyl alcohol) (DP 1000) is added 10 gm of allyl acetate and 0.8 gm of potassium persulfate. The mixture is heated to 75°C followed by the addition of 190 gm of ethyl acrylate with heating for 2.25 hr at 80°-85°C. After stirring for an additional hour and cooling to room temperature, the resultant latex is claimed to exhibit 99.6% conversion of all of the monomer to polymer. The pH of the latex is said to be 2.5. 

Wu and Zhao studied LIPN systems by a two-stage emulsion polymerization technique (Wu and Zhao 1995). A latex seed (polymer 1) was synthesized first in a semicontinuous emulsion polymerization, swollen by the second-stage monomer or monomer mixture (forming polymer 2), and followed by polymerization to form IPN materials. Six kinds of monomers were used acrylonitrile (AN), vinyl acetate (VAc), n-butyl acrylate (liBA), methyl methacrylate (MMA), ethyl methacrylate (EMA), and ethyl acrylate (EA). The effect of composition, cross-linking level, feeding sequence of polymer 1 and polymer 2 on the IPN miscibility, and... 

A multistep emulsion polymerisation technique was used to produce cationic latex particles with surface amino groups. Seed particles of polystyrene were copolymerised with aminoethyl methacrylate hydrochloride or vinyl... 

---