Vinyl seeded

Continuous emulsion copolymerization processes for vinyl acetate and vinyl acetate—ethylene copolymer have been reported (59—64). CycHc variations in the number of particles, conversion, and particle-size distribution have been studied. Control of these variations based on on-line measurements and the use of preformed latex seed particles has been discussed (61,62). 

DSEP direct soapless emulsion polymerization, SSEC seeded soapless emulsion copolymerization, DDC direct dispersion copolymerization, TDSC two-stage dispersion copolymerization, ATES Allyl trietoxysilane, VTES vinyl trietoxysilane, DMAEM dimethylaminoethyl-methacrylate, CMS chloromethylstyrene, GA glutaraldehyde, AAc Acrylic acid Aam Acrylamide HEMA 2-hydroxyethylmethacrylate. 

In another study, uniform composite polymethyl-methacrylate/polystyrene (PMMA/PS) composite particles in the size range of 1-10 fim were prepared by the seeded emulsion polymerization of styrene [121]. The PMMA seed particles were initially prepared by the dispersion polymerization of MMA by using AIBN as the initiator. In this polymerization, poly(7V-vinyl pyrolli-done) and methyl tricaprylyl ammonium chloride were used as the stabilizer and the costabilizer, respectively, in the methanol medium. Seed particles were swollen with styrene monomer in a medium comprised of seed particles, styrene, water, poly(7V-vinyl pyrollidone), Polywet KX-3 and aeorosol MA emulsifiers, sodium bicarbonate, hydroquinone inhibitor, and azobis(2-methylbu-... 

Hollow and porous polymer capsules of micrometer size have been fabricated by using emulsion polymerization or through interfacial polymerization strategies [79,83-84, 88-90], Micron-size, hollow cross-linked polymer capsules were prepared by suspension polymerization of emulsion droplets with polystyrene dissolved in an aqueous solution of poly(vinyl alcohol) [88], while latex capsules with a multihollow structure were processed by seeded emulsion polymerization [89], Ceramic hollow capsules have also been prepared by emulsion/phase-separation procedures [14,91-96] For example, hollow silica capsules with diameters of 1-100 micrometers were obtained by interfacial reactions conducted in oil/water emulsions [91],... 

A reactive surfactant shown next (RS) was used as a comonomer in a seeded polymerization. RS was easily adsorbed on seed particles due to their amphiphilicity. If dialkyl fumarate was preabsorbed in the particle, the polymerization proceeded quickly and resulted in the formation of skin layer of RS-fumarate copolymer. Because the vinyl group in RS is an allyl type, RS in aqueous phase hardly polymerizes and no water-soluble homopolymer was formed. The active ester group of RS on the skin layer was used for the preparation of functional microspheres (18). 

Seeded Emulsion Terpolymerization of Vinyl Acetate, Butyl Acrylate, and Vinyl Neodecanoate with Gradual Monomer and Initiator Additions... 

Add the monomer seed solution consisting of 12 g of vinyl acetate, 3.00 g of butyl acrylate, and 5.00 g of vinyl neodecanoate followed by 0.16 g of ammonium persulfate. 

The emulsion polymerization of vinyl hexanoate has been studied to determine the effect of chain transfer on the polymerization kinetics of a water-insoluble monomer. Both unseeded and seeded runs were made. For unseeded polymerizations, the dependence of particle concentration on soap is much higher than Smith-Ewart predictions, indicating multiple particle formation per radical because of chain transfer. Once the particles have formed, the kinetics are much like those of styrene. The lower water solubility of vinyl hexanoate when compared with styrene apparently negates its increased chain transfer, since the monomer radicals cannot diffuse out of the particles. 

Kinetics of Vinyl Hexanoate. A series of standard polymerizations was conducted using 10 ml of vinyl hexanoate in a total volume of 140 ml with varying amounts of emulsifier and initiator. The effect of varying initiator, particle number, and organic volume fraction in seeded runs, as well as for unseeded polymerizations, were also studied. The results are summarized in Table II. 

At low seed concentrations, R. > R dN/dt> 0, and new particles will be formed. As the number of seed particles is increased at a given size r, a condition will be reached at which no new particles are formed, i.e. dN/dt =0. At this point R = Rc If R. is independently known, R is immediately obtained. In seeded polymerizations with MMA, Fi ch and Shih (23), and with vinyl chloride, Gatta and coworkers (24) found the rate of capture proportional to N r, in support of Equation 7. A problem with Equation 7 arises from the fact that the concentration of free radicals in solution, C, cannot be determined, so that absolute values of R cannot be predicted. There is the further complication that C and R may be interdependent, so that strict proportionality ofCR to N r may not hold in all cases. A way around this difficulty was given by Ugelstad and will be discussed later. 

Azad and Fitch (5) investigated the effect of low molecular weight hydrocarbon additives on the formation of colloidafr particles in suspension polymerization of methyl methacrylate and vinyl acetate. It was found that the additives n-octane, n-dodecane, n-octadecane, n-tetracosane and mineral oil exerted a thermodynamic affect depending upon water-solubility and molecular weight. Since these effects on emulsion polymerization have not been considered by the earlier investigators, we have chosen n-pentane and ethyl benzene as additives with limited water-solubility and n-octadecane, and n-tetracosane as water-insoluble ones. Seeded emulsion polymerization was chosen so that the number of particles could be kept constant throughout the experiments and only the effect of the other parameters on the rate could be determined. 

The comparison of seeded emulsion polymerization, Rp, of three monomers (vinyl acetate, vinyl tri-deuteroacetate, and trideuterovfnyl acetate) at various initiator concentrations. The polymerization was run at 60°C with K2 2 8 as n t ator ... 

Experimental Study of the Seeded Polymerization of Vinyl Acetate in a Tube... 

While vinyl acetate is normally polymerized in batch or continuous stirred tank reactors, continuous reactors offer the possibility of better heat transfer and more uniform quality. Tubular reactors have been used to produce polystyrene by a mass process (1, 2), and to produce emulsion polymers from styrene and styrene-butadiene (3 -6). The use of mixed emulsifiers to produce mono-disperse latexes has been applied to polyvinyl toluene (5). Dunn and Taylor have proposed that nucleation in seeded vinyl acetate emulsion is prevented by entrapment of oligomeric radicals by the seed particles (6j. Because of the solubility of vinyl acetate in water, Smith -Ewart kinetics (case 2) does not seem to apply, but the kinetic models developed by Ugelstad (7J and Friis (8 ) seem to be more appropriate. 

The objective of this study was to investigate the feasibility of using a tubular reactor for the seeded emulsion polymerization of vinyl acetate, and to study the effect of process variables on conversion rate and latex properties. 

Initial Batch Reactor Studies. An agitated 2000 ml thick-walled glass reactor was blanketed with nitrogen and operated at 50°C. Vinyl acetate containing about 15 ppm hydroquinone was used without purification. The ionic emulsifier was Sipex EST-30, advertised as a sodium tridecyl ether sulfate, and the nonionic surfactant was Siponic L-25, a lauryl alcohol ethoxy-late. Table I shows the recipes and properties of the three seed latexes produced in the batch reactor. Essentially complete conversions were obtained in 30 to 45 minutes, but with a temperature rise of almost 50°C. 

This study of the continuous, tubular, seeded emulsion polymerization of vinyl acetate has led to the following conclusions ... 

Such hydrophilic macromonomers (DPn=7-9) were radically homopolymer-ized and copolymerized with styrene [78] using AIBN as an initiator at 60 °C in deuterated DMSO in order to follow the kinetics directly by NMR analysis. The macromonomer was found to be less reactive than styrene (rM=0.9 for the macromonomer and rs=1.3 for styrene). Polymerization led to amphiphilic graft copolymers with a polystyrene backbone and poly(vinyl alcohol) branches. The hydrophilic macromonomer was also used in emulsion polymerization and copolymerized onto seed polystyrene particles in order to incorporate it at the interface. 

In the seeded emulsion polymerization of some monomers —e.g., styrene—it is possible to obtain final latexes with uniform, large particles by adjusting, during polymerization, the quantity of added emulsifier the formation of new particles is prevented by the limited amount of emulsifier. For vinyl chloride, limited emulsifier is not sufficient to prevent the formation of new particles in fact, to obtain a monodispersed latex, the surface of the particles seeded in a given water volume must be controlled. It is assumed that the growth of new nuclei is related either to the rate of formation of primary useful radicals or to the rate that these are taken by the surface of sized particles. 

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-... 

Experiment B—Growing Particle Size of Seed Latex No. 2. Water (90 kg.), vinyl chloride (13.27 kg.), and seed latex No. 2 (7.85 kg.) (2.73 kg. solids) were placed in the kettle. About one hour after the start of the reaction, 64 kg. of the remaining VC was fed continuously, while simultaneously a solution of 0.336 kg. Empicol Ser in 2.0 kg. water was introduced, continuously, dropwise. Vinyl chloride (64 kg.) and soap (0.336 kg.) were introduced by the following procedure. In the... 

Behavior of VC in emulsion-seeded polymerization is quite different from that of other vinyl monomer such as styrene and vinyl toluene. For instance, in styrene-seeded polymerization, Vanderhoff (11) did not observe any anomalous seed growing. He reports uniform growing for a mixture of two seeds with a < = 2640 and 5570 A., respectively, by seeding 0.193 X 1012 particles/ml. H20, whose surface per ml. of water is, according to our calculations, equal to 0.121 X 1020 sq. A. 

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