Seed polymerization

The monomer conversion in this seeded polymerization system is independent of the degree of segregation as long as an exponential residence time distribution function is maintained. 

The effect of reaction conditions on h (and Rp, of course) can be observed even with styrene, which shows a very strong tendency toward case 2 behavior under a wide range of reaction conditions [Brooks and Qureshi, 1976 Hawkett et al., 1980]. Seed polymerization... 

Seeded polymerization is defined as polymerization of post-added monomer in the presence of particles. A conventional example of seeded polymerization is the polymerization of styrene (St) and acryronitrile (AN) in the dispersion of polybutadiene (PB) particles. In this polymerization, a portion of St and AN penetrates into the PB particle and the other portion stays in the aqueous phase. The former graft-polymerize with PB or polymerize by themselves in PB particle. The progress of polymerization in the particle leads to phase inversion to form a salami structured particle in which PB islands are dispersed in a poly(St-co-AN) sea. St and AN in aqueous phase may polymerize to form independent particles. 

The already mentioned definition of seeded polymerization is in the broad sense of the word. Seeded polymerization in the narrow sense is polymerization after swelling the seed particle with monomer. Figure 12.2.4 shows what the seeded polymerization can form. Making larger particles is one of popular uses of seeded polymerization, but it does not belong to surface modification. Therefore, making larger particles is not discussed here. 

Seeded polymerization using a slight amount of monomer leads to the surface modification without changing particle size. The resulting particles are a kind of core-shell particles or, more exactly, core-skin particles (Fig. 12.2.4C). Seeded polymerization of sugar-units-containing styrene derivative on polystyrene seed particle was carried out to obtain latex particles covered with sugar units (17). A necessary condition for this is that the monomer is more hydrophilic than the seed polymer. If not, the monomer permeates into the seed particle and only a small fraction remains on the... 

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). 

St and divinylbenzene (DVB) were polymerized in a dispersion of acryl-amide-methacrylic acid-methylenebisacrylamide terpolymer particles (25). Fine polystyrene particles were formed in/on each seed terpolymer particle. The former was smaller by about one-twentieth than the latter. The distribution of polystyrene particles depended on the cross-link density. Different amounts of St and DVB were charged in the seeded polymerization, and the resulting composite particles were used for protein adsorption measurement to assess the hydrophobicity of the particle surface. The adsorbed amount was almost proportional to the amount of St and DVB charged. In contrast, cells were less stimulated by the 5% St-containing particle than by the 0% St-containing one, that is, the seed particle. This phenomenon is attributed to selective protein adsorption on the 5% St-containing particle (26). 

Second stage of polymerization seeded polymerization of already mentioned monomers and divinylbenzene. 

Seeded polymerization Graft polymerization VSolid-phase synthesis, ... 

Another aspect of seeded polymerization is that a seed may be formed from one monomer composition whereas the added monomer may be of a different composition. This may lead to core-shell latex particles. Such copolymers may have substantially different properties then regular copolymers. 

Title Storage-Stable Polymer-Oligomer Particles and Their Use in Seed Polymerization... 

Leth-Olsen et al. (1) prepared single-stage seed polymerization to form polymer particles having a size distribution between 10 and 100 pm with a narrow size... 

Seed polymerization using a polystyrene latex was used by Gaschler et al. (3) to prepare aqueous styrol-butadiene polymer dispersions. 

Most unwanted polymerization events of methncrylic monomers occur because of overheating, leading to inhibitor depletion or oxygen depletion, and in turn to inhibitor inactivation. Care should be taken to avoid stagnant areas in transfer lines or pump heads where polymerization may begin and which may then act to seed polymerization of the bulk material. 

Moles monomer polymerized per liter aqueous phase 6 Unseeded polymerizations c Seeded polymerizations 10.3 420... 

It was further developed the following year (22), and was based primarily on the scheme of Priest (12) with an idea from Gardon (9d). The latter suggested that the rate of capture of oligomeric radicals in solution by pre-existing particles, R, should be proportional to the collision cross-section, or tfie square of the radius of the particles, r. This has been called the "collision theory" of radical capture. In 1975 Fitch and Shih measured capture rates in MMA seeded polymerizations and came to the conclusion that R was proportional to the first power of the radius, as would e predicted by Fick s theory of diffusion (23). In his book, K. J. Barrett also pointed out that diffusion must govern the motions of these species in condensed media (10). 

Experimentally one can obtain absolute values of the capture rates by conducting a series of seeded polymerizations in which N and r are varied. If conditions are set so that no coagulation takes place (R = 0), then Equations 3 and 7 combined give... 

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. 

The seeded polymerization procedure was the same as described earlier (10) except that only. 175 of the recipe was used. Polymerizations of all monomers were run at 60.0C using four different initial initiator concentrations (IQ=2x10 M to 10 x 10 M K2S2O8) at a constant volume of organic phase per unit volume of aqueous phase (Vorg/Vaq 0.33). Rates were calculated from the slopes of the linear portion of the polymer/time curves at 30-85% conversion. 

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

Information on particle growth during either a seeded polymerization or during the growth stage of an un-seeded polymerization at different degrees of conversion also could enhance the understanding of the kinetics. In earlier work (4,5) the rate of polymerization, for polystyrene latexes primarily, has been related to the latex particle diameter and the total number of particles in the reactor. It would be useful to obtain kinetic data and develop the kinetic relationships for styrene (S)-butadiene (B) latexes. 

Aramendia et al. [20] have compared the nonreactive sodium lauryl sulfate (SLS) to the polymerizable sodium tetradecyl maleate (M14), synthesized according to the procedure described by Stahler [21] in the seeded polymerization of methyl methacrylate/butyl acry-late/acrylic acid using tert-butyl hydroperoxide and ascorbic acid as initiator. Nonyl phenol 30 EO (NP30) was the nonionic surfactant used in the seed latex. Latex characterization... 

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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