Polymer seeds

Monodispersed poly (methyl methacrylate-ethyleneglycol dimethacrylate) is prepared by a multistep swelling and polymerization method. When a good solvent such as toluene is applied as a porogen, the seed polymer severely affects the pore structure, whereas no effects are observed with poor solvents, such as cyclohexanol, as a porogen, in comparison with the conventional suspension polymerization (68,69). 

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. 

This equation may be used for the estimation of the swelling capacity of the activated seed particles with the monomer. A typical graph sketched based on Eq. (11) is given in Fig. 18. This graph shows the variation of the swelling capacity of the seed polymer particles VmIVp) with the ratio of interfacial tension-initial particle radius... 

In this work, the characteristic "living" polymer phenomenon was utilized by preparing a seed polymer in a batch reactor. The seed polymer and styrene were then fed to a constant flow stirred tank reactor. This procedure allowed use of the lumped parameter rate expression given by Equations (5) through (8) to describe the polymerization reaction, and eliminated complications involved in describing simultaneous initiation and propagation reactions. 

Figure L Growth characteristics for seed polymer in CFSTR environments (a) growth characteristics for polymer chains in a micro-mixed environment (b) growth characteristics for polymer chains in a segregated environment...

Three polymer seeds were prepared in a batch reactor. The reactor with styrene and benzene was cooled to 0 C in an ice bath, initiator was injected into the reactor and reaction began with a gradual increase in temperature. Table II presents the initial conditions used in preparing the seed polymer and the molecular weights of the seed polymer. The molecular weight distribution of the pol3nner seeds are shown in Figure 5. 

Feed Concentration of Seed Polymer, Pqi (gm-mole/ liter)... 

Evaluation of Mixing Models. The micro-mixed reactor will produce polymer disttibutions with increasing amounts of high molecular weight tail as the degree of polymerization of the polymer product increases over that of the original seed polymer. 

Fraction passing through reaction zone in by-pass reactor o Superscript denotes feed stream of seed polymer... 

Special polymerization techniques are described [298] in which the polymerization is performed in an aqueous solution together with a polyvalent anionic salt in the presence of a water-soluble cationic polymer acting as a dispersant polymer. Furthermore, a seed polymer that is water soluble and a cationic polymer that is insoluble in the aqueous solution of the polyvalent anionic salt are present. 

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 strict vacuum-line technique was used for purifications of solvent, monomer, and initiator, preparation of solutions and polymerization. Polystyryllithium of a degree of polymerization of about 15 was prepared by using n-butyllithium and was used as a seed polymer. Purifications of reagents were most carefully carried out. See the original literature for details 17). 

The polymerization vessel is illustrated in Pig. 8. Ampoules A and B contained dilute and concentrated benzene solutions of the seed polymer, respectively, and ampoules C and D contained tetrahydrofuran (or dimethoxyethane) and a benzene solution of the monomer. The polymerization vessel was connected to a high-vacuum line, evacuated, flamed and sealed off. Then the break-seal on ampoule B was crashed, and the whole vessel was washed with the concentrated solution of living polymer. All the solutions were brought to E and the vessel was washed by condensing the benzene using a pad at Dry Ice-methanol temperature. The solvent was distilled into F from E and E was sealed off. The seals on A, C, and D were broken, and the dilute solution of living polymer was collected into G by turning the whole vessel upside down,... 

The growth ratio M/P of introduced monomer to the initially present seed polymer seems to have no effect. In fact, although most cases of uniform growing have been obtained with small M/P ratios, some runs carried out with almost equal M/P ratios (Runs 940 and 962) have given opposite results. 

Starodubtzev SG (1990) Vysokomolek Seed (Polymer Science USSR) B31 925... 

Bisenbaev AK, Makhaeva EE, Salecky AM, Starodubtzev SG (1W2) Vysokomolek Seed (Polymer Scfence) A34 92... 

By combining thermodynamically-based monomer partitioning relationships for saturation [170] and partial swelling [172] with mass balance equations, Noel et al. [174] proposed a model for saturation and a model for partial swelling that could predict the mole fraction of a specific monomer i in the polymer particles. They showed that the batch emulsion copolymerization behavior predicted by the models presented in this article agreed adequately with experimental results for MA-VAc and MA-Inden (Ind) systems. Karlsson et al. [176] studied the monomer swelling kinetics at 80 °C in Interval III of the seeded emulsion polymerization of isoprene with carboxylated PSt latex particles as the seeds. The authors measured the variation of the isoprene sorption rate into the seed polymer particles with the volume fraction of polymer in the latex particles, and discussed the sorption process of isoprene into the seed polymer particles in Interval III in detail from a thermodynamic point of view. 

Latex IPNs. Latex IPNs are the third type of IPNs and are manufactured according to the general schematic illustrated in Figure 3. Latex IPN synthesis involves the initial synthesis of a crosslinked seed polymer, usually in the form of an aqueous latex. The seed latex is then swollen with a second monomer/crosslinker/initiator system which is then polymerized "in situ" to form an aqueous IPN emulsion. Materials of this type are best suited to coating applications as illustrated by the development of "Silent Paint" by Sperling et al ( ). However, latex IPNs are limited to water emulsifiable monomer/polymer systems, most of which have fairly low service temperatures, less than 150 C. 

The ideal seeded experiment would be where seed latex particles are prepered in which the MWD of the seed is significantly different from that formed during subsequent seeded polym tzation. The instantaneous MWD formed at early times could then be estimated directly. Seed latexes of different sizes could be used to probe the effect of compartmentalization we Stress again that if the system is transfer-dominated, the MWD of formed polymer should be independent of panicle size). 

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... 

Figure 6.7. Schematic crossection of LIPNs at 100%, 75%, 50%, and 25% seed polymer (a) hydrophobic seed ...

Liu et al. also studied LIPN systems for damping control in coating applications [Liu et al, 1995]. A polystyrene (PS)/polyacrylate (PAcr) latex IPN was synthesized in a two-stage emulsion polymerization. Crosslinked PS was synthesized first as the seed polymer by a semi-continuous process,... 

For the emulsion polymerization of vinyl acetate without seed polymer imder purified nitrogen, using sodium laiuyl sulfate as surfactant and potassium persulfate as initiator, at 50°C, with agitation at 400 rpm in a resin kettle of 500 ml capacity, the same research group made the following observations [143]. 

Cationic surfactants, in contrast to anionic surfactants, usually reduce both the number of particles involved in the polymerization and the rate of polymerization. The nature of the stabilizing emulsifier has a marked effect on the polymerization kinetics. For example, addition of a non-ionic stabilizer [e.g., poly(vinyl alcohol), a block copolymer of carbowax 6000 and vinyl acetate, or ethylene oxide-alkyl phenol condensates] to a seed polymer stabilized by an anionic surfactant decreased the rate of polymerization to 25% of the original rate. The effect was as if the nonionic stabilizer (or protective colloid) acted as a barrier around the seed particles to alter the over-all kinetics. It may be that the viscosity of the medium in the neighborhood of the nonionic surfactant coating of the polymer particle is sufficiently different from that of an anionic layer to interfere with the diffusion of monomer or free radicals. There may also be a change in the chain-transfer characteristics of the system [156]. 

In another patent [53], a seeded emulsion polymerization is described. The seed polymer is prepared by emulsion polymerization of vinyl fluoride using tert-butyl peroxypivalate as initiator and ammonium G>-hydroperfluoronona-noate as emulsifier. The process required 9 hr at 40 kg/cm (0.4 MPa). The resultant particles were described as having an average diameter of 18/an (which we would consider a a bit large for emulsion particles) and are said to be present in a concentration of 2.26 X lo particles/dm. In the second stage of the process, this seed latex (400 ml in a total volume of 1.8 dm ) was subjected to the same reaction conditions a second time. 

There is a better chance to obtain a desired core-shell morphology if the interfacial tension between the seed polymer and water is higher than that between the second stage polymer and water (i.e. yiw Yivi)- When yiw an inverted... 

The successful production of kinetically stable core-shell particles will rely entirely on prevoiting radicals generated in the aqueous phase from diffusing into the seed particles, i.e. as long as the mraiomer feed rate keeps pace with the rate of polymerization. Jonsson s conclusions also underline the importance of the Tg of the seed polymer swollen by the corresponding amount of monomer accumulated in the system. He found that the deviations from the designed core-shell morphology were correlated to variations in the tonperature difference between the polymerization temperature and the Tg of the seed polymer. 

Puac, N., Petrovic, Z.Lj., Radetic, M., Djordjevic, A., 2005. Low pressure RF capacitively coupled plasma reactor for modification of seeds, polymers and textile fabrics. Mater. Sci. Forum 494, 291-296. 

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... 

Fig. 6.7 Schematic cross section of LIPNs at 100 %, 75 %, 50 %, and 25 % seed polymer (a) hydrophobic seed (b) hydrophilic cross-linked seed, both polymers cross-linked and (c) hydrophilic seed, second-stage cross-linked...

The encapsulation of seed polymer particles coated by anionic iron oxide nanoparticles is investigated using N-isopropylacrylamide as a main monomer, N,N-methylene bisacrylamide as a crosslinking agent, itaconic acid as a functional monomer and potassium persulphate as an anionic initiator. The magnetic latexes obtained are... 

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