Seeded polymerization

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

We found that the CD sign of the chiral aggregates around the CD reversal point (THF/methanol 55%/45%) is switchable, depending on the solvent addition order either Method I (methanol added into THF solution of the polysilane) or Method II (THF solution of the polysilane added into methanol), as shown in Fig. 21. This solvent polarity dependent CD switching may be related to the polymeric seed chirality in the initial stage of the polymer chirality amplification process, which can be detected as Cotton CD signal active polymer aggregates. 

In the nucleated polymerization type of model, oligomerization/polymerization of PrP is necessary to stabilize PrP-res sufficiently to allow its accumulation to biologically relevant levels. Spontaneous formation of nuclei or seeds of PrP-res is rare because of the weakness of monovalent interactions between PrP molecules and/or the rarity of the conformers that polymerize. However, once formed, oligomeric or polymeric seeds are stabilized by multivalent interactions (Jarrett and Lansbury,Jr., 1993). 

Although good reproducibility can be achieved under laboratory conditions (Figure 4.2), reproducibility of N under plant conditions can be poor. This problem can be overcome by the use of seeded polymerization in which N is predetermined by dilution of a completely polymerized seed latex with a small particle size provided the dilution is not excessive, renucleation can be avoided and reproducibility ensured. 

Fronts of concentrations of 0.03, 0.06, and 0.15% (AIBN to MMA) were run at the temperatures ranges of 42 to 47,47 to 52 and 66 to 68 C. The ranges were a result of temperature fluctuations due to the type of thermostat used. Three samples at each set of conditions were run to determine an average and standard deviation. To ensure that the fronts were initiated by the polymeric seed, controls were run that did not contain seeds. To ensure that the gradient movement detected was not solely seed dissolution, controls using seeds and solutions of 4.0% TEMPO, a free-radical scavenger used as an inhibitor, in... 

In order to better understand the properties of the metathesized plant oils, postmodification of these polymerized seed oils was also examined [25]. To explore the possibilities of new materials that could arise from the polymerized oils, Larock and coworkers evaluated both the hydrogenation and epoxidation of metathesized soybean oils. Normally, thermally polymerized metathesized oils yield a yellow, brittle gel. This brittle gel is often undesirable, so other processes were investigated to develop a more usable material. In order to alter the properties of the material, complete hydrogenation was accomplished with 10% palladium on carbon to produce a white/pale cream-colored, crystalline material with melting points between 53 and 60 C. This metathesized soybean oil was also treated with conditions to invoke epoxidation of the double bonds. Unfortunately, the initial attempts with m-chloroperbenzoic acid (mCPBA) were problematic for the metathesized soybean oil despite being satisfactory for unaltered soybean oil. It was found that material that had been epoxidized by mCPBA would polymerize in a few hours, most likely due to the difficulty in the complete removal of the w-chlorobenzoic acid generated during the epoxidation. To circumvent this problem, conditions... 

Ivanov, V.V., Stegno, E.V., and Pushchaeva, L.M. (1997) Non-thermal frontal polymerization of methyl methacrylate with a polymeric seed modified with cobalt-porphyrin complex additives. Chem. Phys. Rep., 16, 947-951. 

Seeded emulsion polymerization can be used with batch, semi-continuous, or continuous polymerization to give the desired value of N, In batch or semi-continuous emulsion polymerization, seeding ensures batch-to-batch reproducibility of the final particle size in continuous emulsion polymerization, it ensures the reproducibility, not only of the final particle size, but also of the conversion of the exit stream. Seeded emulsion polymerization is equally adaptable to emulsion homopolymerization and copolymerization. Moreover, two-stage or multiple-stage polymerizations can be used to produce core-shell latex particles the variation of the process type---batch, semi-continuous, continuous----as well as the para-... 

Subsequently, there have been many improvements to the dispersion polymerization process that have allowed for AM/ AETAC and AM/DADMAC cationic, AM/sodium aaylate anionic, acrylamide nonionic, and AM//V7V-dimethyl-/V-acryloyloxyethyl-/V-(3-sulfopropyl) ammonium betaine polymeric dispersions [16, 38-41]. These improvements, such as the development and utilization of new dispersants, the use of polymeric seeds to fecilitate precipitation, optimization of... 

Other than fuel, the largest volume appHcation for hexane is in extraction of oil from seeds, eg, soybeans, cottonseed, safflower seed, peanuts, rapeseed, etc. Hexane has been found ideal for these appHcations because of its high solvency for oil, low boiling point, and low cost. Its narrow boiling range minimises losses, and its low benzene content minimises toxicity. These same properties also make hexane a desirable solvent and reaction medium in the manufacture of polyolefins, synthetic mbbers, and some pharmaceuticals. The solvent serves as catalyst carrier and, in some systems, assists in molecular weight regulation by precipitation of the polymer as it reaches a certain molecular size. However, most solution polymerization processes are fairly old it is likely that those processes will be replaced by more efficient nonsolvent processes in time. 

Popcorn Polymerization CO-Polymerization, frequendy referred to as popcorn polymerization because of the appearance of the product, can be a dangerous side reaction if not carefully controlled. The polymeriza tion appears to proceed without external initia tion (69—71), and is catalyzed by the tightly gelled polymer seeds that are a product of the polymerization. Once seeds are present and immersed either in the Hquid or vapor phase of monomer, their weight increases exponentially with time. 

Only particles of linear or very slightly cross-linked <0.6%) polymers may be produced by dispersion polymerization. Obviously, dispersion polymerization may be used for the production of monosized seed particles, which, after transfer to aqueous conditions, are used for the production of different cross-linked and macroporous particles by the activated swelling and polymerization method. 

Two different methods have been used for the incorporation of the activating ogliomer (or monomer) in the seed particles. The first method involves the application of a small organic chemical, such as chloroundecane or dibutyl phthalate, which is incorporated into the particles in the first swelling step. In the second method, an ogliomer compound is formed by polymerization of monomers that are absorbed inside the seed particles. 

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. 

Sheu and coworkers [111] produced polysty-rene-polydivinylbenzene latex interpenetrating polymer networks by the seeded emulsion polymerization of styrene-divinylbenzene in the crosslinked uniform polystyrene particles. In this study, a series of uniform polystyrene latexes with different sizes between 0.6 and 8.1... 

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