Diameter of polymer particles

For emulsion polymerization, the rate of generation of radicals from the initiator is of the order of 10 radicals/cm /s the number of polymer particles is about 10 particles/cm and the average diameter of polymer particles is 1000 A. The rate of diffusion of radicals to the polymer surface is... 

Suspension polymerization of VDE in water are batch processes in autoclaves designed to limit scale formation (91). Most systems operate from 30 to 100°C and are initiated with monomer-soluble organic free-radical initiators such as diisopropyl peroxydicarbonate (92—96), tert-huty peroxypivalate (97), or / fZ-amyl peroxypivalate (98). Usually water-soluble polymers, eg, cellulose derivatives or poly(vinyl alcohol), are used as suspending agents to reduce coalescence of polymer particles. Organic solvents that may act as a reaction accelerator or chain-transfer agent are often employed. The reactor product is a slurry of suspended polymer particles, usually spheres of 30—100 pm in diameter they are separated from the water phase thoroughly washed and dried. Size and internal stmcture of beads, ie, porosity, and dispersant residues affect how the resin performs in appHcations. 

Associated with the class of polymer particles n(t,i)dx in the polymer reactor is a physical property p(t,x) (e.g. diameter or area of particles of class (t,x), etc.). Then, a total property Pit) (e.g. total particle diameter in the reactor at time t) can be obtained by summing (integrating) p(t,x) over all classes of particles in the reactor vessel, viz ... 

Fig. 23 Confocal laser scanning microscopic image of rhodamine-labeled SiP coated with PMMA brush The diameter of silica particle core is 230 nm, and the Mn of the graft polymer is 256000...

Comparison between Experimental Results and Model Predictions. As will be shown later, the important parameter e which represents the mechanism of radical entry into the micelles and particles in the water phase does not affect the steady-state values of monomer conversion and the number of polymer particles when the first reactor is operated at comparatively shorter or longer mean residence times, while the transient kinetic behavior at the start of polymerization or the steady-state values of monomer conversion and particle number at intermediate value of mean residence time depend on the form of e. However, the form of e influences significantly the polydispersity index M /M of the polymers produced at steady state. It is, therefore, preferable to determine the form of e from the examination of the experimental values of Mw/Mn The effect of radical capture mechanism on the value of M /M can be predicted theoretically as shown in Table II, provided that the polymers produced by chain transfer reaction to monomer molecules can be neglected compared to those formed by mutual termination. Degraff and Poehlein(2) reported that experimental values of M /M were between 2 and 3, rather close to 2, as shown in Figure 2. Comparing their experimental values with the theoretical values in Table II, it seems that the radicals in the water phase are not captured in proportion to the surface area of a micelle and a particle but are captured rather in proportion to the first power of the diameters of a micelle and a particle or less than the first power. This indicates that the form of e would be Case A or Case B. In this discussion, therefore, Case A will be used as the form of e for simplicity. 

The emulsion polymerization process involves the polymerization of liquid monomers that are dispersed in an aqueous surfactant micelle-containing solution. The monomers are solubilized in the surfactant micelles. A water-soluble initiator catalyst, such as sodium persulfate, is added to the aqueous phase. The free radicals generated cause the dispersed monomers to react to produce polymer molecules within the micellar environment. The surfactant plays an additional role in stabilizing dispersion of the produced polymer particles. Thus, the surfactants used both provide micelles to house the monomers and macroradicals, and also stabilize the produced polymer particles [193,790], Anionic surfactants, such as dodecylbenzene sulfonates, are commonly used to provide electrostatic stabilization [193], These tend to cause production of polymer particles having diameters of about 0.1-0.3 pm, whereas when steric stabilization is provided by, for example, graft copolymers, then diameters of about 0.1-10 pm tend to be produced [790,791]. 

Particle design is presently a major development of supercritical fluids applications, mainly in the paint, cosmetic, pharmaceutical, and specialty chemical industries [4CM-2]. The particle formation of functional pigments with biodegradable polymer has been successfully performed by gas-saturated solution (GSS) process using scC02 and PEG in a thermostatted stirred vessel [43]. The average diameter of the particles obtained by GSS at different conditions (40 and 50 °C, 10-30 MPa) is about 0.78-1.472 pm. 

As a third advantage, polymer particles in dispersions allow one to control or imprint an additional length scale into a polymer bulk material, given by the diameter of the particle, which is offered by the process of film formation. That way, polymer materials can be generated employing rational structure design not only on the molecular scale, but also on the mesoscale. 

Experimental investigations that deal in detail with particle formation in emulsion copolymerization are scarce. Nomura et al. [78] studied the kinetics of particle formation and growth in the emulsion copolymerization of VDC and MMA using NaLS as the emulsifier and KPS as the initiator. The number of polymer particles produced was determined using particle diameters measured by both electron microscopy (TEM) and dynamic light scattering (DLS) for comparison. They found that where Sq and Iq are the initial... 

The suspension polymerization is conducted using monomer-soluble per-oxy initiators. Water-soluble polymers, such as poly(vinyl alcohol), are typically used as suspending agents to reduce the coalescence of the polymer particles [ 17]. A slurry of polymer particles 30-100 pm in diameter is formed during the polymerization. The particles are washed and dried before further processing. 

Table I shows that the diameters of the polymers from styrene are approximately twice as large as those from 1,4-DVB, and in all experiments with 1,4-DVB at least 6 times more particles have been formed than with styrene. The maximum diameters of spherical particles from 1,4-DVB which can be obtained, are about 500 A. Larger particles are mostly irregularly shaped (see 4.2) whereas in the case of styrene, latex particles of 2000 A and more may be prepared easily. These differences may be explained by a discussion of the SMITH-EWART theory ( ). According to this theory the number N of latex particles formed in the emulsion polymerization of styrene is given by...

The number of polymer particles was determined from the monomer conversion Xj and the volume average diameter of the polymer particles dp measured with an electron microscope. 

Df = particle diameter at end of polymerization N = number of polymer particles per gm of polymer... 

When the toner is loaded with pyrogenic silica particles, these appear as isolated protrusions at the surface (Fig. IB-D). Depending on the modification, the diameters of the protrusions range between 50 and 200 nm. When HMDS is used as the silylation reagent, a silane monolayer is fbrmed. In this case the diameter of the particles is ca. 100 nm. Such particles are adsmbed mainly as isolated aggregates to the toner surface (Fig. IB). PDMS-modified particles seem to coat almost the entire toner particle (Fig. 1C). Their topographical diameter is doubled conq)aied to that of the HMDS-coated particles. This can be explained by the formation of a polymer-like PDMS layer. HMDS/PDMS-coated silicas appear only as isolated protrusions with a diameter up to 250 nm (Fig. ID). 

Spherical silica nanoparticles, with an average diameter of 70 nm, modified with the initiator moiety (S-8) were employed for the copper-mediated radical polymerization of styrene.457 The diameter of the particles and the molecular weights of the obtained polymers increased with conversion. For example, the average diameter of the particles obtained at 58.8% monomer conversion was increased to 188 nm, where the Mn and MWDs of the arm polymers were 26500 and 1.33, respectively. Given a narrow size distribution (<10%), the nanoparticles within the film domains were observed to pack into hexagonal arrays. A smaller silica nanoparticle with 14 nm was employed also for the copper-catalyzed radical polymerization of styrene initiated with S-9.458... 

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