Hollow particles polymer

Since this process depends on the stoichiometry of the reactants, sufficient amounts of EDA must be present to produce fully solidified polymer particles. Incomplete reactions yielded a polyurethane shell, which on the removal of unreacted liquid in the core by evaporation resulted in hollow particles (68). It would appear that the solid encapsulating polymer inhibits the diffusion of EDA into the rest of the original droplet. 

The anionic polymerization of masked disilenes proceeds via living anions, and therefore block copolymerization with a conventional vinyl monomer is possible. Recently, interesting hydrophobic block copolymer of PMHS with poly(2-hydroxyethyl methacrylate) (PHEMA) and poly(methacrylic acid) (PMMA) have been prepared (Scheme 11). These polymers can be self-assembled and are transformed into polysilane micelles, shell cross-linked micelles (SCM), and nanometer-sized hollow particles. ... 

Hyuk Im S, Jeong U, Xia Y (2005) Polymer hollow particles with controllable holes in their surfaces. Nat Mater 4 671-675. 

The shell interior (hollow region) can be empty or filled (with a liquid but not a solid). The shell boundary is typically constituted of materials such as particles, polymers, charged polymers or polyelectrolytes (PEs), low-molecular-weight molecules such as enzymes, or their combinations [41], These structures find wide applications in fields such as encapsulation, targeted and controlled drug delivery, personal care, biosensing, diagnostics, catalysis and paints [13,32,42,43]. 

Hollow phosphazene microcaspules can be prepared by the reaction of poly(dichlorophosphazene) with hexamethylenediamine on the surface of a amino-silanized silica particle. Subsequent reaction of the product particles with an HF/NH4 solution that dissolves the silica from within the partcles, leaving a hollow shell. Polymer (50), which was resistant to degradation under the conditions used to remove the core, is highly crosslinked. 

Latexes made out of composite polymer particles (i.e., particles containing different phases) present definitive advantages in many applications. Thus, particles formed by an elastic core and a hard shell are used as impact modifiers for polymer matrices [14]. Hard-core, soft-shell particles are particularly useful for paints because they have a low MEET and are not sticky at higher temperatures [16]. Hollow particles are efficient opacifiers [15], and... 

Organic spheres are predominantly polymeric, consisting of synthetic or natural polymers. The field of polymeric nano- and microparticles is vast, comprising, for instance, latex particles for coatings, hollow particles for syntactic foams, and microcapsules for foaming and additive release. In addition, there are core-shell microbeads and coated polymeric particles, where the particles can exhibit multiple functionalities, thanks to the individual features of their different layers 1]. As fillers in thermosets and thermoplastics, hollow microspheres and expandable microcapsules are among the most frequently used in commercial applications. 

The particle morphology can have important ramifications for the latex product performance. Because multi-lobed particles have a larger hydrodynamic volume than a spherical particle of equal polymer mass, such types of latexes have been used to raise the viscosity in coatings applications. Hollow particles are used in paper coatings to improve the optical properties and surface smoothness. Particles with core-shell morphologies or with domains have been developed for impact modification. In addition, various microencapsulation techniques have been employed to enclose a wide variety of materials (47, 97,239) for pharmaceutical, agricultural and cosmetic applications. 

Colloid Polymer Science 211, Nos.2-3, Feb.-March 1999, p.252-6 POLY(METHYL METHACRYLATE) HOLLOW PARTICLES BY WATER-IN-OIL-IN WATER... 

PMMA particles with hollow structures were synthesised by water-in-oil-in-water emulsion polymerisation. Sorbitan monooleate was used as a primary surfactant and sodium lauryl sulphate and Glucopen (a polypeptide derivative) were used as secondary surfactants. Urethane acrylate, with a hard segment in the molecular backbone, a long soft segment in the middle and vinyl groups at both ends was used as a reactive viscosity enhancer. Only a few particles contained a void in the polymer phase at low concentrations of urethane acrylate, but as the concentration of urethane acrylate increased, so did the number of particles containing the void. This was because urethane acrylate increased the viscosity of the monomer mixture and helped to form the stable emulsion droplets. At concentrations of urethane acrylate above 7 wt%, multi-hollow structured particles were produced. The mechanism of formation of the hollow particles was discussed. 7 refs. 

The formation of nanocapsules was achieved by a variety of approaches. One of the earliest processes for making hollow latex particles was developed in the research laboratories of the Rohm and Haas Company [51-54]. Their concept involved making a structured particle with a carboxylated core polymer and one or more outer shells. Ionization of the carboxylated core with base under the appropriate temperature conditions expands the core by osmotic swelhng to produce hollow particles with water and polyelectrolyte in the interior. In addition to this approach, a number of alternative processes have also been patented that are complex in terms of process stages and chemistry [55-57]. 

McDonald et al found that the modification of an emulsion polymerization with a water-miscible alcohol and a hydrocarbon nonsolvent for the polymer can influence the morphology and enables the formation of monodisperse particles with a hollow structure or difiuse microvoids [58]. Both kinetic and thermodynamic aspects of the polymerization dictate particle morphology. Complete encapsulation of the hydrocarbon occurs, provided that a low molecular-weight polymer is formed initially in the process. Monodisp>erse hollow particles with diameters ranging from 0.2 to 1 pm were obtainable, and void fractions as high as 50% are feasible. 

Okubo et al. examined the penetration/release behavior of various solvents in-to/from the interior of micron-sized monodisperse cross-linked polystyrene/poly-divinylbenzene composite particles [63]. The hollow particles were produced by the seeded polymerization utilizing the dynamic swelling method [64], Itou et al. prepared crosslinked hollow polymer particles of submicron size by means of a seeded emulsion polymerization [65]. The morphology of the particles depends on the composition of divinylbenzene and methyl methacrylate. 

KON Konishi, Y., Okubo, M., and Minami, H., Phase separation in the formation of hollow particles by suspension polymerization for divinylbenzene/toluene droplets dissolving polystyrene. Colloid Polym. Sci., 281, 123, 2003. 

Abstract. The context of this work is the enhancement of the thermal conductivity of polymer by adding conductive particles. It will be shown how we can use effective thermal conductivity models to investigate effect of various factors such as the volume fraction of filler, matrix thermal conductivity, thermal contact resistance, and inner diameter for hollow particles. Analytical models for lower bounds and finite element models will be discussed. It is shown that one can get some insights from effective thermal conductivity models for the tailoring of conductive composite, therefore reducing the amount of experimental work. 

In addition to realize high ETC composites, one often wishes to keep the advantage of the low density of polymer when metallic particles are added. The main idea is to use hollow particle instead of full one. A similar computer simulation as illustrated on fig. 5 but with hollow particles has shown that having hollow particles with wall thickness of only 20% of its radius does not reduced the ETC values more than 5% but reduces the filler volume fraction by 50% and therefore the composite density by 40% [8]. 

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