Polymer particles morphology

Kissin also explains that the silica-supported catalysts are not suitable for a high-temperature (80-90°C) hydrocarbon slurry polymerization process, as the zirconium catalyst component is not chemically fixed to the silica surface and the zirconium catalyst component is extracted from the silica due to its solubility in the hydrocarbon medium resulting in poor polymer particle morphology. However, the catalyst may be retained in the silica pores during a gas-phase polymerization process and, therefore, may provide good particle morphology necessary for a gas-phase process. Consequently, this unique cocatalyst activator may be able to provide a... 

As discussed above, it was clear that ethylene/1-butene copolymers possessed significantly improved mechanical properties compared to ethylene homopolymer products, so that a commercial particle-form reactor design was needed that could provide polyethylene copolymers over a range of Flow Index values with sustained operability over extended periods of time without reactor shut down. Adding 1 -butene to the polymerization process made the autoclave stirred tank reactor even more difficult to operate, as reactor wall fouling problems persisted and in some cases polymer particle morphology was reduced due to some polymer components becoming soluble in the n-pentane. 

There are limits as to the ethylene partial pressure that may be used to increase reactor production rates. For example, an increase in ethylene partial pressure above a certain amount may significantly reduce polymer particle morphology, leading to low resin settled bulk density (post reactor) and low fluidized bulk density within the reactor. Low resin bulk density will reduce conveying rates of granular polyethylene as the resin is transferred to another production step. Lower fluidized bulk density will reduce the amount of granular polyethylene in the reactor, which will reduce catalyst residence time (lower catalyst productivity) at a constant production rate. Limits on comonomer feed rates may also limit the ethylene partial pressure obtainable in order to produce polyethylene with... 

Granular resin bxilk density is an important physical property of finished polyethylene material. Polymer particle morphology determines the amount of polymer that may be contained within the reactor and determines the conveying rates of granular material as the polymer is transferred... 

Low cost High productivity Proper kinetic Control of polymer particle morphology Efficient comonomer incorporation Comonomer distribution control Influence on melt flow properties... 

Zapata et al. [57] Polyethylene-montmorillonite (PE-MMT) The polymer particle morphology improved with the presence of the clay in the polymerization and the molecular weight for support systems presented an increasing ca. 40 % compared to neat PE... 

In addition to graft copolymer attached to the mbber particle surface, the formation of styrene—acrylonitrile copolymer occluded within the mbber particle may occur. The mechanism and extent of occluded polymer formation depends on the manufacturing process. The factors affecting occlusion formation in bulk (77) and emulsion processes (78) have been described. The use of block copolymers of styrene and butadiene in bulk systems can control particle size and give rise to unusual particle morphologies (eg, coil, rod, capsule, cellular) (77). 

A weU-known feature of olefin polymerisation with Ziegler-Natta catalysts is the repHcation phenomenon ia which the growing polymer particle mimics the shape of the catalyst (101). This phenomenon allows morphological control of the polymer particle, particularly sise, shape, sise distribution, and compactness, which greatiy influences the polymerisation processes (102). In one example, the polymer particle has the same spherical shape as the catalyst particle, but with a diameter approximately 40 times larger (96). 

Morphology of the enzymatically synthesized phenolic polymers was controlled under the selected reaction conditions. Monodisperse polymer particles in the sub-micron range were produced by HRP-catalyzed dispersion polymerization of phenol in 1,4-dioxane-phosphate buffer (3 2 v/v) using poly(vinyl methyl ether) as stabihzer. °° ° The particle size could be controlled by the stabilizer concentration and solvent composition. Thermal treatment of these particles afforded uniform carbon particles. The particles could be obtained from various phenol monomers such as m-cresol and p-phenylphenol. 

Research on the modelling, optimization and control of emulsion polymerization (latex) reactors and processes has been expanding rapidly as the chemistry and physics of these systems become better understood, and as the demand for new and improved latex products increases. The objectives are usually to optimize production rates and/or to control product quality variables such as polymer particle size distribution (PSD), particle morphology, copolymer composition, molecular weights (MW s), long chain branching (LCB), crosslinking frequency and gel content. 

A wide variation exists for the number of active centers of oxidation in polymer samples. This reflects the statistical nature of the catalyst residues in polymer particles. On the contrary, the spreading rate coefficient b is approximately constant for the studied samples of PP. The coefficient a is probably sensitive to the morphology of the particles. 

Electron microscopy, 16 464, 487-495 history of, 16 487-488 in polymer blend morphology determination, 20 339-340 of PVC particles, 25 658-659 of silica, 22 371-372 in surface and interface imaging, 24 75-80... 

Heterogeneous particle morphology, in polymer colloids, 20 387 Heterogeneous photocatalysis, 19 73, 103 principles of, 29 74-75 Heterogeneous polymer blends, 20 343. 

However, for SIN s having up to 10-15% elastomer content, it was found that stirring induces significant changes in the morphology of the mixture. If stirring is not provided, the polystyrene polymer particles will sink and coalesce giving rise to a twolayered system. 

In most practical uses of polymeric particles, their surfaces play a very important role by taking part in interfacial interactions such as recognition, adsorption, catalytic reactions, etc. When we want to use polymer particles, we first check whether the chemical and physical structures of the surfaces meet the purpose. If some of them do not satisfy the criteria, we may seek other particles or try to modify the existing particles. This chapter mainly deals with the modification of surface of existing particles. In addition to chemical modification of particle surfaces, modification of the morphology of particles is also described. 

An issue that has been receiving increasing attention is the deleterious effect of fillers on the scratch resistance of polymers, as measured by the loss in surface appearance. The understanding of this problem is still at a rudimentary stage, but it appears that the problem can be minimised by control of particle morphology [28] and correct choice of surface treatments [29]. 

The inter-relationship between colloid and polymer chemistries is completed by colloidal polymer particles. The formation of 50-nm-diameter, 100- to 200-nm-long polyaniline fibrils in a poly(acrylic acid)-template-guided polymerization, similar in many ways to those produced from polymerized SUVs (see above), provides a recent example of polymer colloids [449], The use of poly(styenesulfonic acid) as a template yielded globular polyaniline particles which were found to be quite different morphologically from those observed in the regular chemical synthesis of polyaniline [449]. 

Two Phase Clusters Two Phase fused Non Porous Fig. 5.4- 3 Morphology of polymer particles resulting from supported catalysts, (see [7]). 

---