Polymer morphology control

In most of the cases, this reaction seems to be very sensitive to the polymer morphology controlled by crosslinking and the nature of the porogen agent which determine the performance of the immobilized catalyst. 

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). 

Mention may also be made of an application in which careful control of polymer morphology has led to the production of novel materials. By treatment of solutions of high-density polyethylene, products are obtained with a celluloselike morphology and which are known as, fibrides or synthetic wood pulp. They are used for finishing paper and special boards to impart such features as sealability and improved wet strength. They are also reported to be used for such diverse applications as tile adhesives, thixotropic agents, battery separators and teabags ... 

The use of interpenetrating donor-acceptor heterojunctions, such as PPVs/C60 composites, polymer/CdS composites, and interpenetrating polymer networks, substantially improves photoconductivity, and thus the quantum efficiency, of polymer-based photo-voltaics. In these devices, an exciton is photogenerated in the active material, diffuses toward the donor-acceptor interface, and dissociates via charge transfer across the interface. The internal electric field set up by the difference between the electrode energy levels, along with the donor-acceptor morphology, controls the quantum efficiency of the PV cell (Fig. 51). 

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. 

Y. F. Huang, C. W. Lin, Facile synthesis and morphology control of graphene oxide/polyaniline nanocomposites via in-situ polymerization process, Polymer, vol. 53, pp. 2574-2582, 2012. 

Ding, J. F, Chuy, C. and Holdcroft, S. 2002. Enhanced conductivity in morphologically controlled proton exchange membranes Synthesis of macromonomers by SFRP and their incorporation into graft polymers. Macromolecules 35 1348-1355. 

In this section, we focus on the strategies of controlling nanoparticle assemblies through functionalized polymer scaffolds, starting from interparticle spacing in bulk aggregates to 3-D morphologically controlled hierarchical nanostrucmres. 

Besides the choice of monomers and solvent, the ratio of template molecule to functional monomer not only affects the imprinting effect [174] but also the morphology of MIP monoliths. Several authors have observed differences in the monolith structure (polymer morphology, pore size distribution, flow characteristics) between the non-imprinted control polymer and the MIP, derived from the presence of the template [158,175]. For example, an MIP imprinted with ceramide III was compared... 

Similar polycondensation giving crystals was attained by the reaction of 4-hydroxybenzoic acid with 4-ethoxybenzoic acid anhydride, which immediately affords 4-(4-ethoxybenzoyloxy)benzoic acid, a monomer, and monofunctional compound [260]. Polyesters with a DP of 38-76 were obtained even if 30-60 mol % of the anhydride was added to the reaction mixture (Scheme 67). This polycondensation is noteworthy not only as a stoichio-metrically imbalanced polycondensation, but also as a valuable method for morphology control of condensation polymers during polymerization [261]. 

Morphology control in a mixing operation is, therefore, very important for utilizing the properties of a blended-in high-performance polymer. It appears that continuity of one or both phases is often essential to obtain optimum properties. This continuity is generated in the blending process, though, unfortunately, not much is known of the ways to control it. 

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