Polydisperse structures

Abramowitz [4] chap. 26). We have demonstrated that the structure parameters of a polydisperse structure are closely related to these moments. /Iq (h) is the norm... 

Let us consider a template, i.e., the average representative particle or the average representative structural entity in a material with polydisperse structure. The template is described by its structure pr (r). The sample is full of dilated images... 

Multiple covalent bonds are formed in each macromolecule and, in general, statistical, polydispersed structures are obtained. In the case of controlled vinyl polymerizations, the average length of the macromolecule is determined by monomer to initiator ratios. If one views these polymerizations as extraordinarily long sequences of individual reaction steps, the average number of covalent bonds formed/chain may be visualized as shown in Scheme 2 ... 

Similar exercises must be performed to identify synthetic nanocomponents. Considerations include suitability for the proposed environment, synthesis and handling properties, polydispersity, structural / chemical properties, as well as amenability to assembly into higher order structures. For medical devices, tolerability and safety of the structural materials is also an issue. Current materials technology offers powerful, but limited capacity to engineer an off the shelf approach to nanostructures. 

Sodium hydroxide, % Viscosity (G-H), cps Viscous flow (C-U), sec Polydispersity Structure Cure rate... 

The combined results are shown in Fig. 21, where it is seen that the transition from spheres to completely developed polyhedra is accompanied by an increase in surface area of 8.3%. As mentioned above, for the monodisperse case one predicts an increase in surface area of 9.7% on the basis of Kelvin s polyhedron as the ultimate drop shape, or 9.4% for the Weaire-Phelan structure. Polydispersity appears to give rise to an even somewhat smaller overall change in surface area. Recent computer simulations of various monodisperse and polydisperse structures by Kraynik et al. (66) confirm this result almost quantitatively. 

ASSEMBLY OF POLYDISPERSE STRUCTURES CONTAINING DISCRETE DENDRITIC COMPONENTS... 

Salgi P and Rajagopalan R 1993 Polydispersity in colloids—implications to static structure and scattering Adv. Colloid Interface Sc/. 43 169-288... 

The polydisperse fluid structure is characterized by the total, / (r, a, (j ), and the direct, c(r, a, (jy), correlation function, both being functions of the particle diameters. These functions are related via the OZ equation (17), which is rewritten in the form... 

Numerical results for the some model polydisperse systems have been reported in Refs. 81-83. It has been shown that the effect of increasing polydispersity on the number-number distribution function is that the structure decreases with increasing polydispersity. This pattern is common for the behavior of two- and three-dimensional polydisperse fluids [81] and also for three-dimensional quenched-annealed systems [83]. 

Data of Figs 8-10 give a simple pattern of yield stress being independent of the viscosity of monodisperse polymers, indicating that yield stress is determined only by the structure of a filler. However, it turned out that if we go over from mono- to poly-disperse polymers of one row, yield stress estimated by a flow curve, changes by tens of times [7]. This result is quite unexpected and can be explained only presumably by some qualitative considerations. Since in case of both mono- and polydisperse polymers yield stress is independent of viscosity, probably, the decisive role is played by more fine effects. Here, possibly, the same qualitative differences of relaxation properties of mono- and polydisperse polymers, which are known as regards their viscosity properties [1]. 

The new knowledge and understanding of radical processes has resulted in new polymer structures and in new routes to established materials many with commercial significance. For example, radical polymerization is now used in the production of block copolymers, narrow polydispersity homopolymers, and other materials of controlled architecture that were previously available only by more demanding routes. These commercial developments have added to the resurgence of studies on radical polymerization. 

See also PBT degradation structure and properties of, 44-46 synthesis of, 106, 191 Polycaprolactam (PCA), 530, 541 Poly(e-caprolactone) (CAPA, PCL), 28, 42, 86. See also PCL degradation OH-terminated, 98-99 Polycaprolactones, 213 Poly(carbo[dimethyl]silane)s, 450, 451 Polycarbonate glycols, 207 Polycarbonate-polysulfone block copolymer, 360 Polycarbonates, 213 chemical structure of, 5 Polycarbosilanes, 450-456 Poly(chlorocarbosilanes), 454 Polycondensations, 57, 100 Poly(l,4-cyclohexylenedimethylene terephthalate) (PCT), 25 Polydimethyl siloxanes, 4 Poly(dioxanone) (PDO), 27 Poly (4,4 -dipheny lpheny lpho sphine oxide) (PAPO), 347 Polydispersity, 57 Polydispersity index, 444 Poly(D-lactic acid) (PDLA), 41 Poly(DL-lactic acid) (PDLLA), 42 Polyester amides, 18 Polyester-based networks, 58-60 Polyester carbonates, 18 Polyester-ether block copolymers, 20 Polyester-ethers, 26... 

Excessive confidence in these methods unfortunately caused some authors to neglect to perform adequate structure and polydispersity characterization, which brought about some misgivings. 

Anionic polymerizations carried out in aprotic solvents with an efficient initiator may lead to molecular weight control (Mn is determined by the monomer to initiator mole ratio) and low polydispersity indices. The chains are linear and the monomer units are placed head-to-tail. Such polymers are commonly used as calibration samples and for investigation of structure-properties relationships. 

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