Dendritic star

Linear-dendritic star copolymers [5], most frequently obtained via processes in which dendrimers function as multifunctional initiator cores for the poly-... 

The localization of counterions in the intramolecular volume is a common feature manifested in dilute salt-free solutions of branched polyions of different topologies, including dendritic (star-burst), randomly (hyper)branched PEs, PE molecular brushes, etc. The physical reason for this phenomena is the same as outlined for PE stars a strongly charged, branched, macroion creates a high electrostatic potential, which attracts counterions and retains them in the intramolecular volume, in spite of a significant loss in the translational entropy. The effect is most pronounced in a dilute solution, where the concentration of counterions in the bulk is extremely low. 

Yin M, Ding K, Gropeanu RA el al (2008) Dendritic star polymers for efficient DNA binding and stimulus-dependent DNA release. Biomacromolecules 9 3231-3238. doi 10.1021/ bm800797j... 

Yuan, W., Zhang, X, Wei, X, Zhang, C. and Ren, X (2011). Synthesis and self-assembly of pH-responsive amphiphilic dendritic star-block terpolymer by the combination of Rop, ATRP and chck chemistry. European Polymer Journal, 47, 949-958. 

Lee, J.H., Orfanou, K., Driva, P. et al. (2008) Linear and nonlinear rheology of dendritic star polymers experiment. Macromolecules, 41,9165-9178. 

Vast arrays of metal-containing polymers have been produced that offer a wide variety of properties. Key milestones in the history of this diverse topic and a sense of its growth and importance were discussed in this chapter. While initial efforts focused on polysiloxanes, today s efforts are quite diverse and include the production of multisite catalysts, variable oxidation state materials, and smart materials where the precise structure can be changed through the introduction of different counterions. These polymers have been produced by all of the well-established polymerization methodologies. The metal atoms reside as part of the macromolecular backbone, in sidechains, coordinated to the backbone, and as integral parts of dendrites, stars, and rods. Truly, many of tomorrow s critically important materials will have metal atoms as an integral part of the polymer framework, which will allow the materials to function as demanded. 

This catalyst system was also appHed to the synthesis of a wide range of functional, block and dendritic star copolymers [25, 28]. Further investigations into the... 

Dendrites can grow at constant speed at arbitrarily small undercooling A, but usually a non-zero value of the anisotropy e is required. The growth pattern evolving from a nucleus acquires a star-shaped envelope surrounding a well-defined backbone. The distances between the corners of the envelope increase with time. For small undercooling we can use the scaling relation for the motion of the corners as for free dendrites [103-106] with tip... 

The use of dendritic cores in star polymer synthesis by NMP, ATRP and RAFT polymerization was mentioned in Section 9.9.1, In this section wc describe the synthesis of multi-generation dendritic polymers by an iterative approach. 

Figure 1.55. The relationships between the concentration product, (Ba " )i(S04 )i, at the initiation of barite precipitation, and morphologies of barite crystals (Shikazono, 1994). The dashed line represents the boundary between dendritic barite crystals and well-formed rhombohedral, rectangular, and polyhedral barite crystals. The 150°C data are from Shikazono (1994) the others from other investigations. D dendritic (spindle-like, rodlike, star-like, cross-like) barite Dp feather-like dendritic barite W well-formed rectangular, rhombohedral, and polyhedral barite. The boundary between the diffusion-controlled mechanism (Di) and the surface reaction mechanism (S) for barite precipitation at 25°C estimated by Nielsen (1958) The solubility product for barite in 1 molal NaCl solution at 150°C based on data by Helgeson (1969) and Blount (1977). A-B The solubility product for barite in 1 molal NaCl solution from 25 to 150°C based on data by Helgeson (1969).

It is usually believed that the growth of dendritic crystals is controlled by a bulk diffusion-controlled process which is defined as a process controlled by a transportation of solute species by diffusion from the bulk of aqueous solution to the growing crystals (e.g., Strickland-Constable, 1968 Liu et al., 1976). The appearances of feather- and star-like dendritic shapes indicate that the concentrations of pertinent species (e.g., Ba +, SO ) in the solution are highest at the corners of crystals. The rectangular (orthorhombic) crystal forms are generated where the concentrations of solute species are approximately the same for all surfaces but it cannot be homogeneous when the consumption rate of solute is faster than the supply rate by diffusion (Nielsen, 1958). 

Several morphologies of dendritic barite, such as feather-like, rod-like, spindlelike, star-like, and cross-like crystals have been recognized when the (niQ. 2+)i(msoj )i values were considerably higher than the equilibrium values, although no detailed studies have been made on the relationship between the various morphologies of dendritic barites and the degree of supersaturation. 

There also exist a variety of syntheses, stabilities, and characteristics, which are unique to each particular material. Further, macromolecules containing metal and metal-like elements can be produced in a variety of geometries, including linear, two-dimensional, three-dimensional, dendritic, and star arrays. 

More recently Frechet and Gitsov [130] used a similar approach as above and synthesized a novel series of dendritic copolymers derived from a central penta-erythritol core unit. These hybrid star molecules behaved as unimolecular micelles with different core-shell conformational-structures as a response to the polarity of the solvent used. 

Polystyrene/polyethylene oxide dendrimers were prepared by ATRP using tri- and tetra (bromomethyl) benzene as the initiators [207]. Each bromine end-group of the resulting stars was transformed first to two - OH groups and subsequently to potassium alcholate, as shown in Scheme 114. These - OK sites served to initiate the anionic polymerization of EO. The synthesized dendritic copolymers were found to display monomodal and narrow molecular weight distribution. 

The chances of a water molecule reaching dendritic ice decrease as sucrose concentration increases, and the distance between the points of the ice stars increases. The addition of polymers reinforces this effect. 

Depending on substrate orientation and formation condition, individual pores may have different shapes. The shape of the pores formed on (100) substrate is a square bounded by 011 planes with comers pointing to the <100> directions.14,77 The shape of individual pores formed on n-Si tends to change from circular to square to star-like and to dendrite-like with increasing potential.20 Low formation voltage tends to favour circular shape while high voltage favours star-like shape. Near perfect square shape of pores can be obtained for the PS formed on n-Si under certain conditions. 

The shape of pores can be square, dendritic, circular, and star-like. 

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