Star macromolecule

Fig.1. Regular star macromolecules with/=3,4, and 8 arms of identical length. The arms or rays can consist of rather stiff chains, but are in most cases flexible chains. The global structure is determined by the overall shape of the whole macromolecule the internal structure is indicated by a domain that is much smaller than the overall dimension but still larger than a few Kuhn segments...

Elementary probability theory shows [82] that on coupling f polydisperse arms onto a star center (this corresponds to an /-fold convolution of a most probable distribution) the polydispersity is reduced The polydispersity index of the star macromolecules (MJM is simply related to the polydispersity index of the arms as [80,82,83]... 

This conjecture was found to hold for flexible chains, stiff worm-like chains, star macromolecules, and hard spheres [156]. A few results are shown in Fig. 32. 

The architecture dependence is also demonstrated in Fig. 33 by the factors of several star macromolecules, flexible cychc chains. Randomly and hyper-branched materials show a more complex behavior because of the large width in the molar mass distribution. Table 5 gives the actual values. The plot of Fig. 33 shows nicely how for a large number of arms the factor for hard spheres is approached. 

Fig. 33. Plot of the factors against the number of arms for star macromolecules ( ), star-...

Macromolecule containing a single branch point from which linear chains (arms) emanate. Note 1 A star macromolecule with n linear chains (arms) attached to the branch point is termed an n-star macromolecule, e.g., five-star macromolecule. 

Note 2 If the arms of a star macromolecule are identical with respect to constitution and degree of polymerization, the macromolecule is termed a regular star macromolecule. 

Polymer composed of regular macromolecules, regular star macromolecules, or regular comb macromolecules. 

Graphic representations (chemical formulae) of macromolecules are used extensively in the scientific literature on polymers including lUPAC documents on macromolecular nomenclature. This document establishes rules for the unambiguous representation of macromolecules by chemical formulae. The rules apply principally to synthetic macromolecules. Insofar as is possible, these rules are consistent with the formulae given in lUPAC documents [2-4] and they also cover the presentation of formulae for irregular macromolecules [5], copolymer molecules [1, 6] and star macromolecules. 

Crosslink, the branch units of star macromolecules and other junction units [5] are optionally specified by their source-based names after the name of the macromolecule with the connective (Greek) v, separated by hyphens. 

In naming non-linear copolymer molecules comprising linear subchains of the same monomeric units in a single type of skeletal structure, the italicized prefix for the skeletal structure is placed before the source-based name of the constituent linear subchains. In the case of star macromolecules with block copolymer arms, the block named first after the prefix emanates from the branch point. 

In naming non-linear copolymer molecules having linear subchains of two or more types, the italicized connective for the skeletal structure is placed between the source-based names of the types of constituent linear subchains. In the case of branched and comb-like macromolecules, the linear chain named before the connective is that which forms the main chain, whereas that (those) named after the connective forms (form) the side-chain(s). The names of different species of side-chain are separated by semicolons. In the case of variegated star macromolecules the prefix is placed before the name of the macromolecule with the different species of arms separated by semicolons. 

Figure 7 illustrates the influence of the increase in the DVB/RLi ratio as well as reaction time for polybutadienyllithium anions. The efficiency is plotted as the ratio of linked to unlinked chains. At the very high ratios (11.9-12.9) nearly quantitative linking is observed as seen from the G.P.C. analysis in Figure 8. However, the moelcular weight distribution is broadened at the higher ratios, possibly indicating intermolecular or inter-nodule star coupling between two different star macromolecules. As mentioned previously, Reaction 5 would be more likely to occur at the higher ratios thus the overlap of the...

Yu, D. Vladimirov, N. Erechet, J.M.J. MALDI-TOE in the characterizations of dendritic-linear block copolymers and stars. Macromolecules 1999, 32, 5186-5192. 

Khasat, N. Pennisi, R.W. Hadjichristidis, N. Fetters, L.J. Dilute solution behavior of asymmetric three-arm and regular three- and twelve-arm polystyrene stars. Macromolecules 1988, 21, 1100-1106. 

Polymer is a substance composed of macromolecules, built by covalently joining at least 50 molecular mers, or the Constitutional Repeating Units or CRU. The longest sequence of CRU defines the main chain of a macromolecule. The main chain may be composed of a series of subchains, identified by some chemical of physical characteristic e.g., tactic placement). The main chain may also contain long or short side chains or branches, attached to it at the branch points. A small region in a macromolecule from which at least four chains emanate consti-mtes a crosslinking point. A macromolecule that has only one crosslink is the star macromolecule. 

Yu, D., Vladimirov, N., and Frechet, J.M.J., MALDl-TOF in the Characterization of dendridic linear Block Copolymers and Stars, Macromolecules, 32,5186 (1999). Leon, J.W., Frechet, J.M.J., Analysis of Aromatic Polyether Dendrimer and Dendrimer-Linear Block Copolymers by MALDl-MS, Polym. Bullett., 35, 449 (1995). 

---