Macromolecules star-shaped

The purpose of this review is to show how anionic polymerization techniques have successfully contributed to the synthesis of a great variety of tailor-made polymer species Homopolymers of controlled molecular weight, co-functional polymers including macromonomers, cyclic macromolecules, star-shaped polymers and model networks, block copolymers and graft copolymers. 

Two types of well defined branched polymers are acessible anionically star-shaped polymers and comb-like polymers87 88). Such macromolecules are used to investigate the effect of branching on the properties, 4n solution as well as in the the bulk. Starshaped macromolecules contain a known number of identical chains which are linked at one end to a central nodule. The size of the latter should be small with respect to the overall molecular dimensions. Comb-like polymers comprise a linear backbone of given length fitted with a known number of randomly distributed branches of well defined size. They are similar to graft copolymers, except that backbone and branches are of identical chemical nature and do not exhibit repulsions. 

Yijin X. and Caiyaun P., Block and star-hlock copolymers by mechanism transformation. 3. S-(PTHF-PSt)4 and S-(PTHF-PSt-PMMA)4 from living CROP to ATRP, Macromolecules, 33, 4750, 2000. Feldthusen J., Ivan B., and Mueller A.H.E., Synthesis of linear and star-shaped block copolymers of isobutylene and methacrylates hy combination of living cationic and anionic polymerizations. Macromolecules, 31, 578, 1998. 

Star shaped macromolecules are polymers, where the one end of f > 2 (f functionality of the star) linear chains is chemically attached by covalent bonds to a small central linker unit, are the simplest form of branched polymers. Modern anionic polymerization techniques allow us to synthesize star systems with a large number of nearly monodisperse arms [133, 134],... 

Elkins C, Viswanathan K, Long TE. Synthesis and characterization of star-shaped poly(ethylene-co-propylene) polymers bearing terminal self-complementary multiple hydrogen-bonding sites. Macromolecules 2006 39 3132-3139. 

For the synthesis of star shaped macromolecules, two approached are possible ... 

Star-shaped macromolecules have also been synthesized by using the monofunctional "living" precursor as an Initiator for the polymerization of a small amount of a divinyl monomer. A small crosslinked nodule is formed, which is connected with the p chains that have contributed to Its Initiation. It turns out that fluctuations on the value of p within a sample remain rather small, and consequently the star polymers obtained by this method can also be considered as tailor-made polymers. Recently star molecules with deuterium labeled central nodule have been synthesized according to the... 

Model networks are tridimensional crosslinked polymers whose elastically effective network chains are of known length and of narrow molecular weight distribution. The techniques used to synthesize such networks are derived from those developed for the synthesis of star shaped macromolecules, whereby the initiator used must be bifunctional instead of monofunctional. ... 

An important group of surface-active nonionic synthetic polymers (nonionic emulsifiers) are ethylene oxide (block) (co)polymers. They have been widely researched and some interesting results on their behavior in water have been obtained [33]. Amphiphilic PEO copolymers are currently of interest in such applications as polymer emulsifiers, rheology modifiers, drug carriers, polymer blend compatibilizers, and phase transfer catalysts. Examples are block copolymers of EO and styrene, graft or block copolymers with PEO branches anchored to a hydrophilic backbone, and star-shaped macromolecules with PEO arms attached to a hydrophobic core. One of the most interesting findings is that some block micelle systems in fact exists in two populations, i.e., a bimodal size distribution. 

Osaki K, Mitsuda G, Johnson R, Schrag J, Ferry JD (1972a) Infinite-dilution viscoelastic properties of linear and star-shaped polybutadiene. Macromolecules 5(1) 17-19 Osaki K, Schrag J, Ferry JD (1972b) Infinite-dilution viscoelastic properties of poly (a-methylstyrene). Applications of Zimm theory with exact eigenvalues. Macromolecules 5(2) 144-147... 

Takano A, Wada S et al (2004) Observation of cylinder-based microphase-separated structures from ABC star-shaped terpolymers investigated by electron computerized tomography. Macromolecules 37 9941-9946... 

Hayashida K, Takano A et al (2006) Systematic transitions of tiling patterns formed by ABC star-shaped terpolymers. Macromolecules 39 9402-9408... 

Dendritic-based macromolecules containing polystyrene were prepared by Frechet [4] and used in specialty medical applications. Star-shaped conjugated dentrimers containing styrene were prepared by Bum [5] and used as components in light-emitting diodes. 

Burchard, W. Statistics of star-shaped molecules. II. Stars with homodisperse side chains. Macromolecules 1974, 7 (6), 841-846. 

Zimm and Kilb have investigated theoretical formulas for the limiting viscosity number of various model, branched molecules in dilute solution. For star-shaped molecules, it was found that the ratio Mbr/Mnn varies approximately as the square root of the ratio of the mean square radii of gyration. Zimm and Kilb then postulated that branched macromolecules, of any shape, will obey this relation to a degree of approximation sufficiently good for practical purposes thus... 

Starburst Dendrimers or Star-Shaped Dendritic Macromolecules. 382... 

The thermodynamic affinity of cyclohexane to polystyrene is known to increase with temperature and, naturally, increasing the temperature must further raise the volume of the polystyrene networks in cyclohexane. There is, however, an additional point we should consider. The plot of Q vs. temperature exhibits a steplike discontinuity at around 30°C (Fig. 1.14). This discontinuity, resemhling very much a -transition, is located 3-5°C below the -temperature for linear polystyrene in cyclohexane and about 8°C above the -point for star-shaped polystyrene macromolecules. This phenomenon is outside the scope of the questions discussed here, but, naturally, the first assumption of the authors [143] seems to be very logical, according to which the discontinuity reflects a transition from Gaussian coil to a supercoiled compact structure on cooling the swollen gel below that temperature zone. 

These types of macromolecules are shown in Fig. 8.1. Many other variants of macromolecules have been synthesized however, their overaU shape represents combinations of the above four basic types, for example, a globule with one or several long-coded chains grafted onto its surface. Simdarly, ad brush-type, worm-hke, star-shaped molecules, dumbbeUs, etc., can be classified according to combinations of the above basic structures. 

One class is polymers capable of forming inter- or intra-polymer associations via secondary interactions (electrostatic, hydrogen bonding, host-guest, or hydrophobic interactions). In Fig. 39a, two linear chains form a star-shaped macromolecule by the association of supramolecular motifs. This star-shaped chain obviously behaves differently in the flow field compared with individual linear constituents (Fig. 26). 

Branched macromolecules have a higher average segment density than unbranched macromolecules of the same molar mass, and have a lower coil volume. This is easily seen by comparing a star-shaped branched molecule with a linear one. The influence of the branching on the dimensions can be expressed by a g factor... 

Discriminating branched and star polymers from linear ones can always be achieved by measuring the properties in dilute solution. In fact, molecules having the same molar mass but different macromolecular architectures exhibit different transport and light scattering properties. More specifically, a branched macromolecule is more compact than a linear molecule having the same molar mass, and therefore it will display less friction and will diffuse more easily in the solvent. Viscometry can be used to detect branched structures, since the Mark-Houwink-Sakurada exponent (Eq. 2.23) for branched and star-shaped polymers is lower tiian that for the corresponding linear chain. Unfortunately, in order to measure the difference, one must have a sample made exclusively... 

The advances in controlled polymerization achieved in recent years have opened up the possibility of synthesizing well-defined star-shaped PEs, particularly those containing a large number of arms. To the best of our knowledge, no publications on the interaction of PE stars with oppositely charged macromolecules or investigations on the properties of the resulting macromolecular co-assemblies can be found in the literature to date, except for a few papers [79-81] that are discussed below. 

Plamper FA, Ruppel M, Schmalz A, Borisov O, Ballauft M, Mueller AHE (2007) Tuning the thermoresponsive properties of weak polyelectrolytes aqueous solutions of star-shaped and linear poly(N, N-dimethylaminoethyl methacrylate). Macromolecules 40 8361-8366... 

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