Copolymers, star shape properties

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. 

Living polymerization processes pave the way to the macromolecular engineering, because the reactivity that persists at the chain ends allows (i) a variety of reactive groups to be attached at that position, thus (semi-)telechelic polymers to be synthesized, (ii) the polymerization of a second type of monomer to be resumed with formation of block copolymers, (iii) star-shaped (co)polymers to be prepared by addition of the living chains onto a multifunctional compound. A combination of these strategies with the use of multifunctional initiators andtor macromonomers can increase further the range of polymer architectures and properties. 

To broaden the window of Z-values corresponding to the formation of water-soluble IPECs, star-shaped polyions can be complexed with double hydrophilic (bis-hydrophUic) diblock copolymers comprising an ionic block and a nonionic hydrophilic block. In this case, the formed macromolecular co-assemblies remain water-soluble even if oppositely charged groups of the polymeric counterparts are taken in 1 1 ratio (Z = 1) [49], provided that the length of hydrophilic nonionic block is sufficiently long. Apart from the enhanced water-solubUity of the formed complex species, one can additionally impart new properties and desired functionalities, such as biocompatibUity, thermosensitivity, etc., through the hydrophilic nonionic block of the copolymer. 

---