Macromolecular engineering block copolymers

Puskas, J.E., Antony, P., Paulo, C., Kwon, J., Kovar, M., Norton, P., and Altstadt, V. Macromolecular engineering via carbocationic polymerization Branched and hyperbranched stmctures, block copolymers and nanostructures, Macromol. Mater. Eng., 286, 565-582, 2001. 

The purpose of this review is to report on the recent developments in the macromolecular engineering of aliphatic polyesters. First, the possibilities offered by the living (co)polymerization of (di)lactones will be reviewed. The second part is devoted to the synthesis of block and graft copolymers, combining the living coordination ROP of (di)lactones with other living/controlled polymerization mechanisms of other cyclic and unsaturated comonomers. Finally, several examples of novel types of materials prepared by this macromolecular engineering will be presented. 

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. 

Handlin, D.L., Trenor, S., Wright, K., 2007. Applications of thermoplastic elastomers based on styrenic block copolymers. In Matyjaszewski, K., Gnanou, Y., Leibler, L. (Eds.), Macromolecular Engineering, vol. 4. Wiley, Weinheim, pp. 2001-2032. 

Cationic polymerization is a very important procedure that has been adopted to prepare block copolymers consisting of monomeric units that cannot be polymerized by other methods, such as isobutylene (IB) and alkyl vinyl ethers (VEs), thus enhancing the potential of macromolecular engineering. Cationic polymerization proceeds through carbenium (or oxonium) sites in a controlled/living mode if appropriate conditions such as initiation/coinitiation (Lewis acid), additives, solvent, and temperature have been chosen. 

Guerin, W., Helou, M., Carpentier, J.-F., Slawinski, M., Brusson, J.-M., Guillaume, S.M., 2013. Macromolecular engineering via ring-opening polymerization (1) L-lactide/trimethylene carbonate block copolymers as thermoplastic elastomers. Polymer Chemistry 4, 1095-1106. 

S. Lietz, J.-L. Yang, E. Bosch, J. K. W. Sandler, Z. Zhang, and V. Altstadt, Improvement of the mechanical properties and creep resistance of SBS block copolymers by nanoclay fillers. Macromolecular Materials and Engineering, 292 (2007), 23-32. 

Well-defined polyphosphazene block copolymers with poly(ferrocenylsilane) (PFS) have also been reported, where the combination of the crystallinity of the PFS block and versatility of the polyphosphazene block crystallisation-directed living supramolecular polymerisations lead to spatially defined and controllable nanostructures [59]. Although not designed specifically for medical applications, they show a prime example of how the tunability of polyphosphazenes can be exploited for advanced macromolecular engineering. 

In this chapter we present an overview of this increasingly active research field. The first section focuses on coordination polymerization with metal complexes, classified by the nature of their ancillary ligands. The spectacular achievements reported recently in organocatalyzed and stereocontrolled ROP are then presented. The third section concerns the macromolecular engineering of poly(a-hydroxyac-ids) by varying both their substitution pattern (with alternative monomers to lactide and glycolide) and their architecture (via block, star and dendritic copolymers). The well-established and rapidly emerging applications of these synthetic polyesters are discussed briefly in the last section. 

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