Recent Advances in ROP

Recent advances in the development of well-defined homogeneous metallocene-type catalysts have facilitated mechanistic studies of the processes involved in initiation, propagation, and chain transfer reactions occurring in olefins coordi-native polyaddition. As a result, end-functional polyolefin chains have been made available [103].For instance, Waymouth et al.have reported about the formation of hydroxy-terminated poly(methylene-l,3-cyclopentane) (PMCP-OH) via selective chain transfer to the aluminum atoms of methylaluminoxane (MAO) in the cyclopolymerization of 1,5-hexadiene catalyzed by di(pentameth-ylcyclopentadienyl) zirconium dichloride (Scheme 37). Subsequent equimolar reaction of the hydroxyl extremity with AlEt3 afforded an aluminum alkoxide macroinitiator for the coordinative ROP of sCL and consecutively a novel po-ly(MCP-b-CL) block copolymer [104]. The diblock structure of the copolymer... 

Many recent advances in polymer synthesis have involved the development of new controlled polymerization systems proceeding via a variety of mechanisms. A number of architectures maybe produced as a result of the great versatility of the ROP of cyclic esters. Different strategies have been applied for the design of new polymeric materials. 

Many cyclic monomers undergo ring-opening polymerization (ROP) with conventional anionic initiators. As this topic has been reviewed elsewhere, recent advances in the ring-opening living anionic polymerization of some specific cychc monomers are described in the following subsection. 

Recent advances in the metal-free ROP of lactide also contribute to the development of new macromolecular architectures, as illustrated by the preparation of H-shaped copolymers from the ROP of lactide initiated with PEG-(NH2)2 and catalyzed by a triazolyhdene (Scheme 10.18) [69]. 

A correct understanding of the mechanisms, based on fundamental organic chemistry, is essential not only when applying ROPs in the production of materials with desired performances and functions, but also when designing new monomers, initiators, catalysts and polymerization media, all of which will surely afford unprecedented polymeric materials to support future industries. In this regard, recent major advances in the analytical techniques used to characterize macromolecules-including MALDI-ToF mass spectrometry and multi-dimensional NMR-have had a major impact on polymer chemists. Moreover, the same techniques will allow the discovery of new reaction pathways previously dominated by other reactions, and in turn lead to development of sophisticated means by which ROP can be controlled in precise fashion. Some key examples of these techniques are provided in later chapters of this book. 

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