Complex architecture

Radical polymerization is often the preferred mechanism for forming polymers and most commercial polymer materials involve radical chemistry at some stage of their production cycle. From both economic and practical viewpoints, the advantages of radical over other forms of polymerization arc many (Chapter 1). However, one of the often-cited "problems" with radical polymerization is a perceived lack of control over the process the inability to precisely control molecular weight and distribution, limited capacity to make complex architectures and the range of undefined defect structures and other forms of "structure irregularity" that may be present in polymers prepared by this mechanism. Much research has been directed at providing answers for problems of this nature. In this, and in the subsequent chapter, we detail the current status of the efforts to redress these issues. In this chapter, wc focus on how to achieve control by appropriate selection of the reaction conditions in conventional radical polymerization. 

ROMP is without doubt the most important incarnation of olefin metathesis in polymer chemistry [98]. Preconditions enabling this process involve a strained cyclic olefinic monomer and a suitable initiator. The driving force in ROMP is the release of ring strain, rendering the last step in the catalytic cycle irreversible (Scheme 3.6). The synthesis of well-defined polymers of complex architectures such as multi-functionaUsed block-copolymers is enabled by living polymerisation, one of the main benefits of ROMP [92, 98]. 

The micellar structure depicted in Fig. 2 is of course only valid for simple AB diblock copolymers. The situation can be much more complex for micelles prepared from block copolymers with complex architectures, as will be discussed later. 

Then we address the dynamics of diblock copolymer melts. There we discuss the single chain dynamics, the collective dynamics as well as the dynamics of the interfaces in microphase separated systems. The next degree of complication is reached when we discuss the dynamic of gels (Chap. 6.3) and that of polymer aggregates like micelles or polymers with complex architecture such as stars and dendrimers. Chapter 6.5 addresses the first measurements on a rubbery electrolyte. Some new results on polymer solutions are discussed in Chap. 6.6 with particular emphasis on theta solvents and hydrodynamic screening. Chapter 6.7 finally addresses experiments that have been performed on biological macromolecules. 

The examples discussed above demonstrate that the complex architecture of hy-perbranched and brush-like macromolecules can lead to properties and charac-... 

The natural product ( )-carpanone, possess an attractive and relatively complex architecture that can be rapidly assembled from very basic starting materials [108]. 

Hadjichristidis, N. Pitsikalis, M. Pispas, S. latrou, H. Polymers with complex architecture by living anionic polymerization. Chem. Rev. 2001, 101, 3747-3792. 

One may expect that by taking advantage of suitably designed supramolecular features it will be possible to generate a variety of highly complex architectures that would not be accessible otherwise (or only with low efficiency). Such supramolecular assistance adds a new direction with powerful means to organic synthesis. 

The promoter deletion analysis data and the CHX data are summarised in a model of the PR-la promoter shown in Fig. 5. The promoter appears to have a complex architecture comprising several cw-acting domains... 

Although this chapter focuses on colloidal nanocrystals, one of the motivations for preparing materials in this form is the flexibility they offer for further processing and application. In this section, we introduce a few examples in which colloidal nanocrystals were used as building blocks to construct more complex architectures having interesting and potentially useful physical properties. 

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