Structural Control of Linear Macromolecules

It should be emphasized that for the Markovian copolymers, the knowledge of these structure parameters will suffice for finding the probabilities of any sequences LZ, i.e., for a comprehensive description of the structure of the chains of such copolymers at their given average composition. As for the CD of the Markovian copolymers, for any fraction of Z-mers it is described at Z 1 by the normal Gaussian distribution with covariance matrix, which is controlled along with Z only by the values of structure parameters (Lowry, 1970). The calculation of their dependence on time and on the kinetic parameters of a reaction system enables a complete statistical description of the chemical structure of a Markovian copolymer. It is obvious therewith to which extent a mathematical modeling of the processes of the synthesis of linear copolymers becomes simpler when the sequence of units in their macromolecules is known to obey Markov statistics. 

When macromolecules are formed by radically initiated vinyl polymerizations, it is possible to control the formation of new stereogenic centers with suitable templates by a repetitive one-dimensional property transfer along a long chain and to obtain, e.g., structurally defined, chiral linear chains (for reviews, see [4-7]). An information transfer to a plane surface in a two-dimensional manner may also occur [8, 9] or, if a crosslinking reaction is performed during the transfer, a real three-dimensional transfer can be achieved (for reviews see [10-16]). 

Dendrimers are a class of macromolecules with a precisely controllable branched structure, consisting of three structural units a core, a hyperbranched scaffold and an external surface [16]. Dendrimers have been shown to possess unusual physical and chemical properties that differ significantly from those of linear oligomers and polymers. By using a fluorescent chromophore as the core of a dendrimer, one can apply fluorescence spectroscopy to study stmctural aspects and the conformational mobility of dendrimers in solution [17, 18]. At the same time, the dendritic shell provides a unique nanometer-sized environment for the spatial isolation of the chromophore, making them interesting materials for investigations by SMS. The synthesis of dendrimers with fluorescent chromophores attached to the rim serves as an efficient way to obtain a weU-defined number of chromophores in a confined volume [19-25]. Not only can the number of chromophores be easily controlled. 

The development of a hierarchical architecture, that is, the existence of more than only one distinct morphological feature, is a universal aspect of the semicrystalline polymers. The scale of relevant structural details ranges from some nanometers to millimeters and is controlled by the architecture of the macromolecules and the processing history. The easiest example of a macromolecule is a linear arrangement of CH2 groups in high-density polyethylene (HDPE). Constitutions of some typical semicrystalline polymers are collected in Table 2.1. 

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