Star-branched telechelic

The problem of molecular weight distribution (MWD) and functionality type distribution (FTD) belongs by definition to an extensive problem of molecular heterogeneity of polymers. In the synthesis of a polymer with the requested properties, e.g. a telechelic polymer, one is always faced with different types of polydispersity the macromolecules can be of different length, they can have a different number of functional groups, i.e. be mono-, bifunctional, etc., they can be branched (star-, comb- or tree-like) and, finally, they can be cyclic. 

Alternative approaches involve the reaction together of preformed blocks, such as in telechelic polymers and coupling reactions. The latter allow highly branched architectures such as star polymers to be formed by linking living anionic chains to a multifunctional core such as SiCl4 (Cowie, 1989a). 

FIGURE 2.1 Various possible architectures for amphiphilic copolymer (a) linear block copolymers with different numbers of A and B blocks, (b) cyclic block copolymers, (c) star block copolymers, (d) graft block copolymers, (e) block copolymers with dendritic or hyper-branched blocks, and (f) semitelechelic polymer (upper), telechelic polymer (middle), and asymmetrical telechelic polymer with different hydrophobic chain ends [9]. 

Figure 2 schematically shows linear oCG-DMAC, star-shaped oCG or oLG tet-role, and branched oCl octole telechelics and the expected structural orientation after cross-linking. While all telechelics were seml-crystaUine, oCG tetrole networks were amorphous although cross-linked by the same diisocyanate as the oCl... 

Telechelic polymers can be used as cross-linkers, chain extenders, and precursors for block and graft copolymers. Moreover, star and hyper-branched or dendric polymers are obtained by coupling reactions of monofunctional and multifunctional telechelics with appropriate reagents. Various macromolecular architectures obtained by the reactions of telechelics are represented in Figure 1. 

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