Comb-like PLCs

Figure 3.8 Molecular components used in the hydrogen-bonded comb-like PLCs of Kato and Frechet and coworkers.

Figure 3.14 Structure proposed for a doubly hydrogen-bonded comb-like PLC complex [20].

The use of ionic bonds to couple dissimilar components has been shown to be a viable alternative to hydrogen-bonded assemblies in constructing PLCs. The ionic bond concept has been applied almost exclusively to comb-like PLCs to date. In general, the architecture of the examples published resembles that of the (potentially) hydrogen-bonded system in Figure 3.15, except that the hydrogen bond is replaced by an ion pair that is, the flexible spacer is part of the small molecule constituent. 

It is useful to compare the thermotropic behavior of noncovalently complexed PLCs with their analogous all-covalent PLCs. For the case of the ionically complexed comb-like PLCs, recently published series of particularly appropriate PLCs must be mentioned, one involving quatemized poly(4-vinylpyridine) [45-47], and another quatemized poly (ethylene imine) [48-50], In both series, the quatemizing moiety is a flexible spacer (based usually on methylene, but also on ethylene oxide) CO-terminated by a mesogen. The result is a pair of ionic groups at or near the polymer backbone, just as in the ionically complexed systems described above. These systems are compared schematically in Figure 3.27. 

Figure 3.34 Molecular components for comb-like PLCs assembled through donor-acceptor interactions.

Hydrogen bonded PLC structures 3.2.2 Comb-like or side chain architecture... 

Dense PLC networks (thermosets) are often prepared from mixtures of mono- and bifunctional monomers resulting in a one-comb polymer-like structure with crosslinks. 

---