Supramolecular Interactions in the Formation of Thermotropic Liquid Crystalline Polymers - Liquid Crystalline Functional Assemblies and Their Supramolecular Structures - page 129

Fig. 8 The structure of the ureidopyrimidinone (Upy) end-capped, pendant iptecene
poly( p -phenylene ethylene) derivative ( 10 ) prepared by Hoogboom and Swager [72] to
investigate alignment in the liquid crystal 4- n -pentyl-4 -cyanobiphenyl ( 5CB )

depolymerization of the supramolecular polymer also results in a drop of the
dichroic ratio.
Hydrogen-bonding is not the only supramolecular interaction that can be
used to access main-chain SLCPs. Recently, halogen-bonding [73], namely
the non-covalent interaction D X-Y between an electronegative atom D

(such as O, N) and a halogen atom X, has been used as another approach
to the formation of main-chain supramolecular polymers [74]. In an analo-
gous study to the benzoic acid/pyridine mediated main-chain SLCPs systems
discussed previously, Xu and He prepared a series of 1, n -bis(4-iodo-2,3,5,6-
tetrafluorophenoxy)-alkane compounds ( 11a - d , n = 6, 8, 10, 12) and studied
its complexes with a series of bispyridine derivatives (e.g., 4a - c )(Fig.9).
Thus, in this case, the iodotetrafluorophenoxy moieties replaced the ben-
zoic acid binding units used in the previous studies. It should be noted that
the presence of the fluorines is important here as their electron withdrawing

···

Fig. 9 A halogen-bond mediated main-chain supramolecular liquid crystalline poly-

mer 11 · 4