Chemistry Reference
In-Depth Information
Figure 9.10 Design of supramolecular block copolymers based on the 6-H bonded hetero-
duplex 15†16. Mixing three templated PS chains with three complementarily templated
PEG chains leads to nine block copolymers.
appeared earlier than 15c and 16c. When polar DMF was used as the eluent, 15c†16c
decomposed into two peaks that coincided with the peaks of 15c and 16c. This result
demonstrates that the incorporation of polymer side chains DID NOT affect the
sequence-specific formation of the H bonded duplex.
The NOESY study also confirmed that the duplex template was precisely
registered as directed by the H bonding sequences. Differential scanning calorimetry
analysis indicated the thermally reversible formation and dissociation of these supra-
molecular block copolymers. The H bonded blocks only dissociate at temperatures
above 150 8C. For pairs with sufficiently long PS and PEG chains (15c†16c and
15d†16d), microphase separated nanodomains, typical of covalent diblock copoly-
mers, were observed by atomic force microscopy (AFM). The hexagonally packed
cylinders can be clearly identified in Figure 9.12a. In contrast, the AFM image of
the 1:1 blend of the corresponding PS and PEG chains without the duplex template
showed obvious macrophase separation.
For the pairs with relatively short PS and PEG chains (e.g., 15a†16a and
15b†16b), no microphase separation was observed in the corresponding spin-cast
films (Li et al. 2005). The AFM image of 15b†16b was drastically different, although
Figure 9.11 GPC traces of 15c†16c, 15c, and 16c eluted with DMF/toluene (10/90, v/v,
left) and DMF (right) at 60 8C.
