Thermoreversible cis-cisoidal to cis-transoidal isomerization of helical dendronized polyphenylacetylenes.

High cis content (81−99%) cis−transoidal polyphenylacetylene (PPA) jacketed with amphiphilic self-assembling dendrons, poly[(3,4−3,5)mG2−4EBn] with m = 8, 10, 12, 14, 16, and (S)-3,7-dimethyloctyl, were synthesized by Rh(C⋮CPh)(nbd)(PPh3)2 (nbd = 2,5-norbornadiene)/N,N-(dimethylamino)pyridine (DMAP) catalyzed polymerization of macromonomers. The resulting cylindrical PPAs self-organize into hexagonal columnar lattices with intracolumnar order (Φhio) and without (Φh). The polymers with m = 12, 14, and 16 exhibit also a hexagonal columnar crystal phase (Φh,k). The reversible Φh,k-to-Φhio-to- Φh phase transition in these dendronized PPAs was analyzed by a combination of differential scanning calorimetry and small and wide-angle X-ray diffraction experiments performed on powder and oriented fibers. In the Φh,k and Φhio phases, the dendronized PPAs form helical porous columns. The helical pore disappears in the Φh phase. This change is accompanied by a decrease of the external column diameter that is induced b...