A commodity plastic, syndiotactic poly(methyl methacrylate) (st‐PMMA), has been found to fold into a right‐ or left‐handed helix through the assistance of (R)‐ or (S)‐1‐phenylethanol (1) and encapsulates fullerenes within its helical cavity to form a robust, processable, and optically active peapod‐like complex whose helicity is retained after removal of the chiral alcohols.

The DNA double helix composed of complementary strands is of fundamental importance for the exquisite functions of DNA, such as the replication and storage of genetic information. Since the discovery of the DNA double helix, [1] the design and synthesis of artificial double helices have attracted significant attention but remain a great challenge in polymer and supramolecular chemistry.[2] In particular, double helices of complementary strands are quite rare. [3] The complex formed from complementary strands of isotactic and syndiotactic poly(methyl methacrylate)s (it-and st-PMMAs) with an it/st stoichiometry of 1:2 is commonly described as a stereocomplex and represents a class of unique, polymer-based supramolecules with an apparent melting point in specific solvents.[4] Although the stereocomplex has been known for half a century, the molecular basis of the structure and the mechanism of complex formation are still under debate, in spite of its availability as advanced materials, such as ultrathin films, [5] thermoplastic elastomers, [6] and dialyzers. [7] It is also a versatile structural motif for stereospecific template polymerization [8] in connection with abiotic replication.In 1989, Schomaker and Challa proposed a reliable model for the PMMA stereocomplex on the basis of X-ray analysis of the stretched fiber, that was the double-stranded helix composed of a 9 1 it-PMMA helix (nine repeating MMA units per turn) surrounded by a 18 1 st-PMMA helix with a helical pitch of 1.84 nm (Figure 1 a). [9] Since then, the doublestranded-helix model has been commonly accepted, because the model could explain rationally 1) the stoichiometry of an asymmetric unit (it/st = 1:2), [4] 2) the template-polymerization phenomena, [8] and 3) the fact that stereocomplexation also took place between it-PMMA and st-poly(methacrylic acid), and even when the methyl ester groups of st-PMMA were replaced by other alkyl groups, whereas the methyl esters of it-PMMA were essential for the stereocomplexation. [4,10] However, because of the limited number of diffuse X-ray diffractions, the complicated structure of the PMMA stereocomplex was difficult to determine by X-ray diffraction, and the proposed double-helix model may require further reconsideration.Although the structural elucidation of helical polymers at a molecular level by X-ray diffraction is a laborious task even now, recent significant developments in microscopic instruments coupled with precise polymerization techniques have made it possible to observe directly the helical structures of certain helical polymers. In fact, we succeeded recently in observing the helical structures of helical poly(phenylacetylene)s and polyisocyanides by high-resolution atomic force microscopy (AFM).[11] These polymers self-assembled into two-dimensional (2D) helix bundles on substrates upon exposure to organic-solvent vapors. This 2D structure enabled the determination of the molecular packing, helical pitch, and handedness (right-or left-handed helix) by AFM. We also visualized successfully b...

We report the direct evidence for the macromolecular helicity inversion of a helical poly(phenylacetylene) bearing l- or d-alanine pendants with a long alkyl chain in different solvents by atomic force microscopy observations of the diastereomeric helical structures. The diastereomeric helical poly(phenylacetylene)s induced in polar and nonpolar solvents self-assembled into ordered, two-dimensional helix bundles with controlled molecular packing, helical pitch, and handedness on graphite upon exposure of each solvent. The macromolecular helicity deposited on graphite from a polar solvent further inverted to the opposite handedness by exposure to a specific nonpolar solvent, and these changes in the surface chirality based on the inversion of helicity could be visualized by atomic force microscopy with molecular resolution, and the results were quantified by X-ray diffraction of the oriented liquid crystalline, diastereomeric helical polymer films.

Rigid-rodlike right (P)- and left (M)-handed helical polyisocyanides (P-poly-L-1 and M-poly-L-1) prepared by the living polymerization of an enantiomerically pure phenyl isocyanide bearing an L-alanine pendant with a long n-decyl chain (L-1) with the mu-ethynediyl Pt-Pd catalyst were found to block copolymerize L-1 and D-1 in a highly enantiomer-selective manner while maintaining narrow molecular weight distributions. The M-poly-L-1 preferentially copolymerized L-1 over the antipode D-1 by a factor of 6.4-7.7, whereas the D-1 was preferentially copolymerized with P-poly-L-1 composed of the same L-1 units, but possessing the opposite helicity by a factor of 4.0. Circular dichroism and high-resolution atomic force microscopy revealed that the enantiomer-selective block copolymerizations proceed in an extremely high helix-sense-selective fashion, and the preformed helical handedness determines the overall helical sense of the polyisocyanides irrespective of the configuration of the monomer units of the initiators during the block copolymerizations. The block copolymers are rigid-rod helical polymers with a narrow molecular weight distribution and exhibit a lyotropic smectic liquid crystalline phase.