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...

Polybenzoxazines that can be obtained by the thermally induced ring-opening polymerization of cyclic benzoxazine monomers are expected as a novel type of phenolic resins. Various benzoxazine monomers are easily synthesized from mono-or diamines, mono-or bisphenols, and formaldehyde. Polybenzoxazines have not only the advantageous properties of the traditional phenolic resins such as the high thermal properties, but also other properties that are not found in the traditional phenolic resins such as the molecular design flexibility, and excellent dimensional stability. The disadvantages of the typical polybenzoxazines are high temperature needed for the cure and brittleness of the cured materials. Further enhancement of thermal properties is also expected for the applications in harsh conditions. Herein, we report on our various approaches for performance enhancement of the polybenzoxazine, including the designs of novel monomers, high molecular weight polymeric precursors, polymer alloys, and hybrids with inorganics.KEY WORDS: Thermoset / Ring-Opening Polymerization / Thermal Properties / Toughness / Polymer Alloy / Organic-Inorganic Hybrid / Nanocomposite / The traditional phenolic resins possess excellent characteristics such as good heat and chemical resistance, flame retardancy, electrical properties, low water absorption, and low cost due to the inexpensive raw materials and fabricating processes. Therefore, they are widely used in various fields such as structural materials, adhesives, paints and matrix for fiber-reinforced plastics (FRP). Nevertheless, the traditional phenolic resins has many disadvantages including poor shelf life of the precursors, the use of harsh catalyst for polymerization, evolution of volatiles during the cure leading to a large volumetric shrinkage upon cure and formation of voids, and the brittleness of the cured materials. Furthermore, the volatalization of phenol and formaldehyde into the air during the cure process causes some health concern.A series of polybenzoxazine has been developed as a novel type of phenolic resin.1 It differs from the traditional phenolics in that the phenolic moieties are connected by a Mannich base bridge [-CH 2 -N(R)-CH 2 -] instead of methylene (-CH 2 -) bridge associated with the traditional phenolics. The structure of a typical benzoxazine monomer (B-a) prepared from bisphenol-A, aniline and formaldehyde along with the structure of its polybenzoxazine (PB-a) are shown in Figure 1. The monomers for polybenzoxazines are easily prepared from phenols, primary amines and formaldehyde. The wide variations of raw materials, phenols and amines, allow tremendous molecular-design flexibility for the cyclic monomers. Polymerization proceeds through the ring-opening of the cyclic monomers only by heat treatment without the need of catalysts and without generating byproducts or volatiles, and thus offering an excellent dimensional stability for the cured product.Polybenzoxazines provide characteristics found in the traditional phenolic resins such as excellent...

Isotactic poly(methyl methacrylate) monolayers deposited from a water surface onto mica at different surface pressures were studied by atomic force microscopy, and their structure formation from single chains to two-dimensional folded chain crystals was clearly observed. Furthermore, gentle crystallization of the monolayer by slow compression on the water surface enabled the observation of crystals at a molecular level, thus visualizing the chain foldings and tie-chains for the first time. The resulting molecular level information will provide an important clue toward the understanding of polymer crystals not only in two dimensions but also in three dimensions.

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Optically active poly(methyl methacrylate) (PMMA) stereocomplexes were prepared through the helix-sense-controlled supramolecular inclusion of an isotactic (it) PMMA within the helical cavity of an optically active, fullerene-encapsulated syndiotactic (st) PMMA with a macromolecular helicity memory. The observed and calculated vibrational circular dichroism spectra revealed that the it-PMMA replaced the encapsulated fullerenes to fold into a double-stranded helix with the same handedness as that of the st-PMMA single helix through the formation of a topological triple-stranded helix.

Stereoregular isotactic and syndiotactic poly(methyl methacrylate)s (it- and st-PMMAs) are known to form a multiple-stranded complementary helix, so-called stereocomplex (SC) through van der Waals interactions, which is a rare example of helical supramolecular structures formed by a commodity polymer. In this study, we prepared SCs by using uniform it- and st-PMMAs and those with a narrow molecular weight distribution having different molecular weights and investigated their structures in detail using high-resolution atomic force microscopy as a function of the molecular weight and molecular weight distribution of the component PMMAs. We found that complementary it- and st-PMMAs with the longer molecular length determine the total length of the SC, and molecules of the shorter component associate until they fill up or cover the longer component. These observations support a supramolecular triple-stranded helical structure of the SCs composed of a double-stranded helix of two intertwined it-PMMA chains included in a single helix of st-PMMA, and this triple-stranded helix model of the SCs appears to be applicable to the it- and st-PMMAs having a wide range of molecular weights we employed in this study. In homogeneous double-stranded helices of it-PMMA, it has been found that, in mixtures of two it-PMMAs with different molecular weights, chains of the same molecular weight selectively form a double-stranded it-PMMA helix, or recognize the molecular weights of each other ("molecular sorting"). We thus demonstrate that molecular weight recognition is possible, without any specific interaction between monomer units, through the formation of a topological multiple-stranded helical structure based upon van der Waals interaction.

A one-handed helical polymer, syndiotactic poly(methyl methacrylate) (st-PMMA), recognizes the size and chirality of higher fullerenes through an induced-fit mechanism and can selectively extract enantiomers of the higher fullerenes, such as C(76), C(80), C(84), C(86), C(88,) C(90), C(92), C(94), and C(96). This discovery will generate a practical and valuable method for selectively extracting the elusive higher fullerenes and their enantiomers and opens the way to developing novel carbon cage materials with optical activities.