Molecular Weight Recognition in the Multiple-Stranded Helix of a Synthetic Polymer without Specific Monomer–Monomer Interaction

Abstract

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.

Polymer Crystallization on the Surface of Water or Aqueous Salt Solution

“…This is due to the amphiphilic character of PEO itself, with two hydrophobic methylene groups per monomer unit and a hydrophilic ether group able 23 nm corresponds to the helix-helix distance and 1.08 nm is the helical pitch. This is in good agreement with the data reported in literature [22].…”

“…During this process, i-PMMA chains form a double helix in the monolayer parallel to the water surface. i-PMMA crystals and the i-and s-PMMA stereocomplex were successfully transferred onto solid substrates and helical structures could be observed by AFM [21][22][23][24].…”

Nano‐to‐Macroscale Poly(methyl methacrylate) Stereocomplex Assemblies

“…[12] Nevertheless, PMMA SCs display interesting characteristics, such as stereospecific polymerization-templating capabilities [8] and helix-sense stereocomplexation, [9] as well as molecularweight [13] and peptide-motif recognition. [14] These are remarkable characteristics if one considers that PMMA is a common commodity polymer.…”

“…[23] We postulate that 8 has stereocomplexed PMMA arms, although segmental stereocomplexation or stereocomplexation on the star periphery cannot be ruled out without further analysis. However, molecular-sorting experiments [13] with linear it-and st-PMMA have shown that the complete inclusion of the inner it-PMMA helix in the outer st-PMMA helix is highly favored, as the PMMA SC is the more thermodynamically stable structure.…”

Uniform poly(methyl methacrylate) stereostars: synthesis, separation and stereocomplex formation

“…The st-/it-compositions of the stereocomplex in the mixtures were determined to be 1.61-1.94, indicating the coexistence of at least two types of stereocomplexes with different compositions (for example, st-/it-¼ 1/1 and 2/1). 12 The uniform PMMA was also used to perform atomic force microscopic observations of stereocomplex formation at the waterair interface by Kumaki et al,13 who demonstrated the occurrence of molar-mass recognition in PMMA complex formation.…”