Influence of the Primary Structure of Syndiotactic Poly(Methyl Methacrylate) on the Inclusion Complex Formation with [60]Fullerene: Robustness of the Helix against Primary Structural Errors

Abstract

Syndiotactic poly­(methyl methacrylate) (st-PMMA) is known to form an inclusion complex with fullerenes in toluene. We investigated in detail the influence of the primary structure of st-PMMA, such as the molecular weight and stereoregularity, on the inclusion complex formation with C60. The formation of an inclusion complex with C60 was accompanied by gelation that occurred in toluene by using st-PMMAs with an rr content of 89% and an M n of over 7.8 × 103 in the polymer, with C60 concentrations of 10 and 2 mg/mL, while no gelation was observed when using st-PMMA with an M n of 4.6 × 103. The st-PMMA gelation ratio and the C60 encapsulation ratio increased with the increasing molecular weight and became constant at an M n of over 2.9 × 104. The guest C60 molecule also had a large influence on the formation of the helical structure of st-PMMA. To obtain a gel quantitatively without fullerene, it was necessary to use st-PMMA with a high M n of 5.8 × 105, whereas in the presence of C60, st-PMMA with an M n of 2.9 × 104 was sufficient. The influence of stereoregularity on the inclusion complex formation was also investigated using st-PMMA with a sufficiently high molecular weight (M n > 3.0 × 105) and different rr contents. Even when the rr content of st-PMMA decreased from 97 to 89%, the C60 encapsulation ratio did not decrease. Since the main chain of st-PMMA with an rr content of 89% incorporates approximately one defect (m-diad) per helical turn, it was concluded that the helical structure of the polymer chains is maintained when the defects are at this level.

Triggering the Vapochromic Behavior in C60 via the Supramolecular Wrapping of st-PMMA

“…q 4 at 1.26 Å –1 and q 5 at 1.41 Å –1 can be assigned to the distance ( d 4 = 5.0 Å) between C 60 and the st -PMMA helix and packing distance ( d 5 = 4.5 Å) of side groups of st -PMMA, respectively. Kawauchi et al reported that the formation of the st -PMMA/C 60 inclusion complex can occur at rr content of st -PMMA above 89% . Our structural characterization first indicates that st -PMMA with a lower rr (79%) can still wrap C 60 s to form the helical structure, where the C 60 s align into the 1D molecular wire with CN = 2, as illustrated in Figure f.…”

“…Kawauchi et al reported that the formation of the st-PMMA/C 60 inclusion complex can occur at rr content of st-PMMA above 89%. 29 Our structural characterization first indicates that st-PMMA with a lower rr (79%) can still wrap C 60 s to form the helical structure, where the C 60 s align into the 1D molecular wire with CN = 2, as illustrated in Figure 2f. Furthermore, the OM micrographs in Figure 2c,d reveal that as the transparent st-PMMA/C 60 complex film is heated to over 190 °C, C 60 crystals form in the st-PMMA/C 60 complex film resulting in the diffraction feature of fcc packing (Figure 2e).…”

“…27,28 High rr content st-PMMA (>89%) conducts the helical self-assembly with π-conjugated compounds like phenanthrene, pyrene, and C 60 , through the induced-fit mechanism. 29,30 This supramolecular helix, where the outer helix of the st-PMMA wraps the π-conjugated molecules, confines π-conjugated molecules into a one-dimensional (1D) supramolecular wire. 30 This 1D arrangement effectively restricts the π-conjugated molecules to stacking along the helical direction.…”

“…Host–guest chemistry offers facile supramolecular strategies to enclose π-conjugated molecules through inclusion complexation. , Polymers such as polysaccharide and syndiotactic-poly­(methyl methacrylate) ( st -PMMA) have been found to act as the hosts that can wrap π-conjugated molecules. , High rr content st -PMMA (>89%) conducts the helical self-assembly with π-conjugated compounds like phenanthrene, pyrene, and C 60 , through the induced-fit mechanism. , This supramolecular helix, where the outer helix of the st -PMMA wraps the π-conjugated molecules, confines π-conjugated molecules into a one-dimensional (1D) supramolecular wire . This 1D arrangement effectively restricts the π-conjugated molecules to stacking along the helical direction.…”