Complexation of Syndiotactic Polystyrene with Crown Ethers: 12-Crown-4, 15-Crown-5 and 18-Crown-6

Abstract

Solid-state complexation of syndiotactic polystyrene (sPS) with three crown ether compounds, 1,4,7,10-tetraoxacyclododecane (12-crown-4, 12c4), 1, 4, 7, 10, 13-pentaoxacyclopentadecane (15-crown-5, 15c5), and 1, 4, 7, 10, 13, 16-hexaoxacyclooctadecane (18-crown-6, 18c6) took place when a film of sPS/chloroform clathrate was subjected to a guest exchange procedure assisted by a plasticizing agent. The new guest molecules were incorporated into the crystalline region of the sPS film, without causing a large conformational change of the host sPS helices. X-ray diffraction and thermogravimetric measurements showed that sPS forms co-crystalline structures with 12c4 and 15c5 presented four guest molecules per unit cell, whereas little information about the lattice dimension was obtained for sPS/18c6 because no X-ray reflections appeared in the low-angle region. IR spectroscopic and X-ray diffraction investigation suggested that the (010) uniplanar orientation of the starting sPS/chloroform clathrate was preserved during the course of guest exchange. The comparison of IR spectra between a crown ether in the liquid and crystalline states and its corresponding sPS complex showed that the crown ether incorporated into the host sPS lattice was in a conformational state similar to its liquid state, which was a mixture of two or more different conformers. It was suggested from IR and Raman spectral data that sPS/12c4 complex contained a high percentage of the Ci type conformer found in crystalline 12c4. It was inferred that the larger the molecular ring, the higher its flexibility, which leads to the lower conformational correlation of crown ether between the crystalline state and the sPS complex.