Solid‐state complexation of syndiotactic polystyrene (sPS) with a crown ether compound, 1,4,7,10‐tetraoxa‐cyclododecane (12‐crown‐4), took place when a film of sPS/chloroform clathrate was subjected to a guest exchange procedure assisted with a plasticizing agent. The new guest 12‐crown‐4 molecules were incorporated into the crystalline region of the sPS film, without causing a large conformational change of host sPS helices. X‐ray diffraction and thermogravimetric investigations showed that sPS/12‐crown‐4 complex had a clathrate complex structure which contained four 12‐crown‐4 molecules per unit cell. IR and Raman data suggested that 12‐crown‐4 took a Ci‐type conformation in the sPS complex phase.
Syndiotactic polystyrene (sPS) forms a clathrate phase with a variety of compounds. Not only rigid molecules but also flexible molecules can be stored in the cavities of the clathrate phase. To clarify the adjustment mechanism of a flexible guest molecule to the sPS clathrate system, the host and guest structures were investigated by means of solid-state 13C NMR and Raman spectroscopy, and X-ray diffractometry for the sPS clathrates with a series of n-alkanes from n-hexane to n-decane. Although the 010 spacing of the host sPS lattice expanded slightly on going from n-hexane to n-heptane, it decreased markedly at n-octane and then increased gradually with the chain length of guest n-alkane. The conformational change of guest n-alkane molecules was involved in this anomalous change in the 010 spacing. Majority of the n-hexane and n-heptane molecules took extended chain structures in the clathrates, whereas all longer n-alkanes took bent chain structures. The mean-square displacement of hydrogen atoms in the clathrates was estimated by quasielastic neutron scattering experiments. It was confirmed that the host lattice contraction suppressed thermal motion of the clathrate system. 相似文献
The conformational equilibrium of 1,2‐dichloroethane (DCE) in syndiotactic polystyrene (sPS)/DCE gels has been investigated by using Fourier transform infrared spectroscopy. Results show that the fraction of DCE in the trans conformation (XT) increases with increasing polymer concentration. From these XT values, by assuming that the crystalline phase in the gel presents the clathrate structure, the amount of DCE included in the crystalline phase and the fraction of polymer included in the crystalline phase were evaluated as a function of the gel composition. 相似文献
Abstract The phase behavior of syndiotactic polystyrene (sPS)/1,2‐dichloroethane (DCE) gels has been investigated by differential scanning calorimetry (DSC) and wide angle x‐ray diffraction (WAXD) for different gel formation conditions. DSC data show that the gel melting temperatures are independent of the cooling conditions leading to gel formation, whereas the melting enthalpies of the gels depend on the cooling history. WAXD measurements show that for low concentration gels the sPS/DCE clathrate structure is obtained, whereas for high concentration gels both the clathrate structure and the solvent‐free β phase can be obtained. Furthermore, the onset of formation of the β phase is dependent on the cooling rate. In light of combined DSC and WAXD data, the reliability of the DSC in evaluating the absolute stoichiometry of polymer‐solvent compounds formed in sPS/DCE gels is discussed. 相似文献
Summary: A fluorescence depolarization technique was applied to get the information on free volume among polymer chains in gel form. Four fluorescent molecules with different molecular sizes were doped throughout the gels of syndiotactic polystyrene (sPS) and isotactic polystyrene (iPS) physical gel system, and their fluorescence anisotropy values were examined in detail for a range of polymer concentrations. Consequently, the free volume among sPS chains in sPS/chloroform gels is as large as the size of molecules smaller than 1,5-dimethylnaphthalene and is consistent with that of the cavity size in the δ-empty crystalline form of sPS solids. The cause to produce δ-empty crystalline form of sPS solids and to form cocrystals between sPS and guest molecules is discussed by comparing the molar size of guest molecules with the free volume among sPS chains in gel form. 相似文献
Chemical modification on the stereo‐regular poly(styrene‐co‐4‐methylstyrene) (sPS‐PMS) was attempted in this study. Metallocene copolymerization of styrene (St) and 4‐methylstyrene (MSt) was performed by using η5‐pentamethylcyclopentadienyl‐titanium(IV)tributoxide (Cp*Ti(OBu)3)/methylaluminoxane (MAO)/tri‐iso‐butylaluminum (TIBA) catalyst in the bulk state. Cobalt(II) catalyst was then applied to oxidize the benzylic methyl group on the MSt units of the resulting sPS‐PMS copolymer. Both aldehyde and carboxylic acid in the oxidized products were resolved by the FTIR and 1H NMR. The oxidized sPS‐PMSs exhibit a low and a high‐temperature Tg and Tm corresponding to the transitions in the amorphous and the crystalline regions. Hydrogen‐bond and polar interactions between the aldehyde and carboxylic acids tend to interrupt the regular chain packing of the oxidized sPS‐PMS, resulting in the lowering of Tm with oxidation level. The oxidized sPS‐PMS showed better adhesion to glass fiber than pure sPS‐PMS copolymer as evaluated from the respective SEM fractured micrographs. 相似文献
To provide improved understanding of guest–host interactions in clathrate hydrates, we present some correlations between guest chemical structures and observations on the corresponding hydrate properties. From these correlations it is clear that directional interactions such as hydrogen bonding between guest and host are likely, although these have been ignored to greater or lesser degrees because there has been no direct structural evidence for such interactions. For the first time, single‐crystal X‐ray crystallography has been used to detect guest–host hydrogen bonding in structure II (sII) and structure H (sH) clathrate hydrates. The clathrates studied are the tert‐butylamine (tBA) sII clathrate with H2S/Xe help gases and the pinacolone + H2S binary sH clathrate. X‐ray structural analysis shows that the tBA nitrogen atom lies at a distance of 2.64 Å from the closest clathrate hydrate water oxygen atom, whereas the pinacolone oxygen atom is determined to lie at a distance of 2.96 Å from the closest water oxygen atom. These distances are compatible with guest–water hydrogen bonding. Results of molecular dynamics simulations on these systems are consistent with the X‐ray crystallographic observations. The tBA guest shows long‐lived guest–host hydrogen bonding with the nitrogen atom tethered to a water HO group that rotates towards the cage center to face the guest nitrogen atom. Pinacolone forms thermally activated guest–host hydrogen bonds with the lattice water molecules; these have been studied for temperatures in the range of 100–250 K. Guest–host hydrogen bonding leads to the formation of Bjerrum L‐defects in the clathrate water lattice between two adjacent water molecules, and these are implicated in the stabilities of the hydrate lattices, the water dynamics, and the dielectric properties. The reported stable hydrogen‐bonded guest–host structures also tend to blur the longstanding distinction between true clathrates and semiclathrates. 相似文献
Summary: The influence of the crystalline structure on the pollutant sorption properties of high porosity syndiotactic polystyrene (sPS) aerogels has been made visible by using azulene, a blue dye, capable to form a clathrate phase with sPS. The bluish coloration observed for aerogels with the nanoporous δ-form and the absence of coloration for aerogels with the densely-packed γ-form clearly establish that the crystalline nanopores play a key role for the removal of pollutant traces from water or air. 相似文献
Crystal structures of the macrocyclic TADDOL (α,α,α′,α′‐tetraaryl‐1,3‐dioxolane‐4,5‐dimethanol) derivative A and its clathrate with diethyl ether are presented. Both the host and clathrate crystallize in the same space group (P212121) with very similar cell dimensions, i.e., they are isomorphous. At ambient temperature, diethyl ether escapes from A ⋅Et2O, and clathrate single crystals are transformed into the guest‐free form without breakdown of the crystal lattice. Conversely, crystalline A , when exposed to Et2O vapor, incorporates guest molecules in a ratio of up to ca. 1 : 1. This behavior, usually the hallmark of inorganic nanoporous materials, allows to describe this compound as an ‘organic zeolite'. 相似文献
The interaction of some volatile organic compounds, namely, 1,2-dichloroethane, 1,2-dibromoethane, and 1,1,2,2-tetrachloroethane, included in the δ crystalline phase of syndiotactic polystyrene (sPS) has been studied in terms of conformation, orientation, and dynamical behavior. By combination of X-ray diffraction (XRD), Fourier-transform infrared (FTIR), and solid-state (2)H NMR analyses, it has been shown that despite the differences in guest molecular properties (mass, boiling temperature, and volume), stable sPS/guest δ-clathrate cocrystals are formed since the nanoporous δ crystalline form has a flexible structure able to adapt itself to the guest molecule. As a consequence of inclusion, it has been shown that the guest diffusivity is strongly reduced and the dynamical processes are constrained, particularly when these guests are in trans conformation. This suggests the nanoporous sPS δ form to be an efficient tool for water and air purification through volatile organic compound absorption. 相似文献