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
In-situ small- and wide-angle X-ray scattering (SAXS and WAXS) experiments combined with Raman spectroscopy have been performed to study the phase behaviour of syndiotactic polystyrene (sPS) and benzylmethacrylate (BzMA). In the quenched gels, sPS adopts a helical conformation which is stabilised by the solvent molecules, in fact compound formation occurs. From the combined experimental data it was concluded that two different structural modifications exist within the solvent-included helical δ-phase, respectively the δ' phase in which the solvent molecules are intercalated and ordered between the phenyl rings of sPS and a δ” phase where this solvent ordering is lost. 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
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
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.
To investigate the preferential complexing behavior of isomeric xylenes, syndiotactic polystyrene (sPS) membranes are prepared using varying compositions of m‐ and p‐xylene. Complex formation between sPS and the xylenes was studied by means of thermogravimetric and FT‐IR analyses to determine the exact amounts of solvent molecules present per styrene repeating unit. A preferential complexing ability of p‐xylene was revealed due to its favorable interaction with sPS. 相似文献
Novel three-phase composites were prepared by embedding graphite nanosheets (GNs) and BaTiO3 nanoparticles into syndiotactic polystyrene (sPS) matrix via a solution blending and flocculation method. The dependences of electric and dielectric properties of the resultant sPS/BaTiO3-GNs composites on volume fractions of GNs (fGNs) and frequency were investigated. The percolation theory was employed to explain the electric and dielectric behavior of sPS/BaTiO3-GNs composite. It was found that the sPS/BaTiO3-GNs composite showed an obvious insulator-conductor transition with a much low percolation threshold of fGNs = 1.44 vol%. The dielectric permittivity of sPS/BaTiO3-GNs composite reached as high as 51.8 at 100 Hz at percolation threshold, which was about 18 and 7 times higher than that of pure sPS and sPS/BaTiO3 composite, respectively. 相似文献
Neutron scattering experiments are reported on solution grown crystals of syndiotactic polystyrene (sPS) at small and large q, in order to investigate the chain conformation within the lamellar crystals. From the results in both the Guinier and the intermediate ranges, we come to the following conclusions: The chain folds in one or several sheet depending on the molecular weight, comparison between measured and calculated intensity plots give strong indication that a is the fold direction. The statistical model recently built for the spatial arrangement of stems in a sheet-like structure is successful again, and demonstrate a strong statistical preference for adjacent re-entry. 相似文献
Three‐dimensionally ordered macroporous (3DOM) syndiotactic polystyrene (sPS) and poly(p‐methyl styrene) (sPPMS) are synthesized using silica colloidal crystal templates with varied diameters in the range of 548–214 nm, and the effect of polymerization space on the conformation of the resulting 3DOM polymers is investigated by spectroscopy and thermal analysis. In‐situ polymerizations of styrene and p‐methyl styrene within the silica templates induce the resulting 3DOM polymers with different conformations and packing of chains, which are different from those of bulk polymers prepared in the absence of templates. Polymerizations in restricted silica templates result in un‐helixication of 3DOM sPS chains and helixication of 3DOM sPPMS chains.
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
Summary: The formation of a molecular‐complex crystalline phase of syndiotactic polystyrene (sPS) that contains a stable nitroxide radical compound, 2,2,6,6‐tetramethylpiperidinyl‐N‐oxyl (TEMPO), is confirmed by IR and electron spin resonance (ESR) spectroscopy, X‐ray diffractometry, and thermogravimetric analysis. Through a guest exchange procedure assisted by a plasticizing agent, the original guest (chloroform) contained in the starting clathrate phase is completely replaced by TEMPO. Although the conformational regularity of the sPS helices in the resultant crystalline phase that contains TEMPO is similar to that in the starting clathrate phase, the host lattice expands in the 010 direction. The guest TEMPO molecules exhibit a significantly broadened ESR signal because of their highly concentrated state in the complex crystalline phase.
Thermogravimetric measurement of a powder sample of the sPS/TEMPO complex. 相似文献
Solid phase transition of the a form crystals to the β form crystals in syndiotactic polystyrene (sPS) samples hasoccurred in supercritical CO_2. This transformation is different from those detected under other conditions. The effects ofsome factors (e.g time, temperature, and pressure) on the solid phase transformation of sPS in supercritical CO_2 wereanalyzed in detail. Experimental results show that longer time, higher temperature or higher pressure favors thetransformation of the α form crystals to the β form crystals. 相似文献